Scallop Farming

SCALLOP FARMING SECOND EDITION

DAV I D H A R DY

SCALLOP FARMING

SCALLOP FARMING SECOND EDITION

DAV I D H A R DY

© 1991 David Hardy © 2006 by Blackwell Publishing Ltd Editorial Offices: Blackwell Publishing Ltd, 9600 Garsington Road, Oxford OX4 2DQ, UK Tel: +44 (0)1865 776868 Blackwell Publishing Professional, 2121 State Avenue, Ames, Iowa 50014-8300, USA Tel: +1 515 292 0140 Blackwell Publishing Asia Pty Ltd, 550 Swanston Street, Carlton, Victoria 3053, Australia Tel: +61 (0)3 8359 1011 The right of the Author to be identified as the Author of this Work has been asserted in accordance with the Copyright, Designs and Patents Act 1988. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, except as permitted by the UK Copyright, Designs and Patents Act 1988, without the prior permission of the publisher. First published 1991 Reprinted 1996 Second edition published 2006 ISBN-10: 1-4051-1363-4 ISBN-13: 978-14051-1363-2 Library of Congress Cataloging-in-Publication Data Hardy, David, 1946– Scallop farming / David Hardy. – 2nd ed. p. cm. Includes index. ISBN-13: 978-1-4051-1363-2 (hardback : alk. paper) ISBN-10: 1-4051-1363-4 (hardback : alk. paper) 1. Scallop culture. 2. Scallops. I. Title. SH372.H37 2006 639′.46–dc22 2005034203 A catalogue record for this title is available from the British Library Set in 10 on 13 pt Times by SNP Best-set Typesetter Ltd., Hong Kong Printed and bound in India by Replika Press Pvt, Ltd The publisher’s policy is to use permanent paper from mills that operate a sustainable forestry policy, and which has been manufactured from pulp processed using acid-free and elementary chlorine-free practices. Furthermore, the publisher ensures that the text paper and cover board used have met acceptable environmental accreditation standards. For further information on Blackwell Publishing, visit our website: www.blackwellpublishing.com

Contents

Preface Section 1 General Information 1 Some Background Information about the Species History Why farm scallops? Choice of species World symposia World interest Problems with toxins Regulatory factors The way forward

viii 1 3 3 4 6 8 10 17 19 20

2

The Farm Environment and Its Microscopic Inhabitants Plankton Sustaining plankton life Seasonal variations

22 22 28 35

3

Scallop Biology and Ecology General overview Reproduction Scallop hatcheries

40 40 44 53

Section 2 Hands On 4 Choosing a Site Regulating factors Natural factors Regulations on food safety and water purity Choosing a bottom culture site 5

Collecting Spat Equipment and method of collecting Spat handling The science of monitoring

57 59 59 61 63 64 66 66 74 75 v

vi

Contents Species identification Gonad analysis Comprehensive monitoring programme

86 89 93

6

Getting Underway Longlines Rafts The farm boat Moorings and navigation Shore base and shore facilities Business structure Fish farms and the law Regard for the environment

97 97 117 120 128 129 131 133 134

7

Methods of Cultivation Hanging culture Bottom culture Enclosed culture Analysis of techniques

137 137 153 161 161

8

Moorings Mooring properties Mooring sites Specifications, weights and loads Homemade anchors Concrete blocks Use of geology Laying concrete moorings Maintenance and inspection

167 167 172 179 184 185 185 186 186

9

Design and Manufacture of Equipment Lantern nets Pearl nets Rafts Anchors Grapnels Sorting equipment Pressure washer Star wheel roller Navigation buoys Mooring buoys Breakwaters Weights

190 190 195 196 202 204 205 207 207 209 210 211 212

10

Diving Work Diving teams The role of the diving representative

214 214 215

Contents Potential diving work Diving practice

vii 216 218

Section 3 Getting Down to Business 11 To Collect or Not To Collect The reality of settlement Methods of sorting

229 231 232 233

12

Farming Logistics Stocking densities Equipment changes Equipment dimensions Mortalities Work rates Growth periods Production reference

239 240 242 243 244 249 250 251

13

The Business of Farming Efficiencies Longlines and buoyancy Production levels and culture periods Sales Equipment levels Manpower requirement Examining costs Production alternatives Line management Lantern management Profitability

254 254 255 257 260 261 261 262 265 266 268 269

14

More Strings to Our Bow Cultivating other species Fishing Tourism

272 272 282 289

15

Marketing, Handling and Processing Marketing Handling Quality control Processing Packaging and distribution

290 290 293 294 297 301

Bibliography Index

306 309

Preface

Although aquaculture is being adopted by many countries with a sea border it is, as yet, only in its infancy. For the potential farmer the prospect of being involved in an industry with so much scope is a truly exciting one bearing in mind that we know more about the mountains on Mars than the huge ranges at the bottom of our own oceans. Sea farming is gradually guiding our awareness to the potential of this vast resource and, as each year passes, new and improved techniques have been adopted to assist in the development process. Every farmer can contribute to the progress of aquaculture and hopefully, as his commitment increases, his thirst for knowledge will grow likewise. Scallops offer almost anyone the chance to be involved in aquaculture and the end-result can be both profitable and intellectually rewarding. They are being farmed in many countries worldwide and interest in them is increasing at a fast rate. Those entering the industry now can content themselves that they are directly contributing to a type of farming that has a vast potential in the framework of aquaculture as a whole. I have had the good fortune to be involved in both fishing and farming scallops since 1970. During the latter part of this period interest in scallop farming escalated and I directed some of my efforts to helping others get underway. A general lack of printed information and thirst for knowledge on behalf of the potential farmer encouraged me to put pen to paper and outline the basic principles the industry has developed on to date. I have outlined the main points a farmer would require to know when both setting up and running his farm and, in the process, offered him practical information as well as an introduction to the farming world as seen from the position of the marine biologist. I would like to take this opportunity of thanking my wife, Margaret, for putting up with endless discussions about scallops for the past 30 years and for her assistance in completing the book. David Hardy

viii

Dedication

This book is dedicated to two young men who are important in our lives.

Michael David Hardy

Ben Michael Anderson

ix

Section 1 General Information

Chapter 1 Some Background Information about the Species

There are roughly 360 species of scallops worldwide and most of these are found in coastal waters to a depth of 200 metres. Being rich in glycogen and protein, the meat is highly nutritious and has become much sought after. They belong to the phylum Mollusca, which also includes snails, limpets, cuttlefish, oysters and mussels. Scallops, being bivalves, are characterized by two calcareous shell valves enclosing and protecting a soft fleshy body. Possibly the most characteristic symbol of the scallop is the Shell petrol sign, which depicts the king variety. Scallops are among the few bivalves that have the ability to swim. In the larger varieties this seems to be rather unnatural but the smaller types can travel through the water much like butterflies through the air. They move by means of jet propulsion with a biting action, the water being taken in at the ventral edge and forced out at either side of the dorsal hinge. The scallop feeds by filtering plankton out of the water that it pumps through its shell. In common with other filter-feeding bivalves, it is a very efficient converter of food because, unlike fin-fish, it uses no energy in pursuit of it. Of all the varieties not all have become viable propositions for farming, usually because of either size or excessive length of time to reach maturity. It would be almost impossible to cover the potential of all species, but, in general, farming techniques are fairly standard throughout the industry and between species, as also are the logistics of culture equipment. It will only be the length of time the species occupies the equipment that varies, along with maybe some collection techniques. These techniques are discussed with an emphasis on economic levels of collection but it must be remembered that the process is very species specific and whereas for one species a small number may be viable, for another species a large quantity may be required.

HISTORY In the period a few hundred years BC, the Germanic tribes inhabiting Central Europe had a word that we are fairly sure produced the original sound, which today we have shortened to scallop. The sound was SKAL, followed by various endings and meaning hard covering. By the middle ages the term escalop was in fairly 3

4

Scallop Farming

common use and it actually meant shell. Being of French origin, the English had a bit of a problem with the word and their subsequent mispronunciation ended up as scallop. This is now a truly worldwide term and, whereas in the 1500s it was almost entirely confined to Western Europe, today the word scallop is used wherever English is spoken, and escalop wherever French is the language. The familiar shape of the shell is common to art forms worldwide, dating from pre-history to modern day and there is much myth surrounding it. In some areas, for instance, it was regarded as the symbol of eternal life, and it is still not uncommon to see the shell used as a christening vessel. However, while most shells have been used throughout the world either for their intrinsic decorative qualities, for tools, or as raw materials, being cut up or ground down into pleasing shapes not connected to their original form, the scallop shell has a limited utilitarian value, its shell being too brittle to be used as a tool. Perhaps then its prime use lies in its value as a receptacle for the cooked product, or as an ashtray, the use most generally made of it. Until the Renaissance almost every element of nature had been used in one way or another as a symbol in the church. The scallop had been the symbol of St James and it took many forms. It was a great symbol for pilgrims across Europe, especially in Spain, and was worn in hats as a mark of devotion showing that they had really travelled. However, with the Renaissance, this symbol, like everything else, became secularized. From this point on, what had until then been a religious emblem became primarily decorative, to be used with little significance and at the whim of the artist. However, it still remained a symbol of eternal life for many of its devotees. Figure 1.1 shows some familiar examples of how the shell appears in both family crests and coats of arms.

WHY FARM SCALLOPS? When a good money-making proposition comes onto the horizon there is usually much interest from companies wanting to invest, and in the past much farming activity has required a vast amount of capital and expertise before it has successfully got off the ground. This is especially true of fin fish. Consequently most of the interest in scallop farming has come from large companies wanting either to expand or diversify their activities. Scallop farming, like many other types of bivalve farming, is different. This is an activity that can be successfully undertaken by anyone who is not scared of hard work. Although it does eventually require a fairly high capital outlay, the stock does not require feeding and much equipment can be built as and when required at a considerable cost saving.

Diversity in fishing Scallop farming is a natural choice for inshore fishermen wanting to diversify into something fairly compatible with what they have been used to. An understanding

Some Background Information about the Species

5

Smyth crest

Hopwood crest

St James arms Fig. 1.1 The familiar outline of the scallop shell as it appears in family crests and coats of arms.

of the sea, and especially local conditions, is an advantage when starting out, and considerable cost savings will be made in not having to purchase an additional farm boat. For the fisherman it is a means of adding to an already extensive knowledge but in a way that is more subtle than perhaps he is used to. However, it is not always possible to turn a natural hunter into a farmer/gatherer and for this reason fishermen have often been reluctant to take up the challenge, be it possibly only a parttime one.

Local economics Similar to fishing, a box of scallops, when viewed with an economic multiplier, will have created quite a lot of employment: equipment manufacture, transport, processing, serving, etc. Generally speaking then, not only is the farming of this species of bivalve good for the environment but it also has extensive economic benefits.

Understanding of the marine environment Examining and understanding the plankton population involves a new science for many, especially those already making their living from the sea. This has been the

6

Scallop Farming

most interesting side for many farmers. Whereas, the study of tiny organisms under a microscope and following their growth to maturity was once the prerogative of the marine biologist, the farmer is now conversant with this field and greatly relishes his new-found knowledge. A very positive result of this has been an identification of the fragility of nature and with it the added drive to protect it.

Respect for the environment There is growing awareness today of the environment and all that it means to our survival. Fish farming, especially of salmon, has come in for some criticism and some points are valid while others are not. Scallops, like other bivalves, do not harm the environment when farmed. They tend to produce a gradual increase in larvae in the plankton, which helps to replenish natural stocks, these also being food for both fish and shellfish. They require no artificial feeding, no chemicals for cleaning, and no antibiotics to combat disease. Unlike salmon, scallops can be farmed inconspicuously, the only visible things being the grey, longline, surface buoys. This reduces the impact from the shore, which is especially relevant in scenic areas.

CHOICE OF SPECIES The species Pecten maximus, the ‘great scallop’, will be a useful model for our discussions on biology and habitat because this is the one that most people seem familiar with. This species, often referred to as the ‘king’ scallop, is common in temperate waters, populating the European Atlantic coast and extending from northern Norway southwards to the Iberian peninsula. Examples have been found bigger than 200 millimetres and as old as 25 years. In many instances it inhabits the same areas as the slightly less popular Chlamys opercularis, to which farmers have given the name ‘queen’. Throughout this book we will refer to these two species quite frequently because they characterize two fairly distinct species. Queens have two round shells, are smaller, very mobile and tend to move around in groups. The larger kings prefer to recess into a favourable seabed and pass their time lying in peace. If and when they do move, it tends to be a bit ungainly and quite often they will end up the wrong side up and in a situation further away from their intended goal. These two are nice role models also because although they both take well to suspended culture and are collected in the same manner, their choice of habitat differs. The king is most suitable for bottom culture, the queen certainly is not. There are other species that bridge this gap, and viewed globally farmed species will be seen to range between these two fairly extreme types. For our purposes we will refer to scallops in general as Pectinides. Figure 1.2 shows our target species, which have all come from a farm: the familiar Pecten maximus (king), and its smaller cousin Chlamys opercularis (queen). Figure 1.3 shows both species at approximately 9 months of age. At this stage the queens are often larger than the kings but this situation is eventually reversed.

Some Background Information about the Species

7

Fig. 1.2 Farmed examples of the familiar Pecten maximus (king) and its smaller cousin Chlamys opercularis (queen).

Fig. 1.3 Kings and queens aged approximately 9 months of age. At this stage the queens are often larger than the kings but this situation is eventually reversed. (Photograph by kind permission of Bob and Sandra Parry.)

8

Scallop Farming

WORLD SYMPOSIA In order to advance aquaculture in general, symposia on ocean ranching have been held in various countries around the world. The interchange of ideas at meetings of this kind has proved to be invaluable to the industry as a whole and, to date, has prompted many countries to take up the challenge of scallop farming. All the information is published in journal form so those who cannot attend are given the opportunity of keeping abreast of new developments.

Research The level of commitment to scallop research varies between countries. Some have poured vast amounts of money into research programmes, while others have left it up to private individuals to get the industry off the ground. Although information on culture is quickly being gathered, there are still gaps that require filling and some of these can only be realistically tackled by research establishments. One particular problem has been the difficulty hatcheries have had in producing economically priced spat but now many countries have centred their resources on this and the results are very positive. In many countries great efforts have been centred towards pinpointing natural spat settlement and it has usually been the farmer who has had more luck with this rather than the scientist. Once reliable spat levels have been ascertained, it is then a case of undertaking trials in hanging culture to see if the particular species is suited to this form of captivity. From this point on, providing the species is suited to seabed culture, trials can progress to observing how they take to the bottom in larger numbers than they would normally be used to. Although information may be common to some types of farming, it is usual that trials of this nature are site specific and, as such, the whole growth process usually has to be observed from start to finish. In areas where this has been carried out correctly, good results have been obtained, and fortunately for the rest of the industry most of what has been learned has been put in the public domain.

Academic interest There is a positive movement in universities and similar research establishments to undertake projects that have some kind of economic outcome and, as such, it is fairly easy to solicit their support. The burgeoning scallop industry in Scotland had ties with Aberdeen University and this led to much valuable research being undertaken, which the farmers themselves neither had the time nor the expertise to embark on. One special breakthrough came with the use of the university’s electron microscope to examine scallop larvae at various larval stages (between 120 and 500 microns). Until then the farmers had relied on ordinary microscopes, and although useful enough, these did not always give a complete picture. The results from the electron microscope demonstrated to the farmers what the larvae were truly like and this

Some Background Information about the Species

9

Fig. 1.4 Pecten maximus larvae at 100 microns. (Photograph reproduced by kind permission of Aberdeen University.)

Fig. 1.5 Pecten maximus larvae at approximately 25 days old. (Photograph reproduced by kind permission of Aberdeen University.)

Fig. 1.6 Pecten maximus larvae at 450 microns. (Photograph reproduced by kind permission of Aberdeen University.)

encouraged a fresh interest in their work and research. Figures 1.4, 1.5 and 1.6 are reproduced with kind permission of Aberdeen University and show Pecten maximus larvae at various early growth stages. Figure 1.7 is included as an ordinary microscope photograph of P. maximus to show the difference between the two systems.

10

Scallop Farming

Fig. 1.7 Pecten maximus larvae at approximately 120 microns as seen through a standard microscope.

Unfortunately, whereas taking a photo through an ordinary microscope is relatively inexpensive, those taken through an electron microscope certainly are not.

WORLD INTEREST Many countries have a history of successful aquaculture practices, some going back many centuries. Certain species of both fin fish and shellfish have shown a particular suitability for being farmed. As well as being an excellent source of income these have provided a basis to examine the possibility of culturing more difficult types. Scallops have been a late entrant on the shellfish farming scene, but as more countries have shown interest, so culture techniques have become more refined. Farming is now a successful activity, generating revenue in many of the countries involved. Scallops of one species or another can be found inhabiting almost every seaboard shore and although not all types are yet commercially viable, as demand increases, so more are drawn into the commercial net. There are of course many variations in growth rate, meat yield and market demand, and consequently certain species have tended to become more popular in farming than others. An important development of this has been the introduction of new species to countries with favourable growing conditions. The Japanese scallop Patinopecten yessoensis has proved to be very adaptable when transferred to other countries and there is much interest worldwide in its culture. There is, however, a danger of upsetting the ecology of an area and of introducing pests and diseases. Although the Japanese model provides the best evidence of the potential for scallop farming, there are other countries that are progressing slowly but surely towards a well-run aquaculture industry. Culture techniques are becoming fairly standardized and information is now being gathered on the feasibility of farming

Some Background Information about the Species

11

many differing species. Some countries have lagged behind because their natural species has proved to be either difficult to reproduce in hatcheries or reluctant to comply with man’s desires to farm it. Persistence has, however, eventually won most of them over to the general concept of aquaculture. Many countries are now involved with scallop culture both as a means of restocking after overfishing, or of exploiting a natural resource in the hope of creating a new industry and consequent employment. There follows a brief outline of the industry in some of the countries involved with scallop culture.

Japan Most of our current information on culture techniques has come from Japan and the industry there is a good example of what can be achieved with both perseverance and well-coordinated research. It has been boosted by money and additional research coming from central government and it now forms a model on which other countries can base their own industries. Figure 1.8 shows the now famous ‘Japanese shellfish efficiency model’ and this has been an incentive for growers in many parts of the world. Section A in the model represents the deep water cages where pearl nets are hung up to 30 layers deep – increasing this number was found to be counterproductive in terms of labour efficiency. Pearl nets were also found to withstand tidal and storm motion, which caused a pendulum effect in other types of equipment. Section B is made up of lanterns ranging from 5- to 15-partition nets. In the shallower water the lanterns were found to be less affected by tidal surges, but anything larger than 15 partitions was found to be difficult to handle. Section C is for ear hung stock, and in this case the Japanese found that hanging horizontally between two anchors was the best approach. Section D, the closest to the shore and consequently the shallowest area, is used for bottom-sown stock and here the shells are put down after one cultures growth in pearl nets.

Bottom culture As long ago as 1936 the Japanese were experimenting with bottom seeding in the Abashiri District (northern Hokkaido). Useful information was slowly gleaned and it was not until 30 years later that the real benefits were felt. In 1967 approximately 23 million seed shells and 1 year-old seed scallops were sown on the Tokoro coast. At 2 years old it was estimated that the rate of survival was almost 55 per cent, a very good result for all involved. Bottom sowing therefore began in earnest and by 1970 was in full swing. By 1982 the shores of the island of Hokkaido were being sown with almost 1500 million scallops per year. Most of these were produced locally but a proportion had to be imported from other areas. The result has been that to date, over 50 per cent of Japan’s total scallop landings are produced from bottom culture.

12

A

180

B

50

C

35

not to scale

Fig. 1.8 The Japanese shellfish efficiency model.

D

Scallop Farming

12 km

Some Background Information about the Species

13

A 1 hectare area of seabed can now produce 70 tonnes of scallops. They are left to grow for 4 years and are then harvested by dredging, each age group having its own strip of seabed. The dredge itself is referred to as a kati-ami dredge and this will lift all predators such as starfish and crabs, along with the scallops. Following this process, one-year-old scallops are re-laid on the same ground, which is now hopefully predator free.

Hanging culture In 1977 a 200 mile exclusion zone around Japan reduced distant fisheries. To help make up the deficit in landings much effort was put into promoting other methods of scallop farming. The native scallop, Patinopecten yessoensis, responded well to hanging culture and production gradually increased from 1970 onwards. Full-scale lantern production was in operation between 1977 and 1984, with over 80 per cent of the landings coming from around Hokkaido. This island has always played an important part in the traditional scallop fishery of Japan. The natural fishery in this area, although very productive, tended to fluctuate because a stratification within the water produced anaerobic conditions (reduced oxygen levels) close to the seabed.This resulted in high mortality rates among young spat. The stratification broke down at intervals of between 7 and 20 years, leaving periods of more stable growth.

Administrative control Hanging culture is now practised in Mutsu Bay, which has a total surface area of over 1600 square kilometres. A prefectural local government regulates the farms through their own cooperatives. In return for contributing 4 per cent of their gross income, the governing body supervises all aspects of farming.

Scientific research The Aomori Prefectural Aquacultural Research Station on Mutsu Bay carries out much scientific work, which is of general use to the cooperatives under its jurisdiction. Regular plankton tows are carried out and the specimens gathered are identified and analysed. With the help of five automatic monitors moored on the seabed within the bay, information is gathered on dissolved oxygen levels, temperature and salinity, and speed and direction of current. All of this is used to help determine both spawning times and spat settlement.

Farming practice Water movement is monitored throughout the whole of the bay and collectors are set where there is likely to be a concentration of spat resulting from the formation of an eddy. This would normally be in late April. By the end of July the bags are

14

Scallop Farming

ready to be lifted and it is not uncommon to find as many as 20 000 spat in each collector. Pearl nets are used for the first period of suspended culture and net changes are carried out every 6 months. Revenue is produced by selling off scallops at different stages during thinning, and what is not sold goes for either bottom culture or ear hanging. Farmers now use very low stocking densities in both pearl nets and lanterns and, although this is more labour intensive, the increase in meat yield and decrease in mortality is regarded as sufficient compensation. Once the shells are 100 millimetres in length, and provided they are healthy, the harvest begins. Although there will be many scallops reaching the same size at the same time there will be others, which, through selective culture, have matured early. This allows a constant supply throughout the year, with peaks being reached when the majority reach market size. Activity within the cooperatives is intense during this period and whole families are involved in bringing it to its conclusion. The average production cost for a Japanese scallop farmer is roughly 30 per cent of his gross revenue. This is an excellent ratio for such an industry and a high standard has been set for other countries to follow. Abundant natural spat and excellent growing sites have helped to keep costs down, and this has been further assisted by accurate monitoring and easy access to good markets.

Predators Although most of the bottom predators are removed prior to seeding, there are others, which, although very small, can cause much damage. Japan’s warm waters, although excellent for growth, encourage these undesirable organisms. The most problematic are worms, which settle on the outer shell and proceed to bore through it, causing the scallop to weaken considerably. Also, at the height of the summer, algae often appear in the water and when filtered by the scallop cause toxins to accumulate in its digestive system. If this meat is sold for human consumption it can cause severe gastric problems (discussed later in this chapter). These factors must be borne in mind when choosing the most suitable time to harvest the scallops.

Ear hanging This process was initially regarded as a breakthrough in scallop farming because it made costly items of culture equipment like pearl nets and lanterns redundant. The process is fully automated and each machine can drill and secure one scallop every second. Japan adopted this technique in its infancy and by 1984 ear-hung scallops accounted for 60 per cent of the total hanging culture in the bay. The technique produced more meat over the same growth period and was cheap to install and maintain. The popularity of this technique has, however, started to decline a little because of excessive fouling on the shells making them unattractive and difficult to handle.

Some Background Information about the Species

15

Marketing The Japanese consume most of the scallops they produce. This provides a good market for the farmers and little revenue is lost in shipping costs. Although the live meat trade is important, many recipes have been introduced to cater for a population with a variety of tastes. Pickling, smoking and salting are popular preparations and exotic herbs and spices are used to enhance the taste for those with a more adventurous palate. The cost to the consumer has been kept relatively low so most of the population can enjoy the luxury of eating scallop meat.

China Although China is close to Japan, it has not necessarily copied Japanese farming practices to the letter. The Chinese approach has been to use hatchery techniques to rear scallops and hold them until they are large enough to be brought- on in either pearl nets or other pieces of culture equipment. Most of their success has been with the New England Bay scallop, which is a very fast grower. China’s main species are Chlamys farreri and Argopecten irradians.

New Zealand Pecten novazealandiae is native to New Zealand and this is a suitable species for bottom culturing. This country adopted the Japanese culture technique of bottom re-seeding, which today has proved to be a success. They have managed to harvest nearly 70 per cent of those seeded, and obtain around a 40 per cent survival rate.

Chile Argopecten purpuratus is native to Chile and their fishery has been very much diving based. Their farms are based mainly on hatchery-reared stock and this is brought on in hanging culture. In 1996 Chile had 180 000 000 suspended in this manner.

Peru Like Chile, scallop farming in Peru has developed naturally from traditional fishing. Scallop divers have been making a good living for many years and adopted a policy of selling undersized shells to farmers with an interest in bottom culture. Six months on the seabed sees the scallops grow from 30 millimetres to a marketable size of over 70 millimetres. The main species found in Peru is Chlamys purpura.

France In France, the king scallop, Pecten maximus, is the prime product and much research has been centred on its cultivation. Hatcheries have produced stock and brought them on in Japanese hanging culture equipment. These were then used to re-

16

Scallop Farming

seed the seabed for the benefit of local fishermen and the recovery rate is around 25 per cent.

Magdalen Islands Here the prime object has been to re-seed ground for local fishermen and this seems to have been a great success over a relatively short time period. Based on the Japanese model, scallops have been cultivated by hanging culture and then finished off with bottom culture. Unfortunately the industry has been held up a little with disputes between fishing boats. Their local scallop is Placopecten magellanicus.

Canada The Canadian scallop farming industry has still to realize its full potential and, although some hanging culture trials have been carried out, their aim to reseed with hatchery stock has been held up. Their local species is Placopecten magellanicus.

Australia Chlamys asperrima, Mimachlamys australis, Notovola fumata are all native to Australia but the main farming interest to date has been on the east coast of Tasmania. This island state has had a stable scallop fishery for many years but unfortunately overfishing led to a general decline in stocks. Research was therefore started on the native Pecten fumatus to ascertain the feasibility of farming. Larval concentrations, settlement times, growth and spat survival were all studied and the conclusion was that there was a basis for a very sound industry. Although both duration and exact time of settlement varied slightly from year to year the actual number caught was very good. From 400 to 500 per bag was a fair average at peak settlement. The industry developed on the Japanese model with suspended culture and bottom seeding. An area of approximately 20 square miles was sown with scallops and the recovery rate was deemed high enough for the industry to develop. Once again, the industry is greatly influenced by the Japanese model.

United Kingdom Pecten maximus and Chlamys opercularis are the two main species farmed in the UK and they have both proved to be prime candidates for suspended culture. Prime collection areas are on the Scottish West Coast and numbers per bag can be as high as 600 to 700 during peak activity. For other areas, hatcheries are now starting to produce spat in reliable quantities. Pecten maximus has proved most favourable to bottom culture but Chlamys opercularis has to be reared all the way in suspended culture. Fortunately the growth time for this species can be as little as 2 years.

Some Background Information about the Species

17

PROBLEMS WITH TOXINS Scallop farming has had its difficulties, not least of which has been the fairly recent realization that toxin-bearing algae can be passed on to humans via the meat. No doubt these toxins have always been present but testing procedures were not in place to detect them. Possibly the old maxim that you should not eat scallops when there is an ‘r’ in the month (especially relating to the UK) may not be as daft as it sounds, and may not just relate to spawning times. Many of us are familiar with the term ‘red tides’ but the total consequences of them are often not fully appreciated. Unfortunately, these tides are often made up of certain microscopic marine algae, which can be extremely toxic if consumed by humans in any quantity. To most bivalves these algae are their principal diet but when passed on in the food chain to humans problems can occur. Like plants on land, these single-celled plants (algae) capture the sun’s energy to promote growth and this is the first step in transferring solar energy into aquatic food webs. During the spring and summer these organisms, in response to favourable light, salinity and nutrient levels, often bloom – each cell may replicate itself one million times or more within a couple of weeks. During this bloom the water may become coloured because of the sheer concentration of algae seeking sunlight. Colours may vary depending on the species of algae present but as red is the most common pigment, the phenomenon has become known as red tide. The majority of the algae contributing to the bloom cause humans no harm but there are others consumption of which can range from being mildly poisonous to seriously toxic. Some other effects of these blooms are oxygen depletion in the sea water, robbing bottom weeds and grasses of sunlight, and clogging the gills of fish, especially on fish farms. However, what we are concerned with here is the poison transferred to humans after eating shellfish such as scallops. Tiny quantities of domoic acid (an amino-based toxin) are potentially lethal and it is this poison that seems to cause the most harm, especially in amnesic shellfish poisoning. There are potentially four types of poisoning that we will need to be aware of as scallop growers: amnesic shellfish poisoning, paralytic shellfish poisoning, diarrhoetic shellfish poisoning, and neurotoxic shellfish poisoning.

Amnesic shellfish poisoning (ASP) Amnesic shellfish poisoning (ASP) first hit the headlines in 1987 when four people in Canada died after consuming toxic mussels. It is therefore life threatening. The toxin produced is domoic acid and the causative organisms are Pseudo-nitzschia. Usually within 24 hours of consumption the victim will develop gastroenteritis and, in severe cases, neurological symptoms may also appear. Cases of ASP have caused considerable problems among shellfish farmers in general and scallop farmers in particular. Some markets will only accept the scallop’s adductor muscle, with the rest of the meat, including the valuable roe, having to be discarded. The adductor itself is the only part of the flesh that takes

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Scallop Farming

up very little of the toxin. In many countries, especially the UK, acceptable levels of the toxin are set at such a low level that many farms spend much of their time closed. At present there is some confusion over just how to tackle the problem yet tests have shown that the toxin can be almost completely eliminated simply by thoroughly washing the meat, with roe attached-a simple solution, but one that has to overcome several bureaucratic hurdles before being acceptable to the governing bodies.

Paralytic shellfish poisoning (PSP) Like ASP, paralytic shellfish poisoning (PSP) is life threatening, with neurological problems becoming quickly apparent in those consuming affected species. In severe cases respiratory arrest can occur within 24 hours. The toxin produced is Saxitoxin and the causative organisms are Alexandrium ssp., Gymnodinium catenatum and Pyrodinium.

Diarrhoetic shellfish poisoning (DSP) The toxin produced in diarrhoetic shellfish poisoning (DSP) is okadaic acid and the causative organism is Dinophysis. It is not fatal but does produce some nasty symptoms, usually within a few hours of consuming the toxic shellfish. The symptoms are mainly gastrointestinal, characterized by diarrhoea, nausea and vomiting, and these may take up to 3 days to pass.

Neurotoxic shellfish poisoning (NSP) The toxins produced in neurotoxic shellfish poisoning (NSP) are brevitoxins and the causative organism is Karenia brevis. Although not fatal, NSP produces both gastrointestinal and neurological problems in those affected by it. Recovery usually takes a few days.

Bureaucratic anomalies Because of the problems with toxins, the regulatory authorities have had difficulties in trying to monitor the situation successfully, especially in the UK, where a large area of sea may be tested using only a few samples of scallops and deemed either fit to land the species or not. Farms within these blocks, because they dispatch samples very regularly, often found themselves shut while the block around them was open. The problem then arose as to just how far over the farm boundary the scallops were deemed to be safe. Another anomaly arose where several farmers who were originally closed, gave up their seabed leases to find that their stock was then seemingly healthy. This seemed to be because they were not regarded as farms any more and hence their stock was then regulated by the testing carried out in the

Some Background Information about the Species

19

whole block, instead of just in the limitations of their farm leases. Problems like these look like they will be sorted out by having each batch of scallops tested before landing.

REGULATORY FACTORS Ventures such as shellfish farming, because they are fairly new, have had to seek different ways of securing rights to both equipment and stock. Whereas the law has been seen to be fairly adequate over the years, once tested by major expansion it has often been found to need tightening up. The big push in scallop farming, and in many similar ventures, is to seek total security and to examine the possibility of large scale shellfish/fish farming management. It is for this reason that both Several orders and Regulating orders have come to the fore.

Several orders Where hanging culture is successful (usually with species with a short growing period) there has not been too much of a problem with rights of ownership of stock. However, there has been a large movement into bottom cultivated stock and this has uncovered some administrative problems. To take the UK as an example, a shellfish lease supplied by the Crown will afford some protection to hanging culture but none to those placed on the seabed. For this reason a new order has to be used. These provide for farmers to have sole rights to an area of seabed to cultivate oysters and other shellfish, usually for a period of 7 years. They will usually exclude the use of most types of fishing gear except in some cases for traps. Harvesting must therefore be carried out by diving. Unfortunately, these orders have caused some conflict between farmers and fishermen in areas where they have been granted. This is understandable because the fishermen have often had a traditional right to the ground for many generations. Solving problems like these is often difficult so the farmer should proceed with sympathy and understanding.

Regulating orders Similar to Several orders, Regulating orders provide for responsible organizations to regulate fishing for shellfish and other species within a specific area of seabed. In general they would be very much larger than a Several order and may in fact issue Several orders to prospective farmers within the regulatory boundary. They do not prevent public rights of fishery, but allow it to continue subject to licences being granted. It would be usual for an association taking on a Regulating order to be responsible for both the management of stocks and any conservation that is deemed necessary.

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Scallop Farming

THE WAY FORWARD Hopefully, scallop farming will ride out the recent problems it has had with algal toxins and confidence in the product will return to normal. There is little that can be done to combat natural factors like this and they could easily disappear in the same manner as they seemed to suddenly appear. All the industry has to do is to remain diligent in its testing procedures and to ensure that nothing slips through the net. There is no doubt that Several orders are a positive way forward, and, for general overall management of the sea resource, so are Regulating orders. Within these frameworks large, well-run cooperatives can be set up to ensure that both farmers and fishermen can get the best deal possible. Where these are already in operation the members only land to order and hence there are no surpluses to upset the market. One regulation would be, however, that members solely land within the cooperative, therefore not upsetting any market factors out with its control. As with other types of both fish and shellfish, the farming of scallops is starting to gain a footing as producing a very viable cultured product, creating industry and employment in areas that may once have been lacking in both. Those pioneering this industry have been both innovative and buccaneer in their approach to making it a success and hopefully their enthusiasm will continue as new entrants enter this interesting activity.

SUMMARY •

• •

• •

•

•

There are roughly 360 species of scallops worldwide and most of these are found in coastal waters to a depth of 200 metres. Out of all the varieties not all have become viable propositions for farming, usually because of either size or excessive length of time to reach maturity. The familiar shape of the shell is common to art forms worldwide, dating from pre-history to modern day and there is much myth surrounding it. Scallop farming, like many other types of bivalve farming, is different. This is an activity that can be successfully undertaken by anyone who is not scared of hard work. Generally speaking then, not only is the farming of this species of bivalve good for the environment, but they also have an extensive economic benefit. The species Pecten maximus, the ‘great scallop’, will be a useful model for our discussions on biology and habitat because this is the one that most people seem familiar with. In many countries great efforts have been concentrated on pinpointing natural spat settlement and it has usually been the farmer who has had more luck with this rather than the scientist. The burgeoning scallop industry in Scotland had ties with Aberdeen University and this led to much valuable research being undertaken that the farmers themselves neither had the time nor the expertise for.

Some Background Information about the Species •

•

•

•

•

• •

•

21

Scallops have been a late entrant on the shellfish farming scene but as more countries have shown interest so culture techniques have become more refined. Farming is now a successful activity, generating revenue in many of the countries involved. Although the Japanese model provides the best evidence of the potential for scallop farming, there are other countries that are progressing slowly but surely towards a well-run aquaculture industry. Most of our current information on culture techniques has come from Japan and the industry there is a good example of what can be achieved with both perseverance and well-coordinated research. Although China is close to Japan they have not necessarily copied their farming practices to the letter. Their approach has been to use hatchery techniques to rear scallops and hold them until they are large enough to be brought on in either pearl nets or other pieces of culture equipment. Scallop farming has had its difficulties, not least of which has been the fairly recent discovery of toxins caused by algae. No doubt these toxins have always been present but testing procedures were not in place to detect them. ASP has caused considerable problems for shellfish farmers in general and scallop farmers in particular. Because of these toxins, the regulatory authorities have had problems in trying successfully to monitor the situation, especially in the UK. Several orders provide for farmers to have sole rights to an area of seabed to cultivate oysters and other shellfish, usually for a period of 7 years. Regulating orders are similar to Several orders and provide for responsible organizations to regulate fishing for shellfish and other species within a specific area of seabed. Those pioneering this industry have been both innovative and buccaneer in their approach to making it a success and hopefully their enthusiasm will continue as new entrants enter this interesting activity.

Chapter 2 The Farm Environment and Its Microscopic Inhabitants

Prospective farmers often have little knowledge about the microscopic world of the plankton and not much about the marine environment other than the effect of waves and tides. Unfortunately, if they are to undertake farming seriously this gap in their knowledge will need filling and consequently this chapter will be most important. It is often believed that what lies beneath the surface is only for the interests of marine biologists and, as such, far too complex for the ordinary man. Luckily this is not so and an understanding of the marine environment is within everyone’s capability, providing they are prepared to take a little time over it. Figure 2.1 gives an introduction to this environment and shows the common zones within the oceans, ranging from shallow to deep, and probably some of the terms the prospective farmer may already be aware of. Although scallop farming is primarily concentrated around the euphotic (photic) zone, the deeper zones are also important, not least, because they often supply the valuable nutrients essential to the chain of plankton succession.

PLANKTON The word plankton originates from the Greek word ‘plankters’, which means wanderer, and basically refers to all floating animals. Two divisions spring from this; phytoplankton and zooplankton. The former are really floating plants and they occupy the zone from the surface to a depth of approximately 200 metres. Scallop larvae are part of the zooplankton and these are basically floating animals, which may occupy all depths. From a farming perspective plankton are most important, being at once a supply of stock, and secondly a source of food for this stock. We need to know as much as we can about them but unfortunately they seem to be shrouded in what may seem strange scientific names. However, for our purposes, a basic categorization would be as follows.

Size Those plankton growing to over 1 millimetre and which can be seen by the naked eye are known as macroplankton. The next category are microplankton and these 22

littoral zone tidal zone

euphotic zone

epiplankton

benthic z

one

bathyplankton

pelagic column

continental shelf

oceanic

hypoplankton 1000 m

Fig. 2.1 Zones within the oceans.

tychopelagic

abyssal

The Farm Environment and Its Microscopic Inhabitants

sublittoral zone 200 m

23

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Scallop Farming

range between 500 microns and 1 millimetre in size. The size range of 5–500 microns is occupied by nanoplankton, and those below 5 microns in size are ultraplankton.

Location There is a surface film on all water and this environment gives a home to what are referred to as neuson. Around them, but sometimes reaching further down are pleuson, floating on the surface and exposed to the effect of both tide and wind. Beneath these, the epiplankton inhabit the surface layer down to around 200 metres. Those inhabiting deep water are known as bathyplankton, while plankton living very close to the seabed are referred to as hypoplankton.

Attribute Protoplankton is the scientific term describing bacteria and unicellular organisms, while seston relates to fine suspended matter. Those species that spend their entire life as plankton are termed holoplankton, while those that undergo some kind of metamorphosis to become fish of one type or other are known as meroplankton. Micronekton refers to those of intermediate size but which swim, and techopelagic species are those inhabiting the benthos (the bottom of the sea), and these will enter the water column if or when the bottom is disturbed.

Classification The theory and practice of classification is the science of taxonomy and this is a very complex subject, made more difficult because different professions have an interest in different parts of an animal’s anatomy. For instance, whereas palaeontologists have an interest in the harder fossilized parts, biologists are mainly interested in the softer parts. Now confuse matters even more by accommodating geneticists, who are concerned with subcellular differences. To demonstrate this confusion the following is a brief description of the various categories relating to Pecten maximus. KINGDOM PHYLUM CLASS ORDER subORDER superFAMILY FAMILY GENUS SPECIES

Animalia Mollusca Bivalvia (Pelecypoda) Ostreoida Pectinina Pectinacea Pectinacea Pecten maximus

Extra terminology within each group further complicates the matter; for instance, there are several names relating to small scallops before their settlement size and

The Farm Environment and Its Microscopic Inhabitants

25

the same applies to crustaceans, which during their larval stages may develop through the stages of nauplius, zoea (containing even more subdivisions) and meggalopa. Now take this complication a stage further and study reference books in which authors have decided to adopt their own preferred terminology.

Phytoplankton Phytoplankton may better be described as a productive biomass, in that they are in a continual state of movement in order to utilize fully the daily budget of light and nutrients. Although they are present in the sea in one quantity or another, increases in population are usually started by small celled diatoms, which are capable of a high photosynthesis rate. This increase is followed by that of slower growing diatoms, which is followed in turn by an increase in numbers of more mobile dinoflagellates. Their very existence depends upon them being in the zone of photosynthesis and it has been suggested that to maintain this they are able to regulate their density in relation to the surrounding water.

Diatoms Diatoms are the most abundant form of life on earth and during spring blooms in temperate waters they can reach a concentration of 0.5 per cent volume of seawater. They are single-celled plants and because they are poor swimmers they usually maintain their position in the water column by buoyancy. A single unit of living protoplasm inhabits a silica shell with slits enabling it to react with the sea environment on the outside. This transparent cell easily absorbs light, which is essential for the diffusion of nutrients and gases. Where the temperature is too low or the nutrients are very poor, the cell may die. However, because reproduction relies on these always being a brood-stock, a procedure known as auxosporulation has evolved. By wrapping themselves in silica, the diatoms become stronger and heavier and this extra weight causes them to sink into the seabed, where they can hibernate through cold and even drought, in shallow waters that might dry up. When conditions are once more favourable they re-establish their original position and function.

Dinoflagellates The infamous red tide represents the dinoflagellates’ main claim to fame. They are single-celled organisms, usually smaller than diatoms, and they create this red tide when levels of bloom deplete the oxygen content of the water and cause other marine organisms to die. Some species are toxic and are the main cause of paralytic shellfish poisoning from consumption of affected shellfish during the summer months. Some will live by eating small diatoms, while others will rely solely on photosynthesis for growth.

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Scallop Farming

Zooplankton Zooplankton can range from the simplest form of animal life (radiolaria) to other quite complex organisms, and in general they are more varied than phytoplankton. They do not have the same mortality problems as phytoplankton and adapt to their environment easily, by spending the summer in shallow water and returning to deep water for the winter months. Much of their feeding is carried out in shallow water at night and it is thought that by utilizing this time they are less likely to be spotted by predators, energy reserves also being maintained by returning to deeper, colder water during the day. Unfortunately, their numbers can increase so rapidly that mortality becomes excessive as a result of collision with other species. For the sake of categorization, zooplankton are either permanent or temporary. Those spending their life as plankton and acting as a food source for other marine creatures are of the permanent variety and may be classified as follows: Protozoa Coelenterates Polychaetes Chaetognaths Crustacea

Radiolaria and Formanifera Jellyfish, Comb-jellies and Siphonophores Worms Arrow worms Cocopods and Euphousides

Those species that only spend part of their lives as plankton are referred to as temporary (lamellibranch larvae). Increases in population quickly follow increases in their main food source, phytoplankton, the herbivores arriving first, closely followed by the carnivores. With abundant quantities of phytoplankton the zooplankton will often indulge in superfluous feeding when much of the food source will pass through their systems undigested. This will act as nutrition for those creatures further down the water column. There is rarely a situation of equilibrium between phytoplankton and zooplankton populations and intense feeding will often wipe out vast areas of the former, creating a food shortage later on. Figure 2.2 shows the patterns of grazing between the two species and also illustrates how sampling may be affected: areas of concentrated animals closely followed by areas of patchiness. Although species like scallops will respond quickly in terms of reproduction when an increase in food stock is sensed, this is not the case for fish reproduction. Although a fish may try to coincide its egg emission and subsequent hatching to an increase in food supplies, there are often instances when the small fish hatch in an environment that is short of food. Figure 2.3 demonstrates the ‘match/mismatch theory’, which shows that the greater the overlap between the peaks of the graph, the higher the recruitment. However, much is dependent on the third curve, which represents the food resource. If the fish lay their eggs too early, there may not be enough for those that hatch to survive.

Copepods Copepods form the single most important group in the sea and within one group alone, the calanoid copepods, there are over 1200 species. Commonly known as the

The Farm Environment and Its Microscopic Inhabitants 1. phytoplankton

zooplankton 2.

3.

4.

Fig. 2.2 Patterns of plankton grazing.

A. low stock

frequency

egg production

larval production

B. high stock

time Fig. 2.3 The match/mismatch theory of reproduction.

larval food

27

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Scallop Farming

insects of the sea, these are crustaceans with a basic diet of diatoms. Their importance to any scallop monitoring programme is that because they are a permanent member of the plankton family and because they are so common, they are an excellent indicator of plankton activity.

Bivalves Bivalves are all temporary members of the plankton family and their presence is usually indicated by the observation of ‘D-shaped’ larvae. They will often be seen in huge quantities when samples are taken during monitoring programmes and it is to be hoped that the scallop is first spotted here.

SUSTAINING PLANKTON LIFE All creatures on the planet are affected by their environment and not least so, plankton. Although from place to place there may be changes in sea conditions, generally speaking the factors of temperature, salinity, food supply, light and water movement are those that have the greatest effect on plankton behaviour.

Temperature Some marine species are able to withstand wide variations in temperatures, while others will only survive small fluctuations. Generally speaking it has a direct bearing on the behaviour and distribution of them all. Despite a wide geographic cover worldwide, temperature variations tend to be small, with surface water usually being more varied than colder, deeper water. Metabolism rates increase with temperature and most marine creatures are better able to withstand lower temperature levels than higher ones.

Thermoclines Nearly all infrared radiation is absorbed in heating the first few metres of the ocean’s surface and this is why, in general, seawater is usually cold and slow moving. The heat that is stored in the surface layers may make its way into deeper water via surface turbulence, conduction and convection and, as such, is referred to as the mixed layer. The depth of this layer will depend on the amount of heat taken and the degree of surface turbulence. Figure 2.4 shows the formation of a thermocline. This, at its peak, is a boundary between the colder deeper water and the warmer surface water and during the summer months it can be quite distinct. Accompanying this temperature barrier there will also be a change in density and this is called a pycnocline. When both factors are at their strongest, the resulting barrier can impede the movement of both nutrients and plankton.

The Farm Environment and Its Microscopic Inhabitants temperature (°C)

12

14

16

29

18

depth 20 (m) 40 MAY

60

20 thermocline 40 60

JUNE

20 40 60

JULY

20 40 60

SEPTEMBER

Fig. 2.4 The formation of a thermocline.

Stratification Changes in temperature and the resulting thermocline and pycnocline often lead to suspended organisms being trapped in differing water masses and, as such are a very significant feature of the yearly phytoplankton cycle.

Effects on plankton Temperature has an effect on the maturation of gonads and the release of gametes (the reproductive contents of the ovary), and so influences reproduction. Mortality rates in the young larvae will be affected, with some having less tolerance than their parents. As the temperature reduces, so too do feeding levels, often resulting in the cessation of food intake. The viscosity of water is also affected by temperature and this can have a bearing on plankton locomotion. Also, as temperatures increase, so water density decreases, and this has a direct influence on the buoyancy of marine creatures. More importantly, increases in water temperature will lead to a decrease in the solubility of gases, the most important of which is oxygen, and this can prove limiting to plant growth.

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Scallop Farming

Salinity Salinity is referred to in parts per thousand and most seawater ranges between 34 and 36 parts per thousand, sometimes rising to 37 parts per thousand in areas of little rainfall and high evaporation. A figure of 25 parts per thousand may be recorded where the reverse situation prevails, with heavy rainfall and little evaporation as a result of limited sunlight and solar heat. The majority of marine creatures have a limited tolerance to fluctuations in salinity (stenohaline) but nearer coastal areas, where there is a greater fluctuation caused by river outlets and so on, the organisms become more tolerant (euryhaline).

Variations Extreme variations in salinity, resulting in differences in density, will present barriers to plankton and cause them to be stratified throughout the water column. Differing levels of water density will cause buoyancy problems and will also enforce a greater barrier around the summer’s thermocline.

Food supply Although sunlight is very important, phytoplankton require both organic and inorganic substances to grow successfully. It is the concentration and composition of these nutrients that trigger initial plankton blooms, and their distribution throughout the water column is affected greatly by localized physical factors such as upwellings, tide, wind and wave action, and convection.

Main elements In general, 99.99 per cent of the dissolved elements in seawater are comprised of sodium, magnesium, calcium, potassium, strontium, chloride, sulphate and bromide. Oxygen, carbon dioxide and nitrogen in a dissolved state are also present.

Dissolved gases Oxygen concentrations will vary with depth and temperature, with high concentrations often appearing at the surface where photosynthesis may produce a situation of supersaturation. Of importance also to photosynthesis is the presence of carbon dioxide and this may often be detected at high levels. The occurrence of this will lead to a rise in pH levels at the surface where carbon dioxide is converted into oxygen. At the surface, nitrogen is taken in from the atmosphere.

Nitrates, phosphate and silicate There are other elements that have an effect on plankton populations. Small quantities of iron and manganese are required, but more important are nitrate, phos-

The Farm Environment and Its Microscopic Inhabitants

31

phate and silicate. Their availability will vary seasonally but their distribution will depend on physical factors. Plankton reproduction and growth depends greatly on the nutrients of nitrate and phosphate, but concentrations of these may vary greatly with depth, higher levels being detected in deeper water. On the surface these nutrients may be patchy, but nearer the coast, because of water influx, they may be more abundant. Silicate is essential for diatom growth and can be found in seawater in much the same way as nitrate and phosphate.

Organic matter This usually consists of carbon, nitrogen, phosphorus, sulphur and iron, all in a dissolved form. They usually enter the system via photosynthesis, the breakdown of dead tissues, excretion, land drainage, vapour and directly from the atmosphere.

Light Only half of solar light reaches the earth’s surface and the amount actually arriving at surface levels in the sea will vary with season, cloud cover and latitude. It is therefore a major factor in the earth’s vitality and because the oceans are so large they absorb most of its energy. Although its heating role is important, its most prominent function in terms of plankton is the powering of photosynthesis. Of specific interest therefore is the level of photosynthetically available radiation and the means by which the phytoplankton cells utilize this energy.

Photosynthesis and light compensation depth Photosynthesis is the process whereby sugar and oxygen are created from carbon dioxide and water using the energy of sunlight, trapped by chlorophyll. Thus the raw materials are carbon dioxide and water, the machinery is chlorophyll, the power is sunlight, and the product is sugar, a by-product being oxygen. Phytoplankton are able to utilize light because they possess chlorophyll (chlorophyll a) and other photosynthetic pigments, the chlorophyll being held within the plants in chloroplasts. Photosynthesis will vary with light intensity up to a point of saturation after which no further photosynthesis will occur. Phytoplankton cells will, in fact, suffer in intense sunlight and it is therefore normal for maximum photosynthesis to occur some metres below the surface. In order fully to understand the relationship of light intensity and photosynthesis, the principle of light compensation depth must be understood. Figure 2.5 demonstrates photosynthesis and respiration in an imaginary phytoplankton population. Assuming the phytoplankton are scattered uniformly throughout the whole of the water column and the temperature is uniform, then the level of respiration will also be uniform. On the other hand, because photosynthesis varies with depth, the amount of oxygen produced near the surface will be greater than that produced at depth. This overproduction of oxygen in area A will be the exact

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Scallop Farming

respiration

A

10 m

photosynthesis water mixing 20 m

30 m compensation depth

plankton population 40 m

50 m

B

60 m

critical depth Fig. 2.5 Photosynthesis and light compensation depth.

amount needed to provide respiratory requirements for cells in area B, the compensation depth being the position of equilibrium where photosynthesis (oxygen production) is equal to respiratory requirements. This will also assume that the water column is evenly mixed, thus enabling the excess of oxygen to be available to the lower-dwelling cells. Beyond the critical depth phytoplankton production fails because of lack of oxygen. The onset of winter will see the compensation depth rising closer to the surface as light intensity starts to decrease.

Water movement Seawater is on the move all the time, both horizontally and vertically, and it must be remembered that although the surface looks flat and calm, there is a great amount of movement below, and even storms are not uncommon. This constant movement is caused by a number of things, the main ones being tide, wave and wind action, upwellings and convection.

Tide The consequences of a strong tide can mean scallop and other such larvae being carried many miles from their initial spawning ground. It also acts to carry food to

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33

greatest tide range spring tide: mean range EHWS neap tide: mean range smallest range of tides

MHWS MHWN EHWN(L) ELWN(H) MLWN MLWS ELWS

Fig. 2.6 Variations in tides and the terminology used. EHWS, extreme high water spring; MHWS, mean high water spring; MHWN, mean high water neaps; EHWN, extreme high water neaps; ELWN, extreme low water neaps; MLWN, mean low water neaps; MLWS, mean low water spring; ELWS, extreme low water spring.

all sea dwellers and it is therefore a very important aspect of any farm. It is the moon that determines both the rise and fall of the tide, varying from very strong during peak spring tides to fairly weak during neap tides. In Figure 2.6 we can see the terminology used to describe the variations in tide levels. Tide range will vary between areas and this can be significant; for instance, where parts of Norway only experience a tide range of approximately 1 metre, areas off South America can experience variations of 25 metres. These are two extremes, and in fact you only have to cross from Norway to the Scottish East Coast to experience quite a significant tide range. These anomalies stem from what is known as a geoid, which is best described as a close representation, physical model, of the mathematical figure of the Earth, in fact of its gravity field. There are very high mountains and very low trenches in the make-up of the earth’s crust and these all have an effect on gravitation. In tidal terms, the closer one is to an influencing factor, the less the tide range, the farther away, the greater the range. A good analogy is when we stir a cup of tea, moving from fairly flat in the centre to high motion at the edges. There are many movements in the sea, usually caused by factors of tide, turbulence (wind action) and temperature differential. Figure 2.7 shows a windrow (Langmuir circulation), which evolves as a direct result of these influences and which is very important in mixing water and nutrients in surface layers. They can be very easily spotted and are quite a feature in inland lakes. With winter’s turbulence these windrows may extend down to a depth of 50 metres, some 35 metres greater than their maximum summer depth. Deep water currents also have an influence on the movement of nutrients and plankton and these can often be quite forceful in nature. A current may often be

34

Scallop Farming ‘windrows’

wind direction

Langmuir circulation

convergence

divergence

Fig. 2.7 ‘Windrows’.

running one way on the surface and in a different direction deeper down. At their boundary there will be turbulence, often in the form of water with differing specific gravities mixing.

Wind and wave action Wind is an important factor in the formation of upwellings but when the two combine the resulting turbulence in the surface layers (splash zone) helps to distribute heat, density and nutrients more evenly. Where the surface offshore wind is very strong the resulting waves can have an effect to a considerable depth (30 to 40 metres) and this wind, if constant and roughly in the same direction, promotes phytoplankton growth in the area providing the upwelled water is nutrient rich. On the other hand, a constant on-shore wind will not usually promote upwellings and therefore will not encourage plankton growth in that area.

Upwellings The main forces behind upwellings are usually wind and tide, which are able to move the surface water causing deep water to rise up and replace it (Fig. 2.8). As this water travels upwards it usually carries with it quantities of nutrients (inorganic ions), which are important for algal production. Nutrients lying deeper than 300 metres are unlikely to be lifted in this manner. However, the power of upwellings can last for between 100 and 250 days over a 12 month period, but if they carry few nutrients there is likely to be little plankton activity. Nutrient traps can form and these are an anomaly of upwellings where there is a constant circular motion from bottom to surface and back down. It begins with nutrients being transported into the system via lateral flow and then these are

The Farm Environment and Its Microscopic Inhabitants

35

wind direction

surface drift

upwellings

Fig. 2.8 The formation of upwellings.

carried in the upwellings to the surface layers. The plankton consume the nutrients but produce waste which sinks to the bottom and forms the nutrients in later upwellings.

Convection When heat is applied to water, turbulence is caused in the form of convection, resulting in an evening out of the temperature. However, not only do these movements redistribute heat, they also help in the distribution of nutrients. Convection cells can often be established when surface water loses heat at night from radiation, evaporation and conduction, causing the surface water to increase in density and sink. Warmer water will replace it and consequently a circular motion is created.

SEASONAL VARIATIONS We have already discussed red tides, but there are also other factors that will indicate the presence of plankton in the sea. Luminescence is quite a common factor and is especially apparent at night, often made more obvious when disturbed by a boat’s propeller. Actual water visibility is another factor, and when it is poor this usually results from an excess of phytoplankton in the surface layers. Seasonal variations are fairly predictable in the life of the plankton and Figure 2.9 demonstrates this interaction of factors, showing how all are interdependent. Figure 2.10 further refines this and shows the interaction of plankton during the peak seasonal period. This highlights the fall of excreta and dead animals to the seabed, later to be placed back into the food chain as nutrients, via upwellings.

36 Scallop Farming

sunlight

wind temperature

concentration

wind speed spring bloom

nu

winter

water movement

ph

tri

en

yto

ts

pla

nk

ton

zooplankt

on

summer

Fig. 2.9 Seasonal variations and their effect on the plankton population.

winter

The Farm Environment and Its Microscopic Inhabitants

sunlight

river nutrients

nutrients

nutrients

phytoplankton

dead cells

37

miscellaneous waste: fish farms forestry

zooplankton

faeces

dead

carnivores

plankton dead animals nutrients

nutrients detritus sediment Fig. 2.10 The interaction of plankton during peak activity.

Winter During the winter sea temperatures will be near their lowest and sunlight at its minimum. Convection cells will be strong because of surface heat being lost to the atmosphere, and, coupled with deep surfacing mixing, nutrients will be caused to rise to the surface. Both phytoplankton and zooplankton populations will be at their lowest, but with the emergence of nutrients all will be in place for increased activity.

Spring Activity is at a maximum for both phytoplankton and zooplankton during the spring months and a stable platform at this stage will culminate in satisfactory spawning of other marine organisms and adequate food resources for all. As weather conditions become more stable the water column settles down, forcing the critical level deeper. As hours of daylight increase water temperature also starts to rise, and because nutrient concentrations are high phytoplankton cells begin to multiply, taking advantage of the adequate food resource. Diatom populations will reach a peak and with the combination of plentiful food and a rise in temperature, zooplankton, in the form of temporary plankton, will join the already increasing numbers of permanent plankton. As a consequence of all this activity, phytoplankton populations will quickly become depleted.

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Summer With long days and increased sunlight, the summer is characterized by a fairly rigid thermocline inhibiting vertical mixing and a restriction on nutrients entering the surface layers. Although dinoflagellates will be at their greatest numbers, phytoplankton levels will be low; zooplankton will often avoid eating dinoflagellates because some species are toxic. Phytoplankton production will still continue in deeper water where there are supplies of nutrients providing it is within the critical level boundary. Zooplankton will be at their highest level but will quickly decline as those in the temporary category settle out and undergo metamorphosis.

Autumn Light will now be declining and water temperatures will also be past their peak. Although the deeper layers will still be quite warm, conventional water mixing will begin again as a result of the breakdown of the thermocline. This will also be assisted by an increase in surface turbulence brought on by predictable bad weather. Nutrients will be able to reach surface layers once again, and consequently phytoplankton production will increase, there still being enough light for photosynthesis. This is followed by a slight increase in zooplankton but this quickly diminishes. Because vertical mixing disperses much of the plankton below the critical depth these cells also soon die off. Once temperature and hours of sunlight approach their lowest levels, both the phytoplankton and zooplankton populations will be at their winter levels.

SUMMARY •

•

•

•

•

There are two divisions of plankton: phytoplankton and zooplankton. The former are really floating plants and they occupy the zone from the surface to roughly 200 metres deep. Scallop larvae are part of the zooplankton and these are basically floating animals which may occupy all depths. The theory and practice of classification is the science of taxonomy and this is a very complex subject, made more difficult with different professions having an interest in different parts of an animal’s anatomy. Although phytoplankton are present in the sea in varying quantities, increases in population are usually started by small celled diatoms, which are capable of a high photosynthesis rate. Diatoms may wrap themselves in silica, becoming stronger and heavier, and this extra weight causes them to sink into the seabed where they can hibernate through cold and even drought. When conditions are once more favourable they can re-establish their original position and function. Dinoflagellates are single-celled organisms, usually smaller than diatoms, and create a red tide when levels of bloom deplete the oxygen content of the water causing other marine organisms to die.

The Farm Environment and Its Microscopic Inhabitants •

• •

•

•

•

•

• • •

•

•

39

Zooplankton can range from the simplest form of animal life to other quite complex organisms, and in general they are more varied than phytoplankton. They do not have the same mortality problems as phytoplankton and adapt to their environment easily by spending the summer in shallow water and returning to deep water for the winter months. Copepods are commonly known as the insects of the sea, and are crustaceans whose basic diet is diatoms. Although from place to place there may be changes in sea conditions, generally speaking the factors of temperature, salinity, food supply, light and water movement have the greatest effect on plankton behaviour. Despite their wide geographic cover, generally speaking, temperature variations are small, with surface water usually being more varied than colder, deeper water. A thermocline is a boundary between the colder deeper water and the warmer surface water and during the summer months this can be quite distinct. Accompanying this temperature barrier there will also be a change in density and this is called a pycnocline. The viscosity of water is also affected by temperature and this can have a bearing on plankton locomotion. As temperatures increase, so water density decreases, and this has a direct bearing on the buoyancy of marine creatures. The concentration and composition of nutrients triggers initial plankton blooms and their distribution throughout the water column is affected greatly by localized physical factors such as upwellings, tide, wind and wave action, and convection. Photosynthesis is the process whereby sugar and oxygen are created from carbon dioxide and water using the energy of sunlight, trapped by chlorophyll. The constant movement of seawater is caused by a number of things, the main ones being tide, wave and wind action, upwellings and convection. When heat is applied to water, turbulence is caused in the form of convection, with a resultant evening out of the temperature. However, not only do these movements redistribute heat, they also help in the distribution of nutrients. During winter months convection cells will be strong because of surface heat being lost to the atmosphere, and, coupled with deep surfacing mixing, nutrients will be caused to rise to the surface. During the summer, although dinoflagellates will be at their greatest numbers, phytoplankton levels will be low; zooplankton will often avoid eating dinoflagellates because some species are toxic. Phytoplankton production will still continue in deeper waters where there are supplies of nutrients providing it is within the critical level.

Chapter 3 Scallop Biology and Ecology

A great deal of scientific research has been directed at studying scallops but much of it is purely academic and therefore may be of only passing interest to the farmer. The following brief look at scallop biology and ecology is tailored to what the farmer needs to know to get started and hopefully will give him more of an understanding for his species. A general overview of scallops will be of much use in farming terms and the close look at reproduction and subsequent larval growth will be almost essential if the farmer is to take up any serious monitoring of his target species.

GENERAL OVERVIEW Habitat Pectinides are happy in a wide range of seabed types and at different depths, which may range from a few metres in sheltered areas to over 200 metres in open seas. Salinity levels are important and most species will not be happy in areas where this falls below 30 parts per thousand. The availability of food is of course of prime importance and where there is little plankton the scallop population will not prosper. However, even in areas where there is food in abundance it is of not much use unless it is supplied with the aid of a fairly moderate tide. Where the tide is strong the ability to feed is reduced. Those varieties of scallop that establish a position on the seabed will usually remain in one spot for a prolonged period. The recessing process is carried out mainly by those species that are typical of the king variety, and this involves the animal actually blasting a recess in the seabed by pumping water through its shell and expelling it either side of its hinge. Once happy with the results of its efforts, it settles into the recess and allows sand or whatever the seabed composition, to settle over its flat top shell, its round bottom one having settled nicely into the hollow. The shell should now be well camouflaged and this light sand or sediment covering will also discourage other organisms like weed and mussels from forming an attachment. Where weed forms, and if it grows large enough, it will actually carry the shell away when the tide is flowing strongly, this being a major problem in bottom culture. On the other hand, the recessing also helps the scallop anchor itself 40

Scallop Biology and Ecology

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against the effect of a strong tidal flow. Other species, that do not recess, will be seen to lie on the seabed in various positions, and they usually have an algae-type coating that deters the settlement of weeds and other bivalves.

Feeding In common with other filter-feeding bivalves, the scallop is a very efficient energy converter of food and feeds by filtering phytoplankton and detrital material from the surrounding seawater. It uses no energy in its pursuit of food and a common theory is that it can also utilize food particles that are part of the bottom sediment, these becoming resuspended when the scallop claps its shell. Analysis has shown that seabed algae (benthic) are important to a scallop’s diet and sometimes these have been seen to be abundantly preferred to planktonic diatoms; our normal assumption of their diet. During the spawning season it has also been noted that actual scallop eggs make up a fairly large part of the stomach’s contents. Experiments have shown that scallops, like other bivalves, are able to discriminate algae from other particles that may have a poor nutritional value. They have also shown that they are able to discriminate between algae of a similar size, rejecting those through pseudofaeces that are found undesirable. Where food concentrations have been seen to be high it has been found that the scallop’s absorption has decreased, a fourfold increase in certain cells lowering the absorption efficiency by 20 per cent. Suspended sediments seem also to cause problems. It is thought these dilute the food resource and this is a possible reason for seemingly higher mortalities in bottom culture than those held in mid-water suspension.

Growth Shell growth is by the secretion of lamellae on the inside of the shell by the mantle, which forms the distinctive outside ridges (striae) at the edge (Fig. 3.1). A cessation in growth each year forms rings that can be used to age the scallop. They must not however be mistaken for shock rings, which are formed when the scallop is disturbed. Growth rings are usually more even than the bolder shock rings, which are formed by the retraction of the mantle at the shell’s edge.

Senses More than 100 eyes nestle around the outer edges of the mantle and those that may sustain damage can regrow within a couple of months. Rows of tentacles are also present and these have touch-sensitive organs at their tips that are sensitive to taste and smell. Juices from predators like starfish and octopus will act on these organs and cause the scallop either to swim away or to close up tight. Figure 3.2 shows the outer edge of the scallop shell with both the velum tentacles and the eyes.

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Scallop Farming mantle striae

shell edge

velum tentacles velum tentacles and eyes

mantle

Fig. 3.1 Scallop shell growth.

velum tentacles

eyes velum or mantle curtain

tentacles on mantle edge

Fig. 3.2 The outer edges of a scallop shell.

Balance The scallop has an interesting internal mechanism that lets it know whether it is the right way up on the seabed. This balance organism is a sphere of cells with sensitive hairs on the inside. A small calcareous stone is free to move inside the sphere and if it touches these hairs a message is passed to the nervous system instructing the scallop to alter its position.

Predators Like most bivalves the scallop is at the mercy of many hungry predators which, like humans, find their meat irresistible. As plankton they form part of a basic food source for other sea dwellers. Their vulnerability after metamorphosis is even greater because at this stage they are less mobile and at the mercy of just about any creature that is larger than themselves. As the scallop grows, its vulnerability

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decreases because previous predator species will no longer be able to pierce its thicker shell. Its enemies become more specific.

Starfish Starfish are nonvisual feeders, but this disadvantage does not hinder them from consuming vast numbers of scallops, especially those recessed into the seabed. They attack their prey very slowly and, once in position, and after the scallop is weakened, they inject their stomach into the scallop and proceed to consume its contents. There are many types of starfish worldwide but in temperate waters one of the most voracious feeders is the spiny variety (Marthasterias glacialis). These may often be seen in abundance, and where bottom culture is planned, their presence is most undesirable. Farmers have made efforts over the years to clear predators of this nature, ranging from liming the seabed prior to seeding, using divers to remove them by hand, specifically fishing for them, and settling other species (Astropecten aranciacus), which actually prey on other starfish. All of these methods have had varying degrees of success but the real problem lies in the fact that it can often be an ongoing process; once some are removed there seem to be plenty to take their place. Apart from diving for them, one of the most successful methods of keeping their numbers down is to position a few lobster or crab pots in and around the bottom-seeding area, mussel meat being a great attractor.

Crabs Any crab that is capable of cracking the scallop’s shell is a potential predator. This is particularly relevant when the animals are very small, but when fully grown (especially king scallops) it will take a very large crab to break through to the meat. Unfortunately the edible brown crab fits into that category nicely and, where prevalent, will be seen to attack them. A saving grace, however, is that this species of crab often prefers other bivalves, especially those living in the sand itself, like razor shells and clams. Where these other food sources are present, the edible brown crab will often be seen to take time digging for them rather than attacking a scallop lying close by. When bottom seeding is carried out the initial onslaught by smaller, faster crabs like the green crab (Carcinus maenas) will be seen to be merciless, but this may be lessened to some extent by luring them away with delicacies like mussel meat. Their numbers may then be kept down by fishing in the same way as that employed for the removal of star fish. Once the scallop shells have had time to settle into the seabed there will be less attacks by the smaller crabs, as they, like their larger cousins, have a preference for other meats if available.

Boring worms In warmer waters the scallop is particularly vulnerable to attack by a number of shell-boring worms and even shell-eating fish. There is little that can be done in

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these situations other than to keeping a watchful eye on the stock. Experience has shown that bottom stock is less vulnerable to this type of worm than is stock held in suspension and, although in some instances the shells avoid this for the first year, thereafter they seem to fall prey to it. Where the worm Polydora has been present, stocking of the seabed can be timed to miss the worm’s settlement.

Others Mussels can be a passive predator of scallops, the damage being done by their byssus thread. Weed also falls into this category and we have already discussed the problems of scallops being floated away by oversized clumps of weed. There are few known viruses that are known to affect scallops but being so delicate and vulnerable to shock they are at risk for much of their lives. Some mortality is caused by pollution and this can sometimes be experienced when using especially dirty culture equipment. Therefore the usual policy is to clean and disinfect all gear thoroughly prior to use. Other deaths are caused by the knock-on effect from the presence of other organisms. Filter-feeding crustaceans (barnacles) and tube worms growing on the outside of the shell can reduce both food and oxygen supply and may result in fatality. Algal blooms and pollution can reduce the oxygen content of the surrounding water, which, in turn, has an adverse effect on the scallop’s health. Some less obvious predators are octopus, otters, oyster catchers and eider ducks. All have been known to take scallops of varying size where conditions have allowed. There will of course be many more in different parts of the world.

REPRODUCTION Unlike other bivalves, Pectinides are hermaphrodites, in that they produce both eggs and sperm. As such most are bisexual but an occasional individual is found that is distinctly one sex. Self-fertilization can occur but successful reproduction relies mainly on cross-fertilization from neighbouring shells. Figure 3.3 shows the main organs of Pecten maximus characterized by a large roe (gonad), and fat, meaty adductor muscle. Figure 3.4 is a more detailed drawing of the roe and digestive system. When referring to both growth and reproduction reference will be made to the organs involved. For the scallop farmer, a basic knowledge of biology will help him to understand what happens at settlement time and how growth is affected by external factors. The roe holds the scallop’s sexual products (gametes) and these are divided into eggs (ovary) and sperm (testis). Between the colourful bright orange ovary and the creamy white testis there is a distinct border. In the colder, temperate waters of Northern Europe the king scallop becomes sexually active at around 3 years, while its cousin the queen needs to reach 18 months before this happens. Sperm and eggs are emitted within about 3 hours of each other and which comes out first may vary.

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ligament mouth foot

adductor muscle

testis (male)

kidney mantle

mantle

rectum

gonad

anus ovary (female)

mantle curtain

marginal tentacles

gill

eyes Fig. 3.3 The main organs of the scallop Pecten maximus.

stomach digestive gland

mouth foot kidney

muscle

alimentary canal (gut)

Fig. 3.4 A closer look at the roe and digestive system of Pecten maximus.

Only the eggs from a mature scallop with a full gonad can be fertilized and this must occur within an hour of spawning.

Gonad stimulation Factors such as neuronal state and hormonal levels will make up part of the scallop’s triggering mechanism, but external factors will also affect it. These will include temperature, food availability, light and the indication that others may have spawned already.

Temperature Seasonal variations in temperature are closely correlated with gonad growth but this does not mean that low temperatures will necessarily restrict reproduction.

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Temperature therefore should be viewed as a conditioning factor, helping to create the right conditions for the contents of the gonad throughout the whole year. Consequently, we may consider first at what point the gonad started to fill, this being critical to when it eventually empties. The most common reference to the effect of temperature, however, is when thermal shock appears to stimulate spawning, brought on by a sharp and distinct change; all other factors being in place and ready for the next step.

Food Gonad development is very energy demanding and consequently reproduction periods in most scallops coincide with periods of highest feeding. This period would also have to coincide with the appropriate temperature differentiation. It has been shown that recovering gonads are highly dependent on the levels of phytoplankton, which may explain why Pecten maximus is slow to recover from an autumn spawning when this has occurred.

Light General observations have concluded that light influences reproduction. The percentage of scallops with a full gonad tends to increase as the full lunar phase approaches, which would suggest some influence, although the effect seems to vary between species.

Presence of gametes Of prime importance to reproduction seems to be the effect of other reproductive material in the environment. The degree of synchronization seems to vary between species but, in general, once a scallop starts to release the contents of its gonad, neighbouring scallops will respond to the stimulus and react likewise.

Gonad states In Chapter 5, gonad states are discussed in relation to spat monitoring programmes. Here we will outline the cycle of gonad states in relation to influences so far discussed and then move on to the development of fertilized larvae. Interestingly, the first, and most important spawning will only be a partial one in many species of scallop, and information is therefore required as to the exact time of evacuation and whether there is any evidence of ‘dribble spawning’, possibly leading to a poor settlement. A good case study is Pecten maximus, which undergoes its first spawning as a direct result of stimuli in the form of food availability and temperature fluctuation. This usually occurs around May/June in temperate waters. Favourable environmental conditions allow the partially spent gonad to recover quickly. The adductor

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muscle gradually increases in weight during the same phase, but often losing a small amount on average in July, and it is believed that this loss is to help fuel the second gonad recovery. The gradual muscle recovery from July onwards will help with the storage of carbohydrates and proteins necessary for gonad recovery during the winter and following spring. The September/October months often see a second spawning providing the correct stimuli are in place, but those spat that settle will rarely be seen to survive. This phenomenon usually coincides with a replenishment of phytoplankton, thought to be stimulated by nutrients released by oncoming winter weather. It is interesting to note that the roe will usually be fully spent after this spawning and that adductor recovery is very slow, indicating that nutrient reserves have been called on.

Postfertilization Successful fertilization will produce a zygote, which develops into a D-shaped larvae after having passed through the trochophore and veliger stages. Before settling into what are recognizable scallop spat, these larvae will have been part of the plankton population for almost a month, being at the mercy of tide and predator. During this time they will have passed through a number of stages and been referred to in various terms. Figure 3.5 shows five stages of growth in these early stages.

Gametes The gametes, sex cells of the gonad, will be released and dispersed with a gentle flapping of the scallop’s upper shell, clouding the water around them for a short period.

Zygote An egg measuring roughly 60–70 microns, and successfully fertilized by sperm will now be known as a zygote.

Trochophore At roughly 20 hours after fertilization the larvae will have reached the trochophore stage. After approximately one further day they will then be flagellated early veliger. During this early stage they will have relied on the egg for food but older veliger, which feed while swimming, will then be regarded as planktotrophic. At this stage the velum (the most characteristic organ of the larvae) is eventually enveloped by shell growth, until then being external. This organ aids the larvae in both swimming and feeding and once substantiated can be retracted when not required.

48

Scallop Farming trochophore velum flagellated early veliger prodissoconch I prodissoconch II

‘D’-shaped larvae straight hinge 80–90 µm

pediveliger umbone 180–220 µm

post metamorphosis wings dissoconch radial markings 250–350 µm Fig. 3.5 Five early stages of scallop growth.

D-shaped larvae The D-shaped larval stage is that most referred to when discussing free-swimming larvae and it is a stage in most bivalve development, all looking much the same. Figure 3.6 is a photograph of scallop D-shaped larvae at early stages of growth, looking the same as many other bivalves at this point. This development occurs after about 50 hours and their new scientific title is now straight-hinged veliger. By the time they reach this stage they will already have secreted what is known as a prodissoconch I shell. They are now starting to feed in earnest and the shell continues

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Fig. 3.6 Pecten maximus at the D-shaped larval stage.

growth to reach the prodissoconch II stage. They will now be roughly 80–90 microns in size. When shell growth reaches a size of approximately 180 microns, the straight edge, which characterized them as D-shaped, will disappear as a result of the development of umbones (the oldest part of the shell). This is the distinctive curve at the top of the shell. The information thus far may seem a little scientific and possibly unnecessary but it is an important prelude to the pointers that characterize larval identification during the preceding stages of growth.

Pediveliger At a size of approximately 200 microns and at an age of around 30 days, a ciliated foot becomes apparent and this is soon utilized by the larva to crawl with when not swimming with the aid of its velum. During this time the larva will have slowly risen to near the surface of the sea and then back down again to the bottom. Aided by its mantle the small scallop larva secretes a lamella, which is the basis of its shell growth.

Dissoconch A distinct shell growth, and one that is very useful in early larval identification, the dissoconch is now apparent and may grow at the rate of 20 microns a day, whereas

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before this stage a growth rate of 6–7 microns was the norm. Hinge teeth will now disappear, being one of the final characteristics of the larval stage. At this stage the hinge once more becomes straight and the characteristic wings appear. The Pecten maximus we are familiar with will be easily recognized at approximately 350 microns.

Organs The stages of growth so far examined should become familiar to the farmer if he is to undertake any serious monitoring and consequent microscope work. To fuel further his interest and understanding, the following is a brief analysis of the biology and ecology of the scallop larvae. It should now be seen that only after a fairly short period, from egg to metamorphosis, the scallop larvae undergo many distinct changes, almost becoming different creatures in the process. Many of the changes result from shell development and changes in the distribution of cilia are therefore very prominent.

Velum As already mentioned, this is the most characteristic organ of the shell’s body and it is almost fully developed within a day and a half of initial shell growth. It is initially a fairly solid body, but once fully developed becomes flexible and capable of being withdrawn into the shell. Its importance lies in the larva’s ability both to feed and to swim.

Larval mantle Throughout the scallop’s life the mantle will be responsible for shell growth and this thin skin, covering the insides of both top and bottom shells, is essential if the larva is to develop.

Musculature During the early trochophore stage there are no functional muscles present but by the early veliger stage both retractor and adductor muscles will have developed.

Digestive tract At the base of the velum there is a mouth through which food enters, assisted by a steady beating of the cilia to help move it on its way. The oesophagus opens onto the stomach which also contains cilia, and this opens onto the liver. From here the food enters a thin intestine, with one or two loops, which leads into the anus.

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Foot Sock-shaped, the foot has a heavily ciliated base with a heel containing a byssus duct and a byssul groove extending forwards along its sole.

Byssus gland The byssus thread is of prime importance to the scallop during its very early growth stages and, as is the case with many other bivalves, it uses the thin thread both to hold position and to re-secrete to change position. A very good example of the byssus can be seen in mussel clumps, but these are more numerous and very much stronger than those secreted by the scallop. Five glands have been identified in the pediveliger’s foot, all involved in the production of the byssus thread. This sticky thread is secreted through the byssus duct into the bottom end of the byssul groove and can be attached and detached at will.

Gills Through metamorphosis the gills have become fairly substantial, but initially there may be only a couple of gill filaments situated on either side of the foot.

Feeding Where the size of the egg is larger than normal, larval survival has been seen to be greater because this is where initial supplies of energy come from. Feeding begins once the shell and velum have developed sufficiently both to capture and digest algae cells. The movement of the velum (ciliation) is important in feeding and its specific motion helps sweep algae towards the mouth. At this stage, the larvae can feed on algae of approximately 6 microns. Before metamorphosis the larvae are capable of taking up dissolved amino acids through the velum but this pattern of feeding changes with the formation of the gills.

Shell development and growth Between the prodissoconch I and prodissoconch II stages, after the trochophore stage, the most distinctive changes in shell shape, composition and texture take place. Concentric growth rings highlight the prodissoconch II stage and these are formed by the secretion of lamellae on the inside of the shell by the mantle. The boundary between these two stages of growth also represents a change in the calcium carbonate composition of the shell itself, and for Pecten maximus this stage will coincide with the valves (shells) being able to close properly for the first time. At this stage the hinge also changes with the gradually developing umbone, obscuring the line itself. The number of teeth along the inside of the hinge will also increase as the shell develops.

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Cell division at early stages of growth is accelerated by an increase in temperature and this is important when discussing the eventual settlement size; in many instances, this being a hint as to larval type. Studies of Pecten maximus have shown that where veliger growth was retarded by a low temperature, the resulting settled larvae were also small even though the temperature may have risen during the Dshaped larval stage. This information only underlines the importance of monitoring sea temperature, especially during the month up to settlement time.

Locomotion Although initial movement seems to be chaotic, by the time the larvae attain trochophore stage they will be seeking a distinct upwards movement. More precise movement and direction is achieved by the veliger stage and this movement is continuous until the veliger larvae is able to retract its velum. As soon as the larvae stops swimming it starts to sink to the bottom and this can be a pattern where it may spend some time on the seabed before ascending to the surface once more. Later larval stages have shown a swimming speed of over 4 metres an hour. Salinity levels, light intensity and pressure changes also have an effect on locomotion. Trials have shown that this up and down movement may be slowed if there is only one salinity band that is acceptable to the larvae, and further experiments show that the same larvae will swim upwards towards the surface more at night than during the day. This upwards motion (and speed of swimming) will also be increased when the external pressure increases, but this may have something to do with changes in water density. After a specific period of free swimming in the water column, the larvae will start to seek a suitable surface to settle on and undergo subsequent metamorphosis.

Metamorphosis Once metamorphosis is achieved, the gills, which have developed during the latter stages of larval growth, will then increase in length and number. Within a day they will be capable of full filter feeding. With the aid of the byssus thread, secreted through the foot, the shell will now seek a suitable settlement material. As the foot undergoes a change so will the thread itself, now becoming very much more sticky. Trials have shown that by introducing a suitable settlement material at an earlier stage, some larvae will show an interest and settle, and therefore bring forward their metamorphosis. This is particularly important to larval rearing in laboratories but should also be borne in mind with natural collection. Is the farmer encouraging early settlement by introducing a favourable cultch at an early stage? Metamorphosis will now be characterized by a fast growing dissoconch and this will have particular markings relating to its species. Although it may still rely on its byssus thread, it is usual for this to be dispensed with once the shell (for Pecten maximus) has reached a size of around 15 millimetres. For other species, this attachment may continue for a longer period, especially for those that do not recess into the seabed.

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SCALLOP HATCHERIES If we are to obtain a working knowledge of the behaviour, likes and dislikes, and various stages of development of scallops during larval and postlarval stages then a brief understanding of how hatcheries operate will be useful. Many hatcheries worldwide are now successfully supplying scallop spat for growing on, and many farms are dependent on supplies from them. In the past there was confusion as to the true basic cost of each animal, mainly because the hatcheries were often sited in marine research establishments and the end-product was frequently produced with the aid of grants. This was always a bone of contention with the farmer who collects and sells spat, often competing with hatcheries. Another point of debate was the survival rate of both types, the farmer often selling his on the fact that they have come from a completely natural environment. On the other hand, the hatchery has the advantage that it can supply all year round. Today, these problems have been overcome and hatchery expertise stands on it own merits. The successful operation of scallop hatcheries requires much scientific expertise as well as a detailed knowledge of larval development. Hatcheries are expensive both to set up and to operate, and good site selection is essential to the overall viability of the project. The main prerequisite is close proximity to a supply of goodquality seawater. This must be unpolluted, of even, high salinity, and of fairly constant temperature. Where the purity is in doubt, wells can be bored to give access to salt water that has been subjected to natural filtering. This is, however, a very expensive undertaking. In most cases it is sufficient to place the water inlet deep enough to miss any freshwater concentrations, temperature fluctuations and plankton blooms, usually concentrated around mid-water. A depth of 20 metres below the surface will usually be sufficient to achieve this.

Algae production Scallops, both as larvae and adults, feed on microscopic phytoplankton and these algae must be cultured. Strict control of light, temperature, salinity and filtering must be maintained during the growing process and the whole culture unit can often take up to as much as one-third of the total space of the hatchery. During the culturing, filters of 1 micron (one thousandth of one millimetre) and less are employed to contain the algae, and the whole success of the hatchery is dependent on this food source being free from disease. Bacterial contamination is the most common cause of failure, and although the algae cells may look healthy they may be toxic to the scallop larvae.

Spawning By controlling the environment through temperature and food availability, a hatchery should be able to produce spat all year round. Mature, wild scallops are held in tanks as brood stock, and water, oxygen and food are provided by circulating pumps.

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Spawning is usually induced by thermal shock, whereby the scallops are removed from the water for an hour and then replaced. The release of gametes by one animal will stimulate others to do the same. Once started the individuals are placed in separate containers until the process is finished. The mixing of the solutions from the containers must be carried out precisely, with regular microscopic examination. To avoid abnormalities, fertilization should be completed within an hour and each egg (around 35 microns) should have a maximum of 3 or 4 sperm attached to it. Antibiotics are introduced at this stage to control bacterial growth.

Larval rearing tanks The embryos reach the D-shaped larvae stage 3 days after fertilization and at this point they can be collected on a fine mesh screen and put into the larval rearing tanks. Mortalities can often be high because of collision through overcrowding and damage incurred at the twice weekly water change. At this planktonic stage they will feed on unicellular algae and actual feeding rates will be a good indication of health. The larvae are brought on to their settling size, approximately 250 microns, and this can take anything from 3 to 4 weeks. They can settle either on the fine mesh screen at the base of the rearing tanks or on a cultch (settlement material), which is placed in the tank. If the settlement material is unsuitable, thus not encouraging settlement, metamorphosis may be delayed and will result in high mortalities. The best cultches have been found to be palm leaves, shells, monofilament netting and polythene bags. Although actual settlement is usually completed within 2 days, it can be influenced by temperature changes, and this can be exploited to good effect in a hatchery.

Nursery tanks One month after fertilization the larvae are ready to be transferred to nursery tanks. Some are set up based on a good supply of seawater, while other systems have favoured a recirculating system that constantly reoxygenates the water. The latter has an advantage in that no impurities are brought in from the sea, but both systems have been quite successful. A further development is the raceway, which is as near to a sea environment as the hatcheries can get. The water is pumped through a long trough, which contains a lot of cultch. This simulates tidal flow. In some hatcheries the nursery tanks are not used and the spatted clutches are put into trays and cultured on sea-based longlines. This allows the spat a greater variety of phytoplankton to feed on and prepares them for an open environment a little later in their development. To date it has proved effective provided the byssus threads attaching the scallops to the cultch are strong and well established. Two months in this situation should bring the spat on to 10 millimetres in size, after which they can be farmed by traditional methods.

Scallop Biology and Ecology

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SUMMARY • • •

•

•

•

•

•

• •

•

•

•

•

Pectinides are happy in a wide range of seabed types and at varying depths, which may range from a few metres in sheltered areas to over 200 metres in open seas. The scallop is a very efficient energy converter of food and feeds by filtering phytoplankton and detrital material from the surrounding seawater. A cessation in growth each year forms rings, which can be used to age the scallop. They must not, however, be mistaken for shock rings, which are formed when the scallop is disturbed. As the scallop grows, its vulnerability decreases because previous predator species will no longer be able to pierce its thicker shell. Its enemies thus become more specific. Pectinides are hermaphrodites, in that they produce both eggs and sperm. Most are, as such, bisexual but an occasional individual is found that is distinctly one sex. The roe holds the scallop’s sexual products (gametes) and these are divided into eggs (ovary) and sperm (testis). Between the colourful bright orange ovary and the creamy white testis there is a distinct border. Successful fertilization will result in a zygote, which develops into a D-shaped larvae after having passed through the trochophore and veliger stages. Before settling into what are recognizable scallop spat, these larvae will have been part of the plankton population for almost a month, at the mercy of tide and predators. Feeding begins once the shell and velum have developed sufficiently both to capture and digest algal cells. The movement of the velum (ciliation) is important in feeding and its specific motion helps sweep algae towards the mouth. The D-shaped larvae is possibly the stage most referred to when discussing freeswimming larvae and most bivalves attain it, all looking much the same. Cell division at early stages of growth is accelerated by an increase in temperature and this is important when discussing the eventual settlement size; in many instances, this being a hint as to larval type. As soon as the larvae stop swimming, they start to sink to the bottom and this can be a pattern, where they may spend some time on the seabed before ascending to the surface once more. Later larval stages have shown a swimming speed of over 4 metres an hour. The byssus thread is of prime importance to the scallop during its very early growth stages and, as with many other bivalves, it uses the thin thread both to hold position and to re-secrete to change position. Once metamorphosis is achieved, the gills, which have developed during the latter stages of larval growth, will increase in length and number. Within a day they will be capable of full filter feeding. With the aid of the byssus thread, secreted through the foot, the shell will now seek a suitable settlement material. The successful operation of scallop hatcheries requires much scientific expertise as well as a detailed knowledge of larval development. Hatcheries are expensive

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•

Scallop Farming both to set up and to operate, and good site selection is essential to the overall viability of the project. By controlling the environment through temperature and food availability, a hatchery should be able to produce spat all year round.

Section 2 Hands On

Chapter 4 Choosing a Site

When seeking a site the advice usually given is to examine spat levels, water temperature, salinity, food availability, water purity, the occurrence of toxins and tidal flow. Couple these with exposure, depth, type of seabed and access and it will be seen that the prospective farmer is faced with a formidable task. His next problem will be to make sense of the many manmade regulations that will have an effect on his proposed venture. However, a logical approach to natural elements and a dogged determination to understand official regulations will quickly bear fruit, easing the task of setting up the farm and helping to make it a success. There is nothing stopping anyone carrying out small-scale on-growing and spat collection trials in a variety of sites, so, if time permits, this may be a good way to proceed.

REGULATING FACTORS Although application procedures may vary there will generally be some kind of control on the allocation of seabed leases and these may be more complex in some countries than in others. The UK has been involved in aquaculture for many years and offers a good example of the variety of controls that may be expected when applying for a site. In the UK, farming activities are regulated by five main bodies and a few minor ones, all of which can affect the outcome of an application.

Crown Estate Commission At present it is usual to first apply to the Crown Estate Commission because commissioners are in a position to know whether or not a third party has an interest in the site. If the site is available for lease, they will then advise as to the other bodies to contact. Regulations are constantly changing in this relatively new industry and it is sometimes difficult to know just what the individual’s rights are. The Crown commissioners, however, are usually forthcoming with their information and will help whenever possible to disentangle what first may seem to be a maze of red tape. This may soon change, however, as there is a move to make control more democratic and possibly the leases will soon be dispensed by the local authorities or councils. 59

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Department for Transport The Department for Transport’s Marine Directorate has a powerful voice with regard to who does what on the seabed, and is primarily concerned with permanent seabed fixtures and hazards to shipping. The Department also charts the sites and notification must be given once longlines are in place.

Government agencies At present in the UK a lease only covers that which is suspended in the water and where it is proposed to extend the lease to incorporate the seabed in the form of a Several Order then permission will usually have to be sought via the relevant governing body. The reason for this is because there is more regulation surrounding ownership of the actual seabed itself so it requires a higher authority to grant permission.

Fishermen’s associations Local fishermen’s associations will understandably want to know where leases are situated, in order to ensure that their own livelihood is not impaired. Consequently they are usually hesitant in supporting too many leases in any one area. This also applies to salmon-netting leases, as a longline or raft may alter the swim of the fish even though the two leases may seem to be a suitable distance apart. There is no reason why there should not be harmony between fishermen and farmers, and by tackling problems before they get out of hand friction can be averted.

Yachting interests Yachting clubs can be vociferous in their objection to sites, especially when sheltered anchorages are leased to farmers. Unfortunately both yachtsmen and fish farmers are looking for the same kind of site so conflict often arises. As a general rule, if a site is marked on the chart as an anchorage it is unlikely that a farming lease will be granted.

Others A final body of would-be objectors include local authorities, environmentalists, local land owners and adjacent fish farmers. It may be found that a particular local authority has a specific bye-law relating to the development of the foreshore or may be in the process of widening its jurisdiction in this area. With increasing interest in fish farming this last point is becoming more relevant. Environmentalists are also becoming vociferous in their objection to fish farms and should not be ignored. Upon receiving an application, the Crown commissioners will automatically contact farmers within the same area to seek their opinion. They already have guide-

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lines on the distances between farms producing the same species and, with increasing problems of disease, these distances are being adhered to more strictly. A shellfish farmer may have a strong objection to a neighbouring salmon farmer, who uses strong chemicals and antibiotics to promote the health of his fish. Disagreements of this nature have led to leases being sited a good distance apart. Finally, it may be necessary to contact the owner of the land adjacent to the shore in order to obtain permission to establish an access to the farm. Although this is not usually a problem, it must not be overlooked because site access is very important. In some instances the land owner may have an actual say over what happens in the sea adjacent to his land so be aware of this.

NATURAL FACTORS Once the red tape and administrative problems have been cleared, the farmer must look at those natural factors that can decide whether or not his farm will be a success. Rarely will a site be totally suitable and compromises will often have to be made. However, a visit to an established farm will often give direction as to just what is permissible. A point worth remembering is that it is not uncommon for a site to be totally successful yet break most of the suitability rules. All we can do is to outline what, to date, has been found to be suitable.

Spat levels Cost savings can be considerable if a site has its own supply of scallop spat, and it could even be true to say that this is a necessity for long-term success. Unfortunately, if there are no other farms collecting in the area the only way of discovering this is to put out some trial collectors. Specific areas may have been scientifically monitored by Fisheries Departments and this information is usually easily obtained. However, remember that these trials are usually aimed at covering quite a large area and there is rarely detailed information for specific sites. For this reason, do not necessarily accept figures that show low or even zero spat levels. A more intense programme of trials may produce quite favourable results. How many species per spat bag will also need to be brought into the equation. Whereas it used to be assumed that if the figure was not in the hundreds it was not worthwhile, nowadays a very much lower figure is acceptable and this is discussed in Chapter 11 (To collect or not to collect). To date the level of research has varied between countries but, generally speaking, its momentum is increasing as the viability of scallop farming becomes more apparent. Discovering no spat in an area does not rule it out for farming providing the other factors for survival are all present. Once more farms are established spat levels might rise very quickly and what may once have been a barren area could possibly become self-sufficient in the future.

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Food availability As filter feeders scallops rely on a steady and adequate supply of phytoplankton. Samples can be taken to assess this level, but by far the best test is to study other scallops in the area to see how they are growing. If there are no scallops, then a study of the growth of other bivalves should give useful information.

Temperature Molluscan growth is also influenced by temperature.Within normal limits, the higher the temperature, the greater the growth. The ideal site is one that has some local heating. Tide rise and fall, bottom type, depth and exposure will all influence temperature, so in order to monitor this properly, readings have to be taken at different depths over a period of weeks in both summer and winter.

Salinity Unlike oysters and mussels, scallops are unlikely to survive in brackish conditions. Clean, fully saline water is essential for their growth, so areas where there could be a build-up of freshwater in the form of river outlets or trapped rainfall should be avoided. Freshwater will usually stay on the surface, so a longline at 10 metres will normally be unaffected. However, if in doubt, tests should be taken at all depths, especially after periods of heavy rainfall. These can then be compared with an open sea reading where scallops are known to prosper.

Tide flow Food will depend on tide flow for its distribution, so this is an important point to consider. A good tide will also help to break down large concentrations of freshwater, therefore helping to keep salinity at an acceptable level. What is needed is a steady flow of water that is not so strong as to make longline work difficult or so slow that it does not support an adequate food supply. Research has shown that in areas of very strong tide the actual feeding rate of the scallop decreases. This can also cause considerable agitation to the scallops growing in nets.

Exposure If a site is too exposed to bad weather or a heavy swell, not only will scallop growth be slowed down but the ease of working may also become a problem. Scallops like peace and quiet and when subjected to constant movement will often die or grow very slowly. It is therefore important to set the line below the level of motion. Where there is a constant battering from the sea, the whole operation can become difficult if not hazardous, and the likelihood of losing equipment becomes more acute. During periods of prolonged bad weather it may be weeks before contact can be made with the farm and valuable orders may be lost as a consequence. A worst sce-

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nario would be a line actually sinking and this is quite possible during periods of intense growth for both scallops and marine fouling.

Depth If the full range of farming activities is to be undertaken, the farm fishery should range between 5 and 30 metres in depth. A minimum of 12 metres would be necessary to establish a longline. Rafts can be sited in sheltered shallow water if all other factors are suitable and provided the culture equipment never comes into contact with the bottom.

Seabed Although not obvious from the surface, the nature of the seabed can have an effect on the type of farming undertaken. The overall farm plan may be to opt for seabed culture, but if the bottom is a mass of boulders this option would prove difficult. Similar problems would be encountered in areas of soft silt. Where irregularities occur on the bottom in the form of rock outcrops, rope and equipment can easily become damaged or chafed if contact is made. When in doubt have the site surveyed either by echo sounder or by diving and, where possible, opt for a sand or shell/sand bottom. This will enable seabed culture to be undertaken, providing the scallops find it acceptable, and will also be more suitable for moorings and culture equipment.

Access A road to the shore and a small jetty would seem a luxury to some farmers who expend much energy and time in physically lifting and transporting vast amounts of equipment. The sea journey is also important. Travelling long distances in heavy seas can be time consuming, costly and uncomfortable, so access should be as near to the site as possible. Ideally it should be a short distance from a slip or jetty as well as being in full view from the point of embarkation. This would enable observations on the state of the longlines or rafts to be made from the shore.

REGULATIONS ON FOOD SAFETY AND WATER PURITY Regulations regarding food safety have become more and more stringent in recent years and bodies like the Food Standards Agency are researching almost everything that may be seen as a potential danger, be it immediate or in the future.

Toxins The opening chapter examined the problems with food safety in scallops with regard to amnesic shellfish poisoning (ASP), diarrhoetic shellfish poisoning (DSP), neurotoxic shellfish poisoning (NSP) and paralytic shellfish poisoning (PSP). Unfortunately there is little way of knowing when or where these toxins will strike next and

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an area may be clear for a number of years between bouts of closure. So can a site be chosen based on past statistics? Possibly yes, because if a specific area has been continually closed for, lets say, the previous 10 years, then it would not really be worthwhile taking a chance on growing scallops there. On the other hand, if a specific area seems to be clear for most of the time, then this may be a positive factor regarding choice.

Water purity Many areas are now classified with regard to their water purity, and for bivalves this is based on Escherichia coli levels tested on a regular basis. Classification is usually as follows: A B C

Less than 230 E. coli organisms/100 g flesh, or less than 300 faecal coliforms/ 100 g flesh Less than 4600 E. coli organisms/100 g flesh (in 90% of samples), or less than 6000 faecal coliforms/100 g flesh (in 90% of the samples) Less than 46 000 E. coli organisms/100 g flesh.

An area designated as category A may place its product straight on to the market, but a category B site must have the scallops depurated or heat treated. Any area designated category C must relay their product in a category A environment for at least 2 months, followed, where necessary, by treatment in a purification centre to meet category A requirements. Obviously if historical information shows an area to be classification B or even C for most of its life then it would be almost pointless to set up a farm there, unless there was a category A site near at hand within which the shells could be easily purified before being dispatched to market.

CHOOSING A BOTTOM CULTURE SITE Nobody will really be able to state whether or not a site is suitable for seabed culture. Because there are some wild scallops present does not necessarily imply that it will sustain densities in excess of 5 to the metre so the only way to find out the true potential is to run a trial. Unfortunately not enough research has been undertaken on the complete habits of the scallop and for some reason or other, what may seem an excellent site, may be totally shunned by the shells during a trial.

SUMMARY •

A logical approach to natural elements and a dogged determination to understand man’s regulations will quickly ease the task of setting up a farm and help to make it a success.

Choosing a Site • • •

• • • •

• •

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• • •

•

65

In the UK farming activities are regulated by five main bodies, and a few minor ones, all of which can affect the outcome of an application. Local fishermen’s associations will understandably want to know where leases are situated to ensure that their own livelihoods are not impaired. Upon receiving an application the Crown Commissioners will automatically contact farmers within the same area to seek their opinion. They already have guidelines with regard to the distances between farms producing the same species, and with growing problems of disease these distances are being adhered to ever more strictly. Cost savings can be considerable if a site has its own supply of scallop spat, and it could even be true to say that this is necessary for long-term success. As filter feeders scallops rely on a steady and adequate supply of phytoplankton. The ideal site is one that has some local heating. Tide rise and fall, bottom type, depth and exposure will all influence temperature. The problems with ASP, DSP, NSP and PSP have escalated in recent years but unfortunately there is little way of knowing when or where these toxins will strike next, and an area may be clear for a number of years between bouts of closure. Many areas are now classified according to their water purity, and for bivalves this is based on E. coli levels tested on a regular basis. Scallops are unlikely to survive in brackish conditions. Clean, fully saline water is essential for their growth, so areas where there could be a build-up of freshwater in the form of river outlets or trapped rainfall should be avoided. Food will depend on tide flow for its distribution, so this is an important point to consider. Where there is a constant battering from the sea the whole operation can become difficult if not hazardous, and the likelihood of losing equipment becomes more acute. If the full range of farming activities is to be undertaken, the farm fishery should range between 5 and 30 metres in depth. The overall farm plan may be to opt for seabed culture, but if the bottom is a mass of boulders this option would prove difficult. A road to the shore and a small jetty would seem a luxury to some farmers who expend much energy and time in physically lifting and transporting vast amounts of equipment. Because there are some wild scallops present on a site does not necessarily imply that it will sustain densities in excess of 5 to the metre, so the only way to find out the true potential is to run a trial.

Chapter 5 Collecting Spat

The most important commodity on a scallop farm is its stock and this will either have to be collected naturally or purchased elsewhere. It may be brought in at any size providing there is a suitable supply, but by far the best way forward is to investigate the prospect of finding it locally. Scallop farms situated in areas of natural settlement are very fortunate, and it could even be said that the resource is a necessity to their viability. The economic implications of numbers collected per bag will be discussed in Chapter 11 (To collect or not to collect). Setting trial collectors can indicate settlement levels, but good productive sites may be scarce so a potential scallop farmer may be forced to take up a lease which has no natural spat fall. However, as long as the farm is sited within 10–12 hours’ travelling from a good spat area he should be able to obtain supplies and bring them on with few mortalities. For now let’s assume that there is a natural spat fall on the site and the prospective farmer is going to collect some stock. For this he will use what are known as spat collector bags.

EQUIPMENT AND METHOD OF COLLECTING Spat bags The principle behind the spat bag is simple. Scallop larvae are encouraged to settle on suitable cultch (usually a filamentous filler) inside the bag by means of their byssus thread. They will stay attached in this way until approximately 10 millimetres and above in size, after which they abandon their attached position. With the mesh size of the bag being only 6 millimetres, they will be effectively trapped inside. A wide variety of bags and filling materials have been used to find the most effective combination, and there can be an obvious fall in settlement where the wrong type is used.

Filler It can be safely stated that scallop larvae have a preference for old, clean, monofilament netting as used in gill net fishing. This is not always easy to obtain because in many countries it is illegal to catch fish using this material. However, there are 66

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other materials on the market that, although not being quite as effective as monofilament, will still perform well. Garden shops display many varieties of monofilament-based plastic netting, which are very effective as cultch. Beware though of their price; just use them as a handy reference as to what is available and then go to the wholesaler and buy in bulk. Many suitable netting types are used in the food industry for loose packaging, and these can be purchased in rolls of up to 1000 square metres at very reasonable prices. As only 2 square metres is used to fill each bag, one roll goes a long way.

Bags The spat bags themselves are available in a variety of sizes and materials, all of which will have varying degrees of usefulness. The first point to bear in mind when buying is the mesh size. This should be a maximum of 6 millimetres and be evenly distributed throughout the whole of the bag. Although most bags are made up from synthetic netting they may sometimes be sewn with natural fibres. Try to avoid these because the stitching will quickly rot (to test, try setting light to a bit of the thread and if it melts then it is synthetic). The netting knots should also be checked to see whether they tighten when a thread is pulled. If they do not, the bag can easily be split open and become ineffective in the water. The most common spat collector is a type based on the onion bag but a little stronger in construction. Certain materials may seem to work better on one farm than on another and each farmer will have his preference in the bag’s netting type. Filler and setting will also vary from farm to farm and once again this will be based on past performance.

Making up the collectors For the best results the collector bags should be filled in a way that pushes the sides out, thus creating a large volume of space inside the bag.Two square metres of industrial monofilament netting stuffed into an onion type bag will give the required effect and also offer plenty of surface area on which scallop larvae can settle. When monofilament fishing net is available, a technique is used that ensures the net bundles maintain their form when in the bag. Otherwise it has a tendency to lie flat and compacted. The sheet of netting will close up with the run of its knot, so it has to be stretched against this and secured in position. This is achieved by stretching the whole length of the net (against its natural form) and tying off 1 metre lengths (Fig. 5.1). Each length when cut will be able to spring only partly back to its natural form, thus creating a rugby ball shape. To utilize this fully when it is placed into the bag the top end should be secured with the top end of the bag, thus preventing it from collapsing (Fig. 5.2). Many combinations of both bag and filler have been used for spat collection. Figure 5.3 shows the Netlon ‘humbug’ bag and the mussel stocking as a means of spat collection. The ‘humbug’ bag is large and fairly rigid, and, where spat is plenti-

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natural lay of net

cut net stretched and tied

shaped filler Fig. 5.1 Making up collector bags with monofilament netting.

filler secured at top of bag

Fig. 5.2 Hanging the bags from the line to ensure filler is in correct position.

ful, collects vast quantities. It is, however, restrictive owing to its size, and takes more time to rig. Mussel stocking filled with monofilament net is an alternative type of collector that is fairly easily rigged and worked. To set this up, a predetermined length of mussel stocking is cut, and secured to a length of 6 millimetre line. The

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humbug collectors

oyster bags

mussel stocking

Fig. 5.3 The ‘humbug bag’ and mussel stocking collector.

rest of the net is then loaded onto a plastic drum open at both ends. Roughly 400 millimetres of net is then pulled down and some filler is inserted into this via the openings in the loading drum. This filled portion is then secured to the line some 300 millimetres from the starting point. This process continues until all of the net is used. In some countries where predation is not a problem, the collectors are left out for a full year and consequently need a flat base to allow the scallops to grow. These can take the form of either a pearl net or even a fine-meshed lantern stuffed with filler. Both of these items of culture equipment are discussed in Chapter 7 (Methods of cultivation).

Setting collectors It is usual to set the collectors in mid-water to obtain the best settlement. Therefore if the average depth is 30 metres the collectors would be attached to the longline, which is lying in 10 metres and run to within 10 metres of the seabed on a rope dropper. This gives 10 metres of down line on which to attach the collectors themselves. At half-metre intervals this will give enough room for 20 collectors, but more can be attached provided none overlap. Methods of attachment are a matter of preference and Figure 5.4 shows some of the more popular ones. When many thousands of collectors are set, it is obvious that

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clove hitch

bight knot

cable tie

hog ring

Fig. 5.4 Methods of securing the bags to the down line.

speed is of the essence when bringing them in. By cable-tying the bags to the line they can easily be pulled free once aboard the boat. Some farmers prefer a clove hitch or bight knot as the most secure forms of attachment, but once tightened on the neck of the bag they require much effort to undo. In fact, they are usually so tight that the knots require cutting to release the bags. This will take a great deal of time when many thousands of bags are deployed, consequently many farmers prefer tie wraps as a form of attachment. Past experience may show that certain depths give better settlement than others, and this can be exploited by arranging the collectors to suit. On some farms the collectors closest to the bottom work the best, but this need not be the norm and trials must be carried out to check on the best settlement levels.

Hanging the bags Methods of hanging the droppers from the longline will vary according to tide, depth of water and line space available. Much thought must be put into the best method to suit a site’s particular conditions, because tangles can easily be formed and valu-

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subsurface buoys longline

weights

Fig. 5.5 Three ways of securing spat collector lines.

able equipment lost as a consequence. Some farmers prefer short, lightly weighted droppers spaced at 1-metre intervals, while others take the line with a heavier weight attached right to the seabed. Figure 5.5 shows three ways of working droppers from a longline. In some instances a farmer may need to set a small number of bags to collect spat for a trial growing scheme. To avoid having to put out a longline, the bags can be set as in Figure 5.6. This gives flexibility and a means of cheaply collecting small quantities of spat. Once the collectors have been set and the correct amount of buoyancy has been attached to give full support, they can be left to fish. After a month the longline surface buoys will show that the bags are becoming heavier and more buoyancy will need to be added. The weight increase will become even more apparent as harvest time approaches and care must be taken to ensure that none of the lines go under. All varieties of growth combine to form this weight, and another problem is added, excessive tidal drag. This can be a major problem for the scallop farmer. One unique method of setting bags is to use droppers that do not go directly to the seabed but lie within a few metres of it. Attached to the ends of these are stones inside very light mesh stocking. When the weight from settlement affects the lines, the weights will usually be the first thing to reach the bottom but after a few days

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200 mm subsurface buoy

25 kg cement block

Fig. 5.6 Setting a single line of bags.

of abrasion the stone will burst out of the net. Consequently the line will rise again, the settlement and fouling being sufficient to keep the droppers themselves weighed down at this stage.

Harvesting When the scallops attain a size of approximately 10 millimetres, preparations can be made to harvest them. Experience has shown that quick and efficient handling at this stage will help avoid mortalities, so much thought must be put into the whole operation. Once the bags are aboard the boat they are removed from their lines and carefully stowed in order not to damage their contents. The bags are emptied into a large plastic dustbin and the recovery rate at this stage will depend on the amount of time spent in removing every last scallop from both bag and filler. The filler is removed and shaken vigorously inside the bin to release spat that may still be attached, and the bag in turn is shaken to free those clinging to the outside. The bag is then turned inside out and the same process is performed, with special attention being paid to the corners to ensure that no spat are missed. The filler can then be put back into the bag for stowage.

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When dealing with a delicate species of scallop it may be found to be more appropriate to undertake all of the emptying within a bath of seawater, being far less vigorous with the shaking out. This is fine but it will take much more time because often the attachment can be quite strong, being assisted in many instances by other organisms growing alongside. The next stage will depend on what is collected. In many instances the bin will quickly fill because of the inclusion of marine growth like sea squirts and, if this is the case, then it should be allowed to reach about one-third its volume before proceeding to the next stage. The best way to remove the unwanted weed-type debris is to float it out. This involves filling the bin with seawater and gently tipping it, the seawater taking with it all that now floats on the surface. If what is collected is fairly clean and the bin takes time to fill, the best procedure is to move to the next stage after about 20 minutes’ handling. Although sorting is not totally necessary at the stage, the farmer will have to remove any predators, debris, fouling organisms and pests, which may have also settled as larvae. Starfish and crabs are obvious ones but mussels can cause devastation if left to grow, so they must be removed. The mussel can secrete many byssus threads and these will strangle any scallop spat that may lie in its path. Procedures in riddling and sorting and the equipment used are discussed in Chapter 7 (Methods of cultivation) and Chapter 9 (Design and manufacture of equipment), but it is sufficient to say at this stage that a combination of methods will have to be employed by the farmer because no one situation will be the same as another. One important point to bear in mind, however, is to wash the stock, be it still mixed or otherwise, with clean salt water at regular intervals. Once sorted, the juvenile scallops are put into either pearl nets or lanterns, which are, in turn, quickly tied onto a longline. The quantity for each layer is first counted out and then roughly measured in terms of plastic scoopfuls, thus greatly speeding up the loading process. As the aim is to put the spat back into the water as quickly as possible, it is best to lift only a small number of bags at a time. The number will, of course, depend on the quantity of spat in each bag and the level of fouling and non-useful settlement, but as a rough guide 100 bags each containing 150 scallop spat will take one man approximately 6 hours to handle. In this situation it would therefore be better to lift only 50 bags at a time. It must also be remembered that the farmer can often be caught out by the weather, preventing him from returning to his longline. Unless he has facilities ashore to cope with this situation he will be forced to hang the lanterns off the side of his boat in the hope that no harm will come to them in the short term. What he must not do is to fill collector or other net bags with them and leave them underwater like this for any extended period. This is one of the quickest ways of achieving high mortalities and, although mature shells may survive limited amounts of this kind of handling, spat certainly will not. Most large farms have a tank on shore which has seawater pumped to it. With this they can take the spat ashore and sort it in their own time as they are not at the mercy of the weather. Care must be taken though, to ensure there are no dif-

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ferentials in temperature between the offshore and onshore sites, because this can severely stress the scallop spat, resulting in high mortalities.

Predation Although the contents of the collectors may have been thoroughly examined for predators, there are always some that end up in the next stage of cultivation along with the scallop spat. Minchin & Duggan (1989) observed that as many as 90 scallop spat could be tied into the byssus nest of one 10 millimetre mussel. In the research conducted by the Fisheries Research Centre in Dublin it was found that if dog whelks were put alongside the spat they ate any mussels and barnacles that were present. Over a 54 day period, approximately 30 per cent mortalities were caused by mussel predation. This was reduced to 3 per cent where dog whelks were present. Some spat shells were drilled, which showed that they would also fall prey once the mussels and barnacles had been cleared. A continuation of this principle would be to introduce the common periwinkle (Littorina littorea) to the culture trays. These shellfish feed on weed and would consequently help to keep marine fouling to a minimum.

Bag numbers The question of logistics is important in spat collection. On a good site the farmer may only set 500 to 1000 collector bags for his own needs, and these are quite easily handled. However, if he goes into subcontract collecting, which would involve many thousands of bags, he will require much space for both handling and working. As speed is of the essence he will need to establish offshore working platforms to reduce handling time, and these may also be used for temporary storage until the whole harvest is accounted for.

SPAT HANDLING We have already touched on a few of the finer points in spat handling but there are other principles that should be adhered to. Avoiding mortalities during on-site collecting is difficult enough, but keeping them to a minimum when spat needs to be shipped in from other sites requires even more considered attention. In ideal conditions the maximum time spat can safely spend out of water is 12 hours, and even in this situation mortalities will occur. To reduce losses it is essential to ensure that the spat are handled correctly at the supplier’s end. This will mean being there as they come out of the water. They must then be placed in a suitable type of packaging, either trays or very loosely filled onion or spat bags. Trays are superior because they will enable the spat to breathe a little during the journey and the whole package can be put straight into the water on arrival. The trays will, however, usually have to be supplied by the farmer himself.

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75

It is also necessary to maintain a stable environment during the journey. Temperature is critical to survival and it must be kept as constant and as close as possible to what it was when the spat left the water. It is therefore important not to ship spat on hot days. Exposure to freshwater must be avoided, so the consignment will need to be covered to protect it from the rain. However, spat also need oxygen so air must be allowed to circulate around them. Work has been undertaken on what are known as saturated air systems for the prime purpose of transporting spat. The trays are stacked in an enclosed box, usually mounted on a trailer, and a very fine mist of seawater is circulated inside via a high pressure pump with specialist nozzles.The results have been very good but the initial cost in setting the unit up is very high. It is also impeded by the fact that the numbers transported at any one time are quite low relative to traditional methods. Where a journey by sea is undertaken, it is feasible to stop and sluice the trays or bags with a few buckets of seawater. Seaweed spread over the consignment will also help to keep both the surrounding air and the spat moist, and it is a good idea to chill the weed first if temperatures are higher than normal. After a long journey all the spat will be stressed and they will need to be put back into seawater as quickly as possible. If the stocking density in the trays is not too great, they can be left hanging overnight to settle and may then be thinned out the next day. If the spat are in onion bags, they will need to be put either into trays or lanterns immediately on arrival and the bags themselves can be hung in the water while this task is being performed. The rule of thumb is to ship only as much spat as can be both quickly and properly handled at the destination, and in this way mortalities can be kept to a minimum. It is also prudent to have a second option for hanging other than the longline, to ensure that if the weather is bad on arrival the spat will still have somewhere suitable to be housed.

THE SCIENCE OF MONITORING Where there is the slightest indication of a spat settlement, the farmers within the area will want to know more about their resource and how to maximize its potential. The collection of data can be both interesting and rewarding and should lead to more accurate predictions of settlement dates and variety of settled species. This, in turn, will help reduce harvesting costs and make subcontract collection a more viable prospect for a potential buyer. Monitoring can take the form of either a few collector bags being set on a particular site to check for the presence of wild spat, or a very detailed examination of the whole process of spat settlement, including competitors and predators. For worthwhile results a monitoring programme should be run for 3–4 years, with little deviation in procedure. The ultimate aim should be to pinpoint exact settlement times and, if possible, to ascertain whether the spat originates from the local area’s wild population or from elsewhere. Other useful information will also be centred

76

Scallop Farming sunlight rainfall

lunar phases wind temperature salinity

DEC

turbulence

DEC nutrients

gonads zooplankton

phytoplankton tides seabed composition Fig. 5.7 Marine activity throughout the year and what the farmer may want to observe.

around the presence of predators. Initially, support may be sought from local marine laboratories in the form of microscopic identification and gonad analysis but there is no reason why the farmer should not eventually become proficient in these skills. The following text examines a comprehensive monitoring programme, with all of the science that goes with it. It is not a cause for dismay if it all looks too complicated and beyond a prospective farmer’s ability. All that may be required is to set a few bags in some strategic spots, leave them for 2–3 months, retrieve them and sort the contents. It is easier still to watch the other farmers in an area, if there are any, and set your collector bags when they do. However, if there is any juvenile potential in an area and, providing other farmers are willing to lend a hand, much can be learned about its full economic potential and the most effective method of collection. It is also a very intriguing process. Figure 5.7 shows, in pictorial form, just what the farmer will be attempting to observe and record throughout a calendar year, and Figure 5.8 shows what is required to undertake this.

Plankton hauls If an understanding of what happens in the sea during spawning times can be reached, then some advantage can be gained by tracking these events early. This is what the plankton haul is used for; it gives the first indication that something is happening in the reproductive world of the bivalve. Wild spat are usually all settled within their first 4 weeks of life and at this stage they should be approximately 250 microns in size. Up to this point they are part of the plankton population and at the whim of wind and tide. Samples can be taken with the aid of a plankton net. This is when one of the main problems becomes apparent, that of identification. D-shaped

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1. gonad analysis

2. plankton hauls

3. trial collectors

slide preparation

microscope examinations

4. collector bags

5. commercial collection

Fig. 5.8 Stages of monitoring and some of the equipment required.

larvae, already discussed in Chapter 3, are produced by many species of marine bivalves and below 200 microns in size they all look much the same, no matter how powerful the magnification. It takes a very skilled microscopist to make any definite identification at this size and the most that can be hoped for is to ascertain that there are actually D-shaped larvae in the water, among which there might be some scallop larvae. If plankton samples are to be taken over the whole monitoring programme, the system must be regularized. Samples can be taken either at specific depths or through a column of water, the latter being the easiest. With analysis being speculative, the column of water sampled should give a good ground base to work from, although it may not divulge the exact depth the specimens come from. Historical information from test collectors will soon provide this information and it is sufficient that the plankton haul merely indicates that bivalve molluscs have spawned and the larvae are at a size that could indicate an imminent settlement.

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In order to sample a column of water the plankton net is either dropped to the seabed and hauled to the surface with its opening to the top, or it is enabled to collect while both descending and ascending. It is important to sample approximately the same spot each time and a good water depth would be roughly 30 metres, if available. Once the haul is complete, the contents of the net’s sample jar are poured into a flask and taken ashore for further preparation and examination: (1) (2)

The contents of the flask are poured through two filters, one of 250 micron mesh to remove large debris, and one of 100 micron mesh to collect actual specimens. The specimens are then washed off the filter screen with 100 millilitres of clean, filtered water into a sample jar.

If they are to be examined within 12 hours, no more preparation is needed. However, if they are to be kept for future reference then the specimens should be preserved by adding 5 millilitres of formalin to the water in the jar.

Trial spat collectors Once it has been established that there is some spawning activity in the water, the next stage is to try and establish if or when the scallops are starting to settle. This is where the trial collector comes into its own. Much information can be obtained from trial collectors and the more expert one becomes at larval identification the closer one will be to predicting settlement times. Either local information or the results of successive trials will indicate the approximate time of settlement, and this is when intensive sampling should be carried out. To help avoid collecting excessive quantities of sediment, rolls of Netlon (usually approximately 9 millimetre mesh) are used as trial collectors and these are set five to a line at 2 metre intervals (Fig. 5.9). The number per line may fluctuate, depending on the intensity of sampling required. Figure 5.10 shows a sampling programme in which the intervals decrease from 7 to 3 days. The higher intensity of sampling will give a more exact picture of what the larvae are doing and the information from these collectors will determine when the actual spat bags go out. When each string of collectors is lifted, one is removed and set on a separate line to allow growth for a further 6 weeks. After this period the process of identification should be almost 100 per cent accurate and will, it is hoped, confirm the observations of the earlier analysis. Once the trial collectors are aboard the boat, the Netlon tubes should be placed inside a large plastic bag to prevent any drying out or loss of spat during transportation. To isolate specimens for examination proceed as follows: (1) (2)

The Netlon collectors are placed into a bucket full of clean, filtered water containing a 5 per cent chloros solution (sodium hypochlorite). They are then vigorously agitated to detach the specimens from the netting (the chloros dissolves the byssus thread). A second approach to this process,

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9 mm Netlon tube 300 mm high

Fig. 5.9 Trial collector.

(3)

(4)

although perhaps not as scientific, is to brush the collectors lightly with a soft bristle brush that is small enough to also go inside the tubes. Some specimens may be slightly damaged during this process and not all may be recovered, but it is a satisfactory and easier alternative. The contents of the bucket are poured through two filters, one of 400-micron mesh to remove large debris, and one of 100-micron mesh to retain the specimens required. The sample is washed off the filter screen with 100 millilitres of clean, filtered water into a sample jar.

If the specimens are to be preserved for future reference, add 5 millilitres of formalin to the sample jar.

Collector bags So far data will have been collected that hopefully gives some indication of an imminent settlement of scallop spat, and this is a common practice with farmers to ensure they are setting their bags at the most accurate time. However, to ascertain the settlement in terms of overall quantity and to gain some feedback on information gathered from trial collectors, actual spat collectors may be set weekly over a period of 3–4 weeks (around peak settlement time) and allowed to lie for up to 90 days. Methods of setting these have already been discussed. The contents of these are analysed at the end of the growth period and the findings will help paint an overall picture of settlement within an area. The procedure can be extended to incorporate a monthly check to see whether there are any other settlement peaks during the year and this type of programme will be examined later in this chapter.

80

2

4

3

Settlement month 5

Temperature readings – weekly for 52 weeks

Trial collectors – monthly for 52 weeks

Wind speed and direction – weekly average

Gonad analysis – weekly

Plankton hauls – weekly Trial collectors 7 day

3 day

Six week trial collectors Ninety day trial collectors Fig. 5.10 A simplified year-round monitoring programme.

6

Scallop Farming

Month 1

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lead weight

81

jubilee clip 100-micron net

sample jar

Fig. 5.11 A plankton net (plankton haul).

Scientific equipment and practice A plankton net is required for the initial sampling and this may either be purchased or homemade. Figure 5.11 shows a plankton net in its basic form and this can quite easily be constructed by anyone with a little practical skill. For the body 150 micron netting is required, and the sample jar requires netting of 100 microns. Material of this nature can be purchased through suppliers of filter material in such areas as automotive fuel, etc. Trial collectors will be homemade using Netlon tubing but to preserve specimens some small, sealable sample jars will be required. Quantities of chloros and formalin are necessary for sample preparation, as well as some sturdy plastic buckets. It may be necessary to neutralize the formalin if specimens are to be kept in a solution for any period of time, in order to prevent any dissolving of the shell (formalin may break down into formic acid if exposed to sunlight). It is therefore standard practice to neutralize or ‘buffer’ the formalin to prevent this from happening. It must be noted that seawater is used to make up the appropriate strength of formalin when preserving marine specimens, as the solution must be isotonic with organisms involved, that is, they need the same salt balance inside as out. To neutralize the formalin proceed as follows: (1) (2)

Take 900 millilitres of seawater, 100 millilitres of 40 per cent formalin, and calcium carbonate. Mix the two liquids and add the calcium carbonate to excess. Keep adding the calcium carbonate until the solution is completely saturated and there is an excess of powder collecting in the bottom of the mixing jar.

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pipette

Petri dish

grid

Fig. 5.12 A Petri dish and pipette.

(3)

Decant off the clear formalin solution from the top of the mixing jar for use. This will now be referred to as 4 per cent formalin. Any excess calcium carbonate may be re-used.

Two very important items of scientific equipment used in our procedures are the Petri dish and the pipette (Fig. 5.12). The Petri dish is useful not only as a collecting medium but also because some have grids marked into their bases, which is useful for any counting of specimens. The pipette is used to transfer both liquids and specimens between other items of apparatus and is very useful when measured amounts of liquid need dispensing (performed by drops). If the nozzle of this piece of equipment is too narrow, breaking it off further towards the body will increase the size of the opening. With a little practice and the use of a gas burner, the nozzle may in fact be shaped to suit the farmer’s needs. A useful point should be made here about the practice of taking samples via a pipette. Obviously, specimens will lie at the bottom of sample jars and it will be a hit-and-miss matter to obtain a uniform sample. To counter this, a useful practice is to stir up the jar and then take a pipette-full from the middle as the liquid is still circulating. Be sure to use this same principle on all occasions to keep procedures uniform and thus more reliable.

Microscope If samples are collected then they will require examining. The most expensive and possibly the most important item of equipment is therefore a microscope. Very basic models can be purchased quite cheaply second hand and should suffice providing they fulfil certain requirements. Generally speaking the microscope does not need to be high powered but does need to be able to view quite a large area at once. Being able to zoom in on a species is also an advantage. A good model would have twin eyepiece (stereo), and its own light source, this being both incidental (coming

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stereo lens (interchangeable)

light source

variable objective

incidental light

slide holder

light source

transmitted light

Fig. 5.13 A microscope.

from above) and transmitted (coming from below). With regard to magnification, a microscope with a variable objective (×1 and ×3) and two sets of lenses (×10 and ×20) would be ideal, giving a range of 10 times magnification for large areas and 60 times for individual species. On the luxury side it would be nice to have a unit that also had the facility to mount a camera to record specimens. Figure 5.13 shows a practical microscope and some of the terminology relating to it. Although much can be learned from looking at samples, a great deal more can be gained by being able to measure them. To enable this, a graticule (Fig. 5.14) will need to be fitted to one of the lenses in both of the sets. This will then show a small scale of between zero and 100, which, although discrete, will always be in view. The problem is that with so many variations in magnification, the value of the scale will change accordingly so it must therefore be calibrated. There are mathematical formulae to work this out but the simplest procedure is to purchase a gauge with 1 millimetre marked off in 100 segments, each segment being equal to 10 microns. This can then be viewed against the graticule on the particular lens. If for instance 50 segments of the lens graticule equal 100 on the gauge, then when viewing specimens at that particular magnification, each segment will be equal to 20 microns.

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calibration

gauge lens

10

10

20

30

40

20

50

graticule

30

40

50

60

70

60

70

80

90

100

80

90

100

1 mm gauge

Fig. 5.14 A lens graticule.

Preparing slides For those who are more scientifically trained than most, not only may they be able to take photos of specimens but they may also like to mount some on slides for future reference. There are a number of ways of doing this. Possibly the best method is to use slides that have a recess in the middle: (1) (2) (3)

(4) (5)

By means of a pipette the sample is transferred from the sample jar and deposited in the slide’s recess. It is then carefully examined under the microscope to ensure that it contains the correct type and number of specimens. A bead of ‘glass bond’ (glass glue) is then run around the outside of the sample and a cover slip (a small and very thin piece of glass) is placed over the sample and glue. The tricky bit is now to try and expel as much air from the set-up as possible by gently squeezing the cover slip down. The prepared slide is then exposed to direct sunlight to begin the glue curing process.

Figure 5.15 shows this process. This method of preparation, known as nondehydration, forms a small aquarium within which the specimens are free to move. A more permanent procedure is known as ‘dehydration and hystomount’. The object of this method is to replace the water in the larval samples with alcohol before fixing them onto a slide. The procedure is as follows: (a)

Samples are placed onto a Petri dish with a pipette and any excess water is drawn off with the corner of a tissue. (b) With a pipette, a few drops of 70 per cent alcohol are placed on the specimens and left for half an hour. (c) Excess liquid is now drawn off and the process is repeated with 90 per cent alcohol, and finally 100 per cent alcohol. (d) Any excess liquid is now drawn off and a few drops of Histoclear are placed on the specimens. Leave for half an hour.

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glass cover slip specimens

mounting medium

glass slide cover slip sealed with nail varnish

Fig. 5.15 Slide preparation.

150 mm plastic drainpipe

plastic insert

components glued together net screen

filter stack

Fig. 5.16 The construction of filters.

(e) (f)

Place a couple of drops of Hystomount onto a slide and transfer the specimens by pipette. Now seal with a cover slip. The edges of the cover slip may now be sealed with nail varnish.

Filters Filters may be purchased that have varying (certified) mesh sizes, and are able to be stacked together. Because they are quite expensive, most farmers construct their own by sticking a mesh screen to a piece of plastic drainpipe (Fig. 5.16). The material is the same as in the plankton haul but this time four sizes are required ranging

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from 100 to 400 microns. The object of filtering is to isolate the species to be studied and to remove any unwanted debris. In a plankton haul any scallops present will be under the settling size of 250 microns so the larger material can be filtered out. It is unlikely that any positive identification can be made of specimens smaller than 10 microns (only that they are D-shaped larvae of some kind), which means the remaining sample can be collected on a 100 micron filter. The filtering procedure for the specimens from the collectors is different because the average size of the scallop at this stage should be greater than 250 microns. The sample can therefore be poured through a 400 micron filter to take out any unnecessarily large debris and the remainder can be collected on a 200 micron screen. Where monthly samples are taken, the scallops will be much larger, so the specimens between 400 and 1000 microns will be collected for examination.

Recording information Obviously, by this stage, a farmer would have been involved in a lot of extra effort and it would be a pity not to maximize on this by being careless with information. The collation of all figures and observations is important as this will form the basis of pre-empting settlement times in the future. Over a period of 5–6 years some patterns may begin to appear. When a few farms start collecting similar information and then share it, many useful conclusions can be drawn.

SPECIES IDENTIFICATION The farmer will need to be able to make some kind of identification between species and the smaller the stage at which he is able to do this, the more useful the ability will be to him, especially when identifying predators. We have already discussed the problems with identifying specimens in the plankton haul and that it suffices usually to ascertain that bivalves are in suspension and ready to settle at some point (usually determined by size). As the scallop develops it becomes more easily recognized, so the samples taken from those trial collectors that have been in the water for 6 weeks should not pose too much of a problem. Most will be as large as 1 millimetre, and at this size the task is to separate one species from another, be they scallops or otherwise, any bivalve being easily recognized. Where, for instance, Pecten maximus have settled alongside Chlamys opercularis, a quite common occurrence, by being able to distinguish between the two species the farmer may be able to target the one he wants because their exact settlement times will usually differ, even though only slightly. The obvious benefit is a saving on sorting time and a consequent saving on equipment utilization.

Pectinides Many bivalves are classed as D-shaped larvae during their planktonic stage and it is almost impossible to tell them apart. Figure 5.17 shows some larvae sized from

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house mussel

saddle oyster

dog cockle

razor shell

common cockle

otter shell Fig. 5.17 Some common larvae sized from D-shaped to maturity.

D-shaped through to maturity, and emphasizing the problems at the very small state of development. The problem is further aggravated by the shells themselves being almost translucent. To demonstrate just how detailed the differences may be, Figure 5.18 is a more detailed view of Pecten maximus and Chlamys opercularis, showing identification marks on their shell edge. Figure 5.19 is an actual electron microscope photo of a 500 micron P. maximus, and a 500 micron C. opercularis showing the dissoconch detail as the shells grow in size. Unfortunately in smaller shells these differences are very difficult to spot, as are the hinge teeth which are characteristic of many bivalves. Figure 5.20 shows P. maximus as seen through a normal microscope and highlights the problems with shell identification even at the 350-micron growth size. Figure 5.21 is a mixture of species ranging from newly settled to some around 400 microns and once again accentuates the difficulties with identification.

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220 microns Chlamys opercularis

magnified view of edge

220 microns Pecten maximus Fig. 5.18 Shell detail on Pecten maximus and Chlamys opercularis.

Within the Pectinides there will be many specific identification marks, far too many to outline at this stage. Basically, identification at early stages of growth will be based on such things as specific shell markings, hinge teeth, length–height relationship, larval colour, shell outline, size on settlement, and post-settlement development. These are areas in which the farmer will need to gain expertise if he is to go down the road of close scientific research.

Mytilids One other species that settles in abundance almost everywhere, and which is the cause of great mortality when settled alongside any Pectinides is the mussel (Mytilid). One of the most significant clues to identification between these two species is the way they develop their individual triangular shapes. This, coupled with umbone development and size on settlement will give the farmer something to work on when studying the contents of his plankton haul and trial collectors.

Other species There will be many varieties of species collected and this will vary between areas. Figure 5.22 shows just a few and demonstrates just how difficult they are to identify at larval stages. All of them are either predators of Pectinides or a nuisance to the collection process. There is no doubt that the longer spent in examining the species the more accurate will be the attempts at identification. It may end up as literally a feel for the job with an inability actually to identify specific characteristics. Whichever way the

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(a)

(b) Fig. 5.19 Electron microscope photographs showing the dissoconch markings of 500-micron shells: (a) Pecten maximus; (b) Chlamys opercularis (by kind permission of Aberdeen University).

farmer becomes efficient is of no account, the mere fact that he is applying himself to this science and that he can identify, at early stages of growth, maybe even only one or two species, will be worth much to him in the long run.

GONAD ANALYSIS Information on when the wild scallop actually spawns is important to the whole monitoring programme. Each area will be different and it is difficult to predict exactly

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Fig. 5.20 Pecten maximus as seen through a normal microscope.

Fig. 5.21 A typical sample taken from a trial collector and outlining the difficulties with identification.

where particular larvae will end up after being suspended in the seawater for possibly up to 4 weeks or even longer. In some countries satellites have been used to plot the path of ocean and coastal currents in an effort to solve this problem and no doubt this will become more common practice as interest in scallop farming grows.

Collecting Spat

shore crab

edible crab

sea urchin

common starfish

barnacle

91

sea squirt

Fig. 5.22 Some other specimens that may settle, illustrating the difficulty with identification at early growth stages.

What the farmer is looking for is some kind of pattern. If his settlement occurs within, say, a week of his local scallops spawning, it would suggest that the spat comes from parent stock elsewhere. If the time elapsed is up to a month, he may be convinced that the spat originated from his local stocks. Whatever information he gathers must be substantiated over a period of time and it is here that gonad analysis becomes important. Spawning characteristics vary with species and area. It is therefore necessary to establish some kind of pattern in the species that is native to the farm area. In his work on gonad analysis, Duncan (1989) observed many varying spawning characteristics in scallops (Pecten maximus) caught within a fairly small area off the west coast of Scotland. Some areas had scallops that did not spawn in the autumn although were capable of doing so, while in other areas all those capable seem to have spawned. It was also noted that those that spawned early did so over a long period and hence did not recover quickly enough for an autumn spawning. Late spawners emptied their gonads quickly enough and recovered quickly in preparation for autumn. Mason (1958) and Amirthalingam (1928) studied the possibility of lunar periodicity in spawning and discovered that in certain areas spawning coincided with the full and new phases of the moon. The main reason for this phenomenon would probably be the effect of tide, the availability of food, and the changes in light. Mason (1983) gives a good account of gonad states in mature scallops, which is most helpful for the purposes of observation. Figure 5.23 shows stages in the gonad of Pecten maximus from its full state to being completely or partially spent. These are: (1)

Full. Gonad looks large, shiny, colourful and healthy. It is at least half as thick as it is wide and its full state has given it a rounded appearance. Its follicles

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1. full

4. half full 2. spent

3. filling

Fig. 5.23 Gonad development over 12 months.

(2)

(3)

(4)

are highly coloured and tightly packed and there is no sign of the alimentary loop. The gonad actually feels firm and unbending, and its skin is tight. The testis is creamy and the ovary orange/pink. Spent. A fully spent gonad has a brown colour and looks to contain mostly water. It is small and completely flaccid and in some cases there is no differentiation between testis and ovary. Those that are partially spent will still have a differentiation but will be flaccid, small, and angular in shape. In both cases the alimentary canal will be visible and the follicles will appear well spaced and empty. Filling. The gonad’s thickness is about one-third of its width and it contains some free water. Its follicles are filling and therefore closer together and some bright colour is coming back into both testis and ovary. The alimentary canal is visible between the follicles in the testis but not in the ovary. Half full. At this stage the roundness is coming back into the gonad but the tip still tapers slightly. The follicles appear large and tightly packed and the loop of the alimentary canal may still be visible. The colour differentiation is more pronounced and there is little evidence of any free water.

A more detailed analysis of the gonad may be carried out but the processes are usually performed in marine laboratories. One of them however, could, be tackled by a scallop farmer if he required more information on gonad states.

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Wet gonad index Possibly the only problem with using this technique is that it requires the destruction of approximately three dozen shells for each single piece of information. However, the sample figure may be reduced if it is decided that all that is required is an indication of gonad state, and for this six shells would suffice. The process firstly involves removing the gonads from the rest of the shell’s contents and carefully drying them on paper towels. Next, all of the shell’s contents are weighed including the gonads. Finally, the gonad is weighed on its own. The wet weight index is the gonad weight divided by the total tissue weight multiplied by 100. The weight of the gonad is therefore expressed as a percentage of the total tissue weight of the scallop. The index would be calculated as an average based on the number of shells examined. This could be as high as 30 per cent when the gonad is at its fullest, falling to around 5 per cent when it is fully spent.

Dry gonad index For very serious studies a dry index is often preferred because water content will vary seasonally and among different tissues. First, the tissue is processed by either freeze drying for 48 hours or holding in a totally moisture-free environment at a constant 15.5°C for 6 days. The weighing process continues as for the wet index.

Use of gonad analysis to the farmer So just what is the farmer to make of this information? First, if he knows the location of his brood stock then he can almost predetermine settlement by observing when the roes are spent. However, even if the location is not known, he may still tell a great deal from the gonads of local stocks. He may find, through historical research, that when the local scallops spawn he may have settlement some specific number of days later. Also, by observing the gonad both before and after spawning he may be able to predict a good or a bad settlement. If it is only partially spent or if it does not follow the usual pattern, then this may indicate an anomaly in settlement later on. It is worth his while speaking to local scallop processors if there are any nearby and quizzing them as to where stocks originate and the state of their gonad when shucked. In this way he may build up a better picture of what is happening in the sea.

COMPREHENSIVE MONITORING PROGRAMME When trial collectors have indicated the presence of wild spat in an area the farmer must try to collect them in an economic and effective way. Monitoring schemes will help to indicate the presence of scallop larvae, but the information will be out of date by several days when analysed. He must, therefore, speculate with his collectors to be sure of getting some to fish well for him.

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Working the collectors Once in the water, a collector will fish effectively only for a short period. In temperate waters this is approximately 10 days but in warmer areas it will be less. Scallop larvae are particular about the nature of the surface they settle on, and once any weed has taken hold they will be less inclined to choose that surface. Usually, after 10 days, weed and sediment have contaminated most of the settlement material, bag and filler, rendering it ineffective. This is why the monitoring programme is so important, especially in areas where there is only a light spat fall. This programme can be extended over the full year to examine complete settlement patterns and other factors that may have an influence on the outcome. Before monitoring programmes were used, scallop farmers would spread the setting of collector bags over a period of 4–6 weeks in the hope of hitting peak settlement with a proportion of them. This often meant that only one-third of the equipment fished effectively. This no longer has to be the case and nowadays a farmer will be fairly certain of hitting peak settlement and as such will deploy many fewer collector bags. As he accumulates more expertise in species identification, he can be more precise in the setting of his bags. The Japanese work on a system whereby they put out their spat bags when 50 per cent of the spat settled on the trial collectors are over 200 microns in size. Scientists are involved on a full-time basis to compile information of this kind and it is a most enviable situation. Obviously reaching this level of expertise takes many years, so for most scallop farmers there will still be a degree of speculation as to when they should put their bags in the water.

Extending the programme In Chapter 2 we examined those factors that have an influence on what happens in the sea over the period of a year and this has been graphically illustrated. Our full scale programme should therefore encompass as many of these elements as possible, along with settlement patterns, our aim being to construct a calendar of marine settlement and hopefully predict when settlement patterns are likely to change or fail as a result of some previously unforeseen changes. So far we should be able to interpret scallop gonad states in relation to spawning, identify bivalves free-swimming in the water column, identify settled Pectinides (providing they are large enough) on our trial collectors, and identify various other settled larvae. This could therefore be a good basis for a full 12 month monitoring programme and bags could be set accordingly. Over the busy late spring, summer and early autumn months a set of three bags could be hung every 2 weeks, covering the range of deep, mid-water, to shallow, and then reduced to one set per month for the rest of the year. By leaving each bag in the water for only 1 month its contents will be very easily identified and it is important to count and identify, if possible, all that has settled. In this way much useful information can be collected.

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Other trials General observations can be made of hours of sunlight, lunar periodicity, wind speed and direction and rainfall, but in order to ascertain water temperature, salinity, nutrients and phytoplankton levels, other more precise measuring equipment will be required. This would possibly be the stage at which a farmer or group of farmers would bring in a student who might be willing to complete a thesis about some aspect of Pectinide activity in relation to these other factors. This is not an uncommon practice and it often highlights a farmer’s own expertise in a field that he may have thought he was ignorant about. It is surprising just what information you gain by working at it year in year out.

SUMMARY •

Scallop farms situated in areas of natural settlement are very fortunate, and it could even be said that the resource is a necessity to their viability given the success of hatcheries to date. • A wide variety of bags and filling materials have been used to find the most effective combination, and there can be an obvious fall in settlement where the wrong type is used. • For the best results the collector bags should be filled in a way that pushes the sides out, thus creating a large volume of space inside the bag. • In some countries where predation is not a problem, the collectors are left out for a full year and consequently need a flat base to allow the scallops to grow. These can take the form of either a pearl net or even a fine-meshed lantern stuffed with filler. • When the scallops attain a size of approximately 10 millimetres, preparations can be made to harvest them. Experience has shown that quick and efficient handling at this stage will help avoid mortalities. • Most large farms have a tank on shore which has seawater pumped to it. With this they can take the spat ashore and sort it in their own time as they are not at the mercy of the weather. • Minchin & Duggan (1989) observed that as many as 90 scallop spat could be tied into the byssus nest of one 10 millimetre mussel. • Avoiding mortalities during on-site collecting is difficult enough, but keeping them to a minimum when spat needs to be shipped in from other sites requires even more considered attention. • The rule of thumb is to ship only as much spat as can be both quickly and properly handled at the destination, and in this way mortalities can be kept to a minimum. • The collection of data can be both interesting and rewarding and should lead to more accurate predictions of settlement dates and variety of settled species. This in turn will help reduce harvesting costs and make subcontract collection a more viable prospect for a potential buyer.

96 •

• • •

• •

• •

• • •

• • •

•

•

Scallop Farming If there is any juvenile potential in an area and providing other farmers are willing to lend a hand, much can be learned about its full economic potential and the most effective method of collection, by running a monitoring programme. The plankton haul is used to obtain the first indication that something is happening in the reproductive world of the bivalve. Much information can be obtained from trial collectors and the more expert one becomes at larval identification the closer one will be to predicting settlement times. To ascertain the settlement in terms of overall quantity and to gain some feedback on information gathered from trial collectors, actual spat collectors may be set weekly over a period of 3–4 weeks (around peak settlement time) and allowed to lie for up to 90 days. If samples are collected, they will require examining. The most expensive and possibly the most important item of equipment is therefore a microscope. For those who are more scientifically trained than most, not only may they be able to take photos of specimens but they may also like to mount some on slides for future reference. The collation of all figures and observations is important as this will form the basis of pre-empting settlement times in the future. As the scallop develops, it becomes more easily recognizable, so the samples taken from those trial collectors that have been in the water for 6 weeks should not pose too much of a problem. Many bivalves are classed as D-shaped larvae during their planktonic stage and it is almost impossible to tell them apart. One other species that settles in abundance almost everywhere, and which is the cause of great mortality when settled alongside any Pectinides,is the mussel (Mytilid). Whichever way the farmer becomes efficient is of no account. The mere fact that he is applying himself to this science and that he can identify at early stages of growth, maybe even only one or two species, will be worth much to him in the long run. Spawning characteristics vary with species and area. It is therefore necessary to establish some kind of pattern in the species that is native to the farm area. Monitoring schemes will help to indicate the presence of scallop larvae, but the information will be out of date by several days when analysed. Scallop larvae are particular about the nature of the surface they settle on, and once any weed has taken hold they will be less inclined to choose that surface. Usually after 10 days weed and sediment have contaminated most of the settlement material, bag and filler, rendering it ineffective. As he builds up more expertise in species identification a farmer can be more precise in the setting of his bags. The Japanese work on a system whereby they put out their spat bags when 50 per cent of the spat settled on the trial collectors have reached over 200 microns in size. General observations can be made of hours of sunlight, lunar periodicity, wind speed and direction, and rainfall, but to ascertain water temperature, salinity, nutrients and phytoplankton levels, other more precise measuring equipment will be required.

Chapter 6 Getting Underway

Before work can begin on building the farm, much thought must be directed to the proposed scale of operations and the site’s own specific characteristics. If, for instance, the estimated production calls for a total line length of 200 000 metres, then it is highly unlikely that any one site would actually accommodate 1000 individual lines. In reality the actual working capacity of a site represents only a small proportion of its total area because of fluctuations in depth. Governing bodies are also reluctant to see many surface buoys in one area, so a farm of this size would probably have to be spread over a few or even many individual sites. Large-scale farms, aiming for an annual output of 5 000 000 or more scallops, face many obstacles, not least of which is the actual spread in terms of area of their activities. With this in mind the tendency has been to split production into small units, each being semi-independent but under the overall direction of one company. To offer an idea of what is required in setting up and running, our farm example will have the following capacity: 6000 metres of hanging space on 30 lines, 500 metres of hanging space on five rafts, and 20 000 square metres of seabed for bottom culture. Figure 6.1 is an ideal, imaginary site plan for our small-scale farm and shows the proximity to the culture site and a sheltered anchorage for rafts and onshore facilities. A steep shore and level seabed enable the lines to be set close to the working base. From this example a prospective farmer will be able to obtain some idea of scale if he wants, for instance, to work a farm of five times the capacity.

LONGLINES Setting longlines A seabed lease will usually specify the number and position of the lines to be set, based on information from the original application. Where a thorough survey has been carried out, this will usually not pose much of a problem. If, however, a survey was not undertaken, it may be necessary to juggle with the position and direction of the lines to accommodate them properly. Wherever possible, the lines should run in a direction that favours the prevailing wind and main tidal flow. However, enabling both elements to work together may 97

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prevailing wind

navigation buoy

longlines

tidal flow

culture rafts

shore base lease boundary seabed culture boundary Fig. 6.1 An ideal farm site with sheltered shore base and close proximity to the culture area.

not always be possible and a compromise may often have to be reached. The ideal situation is where the prevailing wind runs along the length of the lines and the tide meets it at an angle of 45°. In this position a boat will lie nicely on the line and will be easily worked, not putting too much strain on the anchors. Figure 6.2 shows an ideal position and two other easily workable combinations of tide and wind. Unfortunately, in some situations there is no option but to set the lines in an awkward position.

Anchoring It must be remembered that new, synthetic rope has a stretch factor of up to 15 per cent. This becomes permanent when the load is continuous. When anchoring and tensioning, some allowance should be made fore this, and after 9–12 months’ work the extra slack will need to be taken out. The longline should be partly constructed before anchoring can begin. Figure 6.3 shows the knots used to attach buoy lines and also two useful knots for attaching a lantern or similar piece of equipment. The procedure is to feed the line onto the deck of the boat in its reverse order. A small surface buoy with 40 metres of 10 millimetre line comes aboard first and its end is tied to the crown of the anchor. The longline itself is shackled to the anchor chain and 90 metres is taken aboard before

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99

prevailing wind

(a) tidal flow

wind

(b)

tide

wind tide (c)

Fig. 6.2 Shooting a longline taking conditions of tide and wind into account: (a) an ideal position; (b) the line runs along with the tidal flow; (c) the longline is angled into the tidal flow.

the first surface buoy is positioned. No intermediate buoys are attached except for a temporary 220-millimetre hard buoy which is placed approximately 100 metres along the working part of the line itself (halfway). The remainder of the line is coiled down with the outboard buoy being attached and finally the second anchor and surface line coming aboard.The line is now ready to be run and the only other equipment needed is half a dozen 5 kilogram weights to keep the longline beneath the surface once it is in place. The whole operation should be performed as near as possible to the time of high tide. Figure 6.4 shows each step in the anchoring and tensioning procedure and starts with the placing of the outboard anchor in its rough position. The boat steams into the direction the line is to run and the rope is carefully fed out. The first weight is tied after 40 metres has run off the boat and another is secured where the first surface buoy’s line is attached to the main longline. Two more weights are attached, one at 50 metres further on and another at 150 metres. When the last surface buoy is reached another weight is attached where it joins the main line. The final weight is tied a further 40 metres along. The anchor and

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main buoys to longline (1)

(2)

(3)

lantern to line

general purpose line knots Fig. 6.3 Useful knots for longline work.

chain are finally lowered over the side and kept just below the surface until all of the slack is towed out of the line. Once it is seen that there are no tangles the anchor is slowly lowered to the seabed with tension being continuously applied. The first anchor is now lifted and the same procedure for lowering is carried out, but this time enough tension is applied to pull the central 220 millimetre hard buoy a few metres below the surface. This buoy is finally grappled and removed, allowing the weights to cause the part of the line without buoys to sink. The intermediate surface buoys can be secured when eventual loading takes place. Their spacing will depend on weather conditions and surface buoyancy requirements, but as a general rule 20 metres is adequate. Where there is the likelihood of constant bad weather, buoys with a circumference of 1 metre will suffice to ensure that little wave action is transmitted to the line. In calmer areas slightly larger buoys are permissible.

Tensioning Removing the slack caused by line stretch will require cutting out the increased length and either splicing or retying to rejoin. A splice is possibly the best course of

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22 cm buoys first anchor out

100 cm buoys weights

first buoy out

second buoy and central buoy out

second anchor out

line tensioned with first anchor

Fig. 6.4 The procedure for running out a longline.

Fig. 6.5 A long splice.

action because these can be quick to perform (Fig. 6.5), often taking less time than that spent in undoing a very tight sacrificial longline knot. With lines of a working length of 200 metres or more it will quickly become apparent that by removing a fairly long piece of line slack, the remaining line to the anchor

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surface rope

Fig. 6.6 Tensioning an anchor and retrieving the rope.

can be considerably shortened, thus causing an imbalance in the overall anchoring dynamics. For this reason, if possible, the farmer should try to remove line slack from the actual working part of the line inside either of the outside buoys. Where the seabed is flat and free of rock outcrops it may be policy to retension by towing the anchor but this should only be performed with considerable caution. With a secondary anchoring system the anchors can moved with safety because one will always back up the other. Although it should be emphasized that the proper marking of anchors is most important, there may be times when it is thought unnecessary. In these situations tension the anchors with an endless rope from the surface (Fig. 6.6) and once they are in place one end may be released from the surface and pulled through for recovery. A problem will often arise when working with ropes under any kind of tension and that is actually securing them while a splice or new knot is put in place. Wet rope, especially when new, can be very slippery and it is for this reason that stoppers were developed. The uniqueness of these knots is that most take a firm hold on the rope when required yet can be easily undone when the job is complete. Figure 6.7 shows the main ones in use and possibly the most efficient is number 2 which takes a very firm hold yet can be easily slid along the main line when require. The number of turns taken will depend on how difficult the line is to grip. Knot number 1 is a sacrificial stopper that will take a very firm grip of a line but which is then almost impossible to untie without the use of a knife. Number 3 is quite effective in certain circumstances and is quite often used in chain form by riggers. Number 4 is similar to number 2 but not as effective because it does not allow for the twist of the rope itself, which in some cases will render the knot ineffective.

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103

(1)

(2)

(3)

(4)

Fig. 6.7 Stopper knots: (1) a sacrificial stopper that grips a line tightly but is almost impossible to untie and must usually be cut with a knife; (2) possibly the most efficient, takes a very firm hold yet easily slides along the main line when necessary; the number of turns will depend on difficulty of gripping the line; (3) quite effective in certain circumstances and is often used in chain form by riggers; (4) similar to (2) but less effective as it does not allow for the twist of the rope itself, which may render the knot ineffective.

Anchor marking Anchors are expensive items, not only because that they are deployed to secure valuable farm equipment, but also to purchase in the first place. Unfortunately the anchor marker which was deployed when setting the longline is usually the first item to disappear, either by sinking as a result of excess fouling, becoming unattached from the anchor itself, or by the cable being severed by a boat’s propeller. However the marker is lost, the anchor will be difficult to retrieve in the event of a longline parting from it. It is therefore most important that the marker line and buoy be inspected regularly and that it is firmly secured and chaffed (Fig. 6.8) from the outset. The small surface marker can be replaced by a larger buoy once everything is in place and to help avoid being caught in a passing boat’s propeller a weight should be attached to the line some 10 metres from the surface, once again, in such a way that it does not cause unnecessary wear on the rope (Fig. 6.9). Modern technology in the form of the global positioning navigational systems (GPS) has enabled very accurate markers to be taken and stored as farm data for

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figure of eight knot

subsurface buoy

heavy chaffing

Fig. 6.8 Setting up an anchor marker.

spliced and whipped

lead ‘flashing’

Fig. 6.9 Adding weight to lines and avoiding chafing.

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105

(a)

(b) Fig. 6.10 The use of secondary anchors on both (a) single- and (b) multiple-line systems.

future reference. By marking the anchors in such a way, if lost, they should at least be easily found by divers.

Secondary anchors Where there is likely to be excessive strain on the system, back-up anchors can be employed either on an individual basis or as a security measure for a number of lines. Figure 6.10 shows individual secondary anchors in position and a combination anchor system. The combination system will allow a slightly closer spacing between lines because the ends are kept in a more stable position.

Grid systems Where conditions allow, a grid system is a good layout to ensure there is back-up on every line. The system would be inadvisable in areas of strong tide, especially if it flowed across the lines. Both buoyancy and working would prove difficult. Setting up a grid system of up to 10 lines needs much thought and preparation and will certainly take time to complete.The construction of joining posts (Fig. 6.11) is an advantage because they allow systematic building of the grid. Figure 6.12 shows an alternate design. They also ensure that most of the line is kept beneath the surface during the layout process, an important point where there is passing shipping. The two grid lines are set individually in the same way as running a normal longline, but the joining posts have their buoys attached beforehand. Once roughly in position the ten precut longlines can be shackled into the system with weights and 220 millimetre buoys can be attached at the centres. Figure 6.13 shows a ten-line grid system with the position of the anchors. The grid line between anchors 1 and 3

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to surface buoy

10 mm half chain link

cross line anchor line

20 cm cross line

main longline

cement filled 5 cm

Fig. 6.11 A joining post for a longline system.

Fig. 6.12 An alternative type of joining post.

is tensioned and the ten individual anchors are placed carefully in position, one at a time. The other ten anchors are then run out and these are used to tension each line in turn. Finally, the grid line between anchors 2 and 4 is tensioned. Once complete, the system has the advantage that it can be easily extended. Figure 6.14 shows a jumbo grid system, which is favoured by the Japanese. This takes up a good deal of space and takes time to build. With a system of this kind the tendency has been to use heavier ropes for both anchors and longline to make

Getting Underway 2

1 grid lines 200 m 50 m

all lines 16 mm polypropylene

150 cm corner buoys 3

4 prevailing wind tidal flow

Fig. 6.13 A ten-line grid system.

20 m

200 m

150 m Fig. 6.14 A Japanese jumbo rig.

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Scallop Farming anchor point steel bar

rope stopper

tail

Fig. 6.15 Winching-in with a Spanish windlass.

it more durable. The end result should look symmetrical, but there is often a need to move an anchor or two afterwards to square the system up. Much strain is taken on the corner positions, which is why larger buoys are used on these four points. The rest of the system can use the regular 1 metre buoys.

Replacing corner posts Corner posts may either be secured by tying directly with the rope end, or by shackling in place. Whichever method there will eventually come a time when either the shackles will need replacing or even the whole joining post itself. This can be a difficult job, mainly because, once loaded, the lines will impose considerable strain on these areas. The farmer should approach this task by first securing the old post to the boat and then attaching, by means of stoppers, 12 millimetre work lines approximately 6 metres in length to all of the lines running to the post, and allowing at least 2 metre tails. Two lines may then be released and these may, in turn, be secured to the replacement post. The remaining lines may then be winched in and each secured to the new post. By way of assistance when close hauling is necessary and space is at a premium, a Spanish windlass may be employed. Figure 6.15 shows one used in conjunction with a rope stopper and the importance of leaving an adequate tail for reworking.

Boat work At this stage it may be useful to realise some of the potential in the proper use of a farm boat and its power. Figure 6.16 demonstrates three situations where the proper setting up of a boat will greatly enhance its use. Situation 1 shows a boat towing a raft but with the towing post forward of the propeller. Maybe this is not always possible to achieve, but if it can be done then the boat’s overall manoeuvrability will be greatly improved as it will enable a 90 degree turn to be accom-

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109

raft

A:

1

2

3

Fig. 6.16 Effective use of the farm boat: (1) towing a raft but with the towing post (A) forward of the propeller to improve the boat’s overall manoeuvrability; (2) pushing a raft with the bow fendered with a tyre enabling it to swing back and forth and making steerage more exact; (3) how to tie alongside a raft and keep the same position for confined manoeuvring situations.

plished at will, not always possible when pulling directly from the stern. Situation 2 shows a boat pushing a raft and how the bow is fendered with a tyre and tied in such a way that it can swing back and forth to commands from the tiller, therefore making steerage very much more exact. Situation 3 demonstrates how to tie alongside a raft and keep the same position for confined manoeuvring situations.

Line breakage The most common form of line breakage is where it severs from its anchor and this is especially a problem on rocky bottoms. Other causes are damage by passing vessels, being cut by the work boat’s propeller, and chafing by farm equipment. When a fully loaded line parts, the resulting tangle can be a nightmare to sort out and by far the best approach is to tackle this with the use of a diver providing this is possible. The correct method of working is described in Chapter 10 (Diving work).

Line setup Individual farmers will have their own preferences as to how they set their lines; much will depend on both local conditions and the type of vessel used to service them. Line lengths may vary from 100 to 300 metres, and directions may have to be changed to cope with conditions on the seabed. The amount of gear hung on a line may also vary. The usual spacing is 1 to 1.5 metres, but where there is competition for space, and providing conditions allow, the lanterns may be hung at a closer

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Fig. 6.17 Hanging lanterns alternately high and low.

spacing alternately high and low. Figure 6.17 shows lanterns loaded in this fashion off a raft walkway, but it is equally feasible to hang them from lines providing the anchors are large enough to support the extra load. In areas of strong tide, however, it is inadvisable because of the likelihood of lanterns chafing against each other. There are various ways of setting a line, as shown in Figure 6.18. Example (a) is a straightforward line that is easily worked. Example (b) has a 50-kilogram weight at either end, which is supposed to offer resistance to excessive travel or swinging. This can be effective in certain situations but can often lead to the end buoys being pulled under. There is also the possibility of gear becoming caught on the downline, a problem with all lines using droppers of this nature. As an extra safety precaution, a central anchor system can be incorporated, as in example (c), but this must be set in a way that ensures tension on the downline at all stages of the tide. This can be achieved by attaching at least 10 metres of chain to each anchor. The final setup (d) is used widely in Japan and allows for a variable number of 25 kilogram weights to be hung along the entire length of the line. Although they offer a certain amount of grip on the seabed their main purpose is to make buoyancy more effective.

Buoyancy As both stock and marine fouling on the lanterns grow, so added weight will come on the line. This is usually supported by subsurface buoys, which may range in size from 180 to 300 millimetres. Where growth is excessive they may have to be added

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100/200 m 100 cm surface buoys 22 cm subsurface buoys lanterns (a)

50 kg weights (b)

(c)

(d) Fig. 6.18 Four alternative methods of setting a longline: (a) simple line system; (b) line system with end weights; (c) with weights and central anchors; (d) with 25 kilogram weights on each surface dropper.

to the line every few days, making it labour intensive and a little disruptive to the stock. Consequently farmers have put much thought into how they can make the added buoyancy more effective. By taking weights directly to the seabed and adding sufficient buoyancy to nearly lift them off, there can be a big margin left to support lanterns. If, for instance, five 25 kilogram weights are set along a line length of 20 metres, a total buoyancy in excess of 125 kilograms will be needed to lift them off the seabed (ignoring weight loss in the water). If 30 loaded lanterns with a total weight of 90 kilograms are tied to this section of longline there will be 35 kilograms of spare buoyancy that must be ‘grown out’ before the line starts to sink. If this principle is taken one step further, the added buoyancy can be increased to just below the total weight of both lanterns and weights combined. Figure 6.19 demonstrates this principle. If worked to its best advantage, rebuoying can be cut down considerably. The total lift is 125 kilograms and this is held in place with the combined weight of both lanterns and bottom weights totalling 131 kilograms. As the lanterns weigh only 56 kilograms, the total grow out weight is 69 kilograms. There are variations to this principle but all are aimed at the same outcome, to cut

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lift from sub surface buoys = 125 kg total weight of lanterns = 56 kg

25 kg bottom weights

Fig. 6.19 The use of bottom weights to keep an extra buoyant line in position.

down on excessive line handling. The more weights used, the more grow out time available. Surface buoys will indicate the condition of the longline, and once they show signs of taking weight more subsurface buoys will need to be added. Once again this can almost equal a combination of both bottom weight and new lantern weight. In an effort to cut line handling costs much thought has been put into devising more effective buoyancy systems. Research has been centred on devising a buoyant longline and progress has been made. Figure 6.20 shows a system that allows the subsurface buoys to be inflated from the surface. It is greatly dependent on the use of heavy bottom weights and has to be backed up with both subsurface and fairly large surface buoys. Unfortunately it is at the mercy of buoyancy fluctuations caused by the rise and fall of the tide (Boyle’s law). A totally enclosed buoy with both inlet of air and outlet of water at the surface would help to overcome this.

Transmission of motion Because of the danger of transmitting excessive movement to lanterns via surface buoys, there has been a reluctance to use large ones to support the longline. The transmission of motion, when excessive, can have a twofold effect. First it may cause stress on the scallops housed in lanterns close to the down line, and second it can cause chafing of gear and possibly an eventual line break. This may be a danger in areas where surface conditions are constantly bad, but many more sheltered sites can use large surface buoys quite safely. Figure 6.21 shows the difficulty with which motion is actually transmitted from buoy to line. First, the buoy itself gives to wave

Getting Underway 125 cm surface buoys

113

air line 25 litre adjustable buoyancy

50 kg weights vent tap subsurface buoy with adjustable buoyancy air in

water out

Fig. 6.20 The use of adjustable buoyancy on a longline.

surface buoy soaks up some wave action

stretch in rope soaks up motion lever effect from line to line takes out more motion

Fig. 6.21 Absorbing the shock from surface buoys. Motion is soaked up via line stretch, spring and lever.

movement, thereby eliminating any jerking action. There is also a stretch factor in all the ropes used, and finally the lever effect built into the structure will help take out much of the movement. More important for the sake of the stock is to ensure that the lanterns are held at a depth below the splash zone of the waves. This motion can cause excessive stress to the stock.

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Where there has been evidence of shell wear through excessive contact in the lanterns, the blame is often put on motion being transmitted from the surface. In some instances this may be correct, but another cause of shell movement is tidal motion. A tide flow of one knot or more will cause the lanterns to lie at a dangerous angle to the line. This, in turn, allows the scallops to fall into the lowest part of each lantern layer. Couple this with swirls caused when the flowing water passes neighbouring lanterns and it becomes obvious how tidal flow creates problems. If in doubt about the use of large surface buoys, a good approach is to experiment with different sizes and carefully monitor the results. There is no need to load the line right to the junction where the surface line is attached. By leaving a space of 1 metre either side, the likelihood of transmitting motion can be greatly reduced. It may be found that a particular site will handle surface buoys well in excess of 1 metre circumference. Twenty of these set along a 200 metre line will offer much support. Of prime importance is the need for a back-up to ensure that the line never actually sinks to the bottom. This has happened on many farms where the buoyancy has been delicate. By having surface buoys of a reasonable size and ensuring that they are never fully loaded, the farmer should have fair warning of any extra weight coming onto his line. Experimentation is essential and each farmer must monitor his conditions and set his line in accordance with his findings.

Working the line How best to work the line is the aspect of scallop farming that requires considerable knowledge of local conditions. Expertise in handling therefore takes much time to acquire.

Star wheel roller Working the line is made easier by using star wheel rollers, which allow the line, along with attached lanterns and subsurface buoys, to pass over without snagging. Figure 6.22 shows how they operate and how the guide bar causes the gear to pass over smoothly. One situated at each end of the boat can enable speedy line handling. The vessel moves along either under its own power or with a crew member pulling the line over the rollers. It is a fairly simple operation to power one of the rollers hydraulically and this enables more precise movements to be made. Chapter 9, which deals with equipment design and manufacture, describes this more fully. A special application is when conditions restrict the use of the vessel’s propeller or when the wind prevents manual handling of the line. The working procedure is to lift the line at roughly the position desired, either via a line and buoy purposely left for continuation of work, by a surface buoy and line, or by grappling for it. The line is then lifted onto the fore and aft rollers assisted by the derricks (if fitted) (Fig. 6.23), and the vessel steams either ahead or astern to

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longline guide bar

Fig. 6.22 The star wheel roller, showing how the guide bar causes culture gear to pass over without becoming snagged.

block

derrick

rope guide capstan

Fig. 6.23 The use of a derrick to position the longline onto the star wheel rollers.

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bolted through gunwale

Fig. 6.24 The use of metal horns bolted to the gunwale of a boat as an alternative to star wheel rollers.

obtain a more exact position. With hydraulic rollers the vessel can be manoeuvred into position without the danger of fouling the propeller with culture equipment. Another way of avoiding this problem is to pull the boat along the line, but this can be difficult if both wind and tide are working against it.

Stag’s horns Many farm vessels use metal horns on which to run the longline (Fig. 6.24). This does not allow the flexibility of running freely along the line and can be used effectively only when equipment is removed before it reaches the forward horn. Clean nets are then loaded behind the aft horn. For the purposes of rebuoying, the procedure is to lift sections of the line by grappling and to add buoys for one boat’s length at a time. A special grapnel is used for this and its design is discussed in Chapter 9. The whole procedure creates more work so it is essential to ensure that rebuoying is kept to a minimum by correct setting up in the first place. Farmers may be asked why they do not use rollers. It is usually because of cost and restrictions in flexibility. They are expensive to buy and, once in place, tend to restrict the vessel to farm use alone. Many small farmers have to supplement their income by fishing, and this often requires the boat to be rigged in a certain way. Star wheel rollers often get in the way of this and are consequently not employed. Horns can be discreetly installed on the boat with little likelihood of interfering with other activities.

Lying on the line Correct positioning along the line is important if equipment damage is to be kept to a minimum. Strings of collectors, pearl nets and lanterns are notorious for lying

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correct position on line

tidal flow

incorrect position on line

tidal flow

Fig. 6.25 Positioning the farm boat to ensure culture equipment does not suffer damage. The incorrect position illustrates how damage can occur when equipment flows under the boat.

at an angle to the tide. When a line is lifted, care must be taken to ensure that these are being swept away from the hull and not under it (Fig. 6.25). The boat’s position on the line can be altered to ensure that this happens, and it may have to be changed periodically to allow for changes in tide direction. Line expertise will develop as the farmer becomes more aware of the effects of both wind and tide. Sometimes, even after everything has been done by the book, a situation will arise that could cause trouble. The tide flow may be correct for his position, but if the wind is blowing in the same direction it will be adding more tension, creating a problem when the line is released. If the line takes time to sink it is likely to snag either the boat’s propeller or its keel. The vessel’s propeller cannot be used in this situation, so usually the only way out is to push the line down quickly with the boat hook, hoping it will run clear. These points may seem obvious but the need for care with line and gear cannot be overstated. Having a line caught in a propeller or a string of collector bags, etc., creates a dangerous, damaging and often expensive situation, often aggravated by rough weather.

RAFTS Although not all sites will be suitable for raft culture because of exposure to weather, rafts are certainly useful to some farmers. Their greatest advantage lies in their ease of working and this more than compensates for the increased cost over longline culture. Their inbuilt buoyancy is cheap and permanent compared with that used on lines and there is no need to continually add buoyancy as the scallops grow.

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pontoons walkways Fig. 6.26 A culture raft, showing railings and positions of pontoons.

Culture rafts For basic stability the minimum pontoon length for a culture raft is 10 metres. Two of these placed 3 metres apart will safely support a frame with a total area of 60 square metres. Figure 6.26 shows a design for a raft that will provide over 100 metres of hanging space. With alternate hanging, one high and one low, a raft of this design will be able to support nearly 300 lanterns. Although the practice of alternate hanging makes work on a longline difficult, the same does not apply to a raft. If the facilities are available to build larger pontoons, then an extra 5 metres will prove cost effective in terms of both construction and stability. By making it less vulnerable to wave action, its overall life-expectancy will be increased. A good culture raft will have more than enough buoyancy for its needs, will be equipped to support a boat against its side in bad weather, and will enable men to work safely and easily from its deck. In a sheltered situation a raft can be moored in such a way as to avoid worries during stormy weather. It is usual to use a four-point mooring system for each raft, and where appropriate, shore mooring points can be incorporated. Figure 6.27 is an imaginary plan of a raft setup and demonstrates access to each unit. Before the completed rafts are put to sea the moorings would have been set up. Pieces of rope cut to the same length as the rafts are used for positioning purposes, although the final tensioning is best undertaken at high tide with the rafts in place.

Work rafts The purpose of a work raft is to provide a large, stable platform, which can carry much weight, has room for storage and is easily worked. Two rafts, each of 30 square metres and capable of supporting 3 tonnes, will prove useful to any scallop farm. While one may be used for storing equipment, the other can serve as a mobile work platform. The ability to site them as and when required in a number of useful positions is a great advantage, and where there is no jetty on site they can be grounded at low tide to facilitate unloading. Features can be built into the rafts that will offer greater flexibility yet not cut down on work space. A wet well (Fig. 6.28) is something that is of great use for temporary storage for all sizes of scallop and this can easily be incorporated into the

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Fig. 6.27 Mooring rafts, accessed by farm boat, along an acceptable shore line, using shore points for anchoring.

deck planks

metal mesh screen Fig. 6.28 A work raft incorporating a wet well. This can be used for temporary storage of stock as well as for work.

basic design. When the well is not in use, the opening can be covered with heavy planks, thus converting it back to a working or storage platform. There will be certain considerations regarding safety when personnel work aboard rafts and these will vary within countries. The farm boat will have to maintain a standard regarding this and what is involved will be examined when we look at choosing a boat. As the farm boat will always be beside the raft when there is work being undertaken, certain of the safety requirements will have been already met. However, a basic requirement would be for adequate safety railing, safe walking platforms, life buoys with lanyards, and an insistence that personnel wear life jackets at all times. Unless a farmer elects to work totally on his own, it is good practice always to work with a partner if there are two or more of you, especially when on the sea.

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THE FARM BOAT Choosing the right boat is important for many reasons. First, there is the question of cost. Most good craft are expensive and a mistake at this stage can prove costly in the long run. Second, it is essential to ensure that the boat’s design is compatible with the way the farm is worked. A big, heavy boat, for instance, can do much damage when lying on a longline during rough weather. Third, there is the problem of maintaining the boat’s value. High spending on an article that may rapidly depreciate in value should be avoided where possible. By ensuring that the farm boat is suitable for an alternative use such as fishing, its market value should always remain high.

Requirements in a farm boat There are many designs and layouts of boat that are suitable for farm work. The best approach is to try to find the most suitable combination of factors that fall within cost constraints and operational limits. The following are the main points to bear in mind when looking for a suitable vessel.

Size and displacement A suitable farm boat would be between 6 and 10 metres long, with a maximum displacement of 3–4 tonnes. Anything above this size tends to impose too much strain on longlines, especially where both wind and tide are strong. The minimum size is determined by the scale of operations and external natural factors. There is no reason why a small, lightly stocked longline could not be serviced by a 5 metre rowing boat providing it was fairly stable.

Stability By ensuring that the vessel has a good beam in relation to its length (a minimum ratio of 2 : 5), stability should not be a problem. A good draught is also important if the hull is a displacement type, and a pair of deep bilge keels will help to increase the overall grip of the water.

Durability A working boat has to endure much hard usage and will quickly show signs of deterioration if the correct materials were not used in the construction. Wood, fibreglass and metal are basic materials used in most hulls and each can have varying degrees of strength and longevity. The durability of a wooden hull can usually be judged by the size and number of the ribs and the thickness of the planks. Assuming there is no rot and that the wood types are compatible (i.e. larch planks on oak ribs), the overall condition can be fairly accurately determined.

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Fibreglass is a material that, at its best, is almost indestructible and, at its worst, is a safety hazard. Where the glass fibre mat has been penetrated with ample quantities of resin, with all of the air expelled, the final product should be very strong. When this process is scrimped the fibreglass sheeting will be seen to be brittle. A close examination of the inside of the hull and the edge of the fibreglass will give a good indication of its strength. There should be no flaking and the overall appearance should be both translucent and smooth. Thickness will vary, but for a 7metre hull it should be in the region of 12 millimetres. Rot can occur in fibreglass through osmosis and this can be spotted, usually on the outer gel coat, in the form of tiny bubbles or pinholes. If treated quickly no permanent damage need be incurred. Metal hulls used to be mainly of steel but aluminium is now popular, especially in farm boats. Determining the condition of a steel hull requires careful examination of the whole of the underside of the vessel. An ultrasonic gun can be hired to measure metal thickness, and attention must be directed at any areas inside that may act as water traps and therefore encourage corrosion. Aluminium is expensive but in the long term offers many advantages over steel. Although it is vulnerable to corrosion, especially when situated close to another metal such as brass, it is very strong and durable, and if the right alloy is used and it is carefully fitted out, it should maintain its value and remain in use for many years. To give the hull more durability, it is usual for vessels built from aluminium to be fairly heavily framed from the inside. There may be a need to strengthen a hull when adapting it for farm work. Where star wheel rollers are mounted, the gunwale may need extra reinforcing, and sheathing may need to be attached to the vessel’s side to prevent wear when lanterns are being hauled aboard. By capping the top of the gunwale with either rubber or plastic piping, wear to both boat and culture gear can be kept to a minimum. Individual farmers will have their preferences in hull composition and this is often based on the speed with which a repair or alteration can be made. Wooden hulls may be fairly easy to adapt for use, but replacing or repairing a plank or rib is usually something that only an experienced shipwright can tackle. Both fibreglass and steel are materials that most handymen can work with successfully, and repairs and alterations can easily be undertaken. Aluminium does not offer quite the same flexibility because the welding procedure for this metal is more specialized and, consequently, more expensive than steel. However, new equipment is being developed all the time in this field and a modern aluminium welding machine could be handled by anyone with some steel welding experience.

Manoeuvrability A vessel that responds rapidly to commands from its rudder both ahead and astern is an advantage when working from a longline or manoeuvring onto a raft. This can be used to even greater effect if there is a good clear view from the wheelhouse.

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Work and storage space A large, clear, strong, self-draining deck is essential for a fish farming vessel. Being able to work from a stable platform of this kind will quickly be seen as an advantage, and where there is storage space below deck the situation is further improved.

Gunwale height It is preferable to have a gunwale at least 1 metre high, but on vessels with a selfdraining deck this is quite often difficult to achieve. A high gunwale allows easier working from the vessel’s side and reduces the likelihood of either gear or personnel going overboard. Where the gunwale is low, a metal rail can be built to compensate.

Engine type and power Most fishing vessels opt for inboard marine engines which are both reliable and cheap to run. The tendency now is for fairly compact and relatively light units, unlike the very cumbersome types of the past. They can, however, be expensive to install. Many farmers have, therefore, tended to use large outboard motors to power their boats. The value of these in the long term is debatable and they certainly have high running costs. It is unfortunate also that, as they tend to be not so popular in the fishing industry, a vessel with one installed would have less resale value in that field. Although to begin with these units were mainly run on petrol the move now is towards diesel units. This has been encouraged because of environmental problems associated with the use of petrol and oil on a two-stroke engine principle. A diesel engine is far more environmentally friendly and consequently in many countries their commercial use is becoming compulsory. The question of engine power is important because extra horsepower allows for greater and more responsive manoeuvrability. Also, provided this power is transmitted through a large, slow-turning propeller, the towing and pushing power of the vessel will be improved. Outboard motors because of their high revving, small, heavily pitched propellers do not offer this type of power. Although a displacement hull has a maximum speed above which no extra power will push it any faster, it is still best to be overpowered than underpowered. This will give it more towing power and the extra push needed when steaming into the weather. A 7-metre 2-tonne displacement hull with a 40 horsepower inboard diesel would be sufficient to cope with most situations. The type of drive is important to a vessel’s performance. Inboard engines properly set up with matching propeller and balanced rudder can offer varying ranges of power and performance. An alternative is to transmit the power through an outdrive (‘Z’ drive), which increases both manoeuvrability and propeller accessibility. Unfortunately these pieces of machinery are expensive to buy and maintain and are consequently beyond the means of most small farmers. They are also primarily

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designed for high performance engines installed on either semi-displacement or planing hulls. In the same vein there are engines that operate a water jet for propulsion. They have a distinct advantage in that there is no propeller to become fouled, but are expensive to install.

Machinery Although we are looking for an uncluttered, clean deck, a few pieces of machinery can prove most useful. Modern hydraulics offer a system of power transmission that can be both discreet and highly efficient. From a basic hydraulic power source run from either the main engine or separately when outboards are used, many useful pieces of machinery can be run. Line haulers, capstans, winches, star wheel rollers and lifting arms can all be run from a central hydraulic power pack and its installation will also increase the vessel’s resale value. Pulleys mounted on the fore end of the engine will allow other pieces of machinery to be run that are invaluable to a farm. A deck wash can be installed, which can pump seawater at a high flow, and when required, may be switched over to be used as a bilge pump. High pressure washers are a necessity for removing fouling from culture gear, and most farms will have a portable one. Installing a fixed unit on the boat and running it through a clutch system from the main engine is both easily done and comparatively cheap. It takes up little room and will prove more convenient than transporting a portable washer out to the site.

Running costs It may be difficult to decide at a glance what a boat would cost to run. There are, however, a number of items that are obviously expensive. Generally speaking, on the basis of maintenance cost, a diesel power unit will be less costly to run than a similar petrol-driven one. High performance, high speed engines consume more fuel, although in real terms they may cover more ground per unit of fuel than a conventional setup. Electronic gear on hire can be a cost burden, especially where some items are not essential. A good quality echo sounder is a great advantage, as is a GPS unit to give highly accurate fixes of anchors, etc. A radar is an expensive luxury but a VHF radio would be deemed essential. It is not only the day-to-day expenses that must be examined. The long-term costs in the form of repairs and replacements can be a burden when running a small farm. Different hull types will attract varying levels of insurance, and high premiums can also be a considerable cost burden.

Hull types and layouts There are three basic hull designs; displacement, semi-displacement and planing. Each has its own qualities and choice will depend on the farmer’s requirements. He may be looking for speed when his site is a long distance from his shore base, or he

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may require towing power to shift rafts around his site. By combining the right size and speed of propeller with an appropriate hull shape any requirement can be met.

Displacement hulls As its name suggests, a displacement hull is deep draughted and therefore has to be pushed through the water. Its optimum hull speed will depend on both beam and draught in relation to overall length. A beamy 7 metre vessel drawing over 1 metre of water may have a top speed of only 7 knots, which may seem slow in comparison with other hull designs. What they do offer, however, is both steerage (way) and towing power. The ability to maintain steerage when the propeller is not turning is important when manoeuvring into tight positions. Other hull types are quickly blown off course when the power is taken away, but a displacement hull will hold its way for a good distance. A displacement hull with an inboard diesel engine offers cheap running, reliability and good resale value. The engines usually have a fairly long life and, with regular maintenance, should need little spent on them during this period.

Semi-displacement hulls The semi-displacement hull was designed to give power at slow speeds and provide the ability to go fast when needed. This combination of factors makes them attractive, although to attain them, running costs will be higher than those of a conventional hull. Much engine power is needed to make both ends of the speed range effective. They are usually driven by a high-powered, high-revving inboard diesel engine, either directly via a propeller shaft or through an out-drive bolted to the stern.

Planing hulls For very fast speeds a hull needs to be able to travel on top of the water rather than push its way through it. Planing hulls are driven by powerful, high revving engines, which turn relatively small propellers. Their top speeds are very high but they lack towing power and way at the bottom end of the scale, which limits their scope. It is common to see them powered by either one or two large outboard motors or a diesel or petrol engine through an out-drive. They are expensive both to run and maintain. Apart from speed, their stability and open clear deck space are good features of their design. Figure 6.29 shows four combinations of hull type and engine drive. To be quite certain of making the right choice, it is preferable to test drive as many different designs as possible in a variety of sea states. A visit to other farms to see what they use would also be beneficial.

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forward wheelhouse displacement hull

forward wheelhouse semidisplacement hull

aft wheelhouse displacement hull

aft wheelhouse planing hull

Fig. 6.29 Some popular hull types and top-side layout.

Other designs Two designs that are becoming more popular are the catamaran and the sea truck (Fig. 6.30) The catamaran offers a stable working platform and can be rigged in a variety of ways. The longline may be worked either between the pontoons or alongside one of them. Either way, there is plenty of useful working space left. Sea trucks offer the farmer a vessel that can be run up the beach for loading. The forward ramp and ample deck space will often allow a Land Rover to be taken aboard. Although this may not be of great use to a farmer, the ability to take a loaded trailer aboard certainly will be. Catamarans are now being built with this design feature in mind and their popularity is increasing.

Deck layout Scallop culture gear can be bulky and very heavy when encrusted with marine fouling. The correct utilization of deck space is therefore important if many lanterns are to be brought in at any one time. There have been instances on farms when

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Fig. 6.30 The catamaran (top) and sea truck (below).

valuable gear has been lost over the side because of poor organization and gear stowage. This can be avoided if the work routine and deck space are properly planned. The working side of the vessel is the line side and this must be kept clear. Some farmers will have a preference as to which side they rig for this, but in general it is the side the vessel kicks into when coming astern. When a propeller turns, it not only pushes the vessel ahead but also pulls the stern a little to one side. The rudder position easily compensates for this, and when going ahead there is little indication of the swing. When coming astern it can be more pronounced and on many boats there is a definite swing one way or another. This can be used with great effect when coming alongside a raft or positioning onto a longline. Figure 6.31 shows how the star wheel rollers are positioned in relation to the wheelhouse and overall deck space. The installation of a steel rail around the remaining gunwale enables work to proceed more safely. The longline, when lifted aboard, can be heavy and usually some sort of hydraulic lifting gear is required to complete the task. Once on the surface it then has to be positioned on the fore and aft rollers. A small capstan, strategically placed by the forward roller, will greatly assist in this lifting, and a hand-operated sheet winch will enable the aft roller to be loaded (Fig. 6.32). When the forward roller is hydraulically driven, the loading process is made more straightforward with the surface buoy and line leading the longline

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derrick hydraulic star wheel roller hydraulic capstan sheet winch

aft roller

Fig. 6.31 A farm boat set up specifically for the job, showing deck layout with star wheel rollers in place, railings for safety, and work space.

hydraulic capstan handle gear housing

sheet winch Fig. 6.32 A capstan and sheet winch.

directly onto the roller. The aft roller will still need loading either by brute strength or with the assistance of a sheet winch.

Rigging A derrick can be of some assistance in lifting and will need to be rigged to be of use on two rollers if a sheet winch is not present. Once the line is positioned, the derrick can be of further use in hauling heavy lanterns aboard.

Deck space and gear It is not good policy to take in too much gear at one time because of the risk of being stuck with it if the weather quickly worsens. Most farmers work directly from their lines because this helps to lessen the time the scallops are out of the water. They may only work a few lanterns at a time as a safeguard against being caught out by the weather. If, for instance, 10 lanterns were brought aboard and emptied,

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the farmer would be faced with several hours of sorting, grading and reloading. If the weather deteriorated quickly, he could easily be left with this stock on deck. Even when only two lanterns are brought in at a time it is good policy to have a back-up system that will allow any unsorted scallops to be quickly put back in the water. Anything that can be quickly loaded, like oyster cages or plastic trays, would be suitable for this. The use of rafts helps to overcome problems like these.

Safety regulations The fishing industry in many countries is regulated in relation to safety procedures and just what is required may vary slightly from place to place. Where a licensed boat is used to work the farm it will be subject to the same regulations and in many countries the same regulations will apply to dedicated farming vessels. As a general guide, for a vessel under 10 metres it will usually be required to have aboard the following items: Enough life jackets with lights and whistles for the number of people aboard Two life buoys with reflective tape and lanyards An inflatable life-raft (in many areas) A pack of flares (in date) Two appropriate fire extinguishers (with up-to-date tests) Shapes to show vessel’s activity, e.g. inverted black cones denoting the vessel is fishing and a black ball to show at anchor One steel fire bucket with lanyard One waterproof torch A compass A VHF radio. Apart from these items, personnel aboard may be required to have certificates relating to the following: First aid at sea Fire fighting and survival Safety awareness A VHF operator’s licence.

MOORINGS AND NAVIGATION It is very likely that a scallop farmer will be required to indicate the position of his site as a warning to shipping. The type, size and colour of the marker buoy will be specified by either the Department of Trade and Industry or the appropriate government body for the area. In the UK they are usually required to be yellow, of any shape that is not already used, and with a flashing yellow light. In most countries they are called special markers.

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radar reflector

1.3 m

light

dan buoy 1.2 m

navigation buoy

Fig. 6.33 A special navigation marker.

Figure 6.33 shows a special marker that would be acceptable in UK waters. It also shows radar reflectors, which can be used to identify each corner of a scallop farm. These will easily be detected by vessels with radar aboard. The actual positioning of the special marker will be determined by the appropriate government department and will usually be at the most extreme seaward end of the farm.

SHORE BASE AND SHORE FACILITIES Having a large indoor store, workshop and general work area is a big asset to any scallop farm, and a nearby pier or jetty will make it even more advantageous. With a suitable electricity supply at hand it may be feasible to build a saltwater tank, which is useful during spat sorting and for general short-term holding. There are many varieties of plastic tank on the market and these can be easily installed. Laying on a seawater supply may not be quite as straightforward, especially if it has to be pumped over a large distance or up to a high level. A three-phase electricity supply will be required to power the pump and the pipe inlet will have to be sited deep enough to ensure that the water is always at the correct salinity.

Jetties Where there is a gently sloping beach a useful jetty can be constructed with gabions (Fig. 6.34). These are plastic-coated wire mesh boxes, which can be filled with 2 cubic

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hinge

pontoon

fenders

gabions

Fig. 6.34 A pontoon and a jetty built from gabions.

metres of small stones. A lid is finally wired in place to create the platform. By placing them end-to-end, a jetty of any length can be constructed. A final touch is to wire in some car tyres along the whole length to act as fendering. If the shore edge is steep where it meets the sea, a hinged jetty can be constructed. There are many pontoons on the market that are primarily designed for this purpose alone and the end-result can be a most useful asset. They do not, however, stand up to the pounding to which a totally open shore is subjected and should therefore be constructed only in relatively sheltered areas.

Moorings Strong moorings situated close to the jetty constitute a useful addition to a shore facility. They can be used as temporary points for the work rafts and are useful if any repair work needs carrying out on the culture rafts. Running moorings for small boats (Fig. 6.35) are also useful, especially in areas that experience large tides.

Shore machinery A certain amount of machinery can be stored ashore. The most necessary items are a pressure washer, an electric welding set, burning equipment and a portable generator to run electric hand tools at sea (115/120 volt). For general transportation and shunting of equipment a tractor and trailer or dump truck will prove invalu-

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surface buoy

endless rope steel ring

Fig. 6.35 A running mooring for dinghy and small boat use.

able. They do not need to be expensive items, and careful shopping will often turn up a bargain. Their depreciation will be rapid, however, if they are exposed to seawater too often. A hose down with fresh water after each day’s work is therefore essential.

Working safely The sea can be a hard master and it must not be assumed that everyone has a natural aptitude to work on it. Courses on seamanship and survival are common today and offer a good opportunity for a farm worker to become familiar with his new environment. Safe work practices need to be employed on the farm boat, with the emphasis on the use of life jackets and always working in pairs. Careful attention to detail can help to avoid accidents and regular checks on the seaworthiness of vessels is most important.

Farm rents Governments can earn revenue from farm rents and they are usually quick to recognize this. Because mariculture is a fairly new activity in many countries the basis for a fair rent is, in some instances, still at the negotiation stage. It is essential, therefore, that the farms be represented through associations and similar bodies to ensure a fair deal. The final agreed figure can be based on turnover, total lease area, or hanging space. Although a rent based on turnover would be fairer all round, the general principle has been to work at a price per metre of hanging space, irrespective of how much is loaded on it. When negotiations take this basis, it is up to the farmer to encourage the authorities to keep the unit price low. Once this is fixed, he can further support his position by negotiating a long-term agreement based on this set price.

BUSINESS STRUCTURE This aspect will be examined in more detail in the next chapter, but viewed simply, the structure and scale of the farm will depend on how many people are involved

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and what level of income is expected. At its smallest it could be a one man unit producing a few thousand scallops and worked on a part-time basis. At its largest it may produce at levels into many millions of scallops and have a large work force dealing with both production and marketing. Whatever the situation it will still have a basic structure.

Partnerships Partnerships are a popular basis for a farm and they usually involve two people with differing skills. No matter how well the partners get on, there will still need to be a written agreement to cater for situations like bankruptcy, buying out, external investment, individual payment and distribution of profits.

Cooperatives Cooperatives often make a good business base but should be considered as a longterm venture rather than as a quick money-making scheme. The main attraction is based on the concept that by sharing both control and decision-making the result will be a greater level of work satisfaction. Consequently, the members must benefit primarily from their participation in the business and not merely because they have a financial stake in it. The Japanese scallop farming industry has made good use of cooperatives and has proved their potential. Each member has equal control through the principle of one person one vote, and the size of his financial commitment does not affect this. Membership usually has to be open to anyone either in the same line or satisfying the qualifications of acceptance.Where the business makes a profit, this can be either reinvested or distributed to the cooperative members on the basis of hours worked or throughput of produce. By amalgamating a number of farms into a structure of this kind much progress can be made through having one united voice. This is true of any amalgamation of interests.

Associations Once an organization has been formed through which the voices of a number of farms may be heard, there is no reason why it should not be extended to incorporate other important aspects of farming. Associations can take on many roles and the member farms can benefit greatly when aspects like marketing are managed by it. Overall policies can be laid out in the form of guidelines and this can help to eliminate internal conflicts. They can also be used as a means of gathering mutually beneficial information and encouraging overall credibility for anything under their wing. When there is the prospect of raising money through government aid the association or cooperative will be on a sound footing to receive support. Their basic concept is much respected by controlling authorities and it is useful to see them helped and encouraged.

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Equipment pools Some form of cooperation between neighbouring farms must be a good thing. Many items of equipment and machinery can be bought on a communal basis, with the resulting savings being of direct benefit to the individual farms. The construction and use of facilities like jetties, access, storage space and moorings are also better approached when a few farms band together. By extending this concept to the workplace there is no reason why farmers should not help each other during the busy times of harvesting and spat collection. By making an agreement to cover for each other if any individual problems arise, they can ensure that all the participating farms stay in business.

FISH FARMS AND THE LAW A scallop farmer is liable when a third party innocently incurs damage from negligently managed farm equipment. This is especially true of floating equipment, which, apart from being kept in proper condition, should be insured against third party liability. Some other laws affecting the farmer concern the employment of personnel, operating floating equipment, the conduct of vessels on the sea, the marking of wrecks, careless anchoring and damage to submarine cables. Where a farm employs outside personnel it is liable for injuries sustained by them while they are working. The farm should, therefore, carry employer’s liability. Every aspect of the job should meet a required standard of safety and this is especially pertinent to boat and raft work. There are statutory requirements for all floating workstations and these are usually rigorously inspected by the appropriate governing bodies. There are also rules of behaviour for vessels at sea, and when these are carelessly ignored the employer can often find himself liable for a third party’s injury. If a farm boat sinks in a place where it is likely to cause a shipping hazard, the farmer is liable for its marking, any pollution caused by it, and its subsequent lifting. Where careless anchoring results in damage the farmer is once again liable. Of importance when laying moorings is the recognition of submarine cables. In some areas there are many of these on the bottom and they can be easily hooked if no attention is paid to their position. Although most are armour-protected, they can sustain damage when carelessly lifted. The resulting bill for repair can be very expensive.

Salvage There is much speculation over the law of salvage. It is not uncommon for a scallop farmer to get into difficulties with a boat or raft in bad weather and often he is faced with the possibility of a salvage operation. The basic concept is that if there is no danger, then there is no salvage. If the vessel was in danger of loss or damage, such services as towing, piloting or navigation must be paid for.

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Payment for salvage cannot be recovered where aid is accepted only on a towage basis. However, when all the salvage criteria are met, the salvager has the right to detention over the property for his services. When an assessment is made, the basis will be on the value of the craft rescued, the risks involved and the nature of the services, including the skills involved. A reasonable sum should be arrived at and will include all salvage expenses.

REGARD FOR THE ENVIRONMENT Fish farms have been attracting much attention from environmentalists and there have been many accusations of poor planning and untidy layout. When setting up a farm it is good policy to bear these points in mind, because a nicely planned farm can be an attractive feature on a shoreline. Longlines need not be conspicuous if the surface buoys are grey or dark blue in colour. They are also less obtrusive when set equidistantly and in neat lines of roughly the same length. This may not always be possible, but even if approached in a limited way can help reduce the overall impact of the farm as seen from the shore. Regard for wildlife is also important when setting up and running the farm. Try to avoid leaving things unattended, like nets that a seabird may get caught up in. This is also true for equipment in the water that diving birds or even dolphins and porpoises may become entangled in. Raft moorings can be positioned in such a way as to blend with the surroundings, and by neatly following the line of the shore and maintaining an equal spacing their impact can be softened. Possibly they are most obtrusive when their design is varied. This tends to draw the observer’s eye and should be avoided if possible, uniformity being the best policy. By generally keeping both the shore and sea sites neat and tidy, there should be no need to attract the attention of either environmentalists or planners. It can also be a feature that is appreciated by the farm workers because there is nothing better than working in an attractive environment.

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The tendency with scallop farms has been to split production into small units, each being semi-independent but under the overall direction of one company, instead of single large units. A seabed lease will usually specify the number and position of the lines to be set, based on information from the original application. Where there is the likelihood of constant bad weather, buoys with a circumference of 1 metre will suffice to ensure that little wave action is transmitted to the line. In calmer areas slightly larger buoys are permissible. Anchors are expensive items, not only because they are deployed to secure valuable farm equipment but also to purchase in the first place. Unfortunately the

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anchor marker that was deployed when setting the longline is usually the first item to disappear. Where conditions allow, a grid system is a good layout, to ensure there is backup on every line. Individual farmers will have their preferences as to how they set their lines; much will depend on both local conditions and the type of vessel used to service them. As both stock and marine fouling on the lanterns grow, so added weight will come on the line. This is usually supported by subsurface buoys, which may range in size from 180 to 300 millimetres. Surface buoys will indicate the condition of the longline, and once they show signs of taking weight, more subsurface buoys will need to be added. Where there has been evidence of shell wear through excessive contact in the lanterns, the blame is often put on motion being transmitted from the surface. In some instances this may be correct, but another cause of shell movement is tidal motion. Working the line is made easier by using star wheel rollers, which allow the line, along with attached lanterns and subsurface buoys, to pass over without snagging. Correct positioning along the line is important if gear damage is to be kept to a minimum. Strings of collectors, pearl nets and lanterns are notorious for lying at an angle to the tide. Line expertise will start to develop as the farmer becomes more aware of the effects of both wind and tide. A culture raft’s greatest advantage lies in its ease of working and this more than compensates for the increased cost over longline culture. The built-in buoyancy is cheap and permanent compared with that used on lines and there is no need continually to add buoyancy as the scallops grow. There will be certain considerations regarding safety when personnel work aboard rafts and these will vary among countries. The farm boat also will have to maintain a standard regarding this. Choosing the right boat is important and a good idea may be gained from examining what other farmers are using. It may be difficult to decide at a glance what a boat would cost to run. There are, however, a number of items that are obviously expensive. The fishing industry in many countries is regulated in relation to safety procedures and just what is required may vary slightly from place to place. Where a licensed boat is used to work the farm, it will be subject to the same regulations and in many countries the same regulations will apply to dedicated farming vessels. It is very likely that a scallop farmer will be required to indicate the position of his site as a warning to shipping. The type, size and colour of the marker buoy will be specified by the appropriate government body for the area. Having a large indoor store, workshop and general work area is a big asset to any scallop farm. The sea can be a hard master and it must not be assumed that everyone has a natural aptitude to work on it. Courses on seamanship and survival are common

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Scallop Farming today and offer a good opportunity for a farm worker to become familiar with his new environment. Because mariculture is a fairly new activity in many countries, the basis for a fair rent is, in some instances, still at the negotiating stage. The structure and scale of the farm will depend on how many people are involved and what level of income is expected. At its smallest, it could be a oneman unit producing a few thousand scallops and worked on a part time basis. At its largest, it may produce at levels into many millions of scallops and have a large workforce dealing with both production and marketing. Many items of equipment and machinery can be bought on a communal basis, with the resulting savings being of direct benefit to the individual farms. A scallop farmer is liable when a third party innocently incurs damage from negligently managed farm equipment. There is much speculation over the law of salvage. It is not uncommon for a scallop farmer to get into difficulties with a boat or raft in bad weather and often he is faced with the possibility of a salvage operation. Fish farms have been attracting much attention from environmentalists and there have been many accusations of poor planning and untidy layout. Regard for wildlife is also important when setting up and running the farm.

Chapter 7 Methods of Cultivation

In an effort to become cost-effective, scallop culture techniques have been many and varied. Some have failed while a few have proved to be a positive advantage to the industry in both time and money savings. As with all developing industries it is hard to predict exactly how things will go in the future, but specific methods of cultivation have shown the way towards viability. Scallops need an environment of clean seawater in which to grow successfully, and, to date, the open sea has proved to be the best place to carry on cultivation. This does not rule out the possibility of tank cultivation in the future, but rearing techniques still need refining before it can be considered totally viable.

HANGING CULTURE As the name suggests, hanging culture is carried out by suspending scallops in the water from either a line or a raft. There are many types and new techniques are being developed constantly in a bid to increase growth rates and reduce both labour and capital costs. Most innovations have centred around new and improved materials, speedier handling, and reductions in cost brought about by large-scale production. The logistics of handling large quantities of culture equipment are of prime importance and these are examined in depth in Section 3 of the book. A small farm may have as many as 200 000 lanterns employed at any one time, and if each one is bulky, problems with both handling and storage will soon arise. Thus, when discussing the pros and cons of any type of culture equipment this aspect will carry a lot of weight. There are many products on the market which, although very suitable, are rigid in construction and therefore difficult to handle. This has tended to restrict their use to the earlier stages of growth when less gear is required.

Longlines and rafts To date, longlines have proved to be an effective support for hanging culture. Rafts can be equally useful, but their situation is governed by the necessity for sheltered water and adequate depth. On a cost basis 100 metres of line hanging space is 137

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considerably cheaper to construct than the equivalent raft. However, there are longterm cost savings based on reduced labour and capital costs while the raft is in operation, and easier access compared to tending a longline during periods of bad weather. These two culture media are discussed more fully further on. A variety of culture equipment can be supported from either longline or raft. The choice will depend either on what is available on the market or on what can be built by the farmer. There is no doubt that as more countries have become interested in scallop culture so equipment design has become more refined. This has resulted in trends appearing based on one specific culture principle or another.The farmer must make his own choice and hope at the end of the day that it was correct. Unfortunately, although what others use may often be a good guideline, it should not totally influence choice. Different sites, even situated close together, have different characteristics, so the farmer must have a very clear idea of just what his needs are. There follow descriptions of the main pieces of equipment used in hanging culture. All have been tried and tested and found to be effective in a variety of conditions.

Pearl nets The Japanese developed pearl nets and they have been effectively used by farmers throughout the world. They appear fragile and cumbersome, yet for the stage of culture they accommodate they are very suitable, not least because they can be folded flat. Figure 7.1 shows pearl nets both singly and in a string.Their design allows the water to flow through both from the sides and underneath.

a string of ten pearl nets

opening

stitched closed

Fig. 7.1 The Japanese pearl net.

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Sizes Pearl nets can be constructed with either a 300 millimetre diameter circular base or a square base with sides of approximately 320 millimetres. Mesh sizes range from 4 to 21 millimetres but are primarily designed to cater for scallop growth up to 15 millimetres. Consequently the maximum mesh size used is normally 12 millimetres, the larger net sizes being preferable in lantern form. Scallop spat of between 5 and 10 millimetres will go directly into 4 or 6 millimetre mesh pearl nets. After a few months of growth they can be transferred to the larger 9 millimetre nets. The nets are usually rigged in strings of ten, but this can be increased where there is a good depth of water and adequate handling capability. The established system of working has been to use pearl nets for the first two stages of growth and then switch to lanterns. This has meant that farmers have had to invest in two sets of equipment. To overcome this, lanterns have been developed that accept interchangeable net covers. A small mesh can be used at spat stage but it can be increased as the scallop grows. Some farmers have adopted this form of culture while others have continued to use pearl nets.

Handling Pearl nets are loaded through their open edge with a measured number of shells and then sealed up by threading the stiff plastic twine several times back down its length. To reopen, the twine is simply pulled at the top and slipped out of the net, no knots having been used. The strings of nets are tied between 1 and 1.5 metres apart on a longline and supported by a 240 millimetre subsurface buoy every 3 to 4 metres. Lifting the nets back onto the boat can be heavy work, especially where there has been a build-up of marine fouling, so care must be taken to avoid unnecessary damage. Providing the boat’s gunwale is fitted with a form of capping like a 300–400 millimetre plastic drain pipe (Fig. 7.2), the strings of nets can be safely and more easily hauled aboard. Otherwise, they should be lifted straight out of the water and then swung onto the deck. Badly fouled nets will need cleaning and this can be done with a portable pressure washer either on the boat or back on the shore.

Lantern nets The lantern net has been in use for many years, having been used in the fishing industry as both keep net and trap. Although they have been the backbone of successful scallop culture, providing a suitable environment for good growth, they have been subjected to much scrutiny and change. Many farmers have tackled their manufacture and the results have been very successful. Most importantly, they have been able to build something that totally suits their requirements. One point that should be borne in mind when discussing the application of lanterns is which term to use to describe each layer – is it a ring or a partition? It has been practice to use the term ‘ring’ during the lantern’s manufacture because that is what it starts out as

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gunwale

plastic drainpipe

Fig. 7.2 Capping the farm boat’s gunwale to protect equipment as it is hauled aboard.

before being covered. However, when viewing logistics, etc., it is usually referred to as a partition.

Japanese type The Japanese folding-type lantern net (Fig. 7.3) was at one stage the only lantern on the market, and, although suitable in many ways, it did have a number of disadvantages that became quickly apparent. The first of these and possibly the most important was their price. They were and still are very expensive and this has deterred many would-be farmers from proceeding with their project. Difficulties in handling proved to be another drawback because they were found to be hard to work with unless special jigs were manufactured to hold them in place. Their very size when stretched also proved impractical on the average-sized farm boat. Each partition has to be unlaced and relaced individually, and with cold fingers on a winter’s day, this could often prove to be difficult. Many farmers thus sought an alternative, and the result has been either a permanently constructed lantern with a quickly opened door or a removable stocking type, once again allowing quick filling and emptying. Which of these types to choose will depend on the scale of investment in the farm and the type of culture desired.

Removable stocking By far the greatest advantage of this design is its ability to cope with all stages of growth. As the partition rings are covered with a standard 4 millimetre mesh net, all that remains is to attach an outside net of the mesh size required for a specific size of scallop. The net is in stocking form, allowing freedom from individually lacing

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ten layer lantern

(a)

(b) Fig. 7.3 The Japanese lantern: (a) showing how each layer is opened and fixed closed; (b) photograph showing the lantern ready for loading with king scallops. The net bag is ideal for short-term bottom storage of shells prior to future handling.

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Fig. 7.4 A removable stocking type lantern holding queen scallops for temporary storage. (Photograph reproduced by kind permission of Bob and Sandra Parry.)

each layer and therefore representing a considerable saving on time and labour (Fig. 7.4). The ‘Walford’ loading system shows each ring being supported by three pegs, enabling them to be lifted upwards but supporting them from any downward pressure (Fig. 7.5). The outer net cover is fed on with a sleeve that is run down over the loading frame. Once in place, the complete lantern is lifted free. The net holds the partitions securely in place by catching on to the small spokes on their circumference. When the lanterns are lifted aboard for sorting and cleaning, the old net is merely lifted away to leave the partitions ready for washing and reuse. An advantage to this system is that the lanterns can be constructed with as many partitions as required. Loading frames can be built to accept 20 rings, with different spacings to suit.

Costs For large-scale production, lanterns with removable stocking are ideal, but for the farmer on a small budget they could prove costly to use. The rings are cheap when

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net loading drum

lantern ring

loading frame

ring securing pegs

lantern

Fig. 7.5 The Walford loading system for removable stocking lanterns.

compared with a Japanese-type lantern and the outer covering works out at roughly 10 per cent of the total cost. However, the outer stocking is not reusable and may require changing two to three times a year in areas with a marine fouling problem. If 10 000 lanterns are employed, net changes could prove expensive, and there is the added problem of transporting and disposing of the sometimes heavily fouled nets.

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loading sleeve

wrap-around netting

Fig. 7.6 Rigged lanterns with both stocking and wrap-around cover.

On the advantageous side is the fact that supplies of net stocking are gradually coming down in price.

Alternate rigging By rigging the lantern with 6-millimetre rope in the form shown in Figure 7.6 there is no need for the rings to have spokes. This system is also applicable where wraparound net is used, and a net of this kind can be reused providing it is thoroughly cleaned beforehand. The stocking net may also be reused providing it is strong enough. An advantage, once again, is that extra long lanterns can easily be constructed if required. The reason that these two systems allow the net to be saved for reuse is because of the absence of spokes on the rings. The riggings holds the rings in place, not the net catching on the spokes. In fact, by removing the spokes, not only does it mean that old netting need not be cut away and destroyed, it also helps prevent lanterns catching on each other when in the water.

Permanent covers Plastic manufacturers are putting much thought into the design of lantern rings, primarily aimed at the disposable net cover market. On the basis of cost and conven-

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ience many farmers prefer their lanterns to have a permanent net cover. All the manufactured rings can be used for this, and the time taken for construction, with practice, is usually around 60 minutes. Chapter 9 covers all the stages in constructing a lantern of this kind and also gives details on how to build individual rings. One disadvantage of this system is that, once the lantern is covered, it may be only specific for one size of scallop. However, that is usually only at the smaller sizes and once a maximum 21 millimetre net is used, this can accommodate shells from that size upwards. In fact, even if the net size is a little as 12 millimetres, there is no reason why it should not accommodate quite large stock, providing there are regular changes to prevent too heavy a build up of marine fouling. So, although this type of lantern may not be totally multipurpose, the farmer will have a quick-loading, durable item which does not require expenditure when nets need changing. For large-scale growing, where investment is high, the stocking lantern is a great advantage and should prove cost effective in the long run. Having a standard system is ideal, especially where production line techniques are used. The smaller farmer, however, will not often have the luxury of spare capital and will usually consider his time to be free when spent in assembling lanterns. He will also want to be flexible both for interest’s sake and for determining suitable methods of work. A compromise is usually reached whereby a farmer will have varying types of pearl net and lantern and will use each according to his wishes.

Ear hanging Ear hanging was developed in a bid to cut the costs of operating from lanterns, and the results, where trials have been successful, have shown that not only is the process cheaper, but over a comparable time growth rates are higher. It must be said, however, that although the prospect for ear hanging looked good in the beginning, some of the long-term results have been disappointing. There have been problems with the ears actually breaking, mortalities because of drilling when the scallop is in a weakened state, excess fouling, chafing on the downline and predation. The process is therefore very site specific and should only be undertaken in areas with no strong tides, no excess fouling, no chance of the ear-hung strings touching the seabed and with a great deal of caution. The term ‘ear hanging’ means attaching the scallops to a line by means of a wire or plastic tag passed through a hole drilled in the ear of the shell. Although the drilling and tagging process is relatively slow to begin with, the savings from then on are considerable because the scallop can be left to grow right through to marketable size. The only extra work needed is to buoy the line periodically to support the increase in weight. The Japanese have used the method extensively, but in areas of colder water the process has been less popular. The shell must be substantial enough to withstand the drilling procedure and this means a diameter in excess of 45 millimetres (usually 2-year-old, king type scallops, in temperate waters). In fact it is quite obvious that

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the process is really only relevant to scallops that require a longer period of growth to reach marketable size. Although it has not been uncommon to drill smaller shells, this has lead to fairly high mortalities. The action of drilling creates both heat in the shell and shock to the scallop’s nervous system. It has therefore to be performed carefully, ensuring that the mantle is not damaged. The shell must be put straight back into the water after the operation, and possibly the best way to work is to carry out the procedure under a fine seawater spray, therefore ensuring minimal shock. Research into ear hanging techniques has been aimed at finding the minimum size at which a scallop can safely be drilled and, although it was hoped that its success may eventually make lanterns redundant, it has still a long way to go.

Attachments Much research has been directed at finding a suitable product with which to attach the scallop to the line. Figure 7.7 shows three types of attachment used as the method of securing to a line. The first is a toggle or anchor tag. To date, however, better results have been found with a fastener called a securatie, and although they are more expensive than the other types, the breakage levels are less so allowing more scallops to reach maturity. The uneven surface of the securatie allowed the scallop’s shell to grow into, and take a grip of, the attachment. The result was less abrasion to both fastener and shell. There will be losses through ears breaking, and the best advice is to secure the bottom rights around the culturing area. In this way, that which falls to the seabed will be protected and should stay safe until lifted.

Procedure Although initially all of the drilling for ear-hanging was undertaken manually, there are now machines available that carry out the whole process automatically, drilling and attaching to the line. However, they are expensive and for many farmers the procedure will be mostly based on manpower alone. For this process, the scallops are placed in a jig attached to the base of a drill stand. An air-powered drill is then brought down to drill the hole. It is usual to attach the shells in pairs with roughly 100 millimetre spacings. The number per line will depend on the depth of water and capability of lifting, but 100 would be a reasonable figure to work from. The individual lines are attached to a longline at 0.5–1.0 metre intervals and supported by subsurface buoys to attain initial neutral buoyancy. Being left for up to 2 years will mean a fouling problem of large proportion, and trials to date have shown that a large proportion of the buoyancy is used just to support this unwanted growth. Tangles can also prove costly because scallops supported in such a delicate manner will easily separate from the line if too much strain is put on them. There is no doubt that if ear-hanging techniques had become more successful, scallop farming would have been more viable for the future. However, where appro-

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6 mm braided line anchor tag

2 mm hole anchor tag pistol

securatie fastener

Japanese fastener (a–ge–pin) Fig. 7.7 Methods of securing scallops by ear-hanging.

priate it seems that at present it would be advisable not to place too much emphasis on this technique and to use it only after extensive trials prove its success.

Rope culture Rope culture was developed in Spain and involves cementing scallops back-to-back onto a central rope. It follows the same principle as ear-hanging, with similar spacings and numbers to each drop, and growth rates and mortalities are comparable. It is possibly cheaper to set up, but in the long term the scallop, being badly fouled, is left with a piece of cement attached to it. It is also difficult in certain circumstances to detach them from the rope.

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6 mm hole

scallops cemented flat side to rope

Fig. 7.8 Scallops glued or cemented to rope droppers.

Process The king scallop once again is a prime candidate for this process because it favours those shells with one flat side. The scallops are laid convex side down in a straight line and a small quantity of quick-setting cement is applied to the flat, upwardsfacing side. A 6-millimetre rope is laid over the shells and lightly pressed into the cement. Another small quantity of cement secures a second scallop, flat side down, on top of the first. After 2 hours the cement is mature and the scallops are ready to go back into the water for growing on right through to maturity. Figure 7.8 shows scallops cemented to a line as described. A natural progression from the use of cement is to employ a quick-setting glue. Modern adhesives can be used to stick almost any materials, but there are certain problems with scallops. The glue would have to set very quickly and generate no heat during the process. The beauty of both cementing and gluing is that the scallops can be set at a smaller size, thus cutting back even further on the use of lantern nets.

Pocket nets Pocket nets are another Japanese invention and, as the name suggests, are based on the practice of placing scallops into individual pockets for growing on. Figure 7.9

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4 mm rope

15 cm sq pockets

4 to 5 m long

21 mm mesh net

Fig. 7.9 Pocket nets.

shows how they are used and their basic construction. Although being fairly useful they are not as cost effective as either the cheaper types of lantern or ear-hanging, and consequently their use has been limited. For the small farmer, however, they offer something he can construct himself out of materials that may be easily obtained.

Hog ringing Mussel stocking is hog ringed onto a 6-millimetre line to form pockets into which three to four scallops are placed. It has been used to great effect in queen scallop cultivation but the results have not been so encouraging for larger species of scallop. Figure 7.10 shows how the system works and the simplicity with which the scallops are loaded. Although growth rates were not as good as in other methods, this system does offer a quick and cheap method of rearing scallops and should not be overlooked if lack of finance is a major concern. As a last resort it can be used to secure stocks until lanterns are either constructed or purchased. The ringing process may be carried out either manually with a pair of hog ring pliers, or automatically using an air-operated machine.

Plastic trays So far we have been discussing items of equipment that can be folded flat. Plastic trays are rigid in construction and take up considerable space when stored. Because they are expensive, few small farms rely on them totally, even though their concept

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scallops put in here

6 mm rope mussel stocking 20 cm dia

ring secured with hog ring pliers

Fig. 7.10 The use of mussel stocking and hog ringing.

is excellent in design, durability and longevity. One aspect of farming they are particularly useful for is the temporary storage and transportation of spat and small juveniles. The standard tray has a mesh size of around 6 millimetres, which puts it at a disadvantage for larger shells. However, there are others on the market that are fulfilling the role for the later stages of growth.

Construction Figures 7.11–7.13 show the types of tray in common use, and how they may be deployed. The square design is of interlocking layers but requires either supporting within a frame or rigging with rope before being placed in the water. It also requires weighting. The circular variety is also interlocking, but has a central bar running up the middle to secure the stack and act as a support in the water, and although it is slightly more expensive it offers advantages in speed of handling, loading and general operation.

Oyster cages Oyster cages are a very durable product and come in a variety of mesh sizes. They are flexible, tough and relatively inexpensive but need a frame for support. Figure 7.14 shows one way of using this type of equipment, but for the innovative farmer

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rope rigging

metal frame weight central supporting bar

weight Fig. 7.11 Plastic culture trays.

Fig. 7.12 A unique method of culturing the scallops. Each plastic layer supports four shells and they may be stacked as deep as required.

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Fig. 7.13 Rigid plastic trays for all types of scallop species.

6 mm galvanized steel frame

securing rope

50 cm 6 cm

45 cm 85 cm Fig. 7.14 Oyster cages supported in a steel frame.

there are sure to be other ways. They are excellent for spat storage and transport. Unfortunately, as their supporting frame has to be rigid, they cannot be classed as collapsible, which makes them bulky to store and handle. Once again, for the less well off farmer they offer a cheap alternative to some of the more traditional products and should therefore be taken seriously. Figure 7.15 shows how these cages can be turned into a permanent culture system requiring no frame. The cages are cut in half, formed into boxes, and roped together into a ten-layer unit.

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oyster cage

reinforced sides

cages cut in half

8 mm rope stitched to edges

opening flaps

Fig. 7.15 Forming oyster cages into permanent lanterns.

BOTTOM CULTURE The bottom culture category covers methods that use the seabed either as a support for equipment or as a growing area itself. Many who farm on a large scale are looking at this form of culture, and in Japan it is a recognized and established method of farming. One of the biggest problems in hanging culture techniques is the cost of buoyancy and the fact that a large proportion of it is used to support marine growth on the equipment itself. By using the bottom and avoiding the need for extra support, the need for buoyancy can be eliminated.

Oyster cages and frames The use of oyster cages and frames offers more scope to the innovative farmer than any discussed so far and the following description aims to fuel the imagination as to what is possible. Unfortunately, by growing near the seabed the benefits of midwater plankton concentrations are missed and, consequently, growing times can be a little longer. On the other hand, it is comparatively cheap to set up and reasonably simple to work.

Construction Up to 20 oyster cages in layers of five can be supported in a frame on the seabed; Figure 7.16 shows how this is constructed. The base of the frame has wide feet to

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12 mm galvanized steel frame 0.65 m

feet

20 oyster cages

1.70 m

0.9 m Fig. 7.16 Frames to house oyster bags directly on the seabed.

help prevent the bottom layer of cages from actually touching the seabed, and the whole construction has a low centre of gravity which should stop it from being rolled by the tide. The frame is constructed of 12 millimetre steel, either galvanized or plastic coated. A 12 millimetre surface line and buoy acts as a marker as well as a means of lifting. There is an overall size constraint because of the problem of ensuring that those scallops in the middle of the pile receive an adequate supply of food.

Operation A structure of this size will require a specially constructed lifting frame or a tailormade craft to work from (Fig. 7.17). Vessels as small as a 5.5 metre assault craft have been converted, showing how cheaply it can be worked. An alternative is to work the frames tidally. By raising them to surface level at high tide they can be towed inshore and set back down on the bottom. When the ebbing tide exposes the frame, sorting and cleaning can be carried out. The next high tide will allow the frame to be towed back out to sea and resited. A few frames may be towed on each tide, thus enabling a fair amount of sorting to be carried out each day. A future development is the use of rafts with adjustable buoyancy. With careful adjustment of the buoyancy system, a raft of this kind, fully loaded with lanterns, can be lowered to the seabed. Figure 7.18 shows a basic design for a system of this kind. The base of the frame would rest on the seabed and the whole system could

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lifting frame frame swung inboard

Fig. 7.17 Adapting the farm boat to haul aboard the bottom cages using a lifting frame at the stern of the boat.

buoyancy control

buoyancy tanks

tubular steel base

Fig. 7.18 An adjustable-buoyancy raft: the whole unit can be lowered to and raised from the seabed.

be raised when required by reinflating the buoyancy tanks. They would have to be employed in fairly shallow water with a flat, firm bottom. Lowering would be tricky in depths greater than 8 metres because of the rapid decrease in buoyancy caused as the water pressure increases. This could be offset by the use of a regulator, which monitors the pressure and compensates accordingly. There is no doubt that systems of this kind will be commonplace in the future and the principle is already being used to good effect in the salmon farming industry. A further move would be to make the system dependent on divers, and, in places like the Adriatic, many fin-fish

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farms are fully enclosed underwater and the fish are fed by divers working from the outsides of the nets. On the face of it this method of working offers considerable advantages over some of the others. Not least is the fact that equipment is unlikely to be affected by bad weather, being safely set on the seabed.

Wild ranching By far the cheapest way of carrying out the final stages of growing on is to place the shells directly onto the seabed. Success has been achieved in putting spat onto the bottom in some areas, but there must be few predators present to allow this. In most instances the scallop will need to be a type suitable for wild ranching, must be at least 50 millimetres in size and have a strong shell. At this size their chances of survival against most varieties of small crab are very good, but the larger, brown, edible crab Cancer pagurus will still be able to crush the smaller shells.

Large-scale cultivation Large-scale bottom culture may be considered to involve in excess of 20 useable square miles of seabed being stocked. Where it is carried out, it is usual first to dredge the ground to remove obvious predators such as starfish and crabs. The ground is then seeded. Harvesting is carried out by dredging, when permitted, otherwise by diving, and the bottom is worked on a rotation basis of two or three segments. Information to date has shown that close to half the stock can be retrieved in this way, comparing favourably with hanging culture if the reduction in capital outlay is taken into account. This can be considered true wild ranching.

Small-scale cultivation Most large-scale operations have been carried out in areas where legislation has given some kind of protection to the stock. Unfortunately this is not universal, and the smaller operator is often faced with an unfair cost burden in having to pay for his own application for protection. When he succeeds and wants to undertake bottom culture, he can tackle both seeding and harvesting in several ways. If the lease encompasses a sizeable area of flat, featureless seabed, the whole area can be seeded on the same basis as for large-scale cultivation and finally dredged at harvest time. Where there are several farmers in an area, the seeding and dredging may be carried out on a cooperative basis, using just one site. The advantage of this is that, with a number of farms involved, protecting the stock will be easier. In order to achieve the most from time spent diving to the bottom, the site should be within the 10 metre range and will also need to be sheltered from the effect of heavy swells to prevent the scallops from being swept away. Where diving is used as a means of harvesting (Fig. 7.19), better results can be obtained by seeding more carefully initially. Providing the area is totally suitable, and with compounds approx-

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Fig. 7.19 Harvesting by diving. (Photograph reproduced by kind permission of Bob and Sandra Parry.)

imately 50 metres square and having only leaded rope marking the boundaries, the scallops will be seen to settle and few will move away. Six to seven scallops per square metre is a reasonable seeding density, and if the conditions are exceptionally favourable this may be doubled. With compounds constructed as shown in Figure 7.20, the diver should miss few shells and the final product will be superior to dredged scallop in that they will be grit free. Best practice for diving harvesting will be discussed in Chapter 10 (Diving work), but it should be pointed out here that it is usual to work on a 2–3 year rotation of ground, depending on time taken to reach marketable size, and the size required to attain the highest price per kilo. The site will rarely be completely cleared during harvest but those scallop remaining should, because of their increase in growth, be more easily spotted on the next visit, which could be between 2 and 3 years ahead. At this stage the shells should be able to attain a premium price. A problem with constructing any barrier on the seabed is that it may act as a restriction to loose seaweed drifting past, which, in turn, can suffocate the scallops if left for too long. Natural barriers are therefore superior and by diving they may be encouraged to develop in a number of ways. Figure 7.21 shows a compound con-

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Scallop Farming 50 m

50 m

Fig. 7.20 Seabed compounds.

50 m

50 m

surface buoy ‘cod end’ ring

Fig. 7.21 A grid system constructed from 8-millimetre leaded rope and buoyed at each junction. This is ideal marking for seabed harvesting.

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small hole cut in net to insert weight

150 mm

stone weight every 2 m 8 mm sole rope

25 m net tunnel stretched between anchors

Fig. 7.22 The construction of a seabed barrier that allows the passage of debris without snagging.

structed of 8 millimetre leaded rope. If this is left in place, weed will eventually grow from it, thus creating a more visible barrier but one that will yield with the tide and therefore not restrict the flow of organic debris past the site. Figure 7.22 shows one method of creating a suitable barrier and, although quite labour intensive to build, one that works very effectively once in place. The endresult is a tunnel, the round surface of which allows floating weed and debris to pass over without catching. If there is a problem with anchoring, more weight may be added by cutting a small hole in the net and inserting a stone into the tunnel at various intervals. There are products on the market that, although being designed to combat erosion, could be of use in farming bottom compounds. They simulate long grass or weed, and when laid in strips encourage the build-up of sand (Fig. 7.23). This could be an excellent way of forming permanent compounds because the material would allow all types of debris to pass by unhindered. It would also sustain little damage from carelessly placed fishing gear. Unfortunately, the cost of setting such equipment is at present prohibitive, but bearing in mind the principle on which it works, the innovative farmer should see his way to constructing something on the same lines using 1 metre lengths of synthetic rope secured in lines on the seabed. Although it can take up to 20 per cent longer to bring the scallop to marketable size when using bottom culture, this is outweighed by the savings in culture equipment and by the production of a more marketable product. Once the scallop settles into the bottom, recessing deters further fouling. Predators will tackle mussels, barnacles and tube worms, and most weed fouling will also be smothered as soon as the top shell is covered in sand (Fig. 7.24). However, there will be certain losses, such as when shells are carried away by weed that has managed to grow to a size large

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Fig. 7.23 The use of seagrass as a seabed barrier.

Fig. 7.24 Pecten maximus ready for bottom culture. Note the heavy barnacle fouling.

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enough to be moved by the tide, lifting with it the scallop clear of its recessed bed.

ENCLOSED CULTURE There is no doubt that as suitable seabed leases become scarcer the tendency will be towards either floating sites in the form of barges or shore-based sites in the form of manmade ponds. Both will need a supply of clean seawater and this will have to be pumped to the installation. Although being dependent on machinery, they will have the advantage of giving more protection against the weather and allowing work to be carried out all the year round. Another advantage could lie in the ability to introduce artificial foods in the form of laboratory-grown algae in the hope of speeding up growth.

ANALYSIS OF TECHNIQUES Growth and mortality rates will vary with the type of culture undertaken and, although some rough comparisons can be made, much will depend on local conditions and general husbandry techniques.

Meat yield Where a king scallop has been cultured in a lantern in temperate water for 4 years its meat yield can be as much as 10 per cent higher than that of a wild scallop of the same size. This is generally attributed to the higher densities of nutritious plankton found in the mid-water levels in which the lanterns are hung. This extra growth can be as much as 20 per cent in the case of ear-hung stock, if all other conditions are favourable. Wild-ranched scallops have shown growth rates comparable to ear-hung stock, but only in exceptional circumstances and with favourable conditions and low stocking densities. The initial 2 years in lanterns gives them a good start and then natural conditions take over to contribute to a high meat yield. On the other hand, if the bottom is not comparable to a natural habitat, growth rates and subsequent meat yields will be poor.

Mortality Good husbandry can produce low mortality rates, and, although figures may vary, the final levels are usually directly proportional to the amount of care taken over the complete growth cycle. For the benefit of budgeting it is best to base the final survival on an overall 50 per cent mortality. With proper care and attention this might be reduced to 35 per cent or occasionally even less. By keeping stocking densities low and net changes to at least two per year mortalities in lanterns can be kept to a reasonable level. For ear hanging the mortality

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(a)

(b) Fig. 7.25 (a) Collector bags loaded and ready for shooting. (b) Some of the collectors now in for sorting. Note the heavy fouling by sea squirts and the dirty nature of the bags. (Photographs reproduced by kind permission of Bob and Sandra Parry.)

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level can sometimes be high owing to scallops breaking their attachment. Actual mortalities however, are usually fairly low for those left on the line, the highest rate being seen shortly after the shells are drilled. Those falling to the seabed can often be seen to survive, although harvesting requires the use of a diver. Mortalities in bottom stock are more difficult to calculate because of variations in harvesting. Even repeated dredging will be unlikely to recover as much as 75 per cent of the stock, partly because of damage to the scallops caused by the apparatus itself. Diving can be fairly effective where the bottom is clean and the shells are close together, but there is still a likelihood of the shells being missed. When seeded at 50 millimetres there is a good chance of between 50 and 80 per cent surviving, depending on the level of predation.

Levels of fouling Each cultivation type will have a different level of fouling which, in turn, will have a direct bearing on the amount of buoyancy required for support. Ear-hung stock suffers the most and in bad cases it can amount to 30 per cent of the overall weight. Those in lanterns are less affected and can expect to accumulate an additional 5 per cent of their total weight, the overall high weight increase being attributable to fouling on the lantern itself, which can be as much as 60 per cent of its overall weight. Figure 7.25 illustrates the amount of fouling that can be accrued on collector bags and Figures 7.26 and 7.27 show similar fouling on lantern nets.

Fig. 7.26 This shows the problems of heavy fouling on lantern nets. (Photograph reproduced by kind permission of Bob and Sandra Parry.)

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Fig. 7.27 Lanterns suspended from a longline. Note the heavy fouling. (Photograph reproduced by kind permission of Bob and Sandra Parry.)

Fig. 7.28 A scallop research vessel undertaking trials in the Adriatic on the scallop Pecten jacobaeus.

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Fig. 7.29 Taking note of growth progress in Pecten jacobaeus.

SUMMARY •

•

•

•

•

•

Scallops need an environment of clean seawater in which to grow successfully, and until now the open sea has proved to be the best place to carry on cultivation. To date, longlines have been demonstrated to be an effective support for hanging culture. Rafts can be equally useful, but their situation is governed by the necessity for sheltered water and adequate depth. The established system of working has been to use pearl nets for the first two stages of growth and then go on to lanterns. This has meant that farmers have had to invest in two sets of gear. The lantern net has been in use for many years, having been used in the fishing industry as both keep net and trap. Although they have been the backbone of successful scallop culture, providing a suitable environment for good growth, they have been subjected to much scrutiny and change Plastic manufacturers are putting much thought into the design of lantern rings, primarily aimed at the disposable net cover market. On the basis of cost and convenience many farmers prefer their lanterns to have a permanent net cover. For large-scale growing, where investment is high, the stocking lantern is a great advantage and should prove cost effective in the long run. Having a standard system is ideal, especially where production line techniques are used.

166 •

• • • •

• • • •

Scallop Farming The term ear-hanging means attaching the scallops to a line by means of a wire or plastic tag passed through a hole drilled in the ear of the shell. Although the drilling and tagging process is relatively slow to begin with, the savings from then on are considerable because the scallop can be left to grow right through to marketable size. Rope culture was developed in Spain and involves cementing scallops back-toback onto a central rope. Pocket nets are another Japanese invention, and as the name suggests are based on the practice of placing scallops into individual pockets for growing on. Hog ringing is a process by which mussel stocking is hog ringed onto a 6-millimetre line to form pockets into which three to four scallops are placed. Plastic trays are rigid in construction and take up considerable space when stored. Because they are expensive, few small farms rely on them totally even though their concept is excellent in design, durability and longevity. Oyster cages are a very durable product and come in a variety of mesh sizes. They are flexible, tough and relatively inexpensive but need a frame for support. Bottom culture is a category of cultivation covering methods that use the seabed, either as a support for equipment or as a growing area itself. Wild ranching is by far the cheapest way of carrying out the final stages of growth by placing the shells directly onto the seabed. Enclosed culture will become more common practice because there is no doubt that, as suitable seabed leases become scarcer, the tendency will be towards either floating sites in the form of barges or shore-based sites in the form of manmade ponds.

Chapter 8 Moorings

Sound moorings are as important to a scallop farm as are good foundations to a house. The sea is a hard master and has much to teach us. We must therefore be prepared to adapt to its constantly changing state. Moorings have to be able to work with these changes, not against them, and considerable thought must be put into their design. However, as all sites differ in one way or another the systems must have a certain degree of flexibility. If a mooring is laid to the correct specification and inspected and maintained on a regular basis, it is unlikely that it will fail. However, this does sometimes happen and sometimes more regularly than it should. The following are some of the reasons for these failures: System not substantial enough: Component failure; shackles coming undone, rope chafing through, rope breaking, mooring posts breaking, swivels breaking, etc. System accidentally damaged by a very large third party. Some of these problems can be put down to poor inspection procedures, wear on metals caused by electrolysis and corrosion, and poor positioning of equipment, which encourages chafing and wear. However, with care, many problems can be anticipated and consequently avoided. One last but important point is that moorings should not just be regarded as what lies underwater. Topside components are equally important to the system so care should be taken to ensure that such items as cleats, Samson posts, bollards and all points that use the system are also in good order and inspected regularly. It has in fact happened on occasions that although a mooring has held, a farm boat has gone adrift because of a cleat being pulled out of the foredeck.

MOORING PROPERTIES The holding power of an anchor is dependent on its weight, design, composition of the seabed and method of use. It is not a case of slinging a hook in the hope that it will catch on the bottom, or dropping a heavy weight and assuming it will support 167

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anchor efficiency (kg)

1000

750

500

250

5

10

15

20

25

30

35

40

45

50

55

angle of pull on anchor (°) Fig. 8.1 Anchor efficiency in relation to angle of pull.

the load attached to it. The effectiveness of anchor types will be discussed later, but at this point it would be useful to look at some of the properties that go into designing a good system.

Weight Both the anchor and chain must be heavy enough to ensure a horizontal pull on the components, irrespective of holding power. Figure 8.1 shows the decrease in holding power of an anchor as the angle of pull increases. It can be seen that a small rise to 15° off the horizontal decreases the effectiveness of the anchor by approximately 50%. This is one of the most important points to bear in mind in using all kinds of anchor.

Spring By introducing a spring or damper into the system, wear and stress can be considerably reduced. Components will wear more rapidly if load is applied sharply in the form of jerking movements, and to help avoid this it is usual to introduce a surface buoy or extra long, heavy chain to act as a spring. Figure 8.2 shows how a spring can be introduced into the system by using a large buoy and long, heavy chain to the seabed. This chain is most important to the system. Figure 8.3 demonstrates its main functions when it is finally shackled into the anchor.

Breaking strain All mooring components have a safe working load within which it is wise to stay. Their breaking point can be as much as double this figure, but should not be used

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169

direction of pull

buoy spring surface buoy

chain

spring

anchor Fig. 8.2 Introducing a spring in the form of a large buoy.

D E A horizontal pull B acts as spring

B

A

C adds weight D beds in

C

E absorbs chafing Fig. 8.3 The mechanism of action of a heavy chain serving as a spring when attached to an anchor.

as a reference from which to work. In general, when installing these components work to a factor of four times what is required in terms of loading.

Components Figure 8.4 shows the basic chandlery that may be found in a mooring system. It is good practice to use as few shackles, thimbles and swivels as possible, because this leaves less to go wrong. Where possible, attach the rope directly to the chain end by splicing and finally whipping tight into the link. With practice, splices can be completed very quickly, and by tying directly to the chain end one shackle fewer will be

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straight shackle

stud link chain

bow shackle

bulldog grip

fish plate

swivel

thimble

ring

Fig. 8.4 Some of the chandlery making up a mooring system.

clove hitch and whipping

eye splice tightly whipped Fig. 8.5 Two ways of securing the rope to a chain end.

needed in the system. Where the end link of the chain is sufficiently wide, a clove hitch can be tied and finished off, either with a splice or by whipping, and this knot will tighten down onto the knot to form a very secure joint. Figure 8.5 demonstrates both these fastenings. There are of course many other ways of attaching a rope to a chain and Figure 8.6 demonstrates some of the most common ones. Where necessary, a thimble can be used to protect the rope, and this can go either directly onto the chain end (Fig. 8.7) or via a shackle. Figure 8.8 shows another popular type of rope protector, known as a tube eye. They come in all sizes and the smaller ones can be opened up if necessary to be secured without using a shackle. Their advantage lies in that the rope is secured with an actual piece of tubing both when it enters and exits the component. When shackles are used they should always be secured either by mousing with plastic-coated fence wire (Fig. 8.9) or by ham-

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171

thimble and shackle

thimble and chain

thimble with bulldog grips

rope on to chain

rope and bulldog grips

round turn and two half hitches Fig. 8.6 Other methods of attaching a rope to the chain.

thimble opened and slipped into chain

thimble squeezed shut

rope spliced onto thimble Fig. 8.7 The use of a thimble.

mering over the protruding end of the main pin. Some farmers resort to welding the pin for security, but this makes replacement difficult. In situations where the shackle remains fairly static a heavy tie wrap can be used to secure the pin. Having reduced the number of components to a minimum it is good working practice to ensure that those remaining are subject to little movement; for instance, where possible use complete lengths of chain to avoid having to use shackles to join shorter pieces. A shackle in this position will be subjected to much movement on the seabed and could easily work loose. Where a rope connects to a chain end it is

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Fig. 8.8 A tube eye.

4 mm plastic coated wire mousing

Fig. 8.9 Mousing with plastic-coated wire.

usual to attach a 300 mm subsurface buoy to lift the joint off the bottom (Fig. 8.10). This helps to reduce heavy chafing. If the support is omitted the chain end eventually forms a hollow and the rope has to pass out over an edge on its way to the surface. This can cause unnecessary wear.

MOORING SITES Although a farmer would look for other qualities in a site over and above its potential as a safe mooring, he would still be advised to bear some geological and phys-

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173

hollow worn in seabed by chain end

chain supported by subsurface buoy Fig. 8.10 Use of a subsurface buoy to keep the shackle off the seabed.

ical factors in mind. Every site will provide a different combination of factors that will influence the mooring design, and thought should be given to each one in turn.

Depth A deep site will mean having to spend more money on moorings because extra tackle will be needed to cope with the depth. There is also the problem of inspections if a diver’s services should ever be employed, because his bottom time becomes greatly reduced the deeper he works; for instance, he can work safely for 55 minutes at 20 metres but for only 5 minutes at 40 metres. Diving regulations vary between countries but, generally speaking, many commercial air divers are only qualified to work up to depths of 30 metres, so if possible it is best to keep systems within this range.

Shelter Not only is a sheltered site easier on the moorings but also it offers more comfortable working. Constant motion can cause havoc on a mooring, so where a site is exposed the specification of materials must be stricter.

Tide It is essential to have a tidal movement, but if it is too strong much strain can be placed on mooring components. Where there is a combination of heavy seas and very strong tides, the strain could become excessive. Fully stocked longlines set across a strong tide will eventually cause the farmer trouble, and unless his moorings are exceptionally robust he will be faced with anchor drag and rope stretch. When the weight of the farm boat is added to this the overall effect can sometimes be too much for the mooring system.

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head fluke

stock shank

crown arm

Fig. 8.11 Anchor terminology. The parts of a traditional fisherman’s anchor.

Seabed The composition of the seabed will directly affect the performance of the tackle placed on it. It is therefore important to know its type and to choose compatible equipment. Very heavy concrete blocks placed on a shingle bottom will be found to lose most of their holding power, as will mud anchors placed on rock. A sand or firm mud bottom will offer the most choices with regard to anchor types but the harder the seabed, the fewer will be the choices. The main components of an anchor have the same name, although they may differ in design. For reference, Figure 8.11 shows a traditional fisherman’s anchor with all its component parts named. Figure 8.12 shows the various types of anchor related to a variety of bottom conditions. Some are excellent in many conditions, while others are suspect even in the most suitable situations. As a general rule, where a bottom is very soft the principle of suction can be used effectively, and this occurs when the anchor or block is sunk into the seabed. When a force is applied the mooring becomes something of a plug with the same properties as a rubber suction cup. A concrete block with a large flat base is useful under these conditions. Where the seabed is hard, it is necessary to use sheer weight to secure a position. On solid rock, the only satisfactory system, apart from drilling and pinning by diving, is an exceptionally heavy block that weighs well in excess of the load to be applied. Between the very soft and very hard bottoms we rely on anchors digging in to maintain their holding power, and this will be accomplished with varying effectiveness according to anchor type.

Water purity With the increasing problems of marine pollution, areas that are classified as category A are becoming fewer. Although scallops can survive in lightly polluted areas, it must be remembered that mooring components will be wearing more quickly where acidity levels are higher. Sometimes a mud bottom can become deleterious to metals, and any chain lying in them will wear especially quickly. Galvanized shackles will be seen to deteriorate faster and should therefore be inspected regularly. If a metal component is stressed at a certain point, it will corrode more quickly

Moorings Type

Characteristics

CQR

mainly small and portable, self-righting, good in many conditions, expensive

Bruce

deep penetration and good in all conditions, self-righting

Fisherman's

portable, self-righting, average holding

Admirality

needs checking to ensure flukes have penetrated the seabed, low holding on soft bottoms

Danforth

good for all conditions if allowed to settle

Mushroom

suction type for mud and soft bottoms

Clump

heavy, good in many conditions, needs careful setting

Mud

heavy and designed for mud, needs careful setting

Samson

good in all conditions and high holding, needs careful setting

Fig. 8.12 Nine anchor types and their effectiveness. CQR, coastal quick release.

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there. Couple this with wear created by pollution and it will be seen that moorings can become quickly unsafe.

Mooring types Mooring designs are many and varied, often tailored by factors of cost, availability of materials and capability of being set. If there are no cost restrictions, the very best of equipment can be bought and maybe a consultant hired to supervise its laying. This is the ideal, but most farmers are faced with having to adapt what is at hand and it is therefore essential to know exactly what is required of a mooring. A final restriction can lie in the physical inability to handle a heavy system. If all that is available is a small clinker dinghy, then it is unlikely to have the ability to place very heavy mooring tackle. On the other hand, at the outset of salmon farming it was amazing to see just what was set up using the minimum of equipment. Man, when set a challenge, can often be ingenious in his approach and solution to it. Innovations in mooring design require considerable expertise to make them completely safe, and most problems occur in this area. It is therefore best to use proven methods to secure the farm and to innovate only when totally necessary.

Single-point moorings A single-point mooring is used mainly for boats, but can also be effective with rafts provided there is enough room for them to swing. Once again, their design can be variable, ranging from a single block on the bottom to a three anchor system forming legs from a single point. The use of a block, although safe enough with regard to actual physical weight, often has an inherent problem, with the bottom chain wrapping itself around the outside and becoming caught fast. This in effect shortens the riser and reduces the level of spring built into the system. Figure 8.13 shows the different types of single-point mooring and Figure 8.14 describes some of the methods of connecting in swivels and buoys. Although it is good practice top keep components to a minimum, it may prove necessary in a system of this design to have a swivel to prevent the chain from twisting. As swivels are particularly prone to wear, they are best sited near the surface to enable inspections to be carried out more easily and therefore more frequently. It must be borne in mind, however, that it is very difficult to ascertain the state of a swivel’s inner pin so possibly a good policy is to change it every 18 months or so just as a matter of course. One failing of single-point moorings is that there is no fallback if they break. Excessive movement caused by the boat or raft constantly circling is also a problem. Unfortunately, in certain areas there is no alternative to using this type because of varying directions of wind and tide.

Two-point moorings Two-point longline moorings have an anchor at either end and this makes them static and unable to flow with weather or tide. One advantage of the design is that

Moorings

single

block

three leg

Fig. 8.13 Setting up a single-point mooring.

raft surface buoy

swivel

anchors Fig. 8.14 Connecting a single-point mooring in swivels and buoys.

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two-point system

four-point system

Fig. 8.15 Two-point and four-point mooring systems.

to surface double shackle

Fig. 8.16 Adding some safety back-up on the bottom.

the anchors and tackle remain fairly stable, being pulled in only one direction at all times. A two-point raft mooring is much the same. Figure 8.15 shows patterns of both two-point and four-point mooring systems. If it is thought necessary, and for the sake of complete safety, the downchain from the surface may be attached with two shackles as in Figure 8.16.

Four-point moorings It is sometimes necessary with rafts to run an anchor from each corner. This is a four point system, and if the anchors are substantial it will prove to be very safe. Each line from the raft could go to either a single anchor or a pattern of anchors like a single-point mooring. Where multiple anchors are used, they are usually strategically placed so that at least two are in the direction of the prevailing wind or the strongest tide.

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179

Placing anchors Placing anchors is fairly straightforward but can be made easier with the use of a mechanical or hydraulic line hauler. The easiest way of tackling the job is to drop each anchor, with surface line attached, approximately in the position desired. If, for instance, a single-point mooring is to be secured by a three leg system at its base, all the anchors would be dropped in their rough positions. One anchor would then be hauled a few metres off the seabed and pulled until tension comes on the line. The remaining two anchors would then be treated in the same way with the farm boat pulling them out from their centre point to the position desired. When tension comes onto the line, the anchors should always be lowered gently to ensure they are upright and in the correct line. They do not necessarily need setting with 120° sections. Two may be set closer and into the prevailing wind to make the system more secure.

SPECIFICATIONS, WEIGHTS AND LOADS The most common causes of mooring failure are underspecification and components coming undone or chafing through. The dragging of anchors can usually be overcome by overspecifying, but the remainder of the tackle sometimes seems to be overlooked, especially with regard to regular inspections. Generally speaking it is more common for moorings to break down through component failure rather than dragging of anchors. The latter usually only happens when either the bottom type has not been matched with the ground tackle or a situation has been created that could not have easily been foreseen; for instance, on a very few occasions a small boulder may lock itself into the anchor fluke thus rendering it less effective and likely to drag because of an inability to move deeper into the seabed. Sometimes it may also be found that the sand or mud layer is not as deep as expected and the anchor fluke once again is unable to be fully effective.

Mooring specifications If the approximate load is known, the simplest method of arriving at anchor specification is to double the figure and work from there. If the load were constant and unvarying, the exercise would be straightforward, but with variable wind, tide and wave action the anchor has to deal with many changing conditions. As a guide, for mooring longlines and rafts the following specifications are generally regarded as being adequate.

Longline moorings For 200 metres of working line set in 25 metres of water on a sand bottom and running along the tide, a 100-kilogram Bruce, coastal quick release (CQR), or Samson anchor shackled to 20 metres of 16 millimetre chain would be needed at

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8-mm stainless wire

cement weight Fig. 8.17 Attaching stainless steel wire, and the use of a weight on the anchor line.

plastic hose

Fig. 8.18 Protecting an anchor line from wear.

each end. The mooring line should be 85 metres of 16-millimetre polypropylene rope. When concrete blocks are favoured, two at approximately 5000 kilograms (5 tonnes) should be employed. If it is decided to use either rope or a length of stainless wire directly to the anchor, then a weight of at least 150 kilograms should be attached to the mooring rope (or wire) at approximately 15 metres from the anchor. Figure 8.17 shows attachment of the stainless wire, and the placement of a weight on the mooring line, being always on guard for potential chafing. Figure 8.18 shows how an anchor line may be protected with plastic hose in situations where small stones or rocks may cause unnecessary chafing. In order to thread the line into the hose, a small wire line must be put in first and this can usually be pushed through without much fuss. It is then attached to the main line and pulled back along the hose.

Raft moorings One raft for scallop culture supported by two 10-metre pontoons moored in 10 metres of water on a sand bottom and running along the tide would have to be located in sheltered water, and so the exposure factor can be ignored. If a singlepoint mooring was preferred, a concrete block of 4000 kilograms (4 tonnes) shack-

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led onto 10 metres of 16 millimetre chain would be required for the bottom. A further 30 metres of 16 millimetre polypropylene rope would join the chain end to a surface buoy of 1.5 metres circumference. The raft would be attached to the buoy via two lengths of 16 millimetre rope approximately 8 metres long, one going to near each corner. As the calculations so far are based on a 100 per cent mark up, if a two-point system is required, the block weights may be reduced by one-quarter. Chain and rope lengths would remain the same and the safety factor of the system would be such that if one block dragged, the raft’s movement would soon be halted once both blocks were acting on it. However, if it is thought necessary to never risk this situation then both anchor systems should be the same as initially prescribed.

Archimedes’ principle Archimedes’ principle states that any object immersed in a liquid experiences an upward thrust equal to the weight of the liquid it displaces. Quite simply this means that all objects will weigh less under water than they do on the surface. The calculations are simple and all that is required are the dimensions of the object and its density. Table 8.1 shows the densities of various materials, usually expressed in kilograms per cubic metre. For mooring work the main materials are cement, steel and seawater. Concrete blocks can vary in density depending on how they are constructed. With plenty of steel reinforcing and proper vibration, their density, strength and weight on the seabed can be greatly increased. As an example we will consider a concrete block measuring 1.5 × 2.0 × 0.75 metres and with a density of 2403 kilograms per cubic metre. The density of seawater will be taken as 1026 kilograms per cubic metre. Weight of block on surface = density × volume = 2403 (1.5 × 2 × 0.75) = 2403 × 2.25 = 5406 kilograms

Table 8.1 The densities of various materials Material Lead Steel Granite Concrete Seawater Freshwater Pine Polystyrene

Density kg per cu. metre 11 342 7 770 2 723 2 403 1 026 999 433 16

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Scallop Farming Weight of block underwater = density of concrete less density of seawater × volume = (2403 − 1026) 2.25 = 1377 × 2.25 = 3098 kilograms.

From these calculations we can work out that the block loses 43 per cent of its weight when dropped to the bottom. Therefore, with varying densities of both concrete and seawater it can be assumed that a concrete block will lose between 40 and 50 per cent of its weight when in use. If a block of the same dimensions were made from steel, it would weigh 17 482 kilograms and would lose only 13 per cent of its weight when immersed in the sea.

Mechanical advantage A Spanish windlass demonstrates both the power and effectiveness of mechanical advantage. This physical principle must not be overlooked when designing mooring systems. Figure 8.19 shows how a heavy load can adversely affect the point of lift if the angle of spread is too great, and Figure 8.20 shows how this principle applies in practice. In a longline system it can quickly be seen that by setting the line tightly across a strong tide the forces on the anchors will be greatly increased. It will also be realized that the same force will apply to an anchor if the rope is too short and

1300 1200 1100

load on each leg (kg)

1000

90°

710 kg on each leg

900 800

1000 kg load

700 600 500 400 1000 kg on each leg 120°

300 200

1000 kg load

100 0

30

60 90 angle of sling (°)

120

Fig. 8.19 Demonstrating how the angles of lift alter the overall loading.

150

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tide and

wind

183

2000 kg

2300 kg

2300 kg

130°

Fig. 8.20 Demonstrating the principle of loading on an actual longline. Table 8.2 Rope types and their properties Type

Description

Nylon

High breaking strain, high elasticity, sinks, difficult to splice, expensive, cuts easily under load High breaking strain, little elasticity, sinks, expensive Not as strong as nylon, medium elasticity, floats, easy to splice, reasonably priced As courlene but slightly more expensive

Polyester Courlene Polypropylene

angle of pull too great. Rafts moored in the same fashion will not only impose added strain on their anchors but also overload their mooring posts.

Ropes and chains There are a variety of types and strengths of rope and chain and their properties can often be used advantageously in a mooring system. Nylon, for instance, has a high breaking strain and is also very elastic, hence making it useful in absorbing shock and acting as a damper. However, it cuts very easily when under load, so if the seabed is made up of sharp-edged rocks, its use will be suspect. When using rope of any kind it must be remembered that certain actions can greatly reduce its breaking point; for instance, a knot will reduce it by up to 50 per cent, a hitch by 25 per cent, a kink by 30 per cent and a splice by 10 per cent. Table 8.2 shows the main types of rope and their differing properties. When buying chain try to avoid the new alloy, high breaking strain types because they lack weight. Breaking strains will vary greatly but provided a minimum of 12millimetres diameter is used there will be little likelihood of this happening. A chain of this size will also add weight to the system. Table 8.3 is a chart of four chain sizes and their breaking points.

Anchor fluke angles Once the type of sea bottom has been determined, an anchor can be made more efficient by ensuring the correct fluke angle. Table 8.4 shows how this angle should

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Table 8.3 Chain strengths Chain size (mm)

Chain type

16

Medium link open Long link open Stud link Medium link open Long link open Stud link Medium link open Long link open Stud link Medium link open Long link open Stud link

19

22

25

Safe load (kg)

Breaking point (kg)

4 800 4 830 10 000 6 800 6 820 15 300 9 100 10 000 20 400 11 800 12 700 26 000

9 600 13 000 15 000 13 600 17 000 21 500 18 200 24 900 28 500 23 500 31 000 37 000

Table 8.4 Anchor fluke angles and bottom type Angle

Bottom type

50° 45° 40° 35° 30° 25° 20°

Soft mud/silt Mud Clay/sand Coarse sand/shell sand Sand Fine hard packed sand Hard packed sand/stone

change as the bottom type changes. Unfortunately not all anchor types offer the advantage of a variety of fluke angles, but if resorting to home construction this factor can easily be incorporated into the design.

HOMEMADE ANCHORS If an anchor is constructed properly and set correctly, it can hold up to fifty times its own weight (the ratio gradually decreases as the anchor weight increases). This applies primarily to burial anchors, which are constructed with an elbowed shank and are subjected to a constant horizontal pull. For the practical farmer the construction of an anchor need not be difficult, and if certain guidelines are followed, the result should be as good as one bought off the shelf. If this seems too difficult to tackle, there is no reason why a local blacksmith or prefabricator should not be employed to do the job. This is often cheaper than going to a specialized manufacturer. Chapter 9 (Design and manufacture of equipment) describes four anchors that can be built by anyone with some welding experience. They are all of proven design and offer good holding properties.

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185

CONCRETE BLOCKS We have already seen how to work out the weight of a concrete block if we know its volume and density.Ascertaining block dimensions for specific weights is equally easy provided the required block shape is known. The most effective shape is one that has a height roughly one-third of its width, offering a large amount of contact with the seabed.Table 8.5 shows nine blocks with weights ranging from 1000 to 5000 kilograms and with a height approximately one-third of the length or width. When fabricating blocks of these dimensions, incorporate chain ends into the middle of all four sides and also the top.This will greatly assist handling and will also make them more acceptable to added components. Sixteen-millimetre looped rope ends may also be set into the concrete, provided they are protected with suitable hose (Fig. 8.21) Table 8.5 Block dimensions and appropriate weights Weight (kg)

Dimensions (metres)

1017 1501 2013 2507 2999 3490 4027 4492 4989

1.10 1.25 1.38 1.49 1.58 1.64 1.73 1.78 1.83

× 1.10 × 0.35 × 1.25 × 0.40 × 1.38 × 0.44 × 1.49 × 0.47 × 1.58 × 0.50 × 1.64 × 0.54 × 1.73 × 0.56 × 1.78 × 0.59 × 1.83 × 0.62

chain ends

plastic hose

synthetic rope Fig. 8.21 Concrete mooring block showing attachment points.

USE OF GEOLOGY There are usually features on the seabed or the surrounding shoreline that can be used in a mooring system to great effect. Apart from being cheap, these features also offer a permanent footing that can be relied on to hold.

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Boulders In some areas, especially those that were once glaciated, there will be many large boulders. By wrapping a chain around one of these, either on the shore or on the seabed, a very effective mooring point will be created. A granite boulder of roughly 1 cubic metre will weigh over 1700 kilograms in the water and will usually be well bedded in, thus offering greater holding power.

Shore points Sometimes a mooring system can be very close to the shore, and there is no reason why some of its features cannot be used as mooring points. This will obviously be out of the question if there are shipping movements around the site. Where there are no obvious boulders present, other features will have to be used, such as gullies, cracks or weathered outcrops. Metal posts cemented into holes or cracks in the rock can prove most effective, and will set even in places exposed only at low water. Some farmers have gone to the extent of drilling the rock to insert pins, which are glued in place. This has been very successful, although locating a compressor close to the site to power the drill can sometimes be difficult.

Concrete keys Although concrete can be used effectively under water it is often easier to prefabricate a key to fit into a gully or crack. This is, of course, a diving job but is straightforward and most effective. Figure 8.22 shows a concrete key and how it is used.

LAYING CONCRETE MOORINGS Setting a mooring can be physically taxing but if certain guidelines are followed there is no reason why most farmers should not lay their own successfully. Moving a 5000kilogram block can seem daunting, but by using buoyancy in the form of boats, rafts or even drums the exercise can be made fairly easy. Figure 8.23 shows how a block can be slung under a boat and floated out on the tide. Obviously some calculations need to be made on buoyancy and weight, and a calm day will be needed to perform the exercise. Large block moorings of this sort are difficult to move once in place, so preparatory planning is essential. Proposed mooring sites should be marked in advance with a weighted line and buoy and all precautions should be taken to ensure that the block falls into place without taking personnel with it.

MAINTENANCE AND INSPECTION Unless there are facilities for physically lifting anchors for inspection, a diver’s services will be required for this task. Once a system has been proved to be secure it

Moorings

concrete key (a)

steel pin

(b)

Fig. 8.22 Use of concrete keys.

cut to release block 125 mm × 50 mm surface buoy for longline or raft

spreader

block surface line and buoy

longline direction

block lifted on rising tide

Fig. 8.23 Use of a small boat to move a concrete mooring block.

187

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Scallop Farming

would be bad practice to lift it, and by using a diver this will not be necessary. A reasonable inspection programme would be to inspect by diving over a 3 year period and to physically lift the anchors in the fourth year. It is very unlikely that the anchor itself will deteriorate, and chain will also have a long life in most areas. Problems can be caused by shackles working loose, swivels (where fitted) wearing out and rope chafing through, so these are the components requiring closest attention, but good practice would be automatically to replace all shackles when the equipment is physically lifted, and also to cut off and resplice any rope ends connected to chain. It should always be remembered that just because the system lies under the water and therefore out of sight, it does not mean that wear will not be occurring. Therefore, carry out inspections regularly and thoroughly. Also, do not ignore those aspects of the mooring that lie above the water line. Sunlight can be most disadvantageous to ropes, as can salt spray to metal components.

SUMMARY • • •

•

•

• •

•

•

•

The sea is a hard master and has much to teach us so therefore we must be prepared to adapt to its constantly changing state. If a mooring is laid to the correct specification and inspected and maintained on a regular basis, it is unlikely that it will fail. Topside components are equally important to the system, so care should be taken to ensure that such items as cleats, Samson posts, and all points that use the system are also in good order and inspected regularly. The holding power of an anchor is dependent on its weight, design, composition of the seabed and method of use, and it is not a case of slinging a hook in the hope that it will catch on the bottom. Components will wear more rapidly if load is applied sharply in the form of jerking movements, and to help avoid this it is usual to introduce a surface buoy or extra long, heavy chain to act as a spring. Having reduced the number of components to a minimum it is good working practice to ensure that those remaining are subject to little movement. Although a farmer will look for other qualities in a site over and above its potential as a safe mooring, he would still be advised to bear some geological and physical factors in mind. The composition of the seabed will directly affect the performance of the tackle placed on it. It is therefore important to know its type and to choose compatible equipment. Between the very soft and very hard bottoms we rely on anchors digging in to maintain their holding power, and this will be accomplished with varying effectiveness according to anchor type. If there are no cost restrictions, the very best equipment can be bought, and maybe a consultant hired to supervise its laying; however, most farmers are faced with having to adapt what is at hand.

Moorings • • • • •

•

•

• •

189

Innovations in mooring design require considerable expertise to make them completely safe, and most problems occur in this area. Placing anchors is fairly straightforward but can be made easier with the use of a mechanical or hydraulic line hauler. It is useful to be able to work out the capability of an anchor and to access its holding power. This can be achieved fairly accurately. Ropes and chains come in a variety of types and strengths and their properties can often be used advantageously in a mooring system. Once the bottom type has been determined, an anchor can be made more efficient by ensuring the correct fluke angle but unfortunately not all anchor types offer the advantage of variety in this feature. There are usually features on the seabed or the surrounding shoreline that can be used in a mooring system to great effect. Apart from being cheap, these features also offer a permanent footing, which can be relied on to hold. Metal posts cemented into holes or cracks in the rock can prove most effective, and will set even in places exposed only at low water. Some farmers have gone to the extent of drilling the rock to insert pins, which are glued in place. Setting a mooring can be physically taxing but if certain guidelines are followed there is no reason why most farmers should not lay their own successfully. Once a system has been proved to be secure it would be bad practice to lift it, and by using a diver this will not be necessary. A reasonable inspection programme would be to inspect by diving over a 3 year period and to physically lift the anchors in the fourth year.

Chapter 9 Design and Manufacture of Equipment

The farmer’s budget will determine his level of involvement in equipment manufacture. Small, one man outfits tend to construct much of their own gear but the actual time involved is rarely calculated. Large farms may centre their manpower on cultivation and purchase all their equipment from aquaculture suppliers. Although economic factors will influence the level of involvement, it is important for farmers to experiment with equipment design and manufacture because this is where good ideas originate. Good designs appear periodically and manufacturers are often looking for those that have potential in the market place. The most useful tend to come from persons actually involved in aquaculture, and when they cannot afford to manufacture equipment themselves, they will sell the idea to a firm that specializes in farm equipment. Only by being involved at grass roots level can these ideas be really practical. The amount of time devoted to experimentation is therefore important. Most designs are born from either a necessity to improve on an existing product or a need to fill a gap in the market. Scallop farming has attracted many new products and these have evolved from a need to make farm equipment both economical and easy to work. Many useful designs have also stemmed from the need to adapt to different conditions. This chapter features items of farm equipment that can be built by the practical farmer, and demonstrates the scope of what can be tackled. The descriptions offer only basic dimensions and should be used as a basis from which to develop personal ideas and innovations.

LANTERN NETS As the lantern is one of the main items of culture equipment in scallop farming, considerable thought must go into its design. Whether they are purchased over the counter or hand built, lanterns must conform to certain design criteria. The following points offer a basis on which to evaluate design features. (1)

190

Handling (a) How quickly can they be emptied and loaded?

Design and Manufacture of Equipment

191

(b) (c)

(2)

(3)

(4)

(5)

Are they well rigged and does this assist general handling? Is the opening large enough to take someone’s hand when there is a need to reach inside? (d) Does the material float or will the lantern need to be weighted? (e) Do they require a handling jig? Durability (a) Is the material protected against sunlight (ultraviolet proofed)? (b) Does the material become brittle at low temperatures and will it always keep its shape? (c) How strong is the external netting? (d) Are there protrusions that are likely to catch on adjacent lanterns? Adaptability (a) Will they be suitable for culture of other shellfish types? (b) Will the external netting stand up to oyster culture? (c) Can the discs easily be made into permanent lanterns as well as maybe taking a stocking cover? (d) Is a wide selection of strong external coverings available? (e) Is the ring netting soft enough to allow the scallops to assume a comfortable and permanent growing position? Storage (a) Do they collapse uniformly for ease of storage and are they easily handled in this state? (b) Will they store easily on the deck of a rolling boat? Cost (a) Are they cost-effective in terms of scallops reared per square metre, calculated over a 6 year lifespan? (b) What is the cost of the disposable netting? Will net changes be expensive?

Based on these points, the following describes the building of a scallop lantern. The completed product makes a most useful culture unit. The rings (partitions) are constructed from 4 millimetre plastic-coated wire; the outer covering is a strong, square meshed, fairly stiff synthetic netting, and the rigging is 6 millimetre synthetic rope. The first task is to build a template on which to form the rings. This can be simply constructed out of plywood (Fig. 9.1). For ease of handling and general effectiveness, the largest ring size should not exceed 500 millimetres in diameter, with the smallest no less than 300 millimetres. As the size is reduced, so the lantern will become easier to work. Conversely, the cost of scallops reared per square metre will increase. A compromise size of 380 millimetres offers both ease of handling and an economic cost per square metre of culture area. The wire is shaped around the template and the crosspieces are crimped in place. It is then covered with netting. This can be either stitched on all the way around or tacked loosely in place and stitched in position while the outer net is being secured. Hog ring pliers are useful for tacking and cable ties can also be used to good effect.

192

Scallop Farming 45 cm

(a)

(b) Fig. 9.1 A plywood template for the construction of lantern rings.

Ten rings make up a lantern 1 metre in length, and although they can be made longer, this size is easily built and handled. The outer netting is cut to give an overlap of 80 millimetres. Its mesh size will vary according to the lantern’s requirements but is unlikely to be larger than 21 millimetres. By using stiff, square-meshed net some kind of form can be maintained during the building process. This is an advantage because building with soft, shapeless net can be very difficult. Figure 9.2 describes each stage of construction and the importance of running the rigging lines correctly. The outer netting is stitched onto the first ring using 2millimetre twine with alternate clove hitch and half hitch at intervals of 50 millimetres. The stitching is terminated 150 millimetres before reaching the starting point, and this gap will eventually form the door. Before a second ring is placed, a central rigging line is tied at the centre of the first ring, with enough spare to run the whole lantern length and allowing for a knot at each layer. This line is optional when small diameter rings are used, but is necessary on lanterns with partitions greater than 450 millimetres in diameter. The next eight rings can be stitched into place and the central rigging secured at each layer. Stitching remains at a spacing of 50 millimetres unless the net covering on the ring has already been stitched. In this case it can be increased to 100 millimetres. The tenth and last ring is positioned with stitch spacing of 50 millimetres and the rigging line is terminated at its centre. The next step is to secure the outer rigging lines. These are necessary for ease of handling and should be no smaller than 6 millimetres in diameter. A line is run down the lantern at the opposite side from its opening and tied at each layer. A fid is used to assist with this (Fig. 9.3). A second line is run down the line of the lantern where the stitching ended to form the door. This helps to protect the opening during emp-

Design and Manufacture of Equipment

193

1m

(1) net stitched onto (2) second ring in place with rigging first ring

(3) all rings in place

(4) outside rigging started

(5) all rigging in place

(6) door formed

Fig. 9.2 Each stage in constructing a lantern.

fid

Fig. 9.3 The use of a fid to help run rigging and stitching.

tying. As an added refinement a line can be run down the other edge of the door and the netting can be stitched to it. Once again, this gives added protection. To form an even lift at the top of the lantern two more lines can be tied in place, each halfway between the two outer lines already secured. Excluding the line

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6 mm rigging wire hooks with rubber bands

15 cm opening 18 cm door Fig. 9.4 Rubber hooked door fasteners in place.

steel frame Fig. 9.5 A support frame used to assist in emptying lanterns.

stitched to the door opening, there should be a central line and four more evenly spaced around the edge of the lantern. These are taken up evenly and tied together at roughly 0.5 metre from the lantern’s top. The final task is to attach five rubber bands with hooks to the door flap. Figure 9.4 shows this most useful feature in more detail. Wire-framed lanterns of this design lie very well in the water and are both easy and quick to use. Although the time spent in construction is initially lengthy, once a routine is established they can be completed in under one and a half hours. The end-result is a competitively priced, long life lantern.

Assisting lantern emptying Figures 9.5 and 9.6 show two pieces of equipment that are useful when lantern changes are undertaken. The frame in Figure 9.5 is fairly self-explanatory and is a useful piece of equipment, especially if the lanterns are long and floppy in handling.

Design and Manufacture of Equipment

195

supports

sorting bay

Fig. 9.6 An emptying and sorting tray to assist lantern handling.

Figure 9.6 is a type of platform that allows the lantern to be emptied through with a little force if necessary. The scallops accumulated at the bottom can be pulled forward for sorting.

PEARL NETS Although pearl nets are tending to be superseded by disposable net lanterns, they can still perform a useful function on a farm. They are cheap and easy to construct and could easily be tackled by a beginner. As manufacturers take more interest in scallop farming, useful items often appear on the market. Plastic rings of various mesh sizes have been manufactured and some of the smaller ones are useful in pearl net construction. For our design the same plastic-coated wire ring will be used, but with a maximum diameter of 300 millimetres. Figure 9.7 shows the four steps in pearl net construction and the completed nets rigged together. Once the ring is formed it is stitched to the bottom of a strong spat collection bag. A central rope of 6 millimetre courlene is tied off at the centre of the ring and a figure eight knot is tied roughly 270 millimetres up from the base. This knot is to prevent the top of the bag from slipping down the rope once the drawstring is pulled. From 10 to 20 bags can be secured on one length of rope, the number and spacing being determined by the farm boat’s hauling capability and the depth of water worked. These nets are easily emptied and filled and can be of much use to a farmer. The wire base gives them a negative buoyancy, which is useful when employed to hold very light stock, and they fold down to be easily stowed when not in use.

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Scallop Farming

(1) 30 cm ring

(2) ring stitched to bottom of bag

figure 8 knot

(4) drawstring pulled

(3) centre rope nets in a string

Fig. 9.7 Stages in pearl net construction.

RAFTS Many raft designs are available. Some have been tried and tested and others have not. Some are straightforward to construct and others are not. The choice is sometimes difficult and the following points should be borne in mind when choosing a design. (1)

(2)

Size and stability (a) Is the raft long enough to ride out wave action? (b) Is the design stable enough to work from? (c) Is a loaded corner likely to go under with the added weight of a man? (d) Can all the hanging space be utilized? Workability (a) Is the raft easily worked or does the farmer have to perform a balancing act when hanging lanterns? (b) Is it suitable to go alongside with a boat? (c) Does it have a railing to prevent personnel from falling overboard? (d) Does it have life rings or a life raft? (e) Is it easily towed and manoeuvred?

Design and Manufacture of Equipment (3)

(4)

(5)

197

Durability (a) Is it likely to withstand severe weather conditions? A look at the fixing materials and obvious stress areas should give an indication of this. (b) Is the design proven? Has a full-sized model been put to work for a long period? Designs for mussel rafts are normally suitable for scallops because they are built to withstand more adverse weather conditions. (c) What is the expected life of the raft? Maintenance (a) Is the raft easily maintained afloat? (b) Are all the metal fittings galvanized? (c) Can the pontoons be easily removed if required? Cost (a) What is the cost per metre of hanging space based on a 6-year depreciation period?

Raft designs Designs can vary from a simple wooden frame supported by four oil drums to a large metal-framed raft with adjustable buoyancy pontoons. Size and complexity will have a direct bearing on cost, so most farmers opt for a proven design that they can either build themselves or have built for them.

Buoyancy Buoyancy is the most critical design element and should always be sufficient to support the raft easily when fully loaded. To assess a pontoon’s buoyancy its volume must be calculated and then multiplied by the density of seawater. The overall weight of the pontoon should then be subtracted; for example, what would be the lifting capacity in seawater of a pontoon weighing 160 kilograms and with dimensions of 10 × 0.5 × 0.5 metres? Volume of pontoon = 10 m × 0.5 m × 0.5 m = 2.5 cubic metres. Lifting capacity = density of seawater, multiplied by volume, less overall weight. = (1026 × 2.5) − 160 = 2405 kilograms. If it is difficult to weigh the pontoon, the best way forward is to weigh the component parts individually prior to construction; for instance, weigh one single sheet of plywood, one buoyancy block, one drum of resin and a full roll of glass-fibre matt. It is easy then to work out the weight of all the items used. Pontoons can be constructed in a variety of ways, and the quality of work applied at this stage will have a direct bearing on their rate of depreciation. They are the most expensive components of any raft and therefore should be built in such a way

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as to ensure a long and useful life. With proper attention to detail and regular maintenance there is no reason why a pontoon should not last longer than 20 years. This can make their buoyancy factor very cost effective. The rest of the raft’s components, unfortunately, do not tend to last so long and consequently a set of pontoons may have two or more deck changes during their working life. It is cheap and easy to build buoyancy into a pontoon during construction, but difficult to add once completed. It is, therefore, advisable to overcompensate on requirements from the start. One possible drawback, however, is that it can make the raft very lively in a high sea and transmit motion to the scallop lanterns. To overcome this it may be necessary to hang weights off each corner until the raft is fully loaded. Unless the requirement is for adjustable buoyancy, any void spaces should be filled with a light, buoyant material. Polystyrene blocks are useful because they make a good former to build around, and a two part liquid mix of the same product (foam) will expand into the most complex cavity. If the pontoons are moulded in glassfibre or fabricated with tubular steel, always ensure they are foam-filled. The series of drawings in Fig. 9.8 describes the building of a simple pontoon. Its length can vary according to requirements, and the foam blocks can be of a size that is easily available, providing they are no less than 0.25 square metre in section (i.e. 0.5 × 0.5 m). The blocks are sheathed in 10 millimetre shuttering ply, using alternate lengths to form rigidity. The complete pontoon is then sheathed in heavy glassfibre matt with 100 millimetre strips adding extra protection to all edges and joints. Glassfibre is an easy product to use and can be a relatively cheap covering if purchased in bulk through an industrial supplier. With the use of a paint roller it can be quickly and professionally laid and the end result is a tough coating that has a very long life.

Raft construction Bearers with a section of 50 × 75 millimetres are nailed along either side of the pontoon at its top.These are further secured by laying up strips of glassfibre, bonding the top of the wood to the pontoon. Glassfibre straps are laid around the pontoon at 2-metre intervals. These consist of two layers approximately 75 millimetres wide. Triangular blocks need to be nailed under each bearer at the point where the strap comes over to supply a solid base for the fibreglass. The purpose of the straps is to ensure that any strain taken up by the bearers is spread around the whole of the pontoon and not only on a small part of it. The walkway dimensions will be determined by the size of lantern used, always allowing enough space for the gear to pass through the gap. The base of the walkways is three 6 metre lengths of larch, 50 × 70 millimetres. Twenty larch planks are then nailed to these bearers, evenly spaced along their whole length. Once the walkways are built they can be secured to the pontoons. Every second one is bolted to the pontoon bearers with four 10 millimetre diameter galvanized bolts. Those walkways that are not bolted should be secured with galvanized nails. The walkway ends are then capped with a length of larch.

Design and Manufacture of Equipment

199

50 cm 50 cm

1

2

3

4

6

5

8 7

1 polystyrene block 2 10 mm plywood sheathing 3 glassfibre coat 4 walkway bearers 5 glassfibre straps 6 walkways 7 attaching walkways 8 walkway ends 9 mooring points

9

Fig. 9.8 Stages in raft construction.

Mooring points need to be strong and firmly fixed. Four points will be required, secured at the pontoon ends. A 400 centimetre length of heavy steel angle can be used for these, and should be bolted both to the underside of the walkways and to the side of the bearers. A 20 millimetre hole drilled at the outer end will take the mooring shackle. For safe working, a railing can be erected around three sides of the raft using 40millimetre galvanized piping. This can be either welded together or bolted with the appropriate pipe fittings. Finally, all the woodwork will need treating with either creosote or a similar product and this can be quickly and effectively applied using a garden spray. The main problem with the wood will be through the effect of the sun and freshwater via rain. To combat this, try to choose a product that will offer some kind of ultraviolet protection. As for the freshwater, this is usually quickly dispersed with spray from waves, and the salt water itself acts as something of a preservative.

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Scallop Farming

wooden bearers

steel support channels

steel pontoons Fig. 9.9 A steel raft with cylindrical pontoons.

Alternative designs The raft described is basic, strong and functional. There are other types that may not be as easily or as cheaply constructed but which may offer other useful features.

Steel rafts A steel raft with adjustable walkways or a raft with adjustable buoyancy may be an advantage in some situations. Figure 9.9 shows a steel raft with cylindrical pontoons, which is both strong and functional. Its length is optimal but can be slightly smaller than a wooden raft because it will lie heavier in the water, so making it less lively. It is unlikely, due to the expense, that all the steelwork will be galvanized, so an alternative coating will need to be applied. Thanks to the oil industry there are now many two-part preparations available that will stick well to steel, are tough and still remain flexible when set. Steel is notorious for corroding, so a coating of this kind is essential. The inside of the pontoons will be difficult to inspect for corrosion, so they should be filled with foam. This not only ensures that buoyancy is maintained if a leak occurs but also protects the steel itself from corrosion. The raft can either be designed to accept a wooden frame or be a complete steel structure. If of all steel construction, the manufacturing costs would be high, but the estimated life of the raft would be longer. The decision would therefore be based on cash constraints at the point of purchase.

Rafts with adjustable buoyancy By allowing the raft to sit lower in the water when only partially loaded, a considerable amount of movement can be avoided. This gives the raft weight and grip in the water, thus making it more compatible with sea state. Because of the risks of corrosion it is not good policy to flood steel tanks, so adjustable buoyancy is usually built into glassfibre pontoons.

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air in and out foam filled baffle

water in and out

Fig. 9.10 Adjustable buoyancy pontoons.

below-deck storage hydraulic crane

machinery shed

rails

walkways

Fig. 9.11 Multipurpose cultivation/work/storage raft.

In the most common design the pontoon is split into three sections. The two outer compartments remain foam filled, while the middle section allows for an adjustable internal water level. Figure 9.10 shows pontoons of both square and cylindrical section equipped with built-in buoyancy. In both, air is forced in at the top and the water is pushed out through holes in the bottom. A small, low pressure compressor or diving cylinder would have enough pressure and flow to perform this task adequately. There need be no changes to the rest of the raft’s design.

Dual purpose rafts Some farmers have experimented with very large rafts, which can be used for cultivation as well as storage and working. These are usually constructed in steel on many square pontoons bolted together. Being large they are not very susceptible to wave action but require very heavy moorings. Figure 9.11 is a design that offers work and storage area as well as ample hanging space. A hydraulic crane is a very useful item of machinery and this can run from a pump housed in the machine shed.

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joists polystyrene blocks Fig. 9.12 A useful work raft.

outboard mounting Fig. 9.13 A motorized work raft.

Work rafts One of the most useful items on a scallop farm is a work raft. A large stable platform that is easily manoeuvred around the site will save time and effort in equipment storage and transportation. Figure 9.12 shows a work platform built from a redundant salmon raft but double its height to allow easier working from a boat. It is not uncommon to see them powered by outboard motors, and this can be a very effective method of propulsion provided the sea state is moderate (Fig. 9.13).

ANCHORS Figure 9.14 shows three designs of steel anchor, all of which can be altered to suit differing bottom types. Their main feature is that they are both long and heavy and should therefore grip the seabed well. Except for the H beam design they all need lowering carefully onto the seabed to ensure that they lie the right way up. A very effective anchor can be built out of steel and cement. This is called a fish box anchor because it uses an old, broken fish box for the basic mould. The components are first prefabricated and heavily painted for protection. The box is filled with a strong mix of concrete, and reinforcing bar or pieces of scrap steel are pushed into it. A length of heavy chain will run from end to end, and rings can be set at its top and sides to assist in handling and to make the product more versatile. The heavily reinforced shank is pushed into the cement at the required angle, and the

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400 mm × 20 mm

12 mm plate

H beam

1.5 m

12 mm plate 2m Fig. 9.14 Three designs of steel anchor for home construction.

300 mm 325 mm 12 mm plate

cement block 150 mm

50 mm pipe

750 mm 450 mm

Fig. 9.15 A fish box anchor.

stock is pushed through precut holes in the sides of the box. The cement is then vibrated by hammering the sides of the box and the completed anchor is left to set and mature for approximately 5 days. Figure 9.15 shows the end-product after the wooden mould has been removed. This type of anchor is particularly effective when

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30 cm 5 cm dia tube

Fig. 9.16 A homemade grapnel.

barbs

50 mm tubing: cement filled Fig. 9.17 A rope creeper (grapnel).

set on a soft seabed, because once the block itself has worked its way in, a lot of effort will be required to remove it.

GRAPNELS It will often be necessary to lift a longline at a specific point, and this can be achieved by catching it with a grapnel (Fig. 9.16). There is a danger that culture equipment can be damaged during this process, so the grapnel is designed in such a way as to reduce this risk. By welding large ball bearings onto its flukes there is less likelihood of nets being snagged and torn. Another important design feature is the addition of extra weight. It is essential that the grapnel sinks fast, so the central tube is filled with either cement or molten lead. Another variety of grapnel is the rope creeper (Fig. 9.17). This is used when such things as mooring lines have been lost and are lying somewhere on the seabed. Like the grapnel, it also functions best when lead filled, and can be built to the size and specification that the farmer requires.

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removable frame net screen

sorting tray

Fig. 9.18 A combined riddle and sorting tray.

SORTING EQUIPMENT A great deal of time is taken up in grading small scallops and sorting different species from one another. Various types of sorting equipment have been designed for this purpose, ranging from simple net riddles to sophisticated motor-driven vibrating units. The main design constraints for these items is the space they take up on the boat’s deck. Where there is a shore base with a tank, it will be feasible to run an automatic sorter driven by an electric motor. At sea there may be room for only a small riddle.

Net riddles Instead of having a different size of riddle for each stage of scallop growth, one can be built to allow an interchange of mesh. This also makes repair easier when the mesh wears out. Figure 9.18 is a combined riddle and sorting tray that allows for both easy operation and storage.

General handling trays Figure 9.19 shows a riddling tray for general handling and cleaning away smaller, unwanted species as well as debris. It utilizes a cut-down bait barrel, but if one of these cannot be found then a plastic dustbin will do. The riddle frame can take dif-

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supporting frame

net insert

bin Fig. 9.19 Alternative sorting equipment.

fixed rop riddle (developed by Highland Aquaculture)

adjustable rods

seawater in hopper

rollers

small scallops rotating rod grader

large scallops

Fig. 9.20 Three designs of rod riddle.

ferent mesh sized inserts and for this reason it is very useful. Its main advantage is that the riddling process is carried out underwater, where it works more efficiently.

Steel rod rollers A net riddle works by preventing scallops above a certain size from passing through it. The mesh size is therefore based on the width of the scallop to be graded. A rod riddle takes the thickness of the scallop as a measurement and is most useful when separating different species at spat stage. Figure 9.20 shows three designs of riddle, the simplest being a fixed rod with preset spacings. This can be improved by making

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the spacings variable, and made more efficient by introducing a vibrating unit. When sorting scallops at their spat stage the equipment has to be used either underwater or with a cascade of water falling over it.

Parallel rollers The most elaborate of the three designs, the parallel roller is used to grade many types of shellfish. It consists of two steel tubes, approximately 100 millimetres in diameter, set side by side. The tubes can be any length, but for scallops 2 metres is sufficient. They are set on a gentle slope and the gap between them increases towards the bottom. An electric motor turns them slowly in opposite directions and seemingly lifts the shells up and out of the gap. Scallops fed in at one end gradually work their way down the slope until the correct gap allows them to pass between the rollers. Once again, when handling spat a cascade of water needs to be directed over the rollers while they are running. The ability to alter the gap between the two steel tubes makes them more versatile over the whole range of scallop grading.

PRESSURE WASHER A pressure washer is a necessary item on a scallop farm for cleaning all types of culture and collection equipment. In order to be fully effective it needs to pump water at a minimum pressure of 1200 pounds per square inch and should be light enough to be transported by one man. For complete versatility a choice of petrol engine drive for the boat, and electric motor drive for the shore base would be most advantageous. A simply adapted base plate would make the change over both quick and easy. All the components for the pressure washer can be purchased separately and its construction is straightforward, allowing for permanent installation or complete mobility. The most important point is to ensure that the manufacturer’s speed recommendation is strictly adhered to. Figure 9.21 shows the components of a basic unit and how it would accept the drive from an electric motor. There are conditions in which it is useful to set the washer’s lance in a permanent position for washing items like pearl nets or spat collector bags. For this, a table can be built with a jig attachment to take the lance. The bags would then be passed by hand under the high pressure spray. More advantageous designs have allowed for a conveyor belt system, which automatically carries the gear past the nozzle of the lance.

STAR WHEEL ROLLER The design of the star wheel roller will vary according to the farmer’s own ideas and what is available for its construction. Its use has already been described but its

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electric motor

HP pump filter water

inlet lance

washing table

lance secured to table

Fig. 9.21 Construction of a pressure washer. HP, high pressure. greasing point locking nuts

bearing guide bar 30 cm hydraulic motor key way

Fig. 9.22 The construction of manually operated and powered star wheel rollers.

specification and style may depend on the load and level of work it is put to. A hydraulically powered roller is most useful but sometimes only practical if there is already a hydraulic source driven by the boat’s main engine. Discarded hauler sheaths make an excellent base for its construction and Figure 9.22 shows the design of both the manually operated and powered models.

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209

lifting lugs

glassfibre coat polystyrene

battery housing

central mooring post flashing light

battery 1.35 m

1.35 m Fig. 9.23 Construction of a navigation buoy.

Other useful design features can be built in, the most important being the ability to remove the unit when not in use. Where a boat is dual purpose, a fixed star wheel roller can often be a hindrance. Lying alongside a pier or other craft can also be made difficult with a roller permanently in place, especially if it is very prominent.

NAVIGATION BUOYS Navigation buoys can be expensive items to buy and are vulnerable in bad weather. Even what seems like the best laid mooring can mysteriously part or drag, leaving the buoy at the mercy of an exposed shore, or worst for all, lost forever. To construct these is straightforward and represents a huge cost saving over buying one off the shelf. Figure 9.23 shows the basis of construction of a navigation buoy and overall dimensions. They are built on a wooden former with hardboard frame and plywood sheathing. Once the base is covered with two coats of glassfibre the inside is covered with a two part polystyrene mix to ensure both buoyancy and strength. Attention must be paid to the central mooring point recessed into the base of the buoy. This should run through the main body, being secured with large plates at both the top and the bottom. It is preferable to have this item galvanized.

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Four metal rings secured around the top of the buoy will double as both mooring and lifting points. These are necessary because handling a buoyant object of this size can be difficult, especially when the weather is unfavourable. With the ability to lift the complete unit out of the water maintenance will be made easier. A small hollow top section is moulded onto the base and acts as a battery housing as well as a support for the light. The light and flasher unit will have to be purchased but the frequency of the flashes will need to be specified beforehand. A secure mooring must be laid for the navigation buoy, and because it is very lively, even in a moderate sea, provision will have to be made for regular mooring checks. For complete security, a 1000 kilogram concrete block will be required. This should be secured to the buoy with 12 millimetre galvanized chain, cut to a length that is 2.5 times the depth of water. A swivel placed 2 metres below the buoy will be in a position that can easily be checked from the surface.

MOORING BUOYS Figure 9.24 shows a customized surface marker buoy fitted out to act as a mooring buoy. The buoy itself can be as large as is required but a minimum size of around 1metre diameter. Discarded buoys, which maybe only have a broken eye, can be used to good effect in this project. The length and specification of the rigging will depend on what use the buoy is put to. The figure shown is for a buoy of roughly 1 metre diameter with six lengths of rigging comprising three of 12 millimetre and three of

4 mm whipping wire 6 mm twine

rope

plait

Fig. 9.24 A customized surface marker buoy.

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6-millimetre stainless steel, plastic-coated wire. The lengths are draw together at the base of the buoy with three actually running through the eye. These are then tightly whipped into place. A 2 metre plait is then completed and eyes are spliced into the rope, and bulldog gripped into the wire. This is then tightly whipped into place. Both wire and rope are evenly and alternately spread around the buoy and secured at the top with very tight whipping. Six millimetre twine holds each rope in place by spiralling around the buoy and securing each rope or wire as it passes over it. The six lengths running from the top can be plaited if required or just run straight, terminating in eyes whipped tightly at their end. The length of this will depend on what it is used for, but as a rough guide use twice the length of the vessel you are tying it to. The six loose lengths (if not plaited) can now be tightly bound with duck tape. This will hold them very securely and will also protect the rope from the adverse effects of sunlight. In the same vein, those ropes exposed on the sides of the buoy can be painted to give them some protection also.

BREAKWATERS The destructive power of waves can be effectively reduced by installing a suitable breakwater. This is useful in keeping motion from the rafts and is especially effective in protecting exposed landings. It can, however, be a navigation hazard and consequently must be very well marked. A simply constructed breakwater is shown in Figure 9.25 and consists of car tyres with a central supporting telegraph pole. Bearing in mind that most telegraph poles are only 6 to 7 metres long this breakwater will be fairly short. Its main use will therefore be as a buffer to waves coming onto a raft. In order to be fully effective, it will need to be secured roughly 6 metres ahead of the raft and across the waves.

car tyres on a telegraph pole

car tyres chained together Fig. 9.25 Examples of breakwaters.

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cement set in polythene bag

6 mm rope loop

plastic drainpipe

120 mm

100 mm Fig. 9.26 Homemade concrete weights.

To protect a large area an effective breakwater can be constructed out of car or lorry tyres secured together in the form shown in Figure 9.25. Chains keep the whole structure secure and its length can easily be extended by adding more tyres. When waves meet a structure of this design its wallowing motion gradually breaks them down. It is often necessary to add extra buoyancy to both types of breakwater because some tyres sink. This can be achieved by filling some of the tyres with polyurethane foam. It is pointless to site a breakwater for raft protection when there is a danger of the breakwater breaking free and causing damage. They must be very securely moored and regularly checked. With the longer designs it is necessary to moor at several points along their length to prevent them from bowing in the middle.

WEIGHTS There are many uses for small weights, both for convenience and for permanent fixing (Fig. 9.26). Strings of spat collectors need weighting, as do lanterns set in areas of strong tide. The quickest way to make weights is to fill short lengths of mussel stocking with small stones and then knot both ends. Longer-lasting weights can easily be made by filling polythene freezer bags with a measured quantity of cement and finally pushing a rope loop into the mixture. Another way is to fill short lengths of plastic drain pipe with cement, and rope in the same way. After a couple of days

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the mould can be removed for reuse. To gain extra weight, add small stones to the cement mix.

SUMMARY •

• • •

• •

• •

• • • • •

• • •

Although economic factors will influence the level of involvement, it is important for farmers to experiment with equipment design and manufacture because this is where good ideas originate. Most designs are born from either a necessity to improve on an existing product or to fill a gap in the market. As the lantern is one of the main items of culture equipment in scallop farming considerable thought must be put into its design. Although pearl nets are tending to be superseded by disposable net lanterns, they can still have a useful function on a farm. They are cheap and easy to construct and could easily be tackled by a beginner. Raft designs can vary from a simple wooden frame supported by four oil drums to a large metal-framed raft with adjustable buoyancy pontoons. Pontoons can be constructed in a variety of ways, and the quality of work applied at this stage will have a direct bearing on their rate of depreciation. They are the most expensive components of any raft and therefore should be built in such a way as to ensure a long and useful life. A steel raft with adjustable walkways or a raft with adjustable buoyancy may be of advantage in some situations. By allowing the raft to sit lower in the water when only partially loaded, a considerable amount of movement can be avoided. This gives the raft weight and grip in the water, thus making it more compatible with sea state. One of the most useful items on a scallop farm is a work raft. A very effective anchor can be built from steel and cement. This is called a fish box anchor because it uses an old broken fish box for the basic mould. Various types of sorting gear have been designed ranging from simple net riddles to sophisticated, motor-driven, vibrating units. A rod riddle takes the thickness of the scallop as a measurement and is most useful when separating different species at spat stage. To be fully effective a pressure washer needs to pump water at a minimum pressure of 1200 pounds per square inch and should be light enough to be transported by one man. For complete versatility, a choice of petrol engine drive for the boat and electric motor drive for the shore base would be most advantageous. Having star wheel rollers hydraulically powered is most useful but sometimes only practical if there is already a hydraulic source driven by the boat’s main engine. Navigation buoys can be expensive items to buy but construction is straightforward and represents a huge cost saving over buying one off the shelf. A simply constructed breakwater consists of car tyres with a central supporting telegraph pole.

Chapter 10 Diving Work

There are many advantages in obtaining a firsthand view of an operation, but this is not always easy when working in the sea. What lies under the surface might be a mystery to many, but the diver can add understanding by direct observation. Not everyone will have the desire or even ability to learn to dive, but fear of the unknown should be dispelled if that is the only thing preventing someone from having a go. There is nothing complicated, frightening or dangerous in this activity if the participant is reasonably fit and pays attention to the safety rules. Although it is not essential to be able to dive when setting up and running a scallop farm, it can be an enormous help.

DIVING TEAMS A team of three divers brought in once or twice a year can accomplish a great deal and could easily prove their worth if a potential problem is spotted in advance. What could seem to be a high price may well become value for money if enough useful work is planned for them. One word of caution is that in many countries it is the person contracting the diving team who is responsible if anything goes wrong and it can be proved to be caused by a broken regulation or unlawful practice. Therefore ensure that the team work completely within the prevailing rules and that all members are fully qualified.

Qualifications In the UK, and in many other countries, any diver earning a reward for his skill must hold a current certificate to show that he has attained a recognized standard in training. Four categories regulate the type of work undertaken and the maximum depth worked, and cover the deep water saturation diver as well as the man earning his living picking up shellfish.Those wanting to undertake fish farm work will usually have attained the simplest category, which also covers the shellfish diver. He must also take an annual diving medical examination and hold a current first aid certificate. 214

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Working practice The minimum team requirement is for three men but usually four are stipulated, with one being nominated as supervisor. The supervisor need not be in date with a medical but must have at one time trained as a diver. If, on the other hand, the supervisor is a diver/supervisor, then he will also be expected to contribute to the day’s work and as such one day’s hire could amount to a considerable amount of dive time. One important point is that many countries now require all diving work to be carried out within a maximum 2 hour journey of a decompression chamber, otherwise one will need to be carried to the site. There will be regulations regarding the equipment the diver carries and the method and depth he works in. One stipulation in many countries now is that the diver has full communication with the surface via a communications set. If its use puts the diver in a dangerous position, then he will at least have to use a line and surface buoy, relying on line signals to relay messages. His basic gear will usually be a full face mask, breathing gas with back-up, depth gauge, knife, weight belt and fins. Depending on the climate he may wear either a wet suit or a dry suit. With a wet suit he may also be required to wear a divers lifejacket and, although this is not always enforced with dry suit wear, it is still a useful safety back-up. The dry suit, however, will be required to have its own means of inflation. All of the diving equipment used will have to be in good condition with an accompanying test or inspection certificate where necessary; diving cylinders, for instance, may require a 2 year test to demonstrate their good condition. If a farmer takes on the diving work himself, then, if working in the UK, he still must abide by the Health and Safety Executive regulations and work in the manner laid out.

THE ROLE OF THE DIVING REPRESENTATIVE Where a farmer brings in a full diving team, as already mentioned, he will be responsible if they work in an unprofessional manner. For this reason it is good practice that at least one farm employee is up-to-date with all the relevant diving regulations. We have mentioned some of the basic ones but there are others he will need to be familiar with. However, as they are often restructured it would be best to contact the relevant authorities directly to inquire about the most up-to-date regulations. It is useful to understand some of the techniques applied when working underwater so that a farmer may ensure that no disasters occur; for instance, how would a diver change out an anchor shackle without putting the whole line or raft system in jeopardy, or just what does he mean when he says a mooring looks safe? Don’t always take it for granted that because a man is able to dive he is an immediate expert on all aspects of fish farm systems. Do not be afraid to ask for credentials and about how a task is to be undertaken. Also, there is a certain amount of time

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and motion in diving work, as certain jobs will be known to take a specific period of time to complete. If they take longer, try to find the reason why, as it may be just down to inexperience. For this reason, while there follows an examination of the main aspects of scallop farm diving work, it will also look at some of the techniques employed by divers to ensure a task is completed without any catastrophes.

POTENTIAL DIVING WORK Anything that can be done on the surface can be done underwater, only at a very much greater price. A scallop farm, by the nature of its stock, is situated mainly underwater. The diver therefore has an important role. Divers can perform many tasks underwater, which can save time and money in the long term, and many teams are specializing in farm work alone to ensure the customer a good return on their investment.

Moorings What could be gained by employing divers? First there is the safety aspect in having all the farm moorings thoroughly inspected and any suspect components replaced. This could help to lower insurance premiums. Anchors can be assisted in their bedding-in process, and even strategically placed if the bottom is of rock or boulders. Mooring lines can be checked to see that they are not chaffing on rock outcrops, this being a major cause of breakages. Many divers are also proficient in mooring design and planning and should be able to give useful advice when the system is being built.

Seabed surveys Although an echo sounder can give much information about the nature and composition of the seabed, it cannot be as useful as the human eye. A visual inspection will quickly determine the type of anchor to be used and may even spot suitable outcrops of rock that could be keyed into. There have been many instances where a longline has been set along a seemingly uniform depth, only for several pinnacles of rock to be found later in the same area. Loaded pearl nets and lanterns sink steadily lower as the scallops grow, and they can easily come into contact with such a pinnacle. The resulting damage can be extensive. A diver will often assess this problem more accurately than an echo sounder.

Removing marine fouling Marine fouling presents the farmer with one of his biggest problems. Not only does it choke equipment, it also adds considerable weight and drag to the whole of the system. Farming would be simpler if there was no fouling, and much planning goes into how

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and when to clean equipment. Ideally the gear should be changed before becoming too badly fouled but labour constraints often get in the way of this practice. It is not difficult for a diver to swim along a line, cleaning it as he goes. There is unfortunately little he can do about the growth on lantern and pearl nets except for breaking off the larger pieces of weed. This exercise can be quickly executed and will result in savings in buoyancy as well as postponing the need to clean the culture equipment. Another useful function will be cleaning mussels, etc., from the bottoms of pontoons and rafts.

Predator spotting It is impossible to plan for all contingencies; for instance, both mussels and starfish must be avoided wherever possible, but unfortunately their settlement is not always predictable. Sections of a longline may be checked for predators and found to be clear. On the next change it may be found, to the farmer’s cost, that the section he looked at was in fact the only section free from predators. While cleaning a longline, a diver can do a quick check on predator settlement because they will be evident on the line as well as the gear. This can be invaluable information in terms of reduced wear on equipment and overall scallop survival.

Tangles In areas where spat is abundant, a farmer may set many thousands of collectors to ensure a sufficient supply of spat. Tangles can often appear at this stage and can be difficult to sort out. By swimming along a line of collectors a diver can often spot the key to a tangle and recommend the easiest way of resolving it. A minimum amount of disturbance will also help to reduce settlement losses.

Bottom culture Farming by bottom culture has many advantages, the foremost being its relative cheapness compared with the more traditional types. It is possibly only something that a diver would contemplate setting up, but should not be overlooked because of a farmer’s inability to dive. It could still be worked by bringing in teams of divers at harvest time, and in ideal circumstances a diver should be able to lift more than 1000 scallops per hour. Given that he will be able to work for 3 hours a day, the end-result represents a very respectable haul. When lifting species like Pecten maximus an efficient diving team would cost between 10 and 15 per cent of the total value of the scallops harvested. This is comparatively cheap when put against the income saved by not having to tie up costly culture equipment for the last 2 years of growing on. There is one small problem, however, when employing outside diving contractors for harvesting. When all is going well and the scallops are easily spotted and lifted, a diver should easily reach his target, but when the ground becomes more sparse

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and the shells are difficult to see, the catch for the day may fall considerably. If the diver is just paid on quantity alone, then he may not be so thorough, only picking the easily reached ones. A payment should therefore be incorporated so that he may be encouraged to clear a patch more thoroughly, sacrificing numbers for efficiency.

Broken lines Every shellfish farmer will, unless he is extremely lucky, at some time have to face the problem of either a broken or dragged line, no matter how thoroughly he plans and builds his farm. It can be disastrous because the culture gear will often form a seemingly irresolvable tangle. The act of physically pulling the gear free from the surface can cause extensive damage and considerable stock losses, the most vulnerable being the pearl net because of the nature of its construction. Faced with a tangle of this kind, a diver should be able to ascertain how it was formed and suggest the easiest way out of it. Merely going in and pulling on the line can cause untold damage and the gear will often end up forming an even tighter knot. In some extreme cases whole lines with many lanterns attached have needed to be towed ashore to sort out tangles and this add a considerable burden of cost to the farm finances. Where a line of spat collectors has parted, it is important to cause as little disturbance as possible when resiting. A diver can suggest the best way of doing this and may even advise securing the tangle in its new position to allow the scallop spat to grow undisturbed.

Boat work Apart from being able to carry out an annual scrape of a vessel’s bottom to remove marine fouling, a diver may also perform such tasks as anode or even propeller replacement. Other general inspections can also be performed to check that all is in order.

Salvage The term salvage can apply to literally anything that has come adrift on the sea, but in the case of diving it is mostly thought of as relating to raising sunken boats. Lifting sunken vessels from the seabed is not a difficult job, providing the team know what they are doing, and often, quick action can mean a farm boat is back in operation not long after it sank.

DIVING PRACTICE As mentioned earlier, it is important to know that a diver is not going to cause more trouble by using unqualified techniques in his work. It is also important to get value

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for money from him, in terms of effective seabed time. Following are some areas where fairly standard practices apply and all fish farm divers should be aware of them.

Seabed searches It is very common for diver services to be requested to carry out seabed searches and success will vary on the experience of the diver and the techniques he uses. If something is lost on the seabed, which on a scallop farm can occur quite regularly, and there is little in the way of a mark to indicate its position, it is probable that the person responsible will tell you that he knows exactly where it is. Obviously, if he has a global positioning system aboard or threw out a marker and weight immediately after the loss, then his positioning will be accurate. However, if it is only marks from the shore that are guiding him, then it is almost certain that his mark will be way off. Much of the diver’s success will be based on the accuracy of the mark, the water visibility, the composition of the seabed and the strength of the tide. There are several ways of carrying out a seabed search and he must always take with him a line and surface marker.

Circular search Figure 10.1 shows a circular search and this involves using a central marker (a heavy weight), and circling out from that point, feeding a hand line out slowly so as to

search area

Fig. 10.1 Plan of a circular search.

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leaded rope

direction of swim Fig. 10.2 Plan of a line search.

work in a spiral around the bottom. It is usual for the diver’s line to be approximately 30 metres so that when he has reached the end he knows he has searched a circular area with a diameter of 60 metres. If he has no success, the central weight can be moved to another spot, within a predetermined pattern, and so the routine continues.

Line search A line search involves laying out a weighted line along the seabed, and over where it is thought the object lies. The diver then swims from one end to the other zigzagging out from side to side as visibility allows or with the use of a small line looped around the main line and moved along each time the diver passes over it (Fig. 10.2). If there is no success, the main bottom line can be either moved along or to either side. Marker buoys at each end attached to fairly heavy weights make this process fairly straightforward.

Grid search Where an area of seabed needs to be examined very thoroughly, a grid search should be set up. This involves laying down two lines of a predetermined length and spacing as shown in Figure 10.3. The diver then runs a line from one corner to the other and swims back down it examining the seabed very closely. Once he reaches his starting point then moves the search line 1 metre along the fixed line and swims back along it once more. Once at the other fixed line he moves this end 1 metre and swims back, thus effecting a close zigzag pattern.

Compass search As its name suggests, this is a search that involves the use of a compass. It requires quite a high degree of expertise to undertake effectively, and is not advised in areas of strong tide.

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swim area

leaded rope Fig. 10.3 Plan of a grid search.

Depth gauge search Where an object has been lost in an area where there is a sloping bank, providing an accurate reading was taken of the depth then a diver may use his depth gauge and swim in a zigzag fashion up and down the bank in the hope of making a discovery. If, for instance, the lost object was in a depth of 12 metres then the search would range from a maximum of 15 metres down the bank to 9 metres up it, ensuring that the search is carried out at the same tidal state as when the object was lost.

Free swim search Where there are features on seabed like reefs, rock outcrops, sand banks, etc., a diver may simply use these as an indication of his search pattern. This can be very effective, especially if the diver already knows the area well.

Setting up a work site Where a diver is undertaking a static job like reshackling an anchor and chain or assisting the digging in of an anchor, he will fare better if he is able to work without surfacing for tools all the time. For this reason a downline is tied to the job and equipment may be run up and down it at the diver’s request, communicated via his communications set (Fig. 10.4).

Assisting the diver In so far as is possible, as much of the work should be completed on the surface as possible. All nuts and bolts should be checked for ease of use and a small amount of grease applied where necessary. Shackles should be treated in the same way. When these objects are passed to the diver, they should not be overtightened; a

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downline

gear, running line

Fig. 10.4 Setting up a job with a downline. safety rope

Spanish

windlass

rope stopper

Fig. 10.5 Replacing shackles on the seabed.

shackle pin for instance needs only a couple of turns to hold it in place and this frees the diver’s time at the bottom end. Tools such as adjustable wrenches should be checked for ease of use and set to the size of the bolts used. If possible, complete a dummy run of the job on the surface to ensure that all the equipment required works reliably. A canvas toolbag can be employed to store the equipment in and to transport it to the diver. This will have its own downline so the diver does not have to carry it back to the surface.

Reshackling Components will often need replacing but when this has to be carried out underwater there will be added problems. If an anchor shackle requires replacing, it may mean disconnecting the main mooring line from the anchor, which in itself would render the system vulnerable. A diver will usually approach such a job at a tidal state when there is least strain on the end of the system he is working. Figure 10.5

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223

shows the setup on the seabed where the diver has secured the chain to the anchor with the use of stoppers and a block and tackle of some kind, maybe even a Spanish windlass. Enough tension is applied to free the shackle of load and it is quickly removed. Prior to this, if the diver thinks that he needs to make the situation safer, he can add a safety rope further along the chain and back to a point on the anchor. A new shackle is then put in place, tightened, and re-moused.

Using lifting bags Lifting bags are a most useful item for all kinds of bottom work and can range from 50 kilograms to over 10 000 kilograms lifting capacity. The larger ones can be fairly hard to handle on the seabed and it is usual to work with a crew who has experience with them. First of all a stout downline is attached to the object being lifted and this is used, first, to run the bags down to the diver and, second, as a tow line once the object is lifted. The diver starts by attaching the bags one at a time, slightly inflating each one as he goes with an air-line run down from the surface. Once all are in place he will add some more air all around but not enough to actually lift the object. Finally, he attaches the air-line to a central bag and leaves it filling while he makes his way back to the surface. If his calculations have been correct, the object will start to rise as the lift comes on the filling bag.As the whole setup rises, the other bags will inflate via pressure differential, giving extra lift and added support on the surface. If only one bag is needed to be used for the job, the diver would follow the same procedure, leaving the bag to fill while he returned to the surface. If, in the interests of safety, it is thought appropriate to be well clear of the operation while the final bag is being filled, it may be appropriate to keep the air turned off until the diver is safely back aboard the diving boat. Another safety point in this operation is to use what is termed a fuse line for any towing operations. This is a line that is light enough to part before pulling the work boat back down with the lift if the buoyancy fails.

Moving heavy weights on the seabed The heavy weights to be moved are usually anchor blocks but sometimes a boulder will require shifting to free an area for navigation. In the case of anchor blocks, it is usual to lift them with lifting bags, but, unlike salvaging a boat, all that is required in this case is to lift the block free from the bottom to a height of a metre or two. To achieve this, the bag is filled close to the surface with an extended line going down to the block. Towing is also done from the block and not the bag (Fig. 10.6).

Methods of harvesting Divers will often be called in to a scallop farm to undertake a harvest. As already mentioned, the farmer will often be at the mercy of both the diver’s efficiency and how conscientious his working practice is. There are certain guidelines to working

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Scallop Farming 1m

lifting bag

tow rope

1m

Fig. 10.6 Moving heavy locks on the seabed.

a harvest successfully and one of the main points is to ensure from the surface that all the diver has to do is to fill bags and not waste his time in other pursuits. Net bags capable of holding between 300 and 400 king scallops (70–80 kilograms) are attached to plastic drums or buoys with a 25 litre capacity. A small part of the bottom is cut away to enable them to be filled with air as the diver loads the bag, thus taking up the weight (Fig. 10.7). He will require an ample supply of these and they must be positioned such that they are easily spotted and deployed. Once filled, the bags are pulled to the surface. When harvesting, a diver will try as far as possible to work into the tide so that what sediment he has kicked up will be swept past him, therefore not impeding his vision. Figure 10.8 shows a system whereby a diver may use a central anchor and line to effect a sweeping motion back and forth until he is back at the central point. The anchor may then be moved forward to another point. Another way of working is to use a gridline of some sort and work along it, swimming out to each side as visibility allows, similar to the line search as already described. Once complete, the line may be moved to a fresh position.

Bedding in anchors Apart from the need to check that an anchor has landed in a proper manner on the seabed and that it is the correct match and there are no obstructions, a diver may

Diving Work

25 ltr plastic drum

160 mm cir buoy

cut away

harvest bags

Fig. 10.7 Harvesting bags with plastic floaters attached.

10 m

harvest

Fig. 10.8 A technique used to collect scallops during a bottom harvest.

area

225

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Scallop Farming

assist in the bedding in process. If there is already some strain on the anchor, then all that may be needed is to pull it from side to side a little while putting bodily weight against it. This is usually enough to help it on its way. A more forceful approach is to either use a water jet or air jet to spray the immediate seabed beneath the anchor and let it fall down into the hollow created. A spare bottle of air can be rigged for this with a plain hose being taken from the high pressure connector on the regulator. A water jet may be provided by the vessel’s deck wash if it has one.

Clearing propellers It is very common for divers to be employed to clear propellers and, although seemingly fairly straightforward, some divers achieve more success than others. The most important starting point is to always ensure that the engine is stopped and that the keys are out of the ignition before proceeding. If scallop culture gear has entered the propeller housing, then it is important to try and free it with as little damage as possible. This will often take time. A potential hazard will occur if the longline itself becomes entangled. In these cases, because of the tension on the system it is often deemed necessary to cut the line free but not before securing a safety line so that the two cut ends can be pulled back together once free of the propeller. A very useful tool for propeller jobs is a hacksaw and this is particularly effective where a tyre fender may have been picked up. Knives blunt very easily but a new hacksaw blade will keep its edge for a long time providing it is prevented from rusting.

Checking the seabed A seabed survey carried out by a diver prior to setting a longline, a raft, or examining the potential for bottom culture will, in the long run, prove worthwhile. In the case of positioning a potential longline, a sinking line will have to be laid along the seabed between the two proposed anchor point. The diver will swim this, zigzagging as he goes to check for rock outcrops, reefs, etc. Where the anchors are to be placed will require special attention because of the problems of chaffing, and the result of his observations will determine the nature of the anchoring system. He may find a rock outcrop that can easily be tapped into for a mooring, or that would be suitable for drilling and pinning. While in this area he will also need to sound the bottom for depth of sand, to ensure that the anchors will bed in satisfactorily. He can do this by driving in a 1-metre long 10-millimetre diameter steel spike with a heavy hammer at several spots within the proposed anchoring area.

General inspection techniques Because a man can dive does not necessarily mean that he will be an expert on everything, so where a diver may be employed to make a mooring inspection it would not be unreasonable to ask him what he will be looking for. If he is experi-

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227

enced in this field, he will take with him a heavy hammer, a large wrench, heavy pliers and short lengths of plastic-coated fencing wire for re-mousing. The hammer he will use to chip at any rust he may see on chains, and other components to check whether it runs deeper than just on the surface. He may also give the shackle pin a good knock to test if it is still tight and if the thread is still intact. If a component is starting to look a little worn, he may have to make a prediction as to when it will need replacing. The wrench will be used to tighten up shackle pins that may have worked loose, and any mousing wire that looks broken or badly worn can be easily replaced with new lengths. If there is any doubt about the condition of a metal component and if there is no apparent way of determining the full extent of any corrosion, then an ultrasonic gun may be hired to make these measurements. These are small, light, compact and easy to use.

SUMMARY • •

•

•

•

•

•

•

What lies under the surface might be a mystery to many, but the diver can add understanding by direct observation. What could seem to be a high price will become value for money if enough useful work is planned for a diving team. There will be regulations regarding the equipment the diver carries and the method and depth he works in. The minimum team requirement is three men but usually four are stipulated, with one being nominated as supervisor. The supervisor need not be in date with a medical but must have at one time trained as a diver. Where a farmer brings in a full diving team, he will be responsible if they work in an unprofessional manner. For this reason it is good practice that at least one farm employee is up-to-date with all the relevant diving regulations. Anything that can be done on the surface can be done underwater, only at a very much greater price. Divers can perform many tasks underwater, which can save time and money in the long term, and many teams are specializing in farm work alone to ensure the customer a good return on their investment. The farmer should not take it for granted that because a man is able to dive he is an immediate expert on all aspects of fish farm systems. Do not be afraid to ask for credentials and how a task will be undertaken. It is important to know that a diver is not going to cause more trouble by using unqualified techniques in his work. It is also important to get value for money from him in terms of effective seabed time. Try to complete as much of the work as possible on the surface.

Section 3 Getting Down to Business

Chapter 11 To Collect or Not To Collect

So far we have examined scallop spat in very close detail, but what we have not discussed is the viability of collection. The importance of being able to collect spat onsite, where possible, cannot be stressed too greatly and if the procedures outlined do not succeed in locating any, then they will have to be purchased elsewhere. It used to be said that if a farmer could not attain a level of 200 shells per collector bag, then it was not worth doing. This statement has long since been overruled and it is now viable to collect in areas that will only yield 10 or so scallops per bag. The actual number will depend much on the species and how profitable it is when fully grown. In fact, if there is no chance of gaining supplies from an outside farm then almost any number may seem acceptable. However, just what the minimum level is will have to be decided by the farmer himself, and much will depend on his dedication, patience and work rate.

Large-scale collection Some farms will be fortunate enough to be situated in areas where there is a large and reliable supply of scallop spat each year. Unfortunately this seems to be the exception and not the rule and it is possibly from these farms that the statement about the necessity of 200 per bag originally came. We have seen the ways in which large-scale collection can be automated, and the obvious advantages of having a reliable source, along with benefits to cash flow where surpluses are sold to other farmers. However, having such a supply on your doorstep still requires a fair degree of expertise to manage and sometimes this takes a long time to master.

What stage to buy in? It is a better policy to buy in 1-year-old rather than 3-month-old spat, three months being the usual age when removed from the collector bags. This is primarily because they will be that much stronger. Reductions in mortalities are therefore obvious. Farmers without a natural supply themselves have been quick to learn this and consequently, primarily for king scallops, this seems now to be the norm. This means that the farmer collecting for himself will have to absorb the initial, usually fairly 231

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high mortalities if he is to enter this market. On the other hand, the shells will be that much more durable when it comes to being transported.

THE REALITY OF SETTLEMENT On some occasions a farmer will collect a bag full of the species he is targeting, all large, healthy, and without competition – a nice situation to be in, but certainly not the norm in many areas. What the farmer usually pulls in is a bag full of every predator imaginable, the beginnings of marine fouling, and a few of the target species mixed in with a whole host of non-target species. So they all have to be separated out, leaving the target species relatively alone. Unfortunately, even the best systems will still allow some of the unwanted specimens through, along with predators, which possibly at that stage are easily missed by the human eye.

Picking out what is needed Eventually, the target stock has to be selected out from whatever is growing beside it and the argument is whether or not to do this from the start or leave it till later. The answer may seem obvious for reasons of growth but because mechanical sorting is not 100 per cent efficient, and because it is often difficult to hand pick cold, wet, 6–8-millimetre spat, they are usually left to their devices along with whatever may have been placed in the pearl nets. However, as mentioned before, they will at some stage need sorting.

Sorting by hand If there are only a few of the target species in each collector, then it is obviously easier to pick them off by hand. With only a few available they will usually be that much bigger because of less competition for food, and as such a little easier both to spot and to pick out. The advantages now become apparent. What will be in the lanterns is exactly what the farmer is looking for, no predators and no other species that will compete for food. Therefore, so long as they have not been stocked too densely the scallops are likely to grow faster and to sustain fewer mortalities. Bearing in mind that a large reliable settlement is fairly easy to manage, the next decision is about what level of settlement is viable when selecting by hand, if that is the farmer’s chosen option.

What number is required? The farmer’s requirement may vary from a few thousand to a few million, depending on the scale of operations, and this will have a direct bearing on how he sorts the collector bags out. If 5 million were required, for instance, and there were only eight shells to the bag, it would be necessary to set 625 000 bags – a handling, storage and management nightmare – and it would therefore be better to try and buy in.

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233

However, if the farmer knows he can process 700 bags per day, for instance, then for a full day’s work he would have secured nearly 6000 scallops to grow on. If he could buy them in cheaper than the cost of the day’s work, then, if available, it may be better to do so because there are other costs involved other than just a day at picking. On the other hand, this may be the only source of supply, and their eventual value may seem well worth the effort.

METHODS OF SORTING There are three basic methods of sorting scallop spat; fully automated, semi-automated and by hand. The choice of one of these is usually based on cost and level of settlement. There follows, first, a look at a fully automated system and what can be expected from it. However, before embarking on any logistics analysis, it is necessary to know the cost implications apart from what is required in manpower. The process of spat collection has already been outlined in Chapter 5 but, to recap, initially, bags and filler need to be made up onto short droppers. These will then need to be hung from longlines, supported with subsurface buoys and weighted so they hang properly through the water column. This will require the use of a boat and the use of a longline. They will then require periodic buoying to ensure they do not sink to the bottom. This process will be the same for any level of activity and the only variation in manpower will be based on the scale of operation. The variable manpower cost starts when sorting begins because differing levels of settlement often require greatly differing manpower input. So for this stage, the bags will need to be taken off the longline, sorted out, graded, and the spat put into lanterns (or other suitable receptacles) and hung back on the line. Finally, the bags will need to be taken ashore, cleaned and stored for future use. A figure for this input will be included in all of the tables when calculating manpower requirement in this chapter.

Fully automatic sorting Because of the size and complexity, a fully automatic sorting and grading machine will usually be housed in a shore base. Consequently it will also require a power supply, a supply of clean seawater and holding tanks for the sorted shells. Chapter 9 looked at how these machines work, but not at what may be expected from them. Table 11.1 is a rough guide based on one man’s efforts. Obviously there will be a team of men tackling the various aspects of the job, some bringing bags in from the longline, some sorting, some filling lanterns and others reloading the longlines. The figures given in Table 11.1 are primarily governed by how long it takes to fill the lanterns or pearl nets after sorting is complete, the sorting process being very fast; for instance, one man is expected to bring in 600 bags (with 70 spat in each), empty them, put the contents into the sorting machine, load more lanterns or pearl

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Table 11.1 The logistics of fully mechanized sorting of 20 000 collecting bags. Total indirect days allowed = 28 No of spat per bag 70 90 110 130 150 170 190 210 230

Bags worked per day

Total spat sorted per day

Total days employed

Total spat collected

600 522 454 395 344 299 260 226 197

42 000 46 980 49 955 51 363 51 561 50 839 49 433 47 534 45 293

61 66 72 79 86 95 105 116 130

1 400 000 1 800 000 2 200 000 2 600 000 3 000 000 3 400 000 3 800 000 4 200 000 4 600 000

nets, transport these back out to the line and secure them. A tall order, maybe, but because the machine works so quickly a large part of his day will be devoted to stocking lanterns. The example in Table 11.1 involved setting 20 000 bags, and the results show the number of spat obtained from them ranges from 1 400 000 to 4 600 000, with a manpower input rising from 61 to 130 days. The economies of a good settlement are well outlined here. At 230 shells per bag over three times more have been collected than at 70 per bag; on the other hand, the increase in manpower requirement is only slightly more than double. With 10 people employed a final stock of 4 600 000 in 13 days can be expected. This looks like a wonderful system, and it is, for those who can afford it. However, it must be remembered that the final product will not be 100 per cent target species. The grader will have sorted scallops into various levels of purity, with possibly the best being 90 per cent uncontaminated by others. Even some predators may have found their way into the stock.

Semi-automated sorting A semi-automated riddling system has the advantage of being fairly compact, and as such can often be operated from the deck of the farm boat providing that it is fairly stable in the water. Unfortunately, as with the fully automated system, there will always be a proportion of unwanted species getting through the system and these will either have to be taken out at the time of sorting or at the next lantern change. Table 11.2 is based on the same format as Table 11.1 only with a reduction in the number of bags set to 10 000, and a slight increase in the indirect manpower requirement. Once again, the system is fairly efficient and with well stocked bags it is limited by the rate of lantern filling by the labour force. The table is based on the number of days it will take one man to handle the 10 000 bags with varying levels of settlement. Bags with only 50 species yield half a million spat after 40 days’ work. With

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235

Table 11.2 The logistics of partially mechanized sorting of 10 000 collecting bags. Total indirect days allowed = 15 No of spat per bag 50 70 90 110 130 150 170 190 210

Bags worked per day

Total spat sorted per day

Total days employed

Total spat collected

400 348 303 263 229 199 173 151 131

20 000 24 360 27 248 28 974 29 791 29 905 29 487 28 671 27 570

40 44 48 53 59 65 73 81 91

500 000 700 000 900 000 1 100 000 1 300 000 1 500 000 1 700 000 1 900 000 2 100 000

this increasing to 210 spat per bag, after 91 days there will be a total stock of over two million spat: a very good reward for the amount of time employed.

Sorting by hand At some stage, the target species will need to be sorted from the rest to be 100 per cent pure, and this can either be carried out when the bags are brought in or at the first net change. Commonsense dictates that if the stock is contaminated, then unwanted species will be competing for food with the target species. If, for instance, there is 50 per cent unwanted species, then approximately double the equipment will be needed to house them if correct stocking densities are to be observed. So not only will extra equipment be needed, but also added buoyancy over the first growth period – a lot of extra work when there is a strong possibility that half of the lantern’s contents will be disposed of at the first net change. There may also be predators like starfish, mussels and crabs that passed through the system, and it is not uncommon to lose as much as 10 per cent of the target species at the first change because of this. The advantages of sorting by hand at this crucial stage are becoming apparent. It is economies of scale that make such a labour-intensive job seem so daunting, and, unfortunately, when a large stock is required then such problems as competition for food, extra equipment requirement and predation tend to be overlooked. However, farmers are gradually seeing the sense in hand sorting and it is becoming more widely practised. It is necessary at this stage, therefore, to decide at what settlement per bag does hand sorting becomes worthwhile. Table 11.3 is based on 1000 bags being set with a settlement range of 4–48 target spat. At 48 spat per bag the total spat collected would be nearly 50 000, with a total input of under 7 days’ manpower not an unprofitable week’s work. Only 4 spat per bag would mean over 3 days’ work to collect just 4000 spat towards the stock: a difficult situation to justify economically. However, 12 spat per bag and a few hours’ more work would represent a stock of 12 000 from 1000 collectors: a situation that

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Table 11.3 The logistics of sorting 1000 collecting bags completely by hand. The difference between total days hand picking and total days employed represents the indirect manpower requirement No of spat per bag

Bags handled per day

Spat picked per man per day

Days hand picking

Total days employed

Total spat collected

700 630 567 510 459 413 372 335 301 271 244 220

2 800 5 040 6 804 8 165 9 185 9 920 10 416 10 714 10 848 10 848 10 739 10 544

1.4 1.6 1.8 2.0 2.2 2.4 2.7 3.0 3.3 3.7 4.1 4.6

3.2 3.3 3.5 3.7 3.9 4.2 4.4 4.7 5.1 5.4 5.8 6.3

4 000 8 000 12 000 16 000 20 000 24 000 28 000 32 000 36 000 40 000 44 000 48 000

4 8 12 16 20 24 28 32 36 40 44 48

Table 11.4 Days needed at varying spat levels to collect 100 000 spat by hand, and allowing 17 days for indirect manpower requirement No of spat per bag 4 8 12 16 20 24 28 32 36 40 44 48 Spat required

Bags worked per day

Number of bags set

Total days worked

700 630 567 510 459 413 372 335 301 271 244 220

25 000 12 500 8 333 6 250 5 000 4 167 3 571 3 125 2 778 2 500 2 273 2 083

79 42 29 23 20 17 16 15 14 14 13 13

100 000

could well be justified when there is no other source of stock available, but not one that would make any profits when selling at spat stage. To view the situation from a more commercial standpoint, Table 11.4 demonstrates the number of bags required and the total man-days input for one man to collect 100 000 spat, at the same varying settlement levels as in Table 11.3. A situation with 12 spat per bag would require a total of 29 days, handling over 8000 bags during this period. Providing good husbandry techniques are employed with regard to the stock, and losses are on the low side, then these initial efforts must be regarded as fairly worthwhile, bearing in mind that what is expended in manpower at this stage will be rewarded when it comes to the first net change with no sorting to do. It cannot be overstated that finding a reliable spat source is very important if the farm is to have any future. Because someone states that there is no natural settle-

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237

ment in a specific area does not necessarily mean that it is true; possibly their investigation was not thorough enough. Because collection is a relatively new science there is a lot for the prospective farmer to take on board and it must also be borne in mind that actually locating a spat supply can take more than one season. Consequently, it is often found that one failure leads the farmer to insist that he is wasting his time. However, perseverance often pays off and testing against the norm can sometimes bear fruit; for instance, it is generally thought that the best settlement is in mid-water, but situations have arisen where there has been a good settlement a few feet above the seabed, with nothing further up. In some circumstances this may have been missed. Buying-in is not always the answer but when it can be stated categorically that there is nothing to be collected from the site, it is the only alternative as long as supplies are not too far away. In this situation, however, the farmer is at the mercy of the reliability of someone else’s collection expertise. If the collector’s supply dries up, or if he ceases business, the farmer will also have to stop farming if an alternative cannot be found. It has been demonstrated above that even a small settlement can be worthwhile, providing expectations are not too high. A large-scale venture may not be able to view this situation with the same understanding, and such businesses should ensure that there are adequate and reliable stocks either on their own site or fairly close at hand. Conversely, for the small-scale or part-time farmer, picking out individual shells from a poorly settled bag may seem well worth the effort if it keeps him in a business he has a fondness for.

SUMMARY •

• •

• • • • •

It used to be assumed that the minimum economically viable settlement per collector bag was 200 shells. This has long since been revised and now small settlements are often regarded as good. It is almost essential for a farm to have its own spat supply or at least one that is within easy reach. Managing a spat resource takes time to learn, and each site will have varying settlement characteristics. Consequently it is often difficult to lay down firm rules. If buying-in, it is best to do this at the 1-year-old stage because at this time the spat will be better seasoned. Regularity of settlement can never be relied on. Even with the best systems, predators will often find their way into the stock and may account for as much as 10 per cent mortalities, or more. Deciding on an acceptable settlement number per bag will depend much on the scale of operations. There are basically three methods of sorting; fully automated, semi-automated, and hand picked.

238 •

•

• •

Scallop Farming The labour cost involved is not based just on the time it takes to sort out the catch. Bags initially have to be made-up onto droppers; these then need attaching to a longline, and the line will require regular buoying. Fully automatic graders are very efficient but, because of their reliance on a power supply, are usually sited at a shore base. Also, they do not produce uncontaminated stock. Semi-automatic grading can be carried out aboard the farm boat, but, once again, this will not produce 100 per cent target species. Hand picking, although slow, produces a stock with 100 per cent target species, and no predators. This cuts out much work at the next lantern change and also allows the stock to grow without competing for food against unwanted species.

Chapter 12 Farming Logistics

This chapter is primarily centred around examining in close detail the many variables that are the economic nuts and bolts of a scallop farm. Control, and a full understanding of the consequences of changes in the many variables are the tools a farmer will require if he is to make a profit. Although there are cost variables like price of equipment, cost of labour, cost of stock and final product price, which the farmer may have little or no control over, what this chapter will concentrate on are those that he is able to influence: stocking densities; frequency of equipment changes; equipment dimensions; mortalities; work rates; and growth periods. For the prospective farmer to be fully aware of the significance of each aspect within the list of farm variables, this chapter will also take note of other related topics that may have a bearing on what is being discussed, and demonstrate where possible their effect. Experience has shown that many would-be farmers are often unaware of the actual logistics of a farm with regard to the quantities of equipment employed and the amount of time directed at maintaining this in the water. It can be very satisfying to set some new equipment with a quantity of juvenile stock and then look forward to 12 months ahead when it is time for a change of net. Farming unfortunately is not like this. First, it would be highly unusual to grow a fixed quantity of scallops through without a follow-on stock, and second, the yearly equipment change is not the most economic approach to farming. For the purposes of best growth, fewer mortalities, less damage to equipment and superior labour utilization, the prospective farmer should look towards twice-yearly changes, and, in some situations, three equipment changes a year. When examining the tables that follow, certain headings will appear that may need some explanation. The term lanterns employed refers to the total number of lanterns used in one complete growth cycle. Where there are two changes a year it must be remembered that if all goes to plan, more equipment will be required in the second 6-month period than during the first. We will therefore be looking at a figure that reflects the depreciation, through use, of the lanterns. Lanterns handled refers to actual work input, but it should be borne in mind that included in this figure is the final emptying of the equipment at harvest. It will be seen that the figures for lanterns handled and lanterns employed can vary greatly over the same growth period. The reference to longline employed will be based on how the lanterns are spaced on the longline. All of the examples in this section use 75-metre spacings, but this may be changed where appropriate. Finally, buoyancy used refers to the 239

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number of subsurface buoys required to support each piece of equipment over the full growth period. A value of 1.2 buoys per lantern is used here, but it is obvious that much will depend on their size. This will be discussed further on. Tables 12.1 and 12.2 form the basis of the logistics scenario and show just how the farming variables affect each other, the exclusion of mortalities being only for demonstration. This gives a chance to demonstrate just how small changes in one factor may have a significant effect on another.

STOCKING DENSITIES As its name suggests, stocking densities refers to the quantity of stock per lantern. Table 12.1 The logistics surrounding changes in percentage cover (stocking densities). These figures are based on good farming practice Month

Stock

Shell size (mm)

% cover

Stock per layer

Stock per lantern

Lanterns stocked

6 12 18 24 30 36 42 48

10 000 10 000 10 000 10 000 10 000 10 000 10 000 10 000 10 000

10 30 40 55 65 75 85 95 105

4 23 33 30 29 35 32 34

60 40 33 16 11 10 7 6

720 480 396 192 132 120 84 72

14 21 25 52 76 83 119 139

Partition size Partition No Lanterns employed Lanterns handled Average % cover

400 millimetres diameter 12 265 668 27

Table 12.2 The logistics involved when undertaking two lantern changes per year for each stage of stock growth Growing time (months)

6 12 18 24 30 36 42 48

Mortality rate (%)

0 0 0 0 0 0 0 0 Lanterns Per cent mortality Lanterns employed Lanterns handled

Stock

Stock per lantern

Lanterns employed

Longline used (m)

Buoyancy used

10 000 10 000 10 000 10 000 10 000 10 000 10 000 10 000 10 000

720 480 396 192 132 120 84 72

14 21 25 52 76 83 119 139

10 16 19 39 57 63 89 104

17 25 30 63 91 100 143 167

12 partitions of 400 millimetres diameter 0 Buoyancy: number 317 265 Metres: longline use 198 668 Scallops landed 10 000

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Table 12.3 The stock logistics of differing shell sizes and differing percentage cover (stocking density) Size mm

10 25 45 60 75 85 105

% cover 5%

10%

15%

80 12 4

160 25 8 5 3

240 38 12 7 4 3

20%

25%

30%

35%

50 16 9 6 4 3

63 20 11 7 5 4

24 13 9 7 4

28 15 10 8 5

400mm partition

More specifically we will look at the quantity per actual lantern partition, which makes it easier to ascertain the percentage cover. What is actually meant by this is the area the shells will take up in relation to the overall area of the partition, one as a percentage of the other. Experience has shown that for most species of scallop it is prudent to stock sparingly during juvenile stages, and increase this as the shells become more substantial and growth increases; however, densities in excess of 33 per cent are not recommended.An exception to this may be during very slow growth periods in the winter, but only if lantern changes are fairly frequent.Table 12.3 shows the area covered by seven sizes of shell and the number per lantern partition at varying percentages. The exclusion of some figures, for instance, 20 per cent cover of 10-millimetre shells, is because this level of stocking density would not be feasible for that size of shell. By keeping stocking densities low, growth rates will improve. However, a basic cost factor has to be examined to decide whether or not a lantern or pearl net is actually earning its keep when stocked very sparingly. There are also the factors of the need for extra lanterns, the extra longline required for hanging them, and the time required physically to handle this extra equipment. Knowing the permissible maximum stocking density for each year class, a farmer can decide for himself through trial and error what his operation figure is. There is no doubt that the less densely the scallops are stocked, the fewer will be the mortalities and the quicker will be the growth rate. This is, however, dependent on good husbandry during the whole growth cycle. Assuming that all other factors are favourable, for optimum growth a scallop requires a suitable source of food. Plankton is in suspension in seawater and the scallop assimilates it along with oxygen and nutrients. It is important therefore to ensure that each shell has access to an adequate supply of plankton-rich salt water. This can be achieved by not overstocking and by ensuring the correct net size for the size of scallop being grown. Also, by keeping the nets clean the competition for food will be reduced. Table 12.4 shows the relationship between the initial stocking density and growth. It becomes quickly apparent that growth rates suffer badly when the lanterns are initially overstocked. The figures were based on the growth of Pecten maximus over a 6-month period including one summer.

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Table 12.4 The loss of growth resulting from initial overstocking. These figures were compiled over a 6-month growth cycle for the species Pecten maximus. The species Chlamys opercularis faired a little better Stocking density (%) 10 110

Growth (%)

15 100

20 91

25 83

30 76

35 70

40 65

Table 12.5 Reducing the percentage cover by 5 per cent leads to a 20 per cent increase in lantern use Month

Stock

Shell size (mm)

% cover

Stock per layer

Stock per lantern

Lanterns stocked

6 12 18 24 30 36 42 48

10 000 10 000 10 000 10 000 10 000 10 000 10 000 10 000 10 000

10 30 40 55 65 75 85 95 105

3 17 25 23 26 28 27 28

50 30 25 12 10 8 6 5

600 360 300 144 120 96 72 60

17 28 33 69 83 104 139 167

Partition size Partition No Lanterns employed Lanterns handled Average percentage cover

400 12 320 807 22

Some farmers work on the basis of an initial 30 per cent cover and change the lantern once it has reached 70 per cent. This is a fairly useful basis to work from, but the higher levels should be regarded as an absolute maximum. A final cover of 60 per cent would be more advantageous and the extra net changes involved in achieving this would be rewarded with a higher growth rate and fewer mortalities. Table 12.1 depicted an average cover of 27 per cent and at that level it could be seen how many lanterns were required for 10 000 scallops to grow through for 48 months. The farmer might consider it prudent to reduce the density by 5 per cent overall (Table 12.5), thinking that a 5 per cent increase in equipment use would be acceptable. Unfortunately it turns out that the 5 per cent decrease in cover leads to a 20 per cent increase in lanterns; something to think seriously about when farming in the millions. Conversely, the figures interact in the same way if the density is increased.The savings in equipment use can seem very tempting but the slower growth and increase in mortalities will quickly demonstrate that it was not a good move.

EQUIPMENT CHANGES The importance of a low stocking density is not only in allowing the scallops more food, but also in providing space for them to grow.Where net changes are performed annually it is often found that the final cover is greater than 100 per cent, and this

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would usually be because the initial stocking density was too high in the first place. In fact, initial stocking densities in excess of 30 per cent can, in certain circumstances, lead to a final cover in excess of 100 per cent just over one summer’s growth period, providing conditions for good growth are favourable. Based on this information, it can be seen therefore that the frequency with which net changes are undertaken requires careful scrutiny. Although growth may be temporarily stopped when the scallop is handled, this must be weighed against potential losses caused by eventual overcrowding, and a lack of food and oxygen caused by the build up of fouling on the net. The Japanese practise frequent net changes and their experience has demonstrated that growth rates are considerably higher and that equipment is not damaged by excessive fouling, thus allowing it to have a longer depreciation period. As a general rule it is policy to start with twice yearly net changes and arrive at a system that, through trial and error, proves to be economically viable. Because of particular site characteristics, it may even mean a three times a year net change.

Lantern net mesh size An adequate water flow is essential for growth and the net mesh size can affect this. In order to obtain the full benefits of low stocking densities it is therefore important to have the correct mesh size for the size of scallop being cultured. This is sometimes difficult at the spat stage because there tends to be a greater size range and the mesh must be able to retain the smallest shells. Where lanterns are constructed with a permanent outer covering, economies in production and stock level will usually limit mesh size to the three main ones of 6, 12 and 21 millimetres. By employing a removable stocking system the range of netting can be increased to incorporate sizes greater than 21 millimetres when required, and so offering even less restriction on the flow of water through the lantern.

Grading At the first lantern change it will be apparent that not all of the shells will have grown at the same rate. There will be a few that seem to have outstripped all of the others and, conversely, there will be those that have not done so well. A very few in fact may be termed runts and these will show signs of the shell thickening but not of developing like the others; for these the seabed is possibly the best destination. As for the remaining majority it would be prudent to pick out the fast growers and bring them on in separate lanterns, because it is not uncommon for these to reach market size up to 1 year ahead of the rest.

EQUIPMENT DIMENSIONS It may seem from the outset that housing as many shells as possible in one very

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Table 12.6 Differing partition sizes in relation to lantern changes and lanterns employed Partition diameter (mm)

350

400

450

500

Lantern changes Lanterns employed

404 202

323 161

258 129

210 105

10000 scallops grown over 48 months with 50 per cent mortalities Standard stocking densities with twice yearly net changes

large container would be the best way forward economically. It is not hard to imagine, however, that a lantern of 1-metre diameter, hanging down twenty or so partitions, would not be the easiest piece of equipment to deal with unless there was some kind of mechanical handling device available. Even then there are other reasons why it is better to keep the lanterns reasonably small. The lantern must not only support the stock, but should allow an adequate supple of food and oxygen, as well as being manageable. A very large partition will cause uneven growth, especially to those scallops that may settle at its centre. Sheer weight will not only be a problem for handling, but will often lead to damage in the lantern itself when taking it aboard a boat for stowage. For this reason, it is better to look towards smaller diameter partitions. Partition numbers may also pose problems in handling and therefore it is better to keep them fairly low. The standard Japanese lantern has ten 500-millimetre partitions overall; nine used for actual growing, and hangs down about 2 metres in the water. Most of our examples will be based on 12 usable 400-millimetre partitions (13 overall) but the overall depths of the lanterns are about the same as the Japanese model. Each site offers differing growing characteristics and where one lantern design may work well in one area, it may be of no use in another. Where there is a poor supply of food a small partition with larger spaces in between may be the answer; in this case the actual partition number may have to be reduced also. Table 12.6 demonstrates how a change in the partition diameter affects the number of lanterns employed.This is based on a 48-month cycle with a starting stock of 10 000 scallops, 50 per cent mortalities, twice yearly net changes, standard stocking density and 12 working partitions. It can be seen that from a 350-millimetre partition, an extra 150 millimetres will reduce the number of lantern changes by almost half; a strong incentive to work on a large scale. However, the operational figure of twelve 400-millimetre partitions was not arrived at without a good deal of experience, so the farmer should think wisely before making any rash decisions that may come back to haunt him in years to come.

MORTALITIES Much of the examples so far has ignored the question of mortalities but in reality this is a variable that could end the farmer’s business if running at 100 per cent; a

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hopefully rare event. In order to demonstrate the effect of mortalities, Tables 12.7, 12.8 and 12.9 show a 40, 50 and 60 per cent rate, respectively, and the consequent change in equipment use, using a 10 000 starting stock figure. From 40 per cent mortalities, a 10 per cent rise will cause an approximate 15 per cent fall in lanterns handled, similarly from 50 per cent mortalities. At least the reduction in stock will be outweighed by a reduction in effort. However, our example is on the basis of what may be roughly expected. Situations will often arise where, even though there was an acceptable mortality of, for instance, 50 per cent, lantern use varied greatly because the majority of the losses came at one specific period in the growth cycle. Table 12.10 shows a 50 per cent mortality with the majority occurring during the first 18 months of growth, and Table 12.11 shows the same 50 per cent but with the Table 12.7 Farm logistics scenario with 40 per cent overall mortalities occurring evenly throughout the complete growth cycle Growing time (months)

6 12 18 24 30 36 42 48

Mortality rate (%)

12 9 7 6 5 4 3 3 Lanterns Percent mortality Lanterns employed Lanterns handled

Stock

Stock per lantern

Lanterns employed

Longline used (m)

Buoyancy used

10 000 8 800 8 008 7 447 7 001 6 651 6 385 6 193 6 007

720 480 396 192 132 120 84 72

14 18 20 39 53 55 76 86

10 14 15 29 40 42 57 65

17 22 24 47 64 67 91 103

12 partitions of 400 millimetre diameter 40 Buoyancy: number 181 Metres: longline use 448 Scallops landed

217 136 6007

Table 12.8 Farm logistics scenario with 50 per cent overall mortalities occurring evenly throughout the complete growth cycle Growing time (months)

6 12 18 24 30 36 42 48

Mortality rate (%)

16 11 9 8 7 6 5 4 Lanterns Percent mortality Lanterns employed Lanterns handled

Stock

Stock per lantern

Lanterns employed

Longline used (m)

Buoyancy used

10 000 8 400 7 476 6 803 6 259 5 821 5 472 5 198 4 990

720 480 396 192 132 120 84 72

14 18 19 35 47 49 65 72

10 13 14 27 36 36 49 54

17 21 23 43 57 58 78 87

12 partitions of 400 millimetre diameter 50 Buoyancy: number 159 Metres: longline use 391 Scallops landed

191 120 4990

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Table 12.9 Farm logistics scenario with 60 per cent overall mortalities occurring evenly throughout the complete growth cycle Growing time (months)

6 12 18 24 30 36 42 48

Mortality rate (%)

19 15 12 10 9 8 7 6 Lanterns Percent mortality Lanterns employed Lanterns handled

Stock

Stock per lantern

Lanterns employed

Longline used (m)

Buoyancy used

10 000 8 100 6 885 6 059 5 453 4 962 4 565 4 246 3 991

720 480 396 192 132 120 84 72

14 17 17 32 41 41 54 59

10 13 13 24 31 31 41 44

17 20 21 38 50 50 65 71

12 partitions of 400 millimetre diameter 60 Buoyancy: number 138 Metres: longline use 335 Scallops landed

165 103 3991

Table 12.10 Farm logistics scenario with a 50 per cent mortalities occurring during the first 18 months of the cycle Growing time (months)

6 12 18 24 30 36 42 48

Mortality rate (%)

25 15 11 5 3 2 1 1 Lanterns Percent mortality Lanterns employed Lanterns handled

Stock

Stock per lantern

Lanterns employed

Longline used (m)

Buoyancy used

10 000 7 500 6 375 5 674 5 390 5 228 5 124 5 073 5 022

720 480 396 192 132 120 84 72

14 16 16 30 41 44 61 70

10 12 12 22 31 33 46 53

17 19 19 35 49 52 73 85

12 partitions of 400 millimetre diameter 50 Buoyancy: number 146 Metres: longline use 361 Scallops landed

175 109 5022

emphasis of losses in the latter growth stages, the result being a nearly 25 per cent increase in lanterns used and handled. An unfortunate situation.

Overstocking There are usually good reasons for high mortalities. Overstocking is a prime cause of excess losses, but it may also be a combination of factors. When scallops are unnecessarily disturbed they will often swim about of their own accord, seeking a more suitable place to settle.This is very apparent at the juvenile stages.With several doing this in a confined space there is a danger of them locking together (Fig. 12.1). However, food and oxygen starvation may also cause them to seek a more suitable

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Table 12.11 Farm logistics scenario with a 50 per cent mortality occurring during the final 18 months of the cycle Growing time (months)

Mortality rate (%)

6 12 18 24 30 36 42 48

9 7 6 8 9 7 9 11 Lanterns Percent mortality Lanterns employed Lanterns handled

Stock

Stock per lantern

Lanterns employed

Longline used (m)

Buoyancy used

10 000 9 100 8 463 7 955 7 319 6 660 6 194 5 636 5 016

720 480 396 192 132 120 84 72

14 19 21 41 55 56 74 78

10 14 16 31 42 42 55 59

17 23 26 50 67 67 88 94

12 partitions of 400 millimetre diameter 50 Buoyancy: number 179 Metres: longline use 437 Scallops landed

215 134 5016

Fig. 12.1 Scallop shells locked together.

spot, resulting in the same problem. A typical instance can be seen where spat have been overstocked in a tray with a small mesh size. In an effort to obtain a more suitable supply of water, the spat will be found crowding around the edges, often dead from locking.

Tidal movement Although excessive handling may cause mortalities, so can the attitude of the lanterns on the longline. A relatively small tide flow can cause a lantern to lie at an unsuitable angle, causing the scallops to fall to one side in a heap. This in fact causes greater mortalities than those caused by motion being transmitted to the longline via the surface buoys. Once again, a high stocking density will aggravate the condition.

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Exposure to freshwater is also a problem and this may even affect lanterns in deep water if there has been high rainfall during a period of large tides. It can be a particular problem with raft culture where the lanterns may be hung at shallower depths.

Predators Apart from actual disease, of which there are few known, there are other factors that cause mortalities amongst the stock. Predators growing alongside the scallops, especially at spat stage, can cause devastation if left unattended. Starfish settling inside the nets will quickly grow and eventually feed on the stock itself; this is especially problematic when the lantern changes are only carried out yearly. The same problem occurs with mussels, whose byssus thread, although not causing the devastation it is capable of at the spat stage, will continue to bring about mortalities even in larger stock. Where there is an abundance of marine growth a problem can arise where barnacles growing on the shells will eventually move around the edges and actually into the inside, thus causing them to remain slightly ajar. This renders them even more prone to predators within the net. The worm Polydora is present in many areas and this has a habit, once settled, of boring into the shell. As a defence, the scallop will create a thin shell over the point of entry – having the appearance of a black blister. This takes up a good deal of the scallop’s energy resource and thus often renders it unmarketable. However, it should be mentioned that this worm is not usually the result of overstocking or of infrequent lantern changes. When stock is left unattended in a lantern for periods up to 12 months, it is often found that a proportion have become stuck to the actual net itself. This will usually happen with those species that are not so mobile, and who, in the wild, will recess into the seabed. A species of jelly-like substance will grow around the shell and the net at the same time, therefore holding one to the other. At lantern change this can become a real problem because each one will have to be separated individually. Many are missed because of this and a small proportion will also be rendered unmarketable when the top shell comes away from the bottom during the effort of separation. The lanterns themselves can also be damaged during this process.

Cleanliness It is good husbandry to adopt the habit of keeping equipment clean from the start. Where lanterns have been unattended for periods of up to 12 months, the amount of fouling on them can be excessive.This will require cleaning off and the best equipment for this is a high pressure washer. Although it will do a good job, it may also damage the net so it should be used as little as possible. On the other hand, those nets that have only been in the water for up to 6 months will often remain fairly clean and not require pressure washing. In this case it is often enough to leave them to dry thoroughly in the sun and then to shake them out before immersing

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them in a bath of detergent and disinfectant. Let them drain off for a few hours and then give them a final wash in freshwater before reuse. The heavily fouled nets should also receive the same treatment after being pressure washed. Mortality levels may vary but they are usually inversely related to the amount of time and care directed towards stock husbandry. There may of course be other factors but these are usually peculiar to individual sites. Actual mortalities may vary from 30 per cent to total loss, and as such it is prudent to base budget forecasts on the higher levels. The bonus will come when the figures show a higher survival rate than predicted.

WORK RATES Any self-employed person will tell you that they can work far more efficiently than the people they may employ. This is usually simply because they are self-motivated and have more interest in the success of the task in hand. Consequently care should be taken when laying down firm rules as to what a man may complete in a day because rarely will ideal conditions prevail, and there is usually much more involved than the task in hand. Farmers need some guidelines as to what to expect from either themselves or their workforce. Table 12.12 outlines some work rates with regard to lanterns handled per day and longline buoyed per day, in relation to total man days, to culture 10 000 scallops with 50 per cent mortalities. It should be remembered that this is a direct labour cost and that there will be many other chores that will need to be undertaken by either the farmer or his labour force. In the example, high handling rates have been linked with high longline buoying. This is only for convenience and to give a rough guide. In fact, a low lantern handTable 12.12 Using the farm logistics scenario, these figures give total manpower days at differing work rates Man days Lanterns handled per day Longline buoyed per day Lanterns handled per day Longline buoyed per day Lanterns handled per day Longline buoyed per day Lanterns handled per day Longline buoyed per day Lanterns handled per day Longline buoyed per day Lanterns handled per day Longline buoyed per day

10 300 m 20 400 m 30 500 m 40 600 m 50 700 m 60 800 m

10000 scallops with 50% mortality. Frequency of buoying: 24 Lanterns: 12 partitions of 400 mm dia Regular stocking

42 23 17 13 11 10

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ling rate may be caused, as it most often is, by the nets being badly fouled. Excess fouling, apart from causing damage to the equipment, can have a huge effect on just what can be handled in a day, often causing strain on those involved in the process. Another factor that may reduce work rate is the weather. It is very difficult to work when the farm boat is rolling about, and as the most productive work is undertaken from the deck of the vessel when on station on the longline, having to transport equipment ashore to be serviced, and then back out again later, is an added pressure on the time resource. Table 12.12 shows that at the lower work rates four times longer will be spent at lantern changes than at the higher rates. The figure of 60 per day may seem high, but in fact if everything is set up properly it can even be bettered. With a well laid out boat, fine weather and lanterns that are manageable and not badly fouled, there is no reason why up to 80 lanterns a day cannot be a target. This would greatly reduce the man days incurred for the overall culture period. Similarly, the same efficiencies may be applied to line buoying, bearing in mind that if only implementing 12-month lantern changes, many of the buoys being attached to the line will, later in the year, only be supporting marine fouling, not scallop growth; some of the original buoys may in fact become almost redundant by the end of the year because of the weight of weed growing from them.

GROWTH PERIODS Table 12.13 is a recap of the culture scenario and demonstrates the reality of a 48month suspended culture growth cycle. It can be seen that the greatest efforts are not exactly well rewarded, and it would be an even bleaker picture if the mortality rate exceeded 50 per cent. It is for this reason that growth periods of up to 48 months in suspended captivity are not the norm unless the final market price is well above the average. It should also be noted that species like Pecten maximus will only just be at a marketable size after 4 years even though their meat yield may be 15–20 per Table 12.13 A recap of the farm scenario demonstrating the logistics involved with each 6-month period of growth Period (months) 6 12 18 24 30 36 42 48

Mortality rate (%)

Stock

Lanterns used

Lanterns handled

Longline used (m)

15 11 9 8 7 6 5 4

8500 7565 6884 6333 5890 5537 5260 5049

18 19 36 48 49 66 73

36 38 72 96 98 132 146

10 13 14 27 36 37 49

With a starting stock of 100 000 scallops and an overall mortality of 50 per cent Standard stocking density: 12 400 millimetre partitions.

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cent higher than those found in the wild of the same age. For the best price it is usual to sell at 5+ years, but this length of time in suspended culture is not practical. So, if the farmer is looking towards this market, to gain the extra growth he must use bottom culture for the final stages. However, if this is not the path the prospective farmer wishes to venture down, there are other species that will attain a marketable size in a much shorter time and for which he will also receive a fairly good price. Close examination of Table 12.13 shows that the effort directed at cultivating a species for an 18-month period is far less than in the same scenario for 36 months. At 42 months (the time at which equipment is deployed to produce a marketable crop 6 months later) the logistics surrounding equipment deployment become daunting. The farmer will have had to handle 146 lanterns to produce just over 5000 scallops that will only attract the minimum market price. If a species could be farmed that would attain market size in 18–24 months and still attract a reasonable price, the savings in manpower and equipment use would be enormous. Based on the scenario in Table 12.13 the yield would be nearly 6500 scallops with only 96 lanterns having been handled for a period such as this.

PRODUCTION REFERENCE Before moving onto the next chapter which will examine in more detail the actual business side of the farm it will be useful to leave this section with a reference of just what is directly required in the form of lanterns and longline space for various levels of production and various sizes of scallop (referred to as number of shells per lantern). Tables 12.14 and 12.15 demonstrate production levels ranging from 20 000 to 100 000 shells, and shells per lantern ranging from 50 to 1000. They aptly demonstrate just what equipment level is required for each year class.

SUMMARY •

• •

•

The nuts and bolts of farming relate to the variables over which the farmer has some control and these are: stocking densities, equipment changes, equipment dimensions, mortalities, work rates and growth periods. Any variation in any of these will affect overall handling and production. From the start, prospective farmers often have little idea as to just what is involved with regard to equipment logistics. When referring to stocking densities it means the number of scallops per lantern partition. This is further refined by relating to percentage cover, where the area of the shells is directly related to the area of the partition. It is rare to let this rise above 30 per cent, and the lower the density, the higher will be the growth and the fewer the mortalities. The maximum they should grow into is 70 per cent. Although a lower stocking density is good for growth, it can greatly increase the number of lanterns employed and handled, a 5 per cent reduction causing a 20 per cent increase in gear use.

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Table 12.14 Logistics reference table outlining total lanterns employed with varying production and stocking levels Shells per lantern 1000 950 900 850 800 750 700 650 600 550 500 450 400 350 300 250 200 150 100 50

20 000

30 000

40 000

20 21 22 24 25 27 29 31 33 36 40 44 50 57 67 80 100 133 200 400

30 32 33 35 38 40 43 46 50 55 60 67 75 86 100 120 150 200 300 600

40 42 44 47 50 53 57 62 67 73 80 89 100 114 133 160 200 267 400 800

Total scallop production 50 000 60 000 70 000 Total lanterns employed 50 53 56 59 63 67 71 77 83 91 100 111 125 143 167 200 250 333 500 1000

60 63 67 71 75 80 86 92 100 109 120 133 150 171 200 240 300 400 600 1200

70 74 78 82 88 93 100 108 117 127 140 156 175 200 233 280 350 467 700 1400

80 000

90 000

100 000

80 84 89 94 100 107 114 123 133 145 160 178 200 229 267 320 400 533 800 1600

90 95 100 106 113 120 129 138 150 164 180 200 225 257 300 360 450 600 900 1800

100 105 111 118 125 133 143 154 167 182 200 222 250 286 333 400 500 667 1000 2000

Table 12.15 Logistics reference table outlining total longline employed with varying production and stocking levels Shells per lantern 1000 950 900 850 800 750 700 650 600 550 500 450 400 350 300 250 200 150 100 50

20 000

30 000

40 000

15 16 17 18 19 20 21 23 25 27 30 33 38 43 50 60 75 100 150 300

23 24 25 26 28 30 32 35 38 41 45 50 56 64 75 90 113 150 225 450

30 32 33 35 38 40 43 46 50 55 60 67 75 86 100 120 150 200 300 600

Total scallop production 50 000 60 000 70 000 Total longline employed 38 39 42 44 47 50 54 58 63 68 75 83 94 107 125 150 188 250 375 750

45 47 50 53 56 60 64 69 75 82 90 100 113 129 150 180 225 300 450 900

53 55 58 62 66 70 75 81 88 95 105 117 131 150 175 210 263 350 525 1050

80 000

90 000

100 000

60 63 67 71 75 80 86 92 100 109 120 133 150 171 200 240 300 400 600 1200

68 71 75 79 84 90 96 104 113 123 135 150 169 193 225 270 338 450 675 1350

75 79 83 88 94 100 107 115 125 136 150 167 188 214 250 300 375 500 750 1500

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The lanterns will require an appropriate mesh size at different times in the growth cycle. • There will be fast growers among the stock and these may be selected and brought on separately. It may mean a 25 per cent reduction in the time to reach market size. • Lanterns with large dimensions can be difficult to handle, cause some stock to slow their growth, and can lead to actual net damage caused by their sheer weight. It is best therefore to use lanterns that are fairly easily handled. • Mortalities can often be reduced if the cause is discovered. Some of the main causes are: overstocking, infrequent lantern changes, predation, lying badly on the line and poor handling on deck. • The amount of equipment deployed may vary greatly depending on where the greatest number of mortalities falls during the growth cycle; for instance, mainly at the start or at the finish. • Cleanliness is most important, and all equipment should be washed and disinfected before reuse. • From the start, the farmer should budget on more than average levels of mortality. If they come in lower at the end then this will be a nice bonus. • When looking at work rates, remember that self-employed people are usually more self-motivated and thus work a little harder for themselves. Do not expect others to always work as hard as yourself. • Excess fouling causes a great reduction in equipment handling, higher mortalities, slower growth, and, often, physical damage to the gear involved. • Long growth periods are not the norm. After 4 years Pecten maximus will only just have reached marketable size even though its meat yield may be as much as 20 per cent greater than a wild scallop of the same age. • The best market price for Pecten maximus will not usually be achieved until year five. This length of time in suspended culture is not really possible. • There are other species that will attain marketable size in well under 4 years, sometimes within as little as 18 months.

Chapter 13 The Business of Farming

So far we have some basic materials for starting our farm; a rough idea of the law surrounding our venture, the biology and habits of our target species, a means of collecting it in the wild (where appropriate), a good idea of how to set up the farm, and a working knowledge of those variables that will have a direct bearing on our efforts. We need now to put all of this into a situation that is as near to reality as possible. The logistics outlined to date have roughly shown what is required in the way of lanterns, longlines and buoyancy, and this chapter will further illustrate this, but hopefully offer more realistic scenarios. Unfortunately, because growing parameters will vary greatly between sites and species, we can only offer figures as a means of getting a feel for the job, and how we may go about improving matters. The last chapter ended by suggesting that a 48-month growing period would be the exception and not the rule so in this section it will only be referred to as a means of contrast to the scenario in question. It may be that a particular circumstance would benefit from such a long culture period so it should not be ruled out. However, if it can be avoided, then it should be.

EFFICIENCIES On an efficiently run scallop farm all equipment and resources should be utilized in the most economic way. Expensive culture equipment will earn nothing if not stocked and in the water. Similarly, it is poor economics to pay rent on longlines and rafts that are not used as well as they could be. Proper planning is therefore important, and decisions will need to be made early regarding total production levels and diversification, when appropriate; for example, there may be instances where a farmer may have spare hanging space, and it may be prudent to lease this to a neighbouring farmer or to someone waiting for a site but wanting to build up some stock in preparation for this. It is not easy to predetermine exactly how a farm will fare because of the difficulties in predicting such things as spat settlement, mortalities and growth rates. However, no venture should be undertaken without some sort of basic plan, and it should be remembered that if there are already farms nearby, much valuable infor254

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mation may be gained from them, providing they are willing to part with it. Unfortunately, not only do geographical areas vary in their growing parameters, but often also so do sites fairly close to each other. Any working model will therefore have to be based on figures that may seem a little harsh; for example, higher than normal mortalities, slower growth rates, etc. One factor becomes apparent from the start: the farm may be built up over a period of years if necessary, therefore making capital outlay a gradual process. Longlines may be set when required, and culture equipment can be purchased when needed. This also gives a reasonable period of time over which the construction of a shore base and other useful facilities, necessary for an efficient farm, may be spread. As mentioned in the previous chapter, growth to marketable size varies between species and according to the conditions under which they are cultured. For some it may be as little as 18 months, while others can take up to 5 years. Pecten maximus, for instance, is a slow-growing scallop, especially in temperate regions, but growth may be speeded up by selective culturing. The fast growers are selected at every stage (by size) and brought on in lanterns of mesh size normally too large for that age of scallop. This facilitates extra feeding, and if their stocking density is kept low they should reach a minimum marketable size in a little over 3 years. This procedure will work for all other species, but for those with a low market value it is often not thought profitable to take the trouble of continually grading them. At this stage it may seem that a farm set up in cold temperate waters would be at a distinct disadvantage over others in warmer climates, with a consequently faster growth rate. This is true to some extent, but the final product from slow-grown shellfish in these colder waters is often regarded as superior to all others. Today’s shellfish market is a live market and chefs are most discerning when it comes to quality. It seems that, in their opinion, a scallop slowly grown in cold, plankton-rich, temperate waters is worth paying that little extra for, and as such these are usually in great demand. It must also be borne in mind that until scallop farming started, the market was at the mercy of the weather and consequently could not rely on regular landings. The situation has now been reversed and a farmer can almost guarantee a supply to a customer. This, chefs have found, is also worth a little extra on the final price.

LONGLINES AND BUOYANCY The logistics of setting longlines and the methods of working them have already been discussed but, as will now be explained, the numbers required for even a small farm are quite daunting. Some farms opt for 200-metre lines but these, when fully loaded, require a very robust anchoring system. Also, if they drag or break the ensuing tangle can take days to unravel. Possibly the best approach is to look at something a little shorter, so a new farmer should maybe start with 100-metre lines to gain some experience with a little less pain. Certainly in the grid systems he would be ill-advised to exceed 100 metres.

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Spacing Obviously if lanterns are packed as close together as possible along the line, more stock can be put on it. Unfortunately, hanging too close can lead to competition for food and sometimes chafing damage caused by the lanterns actually rubbing together. Having lanterns too well spaced out, on the other hand, may mean having to set more lines; a problem if the lease only allows for a fixed number or when one extra puts you in a new cost category of lease payment. The spacing of 0.75 metre for a 400-millimetre diameter lantern is the standard for all of the illustrations in this book, and has been found to be fairly easy to work with. The final decision, however, belongs to the farmer himself.

Buoyancy Although the large surface buoys take up some of the weight, the main support is provided by smaller subsurface buoys tied directly onto the lines. These are hard in structure and offer the same buoyancy, no matter what the depth. They can vary in size greatly but the most convenient is around 200 millimetres in diameter. Table 13.1 gives examples of buoys with diameters ranging from 100 to 300 millimetres, and their associated buoyancy capabilities. It can quickly be seen that a small increase in diameter leads to a very large increase in buoyancy. From this it may seem that it would be economically more beneficial to attach one buoy of 300millimetre diameter as opposed to three 200-millimetre buoys. One of the reasons why this is not often the practice is that the smaller ones offer more control of the line, helping to keep it lying level along its length.

Frequency of buoying At certain times in the year, scallop growth will be seen to accelerate; unfortunately this coincides with an increase in marine fouling. It may therefore be necessary during these periods to add buoyancy to the lines on a weekly basis to prevent the whole setup from sinking. It is good policy to keep the lines as buoyant as possible at all times, only using the surface buoys for back-up and marking. If too much weight comes onto the surface buoys and one or two break free, the line can very quickly sink to the seabed.

Table 13.1 Buoy sizes and their approximate lifting capacity Size (inches) 4 6 8 10 12

Size (mm) 100 150 200 250 300

Lift (kg) 0.5 1.8 4.3 8.4 14.5

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Once growth has slowed down or even ceased for a period, line visits can also be reduced. However, as a basis for calculating labour requirements, and to emphasize that regular line visits are all part of good husbandry, we shall base our line buoying on 24 visits each year, with all of the stocked lines having extra buoyancy added. If it is discovered that fewer visits are required, then this will be reflected in the direct labour cost of the farm. However, for the benefit of all of our illustrations we will assume a visit approximately every 2 weeks.

Weights of culture equipment The farmer should know what a piece of culture equipment weighs both in and out of the water. Because there will be a wide variety of equipment, either handmade or manufactured, the weights will vary. Obviously the weights will vary depending on the stage of growth but the following is a rough guide, based on two totally different items of culture equipment stocked with 10 kilograms of 75-millimetre Pecten maximus. (1)

(2)

Japanese lantern weight out of the water 14 kilograms weight in the water 5.5 kilograms Plastic trays weight out of the water 17 kilograms weight in the water 4 kilograms.

This is a perfect situation and the lanterns and stock have no fouling to add to the weight. However, in 6–9 months they will be quite heavily fouled and each unit could weigh in excess of 25 kilograms out of the water. Their weight in the water will depend on the type of fouling. If this is only weed, then it would be approximately 1 kilogram more, but if mussels and/or barnacles are attached then this could add in excess of 3 kilograms.

PRODUCTION LEVELS AND CULTURE PERIODS As a reminder of just what is involved in long cultivation periods, Table 13.2 illustrates the equipment requirement at 6-month intervals, starting with a stock of 200 000 scallops and applying the overall 50 per cent mortality. If cultivation were to stop after 18 months, before going on to seabed culture for instance, there would be a final stock of 138 000 scallops and 1396 lanterns would have been handled. Compare this to the remaining 101 000 scallops after 48 months’ culture which require 7913 lanterns to be handled. The first illusion to be overcome therefore is that a long growth cycle is both acceptable and profitable. It is rare now to see farms practising much beyond a 30month culture period: first because the longer they are held in captivity the higher

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Table 13.2 The equipment requirement at 6 month intervals, with a starting stock of 200 000 scallops Time (months) 12 18 24 30 36 42 48

Overall mortality (%) 24 31 37 41 45 47 50

Lanterns used

Lanterns handled

Final stock

316 507 866 1345 1836 2495 3226

986 1396 2448 3650 4654 6309 7913

151 000 138 000 127 000 118 000 111 000 105 000 101 000

Starting stock: 200 000 scallops 12 400 mm partitions

will be the overall mortality; second because of the shear logistics; and third because, even after 4 years, some species will still only be at minimum market size and therefore at a minimum price. It is necessary therefore to exploit other alternatives. So just what size of farm is needed? So far we have seen that the quantities of equipment required to run even a small-scale operation are very high; this chapter will further illustrate that. For convenience the operation may be broken down into four categories. First, a setup of less than 10 000 scallops should be regarded as a test, or a supplementary income for someone like a fisherman. Next in line would be a farm where the total output would be around the 100 000 mark, and this we would look on as small scale. A medium-scale farm would be hoping for a 1 000 000 survival figure, and a large-scale setup would be in the tens or even hundreds of millions; much depends on the species being cultivated. To break this down further, if there is an overall mortality of 37 per cent (the figure used so far at the 24 month level in most of the examples given here), to achieve a final production of approximately 10 000 scallops over 24 months it would have been necessary to have started with 16 000 shells. This would require handling around 180 lanterns and applying six direct man days, providing there is a handling rate of 40 lanterns per day and a buoying rate of 1000 metres of line per day. To sell 100 000 scallop, it would be necessary to round the last figures up by ten, and for 1 000 000, by one hundred. For a large-scale setup of, say, 5 000 000 saleable scallops, over 60 000 lanterns would need to be handled, involving the application of nearly 2000 direct man days. In order to gain a more detailed view of just what is involved, Table 13.3 illustrates five levels of production within the 1 000 000 starting stock over a 24-month growth period with the same mortality and work rates as before. If we were to take this scenario once more and streamline it by reducing the overall mortalities to 15 per cent and increasing the work rate to 60 lanterns handled each day, and 1500 metres of longline buoyed each day, the final returns would seem even healthier. At the 1 000 000 starting stock level, although more than an additional 2000 lanterns would have been handled, the final stock would have increased by more than 200 000 scallops; all this, and a reduction in direct manpower of 80 days (Table 13.4).

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Table 13.3 A 24-month growth period with a 37 per cent mortality rate and standard farm work rates Starting stock

Lanterns employed

Lanterns handled

Longline used

Buoyancy added

Man days

Final stock

200 000 400 000 600 000 800 000 1 000 000

866 1731 2597 3462 4328

2 448 4 896 7 345 9 793 12 241

649 1298 1948 2597 3246

1039 2077 3116 4155 5193

77 154 230 307 384

127 000 253 000 380 000 507 000 633 000

Showing logistics over a 24-month growth period. Mortality rate 37 per cent. Lanterns: 12 of 400 millimetre partitions. Spaced every 0.75 metres Work rate: 40 lanterns handled per day. 1000 metres longline buoyed per day. Longline buoyed every two weeks. 1.2 buoys per lantern.

Table 13.4 This is based on Table 13.3, but with reduced mortality and improved gear handling rates Starting stock

Lanterns employed

Lanterns handled

Longline used

Buoyancy added

Man days

Final stock

200 000 400 000 600 000 800 000 1 000 000

1011 2023 3034 4046 5057

2 925 5 850 8 775 11 700 14 625

759 1517 2276 3034 3793

1214 2427 3641 4855 6068

61 122 183 244 304

170 000 340 000 509 000 697 000 849 000

Showing logistics over a 24-month growth period. Mortality rate 15 per cent. Lanterns: 12 of 400 millimetre partitions. Spaced every 0.75 metres Work rate: 60 lanterns handled per day. 1500 metres longline buoyed per day. Longline buoyed every two weeks. 1.2 buoys per lantern.

Choosing the correct species When we examined the varying characteristics between species of scallops it became apparent that the main differences centred around growth periods, size at end of growth and whether they were able to be wild ranched (seabed culture). Generally speaking, the larger species, which take longer to grow, usually adapt well to seabed culture providing their development is at a level that enables them to withstand the onslaught of predators like crabs, etc. A few of the main species within this category are: Pecten maximus (king scallops), P. jacobaeus and P. yessoensis. Those faster growing species, most of which are very mobile and as such will not remain in one spot on the seabed, are usually also more easily farmed and less likely to die in captivity. Good examples of these are: Chlamys opercularis (queen scallops), C. hastate and C. rubida. As market factors change, so some species, which at one time seemed quite uneconomical to cultivate, become quite an attractive proposition. The live market has given almost everything in the sea a value and as such many new species are now being exploited.

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Buying in at any stage Not all sites will have a reliable supply of scallop spat so there may be a need to buy in. If purchased straight from the collector bag, this will not reduce the total growth period for the farmer and he will have to suffer the usual fairly high mortalities accompanying stock at this delicate stage in their development. A more acceptable situation is to buy-in at a later stage in growth, possibly at 1 year, when, providing they have been transported in the correct manner, mortalities should be far lower.

SALES Usually the farm will be based on one type of scallop or another, and the scenarios featured in this book are largely centred around king scallops (like Pecten maximus) or queen scallops (like Chlamys opercularis). Whereas the queens may be grown through in less than 2 years, the kings may take up to 5 years: 2 years in lanterns and 3 years on the seabed. Table 13.3 can be used as a rough guide to what is involved over a 24-month growth period for farms with a starting stock ranging from 200 000 to 1 000 000 for both species of scallop. Figures may vary slightly, but it gives a good idea of what can be expected. Once again, Table 13.4 further refines the situation by demonstrating the effect of culture and work improvements.

Selling at any stage Not only is it sometimes possible to buy in at any stage, but it is also possible to sell at any stage if so desired. The advantages to this are great, especially to a farm just starting out, as it brings in much needed revenue. However, this will be greatly dependent on the farm being self-sufficient in scallop spat. If there is a surplus of stock directly out of the collector bags, then this can be sold on. On the other hand, by far the best way to proceed is to bring them on for either 6 months or 1 year and then sell them; the extra revenue gained being well worth the effort, even accepting that some initial fairly high mortalities may have been incurred.

Meat yields So just what can be expected from the stock once they have reached a suitable market size? First, with kings the best prices will be paid for those attaining a size across the shell in excess of 115 millimetres and weight-wise approximately 4 and 5 to the kilo. Meat yield will depend on the time of year because a full roe can add significantly to the total weight; sometimes as much as 40 per cent more. In their prime the farmer may expect 14 meats to the kilo, and at poor times around 18. As a rough guide, an average conversion rate (weight of meat compared to total shell weight) of between 20 and 22 per cent can be expected.

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Queens, on the other hand, will market at around a size of 65 millimetres across the shell and these should come in at about 20 to the kilo. With regard to meat yield the same rules apply and in their prime the farmer may expect 35 meats to the kilo. An average conversion rate for this species would be between 19 and 21 per cent.

EQUIPMENT LEVELS Thus far we have only examined the logistics directly involved with production with regard to lanterns. Unfortunately the farm cannot operate on exact numbers because they can never be sure of what will and will not survive. Therefore it is not just the estimated stock that will determine what quantity of gear is held; the following points should also be considered. (1) (2) (3)

Three mesh sizes will usually be required for differing levels of growth and this means that at some times there will necessarily have to be a surplus. If all the lanterns are tied up, what is left to change into? Washing used ones takes a bit of time, so there has to be a supply to accommodate this. Lanterns get damaged so a certain number will need to be ashore at any one time. This will further add to the requirement.

So just what equipment level should the farmer carry in order to meet every eventuality, bearing in mind the cost of each item? This will depend very much on the efficiency of the farm itself and where an efficient setup may manage with a 15 per cent surplus, an inefficient farm may need to carry as much as 25 per cent above what was forecast. If there is a supplier at hand who is willing to supply a small number at a time, then this may be a way of overcoming the problem; unfortunately it is usual to buy in bulk to help keep the individual costs as low as possible. A further way of lessening the costs is to have an equipment pool, but this will only be possible when there are a few farms within reasonable contact of each other. Much money could be tied up doing nothing unless equipment surpluses are carefully planned, and the most prudent operator will often find he has misjudged exactly what is required.

MANPOWER REQUIREMENT So far we have only examined that aspect of manpower which is directly involved with production, lantern changes and line buoying, and we have shown how efficiencies at this stage have a marked effect on productivity. It is not surprising then that some of the examples we have looked at seem to require little effort. Although some of the indirect activities have already been touched on, it is worthwhile at this stage therefore to expand a little on them.

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Transporting equipment Lanterns and buoys do not get to the work site by themselves, but have to be transported, and being as bulky as they are, this can often take up a lot of time. Used lanterns are especially problematical because of the added weight through fouling, and in cases where the farm boat is small there may have to be several journeys back to the shore base during the day to keep the decks clear.

Repair and maintenance There are many other parts of a scallop farm that require both maintenance and repair apart from lanterns. Other aspects of the farm that may occupy man-days are: moorings; the farm boat; ancillary equipment; shore vehicles; lantern construction; and the shore base itself.

Net cleaning We have already discussed what is involved in cleaning used equipment and this has given a good idea of the logistics involved. Much can be saved by having a sea platform like a raft, sited close to the lines, from which to carry this out. Unfortunately this is not always possible and those who have to transport everything ashore find this an added cost burden.

General supplies The farm boat will require fuel and oil, as will much of the powered ancillary equipment. There will also be many other bits and pieces to be bought, which are an integral part of a successfully run farm, and all of this will require someone to both secure it and see that it gets to its destination on time.

Travelling Time spent travelling is an important part of our man-power requirement and it is often overlooked when costings are carried out. If the longline site is a long way from the shore base, then many man hours could be lost in travelling. Add to this the problem of hold-ups with bad weather and it can be quickly seen that overall the manpower requirement needs to be examined very closely. Unfortunately as no two farms are the same, and no two farmers have the same priorities, there is no blueprint for manpower utilization.

EXAMINING COSTS However we may try to avoid the business side of the farm there is little doubt that there is an advantage in understanding the bare essentials of both economics and

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costing. They are not difficult subjects and at the end of the day a working knowledge may prevent money being poured into something that is not going to be viable. So at this point there will be a brief examination of some of the basics in this field, in the hope that it will prompt the farmer to expand his knowledge of the topics in his own time. Some farmers will be administration oriented, while others may prefer to be more hands on. The bias towards one situation or another will have a general influence on both capital expenditure and overall running costs. Generally speaking, those farmers who are production oriented will tend to spend less on the control side of the job than someone whose speciality is in administration.

Opportunity cost Is the farmer putting his money and efforts into something that is worthwhile? When an economist or an accountant carries out an analysis of a prospective business, he takes into consideration what are known as opportunity costs. These may best be described as the benefits foregone by the decision maker in choosing one, from several courses of action. It may be that investing in a corner shop, for instance, would bring in a greater return on capital than running a scallop farm. It should be pointed out at this stage, however, that both some accountants and some economists can be notoriously insensitive when it comes to making decisions on ways of life, tending only to be moved by the money aspect of things. Most small-scale and medium-scale farmers are self-motivated and regard their activities as a vocation rather than a straight business opportunity. Although they will have to look towards making a profit, their main concern is to be involved in an activity that they enjoy doing and consequently improves their way of life. Large-scale farms, on the other hand, involving a number of shareholders or even floated on the stock exchange, will have to take note of opportunity costs because there are few who would be prepared to invest substantial amounts of money into projects that may seem to give a poor yield, irrespective of the quality of life they may give rise to.

Capital outlay The prospective farmer will have to pay money out from the start, but, unlike many ventures, this may be spread over the growth period of the initial starting stock. The level of capital employed will depend on what the farmer thinks he needs to run his business. Culture equipment, including collection equipment, longlines, rafts, lanterns and buoyancy, are necessary to the farm and will therefore be a fixed outlay running head to head with stock taken on and stock growth. The farm boat can be cheap in proportion to gross outlay or very expensive, according to what is required and the amount of capital available to purchase it. However, there will be a limit to what is spent on this because it is not a good policy to deploy something large and heavy alongside a longline. It will therefore have a maximum size and as such should fall within a fixed price range.

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The shore base, including farm transport, plant and machinery, office equipment and stores, will vary according to the level of production. This may range from a shed on a raft – or even the boat’s wheelhouse – with a car and trailer on the shore site, to a purpose built store and office complex with company vehicles and workshop facilities. Because scallop farming may involve a significant capital outlay, the Sea Fish Industry Authority in the UK proposed that it would be good for fishermen to take it up if time allowed. This was good policy because not only did they have the skills involved with working on the sea, they also had much of the initial equipment required to run a farm, not least, the farm boat.

Fixed costs There will be certain costs that will have to be met no matter how the farm runs, and their level will depend on the scale of operations and the farmer’s awareness of administration constraints. Rent, rates, leases and insurance are usually regarded as fixed costs, but on a larger scale, salaries and general administration may also be included. If we refer to the optimum factor combination where all resources are working at their most efficient, there will be a fixed cost in relation to each level of this; for instance, as the farmer increases production, he will find that until he finally settles down at the new level, some resources might be wasted, so his fixed cost may also not be quite so economically efficient for, what is hoped, a short period of time.

Variable costs These costs, as their name suggests, will vary with the level of production and output and can give a good indication of overall efficiency. The main variable costs on the farm will be hanging space, culture equipment, buoyancy, labour costs, repairs and renewals, fuel and electricity, protective clothing, post and packing, telephone, transport, landing dues, bank interest and marketing.

Cash flow Most scallop businesses will face a cash flow problem and this is a common cause of failure even though on paper they may seem quite viable. Put simply, cash flow is that money that is immediately available to pay bills, etc. Although the stock may be worth a sum that far exceeds the farm’s liabilities, it is of little use if it cannot be turned into cash when required.

Depreciation Any equipment used at sea will be especially subject to depreciation because of the corrosive effects of salt water. Culture equipment will also suffer but the level will depend much on how it is treated (regularity of lantern changes, etc.). In some

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situations a farmer may obtain 20 years use out of a piece of equipment, and in others as little as 1 year. This is calculated as depreciation.

PRODUCTION ALTERNATIVES As we discussed earlier, there are quite a number of ways to approach farming but, as always, the golden rule is that much will depend on the characteristics of the site. The combinations of varying types of equipment hung on differing suspension mediums will, in fact, often lead to no one farm being the same as another. Careful monitoring and analysis of results is essential to culture planning and by taking batches of 1000 scallops and growing them in a variety of these culture types, the most suitable system for a particular site should eventually be found. It may in fact be discovered that the most unorthodox method proves the best, so it is advisable to monitor continually in the hope of reducing culture costs. However, for now, to make life simple these production alternatives can be divided into four, and the following is a summary of the economic advantages and disadvantages of each method.

Lanterns on longlines Lanterns hanging on longlines is what most people think about when they start up a scallop farm, but in fact the lantern may be replaced by all manner of equipment if it is thought to work properly. It is a popular method because it produces a good yield when compared with wild stock of the same age, and mortalities are usually fairly low. On the other hand the disadvantages are: a high capital cost; a high variable cost; a high labour cost; and a potential problem when left unattended for a longer than normal period of the line sinking and the lanterns being invaded by crabs and starfish on the seabed.

Lanterns on rafts Generally speaking the costs of culturing in this manner will be the same as hanging from longlines because, although the initial costs of the rafts are high, this will be outweighed by a sharp reduction in variable costs (labour). Once again, there is a good yield compared with wild stocks, and mortalities tend to be fairly low if all of the preconditions for citing are met. A high capital cost is a burden as is also the tendency for the equipment to become badly fouled because of its closeness to the surface.

Seabed culture By placing the scallops directly onto the seabed for the final 1–2 years, costs can be kept low because the stock requires no net changes nor buoying so there are advantages in low capital costs; low labour costs, fairly high meat yield, and the product

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being very attractive for the live market. On the other hand, the farmer may be faced with a higher mortality rate, less security over his stock, difficulty in stocktaking, and a high cost of harvest.

Ear-hanging from longlines It has already been stated elsewhere in this book that this type of cultivation has never really proved to be a success, especially when suspension is over a period of years. However, if the species is suitable for it, and it is only for a short period prior to either selling-on as a juvenile, or being placed on the seabed, then in some circumstances it could be a useful alternative. To the farmer it offers a reduction in equipment use and a higher meat yield over the three alternatives discussed so far. Mortalities are manageable over short periods but quickly rise as time lengthens. There is a fairly high labour cost because each shell has to be painstakingly handsorted and attached, a high variable cost, and a fairly unattractive product for the market if sold straight from the line.

LINE MANAGEMENT Presumably at this stage the farmer will be in control of production and costs and his task will be to cultivate the stock in the most profitable manner. However, he should never stop learning and it will become quickly apparent that from year to year nothing can be totally relied on. Settlement patterns, mortalities, levels of marine fouling and growth rate figures will vary and all of these fluctuations should be noted. Once the lines are in place they must be looked upon as a continual source of information. Learning to work them takes time but the data they supply will continue for many years. It may be found that specific sections are prone to excessive predator settlement, while others are found to be in slow-growing areas. One part of the line may experience heavy tidal drag, while another may show no movement at all.

Spat settlement Possibly the most important information a line can divulge is its ability to produce a good spat fall. This will depend much on its position in relation to natural factors such as salinity level, exposure, depth and tidal flow. Variations in settlement can often be seen to be extreme along only a short length of line, and this may be exploited to the farmer’s advantage.

Line marking When the farm reaches a stage where it has every stage of growth being cultured, there will be much work to be done on all of the lines. The farm boat may find itself

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dodging between three to four lines during a working day and this sometimes leads to confusion. By attaching surface markers to the line at the point where the day’s work was completed, continuing the next day will be made all the easier.

Line charts The recording and compiling of accurate information is important. Line charts should be updated at the end of each day, and the data from these are critical to good line management. By having the plan of the longlines engraved onto a Perspex board, the information can be entered as it is completed during the working day. This can then be transferred onto a fresh line chart once ashore. Even on a smallscale operation where to see through 100 000 scallops twenty-four 100-metre longlines will be required, the operation can become quite confusing. Try to visualize then the complexity of continually updating the information from 100 or more lines.

Line buoying Once both scallop growth and marine fouling start in earnest, adding buoyancy will become a regular activity. Ways of reducing the frequency of this have been discussed but it is still something that needs to be carefully monitored. Once again, line charts can be used to update information as and when the work is completed.

Fouling The extent and degree of fouling must be carefully monitored.This is made fairly easy when buoying is in progress and the lines will have to be run along the star wheel rollers for their entire length. The line itself can be kept clean during this process, and the lanterns should be visually checked for their level of fouling. Information gathered here will help determine the frequency of net changes. Where there is excessive fouling on the scallops themselves, in the form of mussels, barnacles or tube-worms, provision will need to be made for their cleaning. This can greatly add to the estimated time set aside for lantern changes and should always be borne in mind during early planning. Whereas mussels are fairly easily removed from the scallop’s shell, both barnacles and tube-worm pose much more of a problem and sometimes the best way of dealing with them is to separate those badly affected and to bring them on in deeper water where there is less likelihood of further settlement.

Bad weather Effective line management must make provision for non-productive days or even weeks lost owing to bad weather. If adequate preparation is not made, a line can quite easily sink owing to increased growth and inadequate subsurface buoying. Net changes will also be affected and the outcome can often be a bottleneck of work in early spring after a particularly stormy winter. This is a very important factor and should be studied carefully when allocating labour and estimating production levels.

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Utilization of space Often it will be found that a situation will arise where a line is split up into sections supporting different culture classes. Sometimes when bad weather comes on suddenly the lanterned stock lying ready on the deck of the boat has to be put back into the water as quickly as possible, and any convenient space will be used for this. Consequently the lines will often become badly loaded, with odd spaces between hanging stock. If time permits, it is good policy to sort this situation out so that the lines are properly utilized and there is less confusion.

Effective use of raft and line Apart from being easy to work from, rafts are popular because they offer continuity of work during bad weather. By part loading them with mature stock the farmer has more chance of satisfying markets during periods of bad weather, and similarly they may also be loaded with lanterns ready for sorting and in this way some useful work can be carried out when access to the longlines is not possible. Planning is therefore important, and by using both raft and lines effectively there is no reason why too many days should be lost during winter’s bad weather.

LANTERN MANAGEMENT We have already looked at the problems of equipment allocation and surplus but obviously situations will arise that will produce an unplanned for situation. This may happen when the farmer has budgeted in good faith on a fairly high mortality level only to find along the way that it is very much less than predicted. A good situation for the bank manager, but not so good if you have nowhere to house the extra stock. Lantern requirements may have been calculated on a 50 per cent overall mortality, but if this was found to be only 30 per cent many more would be required. Farmers faced with this situation will often revert to overstocking so as not to waste the bonus stock; not always a good move. Production rates must therefore be based on historical information, with each year’s sales helping to determine an average level of survival. After several years, more concrete figures can be produced to help determine the ratio of culture equipment to stock in hand. One way of alleviating this problem is to have a fixed number of lanterns, with any excesses going straight on to the seabed as a part of your bottom culture, or sold on to another farm. At early stages these may run the risk of predation but this alternative is usually better than overstocking in lanterns to house the excess. This policy is used to good effect in Japan. Another way is to use a disposable stocking system, which, because of its initial cheapness, allows for extra gear to be carried from the start. However, the cost implications further down the growth cycle must be weighed against this convenience.

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PROFITABILITY From what has been discussed to date it will be seen that certain aspects of the operation can be streamlined to help increase overall profitability. Although the farmer may consider that his vocation and quality of life are more important than profits, he will still, unfortunately, be at the mercy of market forces and as such must be aware of their effect on his livelihood. He may even go so far as to apply time and motion studies to his work routines so see whether productivity can be increased, and most importantly the farmer must always be prepared to adapt both to changes in natural factors and culture techniques. The following points bring together some of the aspects discussed so far and offer a general guide to improving profitability. (a)

Examine stock husbandry. Mortalities can be reduced if attention is centred on general handling. The effect on profits of any reduction below 50 per cent will be beneficial to any working situation. (b) Stock and equipment monitoring. This forms a basis for good husbandry and can be used to find the most suitable type of culture for a specific site. It can also be invaluable in achieving the best results from culture equipment. Be very careful to choose the right equipment from the start. (c) Streamline working practices. By increasing the number of lanterns that can be handled in a day, overall profits will be improved. This applies also to the labour costs involved in ear-hanging and line buoying. By introducing a more efficient system of buoying, visits to the longline can be greatly reduced. (d) Keep lantern costs down. A farmer must pay for quality in equipment, but there is a wide variety in prices and costs of using lanterns. Initial careful purchasing will be beneficial to long-term profitability. (e) Increase lantern capacity. By increasing the number of partitions in a lantern its overall profitability will also increase. However, this must be weighed against general handling costs. (f) Examine depreciation. If equipment can be made to last longer it will be more profitable to the farm. This may be achieved first by careful purchasing, and second by careful handling. (g) Keep equipment working. Try to avoid tying up capital in equipment that is not earning its keep. Do not buy unnecessary items, which may be used for only a short period each year, when they may be more easily hired. (h) Examine fixed costs. These are often non-productive and should be carefully scrutinized to see whether they are totally necessary. One obvious area to examine is administration, where it is accounted as a fixed cost. (i) Examine equipment handling and storage. Apart from damaging gear, poor handling and storage can represent very high labour costs. Ensure, therefore, that unnecessary handling and transporting are kept to a minimum. When not in use the gear should be stored in a manner that will protect it from direct sunlight and rodent damage.

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(j)

(k)

(l)

(m)

(n)

(o)

Labour allocation. Labour is an expensive commodity and as such should therefore always be fully utilized. By selectively stocking rafts, continuity of work may be almost guaranteed, and any spare time over this should be devoted to maintenance ashore. Plan to avoid problems. By adhering to a regular inspection plan of both culture equipment and farm machinery, many impending problems may be spotted in advance. This will also help to increase the working life of the equipment involved. Improve the product. Although the highest quality product should be aimed at, a value may be added by further processing. This may be as simple as cleaning the outer shell and packaging in an attractive manner. Diversify growing. Diversification into other species of shellfish can often be a means of fully utilizing a farm site. It will also enable the farmer to offer a marketing package that could help to increase the price of his prime product. Diversify with farm equipment. There are perhaps items of equipment on the farm that could earn something when not in use. The farm boat for instance, if suitable, could be put over to fishing.There is also a growth market in tourism and fish farming. Keep on top of accounts. Farmers will often avoid this aspect of the job and pass the bulk of the work to an accountant at the end of each financial year. It will be costly to employ him as a book keeper. Use him only for his auditing skills. Book keeping may be tackled by anyone who can add up, and it is a good means of keeping track of how expenditure and income are shaping up throughout the year. There are many excellent computer accounting packages on the market that are very user friendly.

The points outlined should form a basis on which to examine profitability. They may not be relevant to all situations but most will quickly become obvious when the farm gets underway. By keeping these points in mind the farmer should have greater control over his activities and as such, in the long run, increase his profits.

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The tables and figures in them can only be regarded as a rough guide to production and equipment utilization because of differing site and species characteristics. If constant grading is carried out throughout the growing process, the overall time to reach maturity for some can be reduced by as much as 25 per cent. The trend is now towards a live market and farmed scallops fit all criteria for this. A line spacing of 0.75 metres, and the use of lanterns with 400-millimetre partitions is the equipment basis in this book. Also, regarding manpower requirement, it is assumed that the lines are buoyed approximately every 2 weeks.

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The use of small subsurface buoys is preferable to using large ones because they offer more control over the line. Long periods of up to 4 years in suspended culture are no longer the norm because of the net changes involved, the manpower requirement, the risk of damage to equipment, and because the finished scallops only attain a low market price. A test farm would be based on bringing through approximately 10 000 scallops. Small scale would be 100 000 and medium scale 1 000 000+. A large-scale farm would need to cultivate in the tens of millions and more. Most farms would cultivate species with the characteristics of either Pecten maximus (king scallop) or Chlamys opercularis (queen scallop). Buying and selling at any stage of growth is a good way of assisting cash flow during early stages of culture. Meat yields vary greatly between king and queen scallops, but the price gap is gradually closing. Determining exact lantern requirements is extremely difficult because survival rates will not be known until the end. A good way forward is to cultivate an exact quantity and either sell on any surplus or put it onto the seabed. Lantern changes and line buoying are a direct labour cost. Other labour costs include net cleaning, general maintenance, equipment repair, general supplies and transport. Some farmers are hands on, while others are administration oriented. There will be differences in the ways both types of farm are run. Costs must be examined very closely; maybe money and time would be better invested elsewhere. Initial capital outlay can be quite high. A fisherman taking up farming would have the advantage of this being lower because he will already have some of the major equipment items at his disposal; not least, a boat. Culture combinations can be many and varied because few farmers work in the same manner as a result of site and species differences. For those species that take a long time to grow, the practice now is for them to be left for 2 years in suspended culture and then for 3 years on the seabed. Ear-hanging did not really prove successful over long growth periods. Longlines, apart from acting as a means of suspension, can also be used to gather information on growth levels and settlement patterns. Marine fouling is the scallop farmer’s curse, as often buoyancy will be only partially utilized in supporting scallop growth because of it. The occurrence of bad weather is something that has to be thought out carefully when trying to assess manpower requirement. Correct utilization of line space is important in overall planning, and often a raft, by acting as a short-term holding medium, may be used to help this run more smoothly. When the farm is only operating on marginal profits, there are many ways of increasing overall efficiency.

Chapter 14 More Strings to Our Bow

This is a book about scallop farming and as such it may seem inappropriate to give space to the growing of other species, methods of fishing, or alternate means of supplementing a living. However, in the UK at least, when scallop farming was first proposed by the Sea Fish Industry Authority, it was generally thought that it would be a part-time activity alongside something that used the same environment and some of the same equipment. To some extent this is how the industry developed. It should be remembered that in temperate waters Pecten maximus can take up to 4 years to attain a minimum marketable size, which can mean a long wait for a return on capital. So to help solve this, it may be prudent to introduce a faster growing species into the system – not too much of a problem if it is one of the scallop family. What will be examined in this section will go a little further than just introducing a second species. It will examine the possibility of cultivating other bivalve molluscs to make up a ‘market mix’, the possibility of physically catching (by fishing) other species for this mix, and how to tap into the tourist market; after all, if salmon and trout farms can persuade tourists to pay to look at the fish and then further pay to throw them a handful of feed, this is an avenue far worth examining. Diversification as such may at first seem far removed from the farm’s main activity but it should be remembered that the farmer should be able to learn from any situation and apply this knowledge to what he is doing. This is very appropriate when examining the potential for growing other species; techniques may differ, but culture equipment may often be the same and often one species complements another.

CULTIVATING OTHER SPECIES This section will examine the methods used to farm three other bivalve molluscs; oysters, manila clams and mussels. It will only be a means of demonstrating just what is possible and it does not rule out other species that may be applicable to certain areas. What it will show, however, is just how a site may be fully utilized and equipment made available for other uses. Of prime importance, however, will be the ability to bring in cash at earlier stages; especially important to the small-scale farmer, who may be undercapitalized. 272

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Oysters Oysters are excellent for culture alongside the scallop because they can usually be purchased at any stage of growth, thus helping to speed up returns. They have many other characteristics, not least of which is their durability and suitability to varying conditions. Being able to withstand water with a low salinity level and prolonged exposure to the air makes them ideal in many areas. Basically, they are filter-feeding bivalves, which feed on phytoplankton, differing from the scallop in that they remain stationary on the seabed.

Types There are many types of oyster worldwide and they have been farmed since Roman times in both continental Europe and Great Britain. Primarily they fall into two groups, the flat oyster (Ostrea) and the cup-shaped oyster (Crassostrea). The native European flat oyster, Ostrea edulis, is farmed extensively around the coasts of Britain, France, Norway and Spain, while the Portuguese oyster, Crassostrea angulata, occupies the more southerly parts of the continent. In Asia the Pacific oyster, C. gigas, is farmed on a large scale, while in the Americas C. virginica is more common. In an effort to improve productivity, different types have been introduced into areas where they may not be native; for instance, C. gigas was found to grow well in Northern Europe and North America. With a growth period of 2–2.5 years they are now proving more popular for farming than the native European oyster, which can take as long as 4 years to reach marketable size.

Spat collection In areas where there are oyster larvae in the plankton, collection can be carried out with a fair amount of success. The most common type of collector is a semi-cylindrical earthenware tile. They are usually set in piles secured by two synthetic ropes running through predrilled holes (Fig. 14.1). Three weeks before setting, the bundles of tiles are dipped into a lime which is then allowed to harden. Because the lime is fairly soft it allows the spat to be easily removed once the tiles are taken from the water. The bundles of collectors are set on the seabed in specific areas and at a specific time depending on location and usually remain in position for many months. Countries with warmer climates usually have a prolonged spat fall and collectors may be found in position all year round. Oyster spat will also settle on a bituminous surface, and some farmers opt for sticks dipped in bitumen during collection time. Oyster hatcheries can successfully produce spat when and where required and this is invaluable in areas where wild spat is either scarce or unavailable; for example, Crassostrea gigas seldom breeds in northern Europe, where its cultivation depends on hatcheries. A great advantage of a hatchery is that spat can be produced all year round, thus giving the farmer more control over his activities. And, not being

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Fig. 14.1 Equipment for collecting oyster spat.

adversely affected by travelling, the oyster spat can be posted to farms; as long as delivery is reliable, few mortalities are sustained.

Methods of farming Although their durability offers more scope in farming techniques, oysters can be very hard on equipment. Most varieties remain static on the seabed and are characterized by their uneven sharp-edged shell and it is this that causes damage to culture equipment. To keep damage to a minimum, regular sorting is essential, and fortunately the oyster sustains little shock during this process – they can in fact endure very harsh treatment. Farming techniques are many and diverse, with the farmer often relying on his own ingenuity to overcome cost restrictions and to combat inhospitable sea conditions. Suspended culture The Japanese longline has proved to be very suitable as a means of supporting oysters, but traditional-style lanterns have been found to be too easily damaged by shell growth (the shell actually encloses the netting in its growth and the only way to free it is to break the strands that then hold it). Tougher materials have therefore had to be introduced, and although initially more expensive their overall working life is longer. Figure 14.2 shows how oyster bags can be formed into a type of lantern to house the species. Trestles Trestles offer a very popular way of farming oysters and also great cost savings over other methods. For this the farmer needs a stretch of gently sloping, clean, sheltered

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oyster bags stitched at each end

spacers (4 inch drainpipe) placed in each bag

Fig. 14.2 Oyster bags set together to form a type of lantern within which to house the shells.

20 mm reinforcing rods

oyster bags tied to rods

wooden stakes

supports every 10 m

Fig. 14.3 Oyster trestles.

shore with easy access at low tide, and a steady flow of clean, fully saline water. The trestles are staked out at a point just above the average low water mark at a height of approximately 0.3 metre above the substratum. Oyster bags are used as a culture medium and are secured side-by-side along the length of each trestle. Figures 14.3 and 14.4 show the trestle construction and the two main types of oyster bag used in trestle culture. Savings on both gear and buoyancy are significant, but as the farmer is at the mercy of the rise and fall of the tide he may have to work unsociable hours.

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wooden inserts ends stitched

oyster bag

oyster cage

heavy netting on sides Fig. 14.4 Two types of oyster bag used on the trestles.

Although a boat is not always a necessity, a tractor may prove essential when much equipment and produce need moving. Oyster bag and frame These are described in detail in Section 2 and are applicable to both oysters and scallops. Bottom culture Oysters prosper if left in the right conditions on the seabed. The bottom must be firm and offer no chance of the shell being covered with either sand or mud and the animals must be large enough (≥40 grams) to withstand the onslaught of predators. Diving is the best way to harvest and the shells will be found to be clean and in good condition, the small crabs having done a good job in keeping the settlement of mussels, barnacles, weed and tube-worms under control.

Marketing Where oysters are purchased in bulk by a local market, the farmer should nearly always have an outlet for his product. Where no outlet like this is available he will have to promote them himself, but the subsequent increase in price is usually worth it. Many farmers will deal in all sizes of oyster from immature to fully grown, but it is not uncommon for an individual to grow oysters only to a specific size and then to sell them on to other farms to be grown through to maturity. Marketing is often up to the farmer’s ingenuity and his success is often a measure of his own imagination. Because of the oyster’s durability the farmer may sell on a sale or return basis providing they are not kept out of the water for too long. By placing new for old the retailer can be certain of a very fresh product, while the returned stock can be quickly freshened by a short period back in the sea.

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Manila clams The Manila clam is variously called Tapes (Venerupis) philippinarum or Tapes (Vererupis) semidecussata. Its inclusion in this section is because it offers the farmer something totally different in growing technique and type and may utilize a piece of ground that he may otherwise have thought unproductive. Manila clams are filter feeders that live below the surface of the seabed. With the aid of a flexible foot they manage a small amount of motility but in general are not great travellers. Feeding is carried out using two siphon tubes, which extend above the sand and through which a supply of fine organisms are passed. Although growth rates are highest in warm waters at 18–25°C they can tolerate temperatures as low as 6°C which makes them suitable for growth in temperate waters. They are also tolerant of fluctuations in salinity and can withstand exposure to brackish water for short periods. However, their shells are brittle and they must be handled with care if breakages are to be kept to a minimum.

Site selection Both bottom texture and type are important to this animal’s growth and coarsegrained sand is usually ideal. They will grow in a coarser environment but the grain size should not go much above the dimensions of a small pea. It is important that the sand or gravel has a firm substratum and is not prone to either shifting or rippling as a result of wave action, as this could either expose or completely bury the shells. A sheltered bay or estuary with gently sloping clean sand would be ideal, providing most of the bottom is exposed only at very low water. This can narrow the choice, and even with what looks to be an ideal site the only way to find its full potential is to perform a trial.

Methods of farming In order to farm this species on a commercial scale a certain amount of mechanization is required. A tractor is essential for both preparing the ground and subsequent harvesting. Good site access is therefore important. Attachments will be required for the tractor that are similar to those used on an ordinary farm, making them readily available and relatively cheap. A large trailer is also needed for transporting stock and equipment. The farm site is split into three areas to give continuity of supply over a 3-year growth period. The first job for the tractor is to loosen strips of sand about 1 metre wide by 50–100 metres long (varying with the amount of ground available). This also serves to kill some of the many predators that prey on Manila clams. At either side of the strips a 300-millimetre trench is excavated. The ground can be seeded with clams ranging in size from 6 to 12 millimetres and at a density of 8–10 kilograms per square metre. The seed is usually purchased from

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1 × 100 m strips

net edges buried under sand Manila clams protected Fig. 14.5 Setting up strips for Manila clams.

a hatchery and larger sizes can be expected to suffer fewer mortalities. A layer of fine mesh net (4–6 millimetres) is placed on top of each strip of seeded ground and its edges are pushed into the side trenches and then covered with sand (Fig. 14.5). This net must be kept securely in place over the whole growth cycle of the clam or predators will soon destroy the crop. It must also be kept free of weed growth and debris. Like many species of scallop, Manila clams do not respond well to being handled so it is usual to let them grow right through to market size without disturbance. Some farms do, however, opt for grading at around 18 months, but this has not shown as yet to be of great advantage. After 2 years the shells are usually at their minimum marketable size of 18 grams, and a further year’s culture will bring them to around 25 grams.

Marketing As a rule of thumb a Manila clam farmer can expect a mortality rate of around 30 per cent over a 3-year growth period. If he farms 1 000 000 seed he may expect a final crop of 14 tonnes, so marketing becomes a question of bulk supply twice a year. Unlike many other species, the Manila clam is not easily marketed in small quantities directly from the farm, so it is usual to use a wholesaler who is prepared to buy in bulk. Prices may fluctuate, but the current trend shows an increasing interest in Manila clams, especially in continental markets.

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Mussels To some scallop farmers the settlement of wild mussels among their prime stock is a nuisance, so cultivating this species as a form of diversification may seem foolhardy. What is being suggested here, however, is not large-scale cultivation of mussels but a fairly small crop to help support cash flow. The problem lies in them spawning and eventually settling among the scallops, but as the free-swimming larvae are in the water for upwards of 3 weeks there is possibly little likelihood of this; it will probably be larvae from other sites well outside the farmer’s area that cause the damage. However, it is a matter of trial and error to find if the two species can survive in fairly close proximity to each other. Keep them as far apart as the lease allows, and make sure that the scallop lanterns are kept fairly deep on the longlines as mussel spat tends to settle more in shallow water. To many people, mollusc culture implies mussel farming. Mussels are very popular worldwide and are farmed intensively in many countries. Even in temperate climates they can reach maturity in under 18 months and have proved a very durable and easily grown species on farms where lack of capital is the main restraint. Increasing production has meant that prices have fallen slightly in real terms but even so their future looks quite good. After spawning and fertilization the mussel larvae free swim in the plankton for approximately 3 weeks (depending on area) and then attach themselves to a suitable substratum by means of their byssus thread. At this stage they are very much at the mercy of predators and consequently much of the wild settlement is destroyed. A farmer was once asked why mussels were so common around the mouths of rivers and he replied that although they did not necessarily like brackish water, their predators liked it even less. It seems that here we have a shellfish that adapts very quickly.

Species There are many species of mussel but to date only a few are commercially exploited. The one that is possibly common to most of us is Mytilus edulis. This species, which has a black/blue or brown shell, is found in areas from the Mediterranean to the colder waters of northern Norway, as well as in many other parts of the world.

Spat collection It is not uncommon for spat to be collected in areas outside the farm site, and in one respect it is better that the mussels for growing on are relatively free from further settlement. The smaller ones tend to dislodge the larger ones, and during rough weather this can lead to losses. If difficulties are encountered in obtaining spat, it may be useful to talk to the nearest salmon farmer, as many regularly pressure wash their nets, which are often found to be covered with mussel spat. Ropes are hung in the water for spat collection (Fig. 14.6) and these can be of either natural fibre or manmade, with a minimum diameter of 12 millimetres. For

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3/4 coils hung together

peg pushed through rope

single, weighted ropes Fig. 14.6 Setting mussel ropes.

ease of handling they are often suspended in coils. By inserting wooden pegs every 30 centimetres, the growing mussels are prevented from slipping down the rope and are also offered more space to spread onto. Settlement is allowed to continue for several weeks and can be anything up to 3000 to 4000 animals to the square centimetre. Where there is a light settlement, 10 to the square centimetre is adequate for farming purposes. At this stage the ropes should feel gritty and the spat will be changing colour from white to black.

Cultivation Mussels are farmed in most countries by suspended culture, and this can be from either rafts or longlines. In some areas they are cultivated on stakes (bouchots) driven into the seabed at low tide, but this is only possible in areas where the predators are few. The raft designs shown for scallop culture would suit both types, but the longline system would need changing because mussel lines are usually suspended close to the surface. Figure 14.7 shows some of the different types of line used and the system of bouchots culture that is common, particularly in France. Thinning Mussels require periodic thinning to ensure that all the ropes do not become overcrowded. At spat stage this is accomplished by running a hand down the rope and cleaning off everything except for those lying in the spiral groove. Where pegs are inserted these are thinned in the same way. Being persistent travellers, the mussels remaining will soon occupy the cleaned spaces. Once beyond the spat stage all thinnings can be saved and used to stock new ropes. Mussels form clumps when in contact with each other, and this characteristic makes them easily handled and

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25 kg drums

surface longline

two line system

2 m mussel stakes exposed at low water

Fig. 14.7 Three ways of farming mussels.

resited. Where they are collected loosely they can be quickly clumped by half filling a fine mesh bag and leaving it underwater for a few days. Thinned spat can be grown on by filling tubular mesh with the clumps of seed (Fig. 14.8) and either binding it onto a rope or spiralling it around a cylindrical mesh drum. The mussels move out of the mesh tube and settle on the base rope or drum. By thinning in this way many ropes can be stocked from what may have seemed at first to be a light settlement.

Harvesting Mussel farming can be very hard work, especially during harvesting, and the more lucrative farms have gone to much expense to alleviate some of the toil during this period. Heavily stocked ropes need a derrick to lift them, and large double longline systems need to be brought aboard the boat with a lifting frame. Farms can therefore vary from a raft with a simple wooden derrick to tailor-made craft incorporating the latest hydraulic lifting and handling gear. The ropes, once aboard, need stripping and cleaning for reuse, and the mussels will have to be separated for grading. This can be achieved with either a mechanical grader or a simple bench adapted for the purpose. Heavy beards (byssus threads) will need removing and the shells, if dirty, will require hosing or even pressure

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NETLON drum rig

funnel

tubular mesh stocking

filled mussel stocking

1m

mussel stocking wound lightly onto drum 0.6 m

Fig. 14.8 Restocking thinned mussels.

washing. Those mussels falling through the grader can be re-roped for further growing on.

FISHING This section will examine the methods used to catch scallops, crabs and prawns but there will of course be many other species that can be caught; their variety will vary from area to area. It must be borne in mind, however, that in many countries a licence will be required before a boat is able to involve itself in fishing of any kind. There may also be laws regarding health and safety and vessel seaworthiness. To become involved in any type of fishing will usually require fitting the boat out in a specific fashion, and this may necessitate fitting a hydraulic hauler or even, in certain instances, a winch and lifting gallows. The following is a brief outline of what is involved but more detailed information can easily be obtained from local fishery research stations and/or fisheries officers.

Scallops It may seem a little inappropriate to include scallops in this section when our aim is to farm them but much can be learned from the fishery that will be useful to our prime activity. First it must be remembered that we will in fact be ‘fishing’ them (by diving) if we opt for seabed culture in any form because in many protected areas this is the only permissible form of harvesting. Also, where a bottom culture site may be inhabited by predators such as crabs and starfish it will often be necessary to set pots to help reduce their numbers. If these are the brown and velvet crab then

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they may also be put to market. On some sites this fishing process is necessary two to three times a week to keep scallop losses at a minimum. Scallops have been fished for many years in a variety of ways and they were usually so plentiful that the crudest of equipment was capable of lifting them. As demand for this delicacy increased so did the complexity of catching them and this has been an important factor in overfishing. Unfortunately as stocks were depleted, fishing techniques improved to compensate.

Beam trawl Although not the most effective piece of equipment, the beam trawl was used for many years to catch certain species of scallops (those more mobile on the seabed), and while stocks were plentiful it served its purpose well. Today, although still in use, it is not as popular a means of fishing as others to be discussed below. Figure 14.9 shows a typical beam trawl with its chain fishing line and long cod end. This equipment was effective only when the scallops were lying on the surface of the seabed and not recessed. It also had the problem that its mouth had a tendency to lift off the bottom once the cod end filled. Being wide mouthed it is prone to picking up boulders, which damage the catch and make lifting aboard very difficult. The trawl is launched from the boat while going slowly ahead and the tow warp is kept slightly taut as it sinks to the seabed. Once on the bottom, the amount of warp that is let out is usually about three to four times the depth of water being towed in. The towing speed may be increased slightly, but always with the thought in mind that its mouth should be kept in contact with the seabed. To ensure this it is sometimes necessary to attach a heavy weight approximately 10 metres along the

cod end

2 m beam

fishing line

bridle

Fig. 14.9 A beam trawl.

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towing warp from the mouth of the trawl. After twenty minutes’ towing, or whenever it is thought that there is a catch worth lifting, the trawl is hauled to the boat, either with a pot hauler or a winch, and then it is brought aboard with the use of a derrick. It is usual to pick it up with a locking rope around its middle and then undo the cod end knot to release the contents onto the boat’s deck. These may be sorted once the trawl is set back into the water.

The dredge The dredge developed from the need actually to dig into the seabed yet retain only items of a certain size. Initially it was designed with fixed teeth, which angled into the seabed. Figure 14.10 shows a typical scallop dredge with its protective chainmesh belly and shallow mouth to avoid picking up large boulders.They can be towed with as many as six or more on each side of the boat, thus effectively covering much ground. The power required for this is considerable, as is also the wear on the vessel from handling the dredges themselves. Being so aggressive, the modern dredge is fitted with retractable teeth, thus enabling it to travel across rocky ground without becoming snagged.

chain mesh tooth bar steel teeth (fixed) wheels

mechanism for spring-loaded teeth spring (compression)

one spring at either end of tooth bar Fig. 14.10 Scallop dredges.

6 dredges shackled to one tow

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Electronics Modern electronics have greatly increased the efficiency of both the beam trawl and the dredge. Courses may be ‘plotted’ with the aid of global positioning system navigation and a skipper can follow this with considerable accuracy, merely by guiding an icon over the screen of his plotter in his wheelhouse. The ‘course’, if successful, can be stored for future use.

Scallop diving The diver has quite often been accused of plundering scallop beds to the detriment of the industry as a whole, but in most areas landings from diving, when put against the total landings of the industry in general, only amount to a small proportion. Generally speaking the diver is limited to approximately 30 metres depth and this leaves much potentially productive ground that he cannot work. His effect on stock is therefore very limited. To work scallops by diving will require a suitable boat and a team of at least three qualified divers, one being a supervisor (in the UK there are guidelines that are specifically aimed at shellfish divers). They will also require annual diving medicals. Most scallop divers can be proud of the fact that they should eventually become highly skilled fishermen, and it is a matter of fact that it takes longer to produce a good scallop diver than it does to train a hyperbaric welder, one of the top jobs in the underwater diving industry. The method of working is to allow one diver at a time to swim to the bottom and seek out his prey, which he places in a net bag. Attached to his catching bag is a 20litre plastic drum, which he gradually fills with air to support his catch (Fig. 14.11). Once his bag is full he may either fill the drum completely and let it make its own way to the surface, or leave it where it is and make his way up his marker line. Once on the surface, the bag can be lifted, enabling the gas in the drum to expand and ascend under its own power. The diver’s philosophy of working is to lift only marketable-sized scallops, leaving all other bottom creatures undisturbed. Unlike the dredge, there is little evidence of where he has been and the ground he has worked quickly regenerates because he does not disturb the undersized scallops.

Other methods Suction dredges based on both air and Venturi systems can also be effective in fishing for scallops, especially where there is a dense population in shallow water on a clean bottom. Figure 14.12 shows a typical airlift and Venturi system. The principle is to pump a large volume of air into the main lifting tube, usually close to its mouth, but not totally necessary. As the air rushes to the surface it causes the water to follow quickly behind it, thus causing a suction that will usually pick up all in its path. A Venturi system uses water to create the flow and in some ways this is kinder to the shells. It is much the same setup as the airlift except for certain modifications

diver down flag

40 m 10 mm rope

plastic drum floater

catching bag

Fig. 14.11 A scallop diver’s catching bag and floater.

150 mm flexible pipe

air inlet

weighted sledge

(a)

water inlet 150 mm steel tube

net keep bag

suction (b)

Fig. 14.12 Two types of suction dredge, (a) using air and (b) using water.

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‘creel’

‘pot’

a ‘fleet’ of ‘creels’

single ‘end’

Fig. 14.13 Equipment for trapping crabs, lobsters and prawns.

to the actual dredge. Water is pumped in at the dredge end at the rate of approximately 1200 litres per minute (regulated by size of lift hose) and this should in most cases be sufficient to operate an efficient Venturi dredge.

Crabs The fishery for crabs is prolific in many countries and, although it requires some expertise, it is usually more physically taxing than mentally tiring. They are usually fished with some kind of trap (creel, pot, etc.) and the design of this will usually be specific to the area involved. However, the general principle is much the same worldwide and Figure 14.13 shows two types of trap as well as ways of deploying them. To some extent the crab can be termed migratory and its usual habitat is on a sandy bottom, often close to a rock edge. For certain parts of the year they will bury themselves in the sand with just their top shell showing and during this period the fishery slumps.

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The traps are baited either every day or every other day, and lifted on a daily basis, weather permitting. Where a ‘fleet’ of traps is deployed, the second buoy is, first, to enable the lifting process a little choice of position if the sea is fresh, and, second, to act as a double marker for security of equipment. As soon as the crabs are removed from the traps, their claws are rendered inoperable by ‘nipping’ a small tendon, and this prevents them from damaging each other. If there is no daily market, they may be stored quite safely for a number of days in ‘keep’ boxes, providing they are packed together fairly tightly.

Lobsters In general, lobsters are a little more illusive than crabs and thus require a little more expertise in their fishery. Because of their premium price they are highly sought after and in many areas vastly overfished. Generally speaking the technique of fishing and equipment involved is much the same as with crabs but in this case the fisherman usually has to be more accurate when ‘setting’ his gear. The lobster will normally inhabit a rocky reef and some of the best fishing spots will be where the sandy bottom borders on to the rock. Depths may range from 5 metres to 100 metres depending on the area. Different types of bait may be employed but whereas crabs usually require fresh bait, lobsters may often be lured with what may seem to be rotten bait. Once the animals are caught they will have their claws bound with rubber bands to avoid damage to each other, then they may be kept in a keep box until ready for market. Because they survive well in this type of captivity it is not uncommon for fishermen to stockpile for such things like the Christmas or Easter market where prices should be at a premium.

Prawns The type of prawn considered here is the Dublin Bay Prawn (Nethrops) or what has now become commonly called langoustine.These are mainly native to northern temperate waters and are usually caught at depths from 30 metres down to 300 metres. The animals can range in size from 20 grams to over 1 kilogram, and it is the larger ones that command a premium price. Once again, one of the main methods of capture is by a trap (creel) but these are usually much lighter than those deployed for either crabs or lobsters. The creels are usually fished in fleets of 40 or more, sometimes increasing to over 100, but these larger systems are quite often only fished in areas of deep, exposed and distant water. Baiting is with salted herring and this is usually carried out twice a week. The animals are then either stored in bulk or stored in tubes where they can be kept alive with the assistance of a salt water spray, and passed onto the market in that manner where the extra care taken over their handling will usually be rewarded with a higher than normal price. ‘Tubing’ them in this manner will also allow them to be stored in the water for weeks at a time providing they have been handled correctly from the start.

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TOURISM It may seem that we are moving a little too far away from our prime activity by introducing such an aspect of diversification as tourism, but this has proved to be quite a good earner for many fish farms to date. No doubt you may have visited a trout farm and had the pleasure not only of having paid to get in but also to purchase a bag of feed for the fish. The same principle may be employed on a scallop farm and, although you may not go so far as to charge for food (because they filter from the sea), it would be quite feasible to show visitors around the site for a price. This may either be done with the use of the farm boat or in conjunction with a local tourist boat operator, once again, at an agreed rate. A farm shop may also be established to take advantage of the purchasing power of the visitors.

SUMMARY •

• •

• •

•

•

Because scallops may take four or more years to grow (especially relevant to temperate waters), it may be a good policy to look for some means of diversification to ease cash flow problems. It is also in the spirit of how aquaculture has been promoted in many areas. Much can often be learned from being involved in other similar activities that may be of prime use to the target crop. Oysters may easily be cultivated alongside scallops and have the benefit of being able to be purchased or sold on at any stage. Their distinct durability makes them an ideal candidate. Manila clams are also an alternative but only where suitable conditions allow them to survive. Mussels can often be an alternative, but because of the problems centred around their spat, they should only be cultivated on a small basis and as far away from the scallops as possible. There are many types of fishing which could be undertaken with a suitable farm boat but these will vary by area and by country. In temperate waters, however, scallops, crabs, lobsters and prawns would all be suitable candidates. Tourism can often offer the struggling scallop farmer a cash injection during difficult times.

Chapter 15 Marketing, Handling and Processing

In this chapter we will look at marketing, shellfish handling, quality control, processing, distribution and packaging, all of which have a bearing on the final market price. The level and intensity of marketing may vary with the size of the operation. In order to maximize profits, a small-output, one-man farm may put much effort into display and promotion in the hope of attracting local markets. On a larger scale a farmer may put all his efforts into scallop production and rely on others to create the markets. At the other end of the scale, a very large farm actually creates its own outlets, thus covering the complete marketing spectrum. There are, however, some simple ways of increasing the scallop’s appeal and price, and so marketing should not be totally ignored. Both scallop dredgers and divers, in line with fishermen in general, have tended to rely on direct distribution from the quay side. This has many advantages, not least of which is the fact that they are free to direct their efforts to what they are good at. Even at this stage, however, there are ways of increasing returns so long as it is known how the shellfish is going to be processed.

MARKETING Marketing is not considered as being restricted to the point of sale but as covering all aspects of handling from when the scallop leaves the lantern to when it arrives on someone’s dinner plate. What the farmer can offer a customer is almost a guaranteed supply of this delicacy and a consistency of quality. Even bad weather will not usually hinder his ability to land his product, unlike a fishing boat, which is very dependent on good weather. The level of marketing involvement desired will depend greatly on the farmer’s own attitude and ability. Not all will want to be involved with the consumer, so it is fortunate that most marketing circumstances offer varying levels of entry and exit. Generally speaking the principles of marketing state that all business decisions should be made with careful consideration of customer requirements. Factors in the supply market are, however, constantly changing and it is sometimes difficult to make accurate production estimates and to meet customer demands. However, by taking the role of a customer-based industry and progressing accordingly, the final product should be one that is highly sought after. 290

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Any marketing strategy should be considered as a recipe, the ingredients being price, promotion, product and place. To the customer the price is often an indication of quality and an important factor when deciding whether to buy or not. To the supplier it is the sole means of recouping costs and making a profit. The promotion of the product is important, especially where local markets are sought and where value has been added by way of processing and packaging. Its intensity will depend on factors of supply and demand and the level at which the farmer wants to be involved with the consumer. In some situations it may be considered a fixed cost, but the more marketing-oriented farmer will treat it as variable to the stock produced, so increasing his sales promotion with gross income. The basis of the marketing recipe is the product; its quality and the way it is offered to the customer will have a direct bearing on sales and so should occupy much of the farmer’s attention. Although the scallop as a basic raw material may be considered to have a fairly constant demand, where specialized processing has been involved, the final product may be subject to a limited life cycle. The consumer can often reach a saturation point with a particular product, and this must be considered when undertaking specific types of processing. The final ingredient of the mix is place. This represents all aspects of stockholding and transportation and is sometimes referred to as distribution. With a perishable item like a scallop its position in the marketing recipe is very important.

Market forces The price of fish is something that often fluctuates greatly throughout the year, especially when shortages are brought about through bad weather. Although a farm may be able to almost guarantee a steady supply of scallops it must be borne in mind that this will only make up a small proportion of the total scallops landed, fishing being the main contributor, and even if the farmer is able to obtain a premium price because of reliability, he will still be at the mercy to a great extent of general market fluctuations. These will primarily be determined by supply, caused by the farmer, and demand, coming from the customer. Changes in supply are usually brought about by decisions within the farms. Expansion is often undertaken when prices have been at a premium and general growing conditions have been good, but the farmer must always take into account whether or not the market is able to absorb the extra stock, especially if many other farms follow suit. If it cannot, there will be a general price fall, that being the only way to persuade customers to buy the product. Changes in demand are mainly controlled by consumer spending power, the prices of other shellfish, the scarcity or not of the prime product, the prices of competing foods, and the effects of marketing on consumer choice. Consumers can be easily scared away from a product and this has been especially true with scallops and the problems encountered with paralytic shellfish poisoning, diarrhoetic shellfish poisoning and, especially, amnesic shellfish poisoning. It does not take long for demand to fall when bad publicity arises and possibly the only stabilizing factor is

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that a temporary closure of a farm or fishery will in itself cause a lack of supply and as such even up the balance of supply and demand a little.

Selling choices There will be choices to be made when deciding just how to sell. The farmer has to decide whether or not he will process his product, add value in other various ways, seek local or distant markets or combine both. He will also have to decide whether or not to export, stick to one product or go for a marketing mix, employ professional advertisers or undertake that himself; now made much easier with the use of the internet.

Selling at a profit In selling, the key is to choose the correct opportunity for your business, remembering all the time that any market must have the right potential for a profit. Markets may be available, but they may be unprofitable to sell to. Likewise with individual customers, one may be more profitable to supply than another. Value adding is often also not adding profit and as such should be viewed with caution.

Size of business Large businesses have an advantage in that they can seek outlets that require larger volumes. They also have savings in marketing overheads as well as lower transport costs brought about by larger and more frequent deliveries. Risks can also be spread by supplying a wider range of customers. This does not necessarily mean that the small producer is at a disadvantage. He may have many outlets that a large farmer finds it totally uneconomical to supply, and it is also generally believed that the owner-managed shellfish farm is one of the most cost-effective ways of producing shellfish because there is little wastage in all aspects of the business, and the ownerfarmer will generally take more care with his product. If, however, the small farmer finds it difficult to compete among larger units then he should consider combining with other small farms in a joint marketing venture, or even contract growing for one of the larger units.

Marketing groups By marketing with other farmers the small unit should at least be able to compete on equal terms and will also have the benefit of concentrating just on production and leaving the selling to someone else. Combinations of farms for marketing purposes may be put together in a number of ways. A cooperative style is very popular, and there is often outside assistance in getting these off the ground. On the other hand, small numbers of individual farmers may band together to form local marketing groups. The opposite of this is the large-scale organization where all the

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growers of a specific shellfish type sell under the banner of one main marketing association. Anyone belonging to a marketing group must show trust and commitment, and be prepared to give up much of his independence. Production should be to a common quality standard and the farmer must be prepared to work to group, not individual aims.A lower than normal price may also have to be accepted if the group is to be able to raise enough capital to invest in any future mutually beneficial project. Finally, anyone producing within such a group must always be prepared to accept majority decisions and hand over routine decisions to the elected management.

HANDLING Processors are usually concerned with bulk consignments and will either blast freeze the meat or ship the whole animal live to larger markets. Both will require different ways of handling by the fishermen or fish farmer if maximum profits are to be obtained. This is usually a point of conflict, because, while the farmer wants a good price, the processor may not always be willing to pay it. If the meat is destined for the blast freezer, the farmer will normally be paid on a meat weight basis after the shells have been shucked. Much reliance has to be put on the processor’s integrity to ensure that all is done on a proper basis and that the end-product is directly related to what originally went into the factory. This process could take several days and it is only then that the farmer knows what he has earned. The practice has been observed in many factories of placing bags of scallops in a cold store for a day or so before shucking. During this period much dehydration takes place while the meat stays relatively fresh. Once shucked, the meat is weighed and payment to the fisherman is based on this. To regain weight the processor soaks the meat before the process of glazing and freezing. It is not difficult to see that the weight of the fresh meat at the quayside will differ from that declared by the processor after handling. In these circumstances the farmer can improve his lot in a number of ways. First, he may be able to negotiate a price per shell with the processor based on a minimum size. One advantage of doing this is that he will be paid for exactly what he lands and there should be no arguments about numbers. He may be able to persuade the processor to shuck the shells immediately on landing, thus lessening the losses through dehydration. If all else fails, the farmer will have to pay closer attention to handling, with the emphasis on preserving meat fluids. By ensuring that the scallops lie in a position that allows least water seepage, much dehydration can be avoided. This may perhaps be difficult when filling sacks but easy if fish boxes are used for both storage and transportation. When a processor buys scallops for live distribution he will want the farmer to be more careful in his handling of the product. This request is usually accompanied by a premium on the price. Quick distribution is essential to the operation, and it

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is important that the farmer supplies his market soon after the shell’s removal from the water. The fairest form of payment is for the scallops to be weighed on landing with a fixed price per kilo. Obviously by being aware of dehydration problems during any prolonged transportation, the final weight should not alter too much and the processor will be happy with a scallop that should stay alive longer. It often happens that quantities of scallops need to be kept in bulk for a short period before landing, one instance being where a large quantity is built up over a number of days before shipment. It is acceptable to store the scallops in net bags and suspend them, but if left like this for periods of more than a couple of days, especially during hot spells, there may be high mortalities. Best practice is to fill the bags to about three-quarters of their capacity and put them onto the seabed. In this position they can spread out a little and can last safely up to 2 weeks or more. Warm weather can impose added handling problems, both in confined storage in the water and in prolonged exposure out of it. Mortalities may occur when the shells have been warmed up by the sun and then put back in the water for storage. Frost and ice are other conditions to avoid, although it could be deemed extremely bad handling to allow the scallops to freeze to death. Too much shock treatment of this kind will quickly result in high losses, so care must be taken to see that extremes of temperature are avoided. Short-term storage is often carried out close to the water’s surface for ease of lifting and it is here that another handling problem often arises. Scallops quickly perish when expose to fresh or low salinity water, and it is on the surface that this usually accumulates during periods of heavy rainfall. This can be a problem when rafts are used for storage and consequently it is always advisable to suspend the scallop bags at least 2 metres below the surface. Intertidal storage, popular with oysters and mussels, is affected by the same problem of low water salinity. It should therefore be used only for short periods with scallops. Temperatures can be lowered or kept constant by spreading crushed ice over the scallops while in or awaiting transit. Where the shells are destined for shucking, the quality of the ice is unimportant, but if required live at their destination iced salt water is essential for their survival. Melted freshwater ice will quickly percolate through the bags or boxes and run into the shells themselves. Short exposure to this will result in high mortalities and a product that has a poor appearance. Misuse of ice not only accounts for mortalities but causes flavour loss when the melted ice is allowed to percolate through the meat for any length of time. When used to chill shucked meat it is therefore advisable to place a barrier of polythene between the ice and the meat.

QUALITY CONTROL Quality control for the scallop farmer, although important, is basically a question of commonsense, good handling and sensory assessment. In general, quality standards should compare with standards in other foods, meet general legal require-

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ments, and be at a level that the customer expects. In cases where the farmer moves his stock onto a middle man he need not have too many problems in this field. If, on the other hand, he moves into processing as a means of maximizing profits, he will have to be more aware of all aspects of quality control and the legislation governing it, especially in the light of the impact of algal toxins. Where a farm is producing within a trade association, his quality control will usually be governed by a voluntary scheme where a general code of conduct regarding farm husbandry must be adhered to, or there is a controlled code. This is usually more forcefully overseen and the penalties are often more punitive. However, it does have the effect of bringing about a quality standard that can be regarded as general within the particular association. The consumer is more aware now than ever before about the quality of produce, and legislation is moving quickly in his favour, especially in the perishable food market. It would be difficult to find another product that deteriorates as fast as shellfish, or that becomes so harmful to the consumer if not handled in the correct manner. It is therefore important to be aware of quality control when handling scallops. Both fish and shellfish carry bacteria on the surface of their flesh and in their intestines. These are known as resident flora. In normal conditions they cause no harm, but once the meat is dead they may have an opportunity to move into the flesh. Handling may kill off some of these bacteria but add others, according to the type of processing being undertaken. However, the nature of any spoilage will depend on either one or more environmental factors.

Temperature When scallops are exposed to high temperatures they quickly die but bacteria may be present at any temperature level. Many bacteria can survive being frozen and will continue multiplying once the flesh is thawed. Boiling, however, kills off a very large proportion of these.

Oxygen There has been much research into the effects of gases on the shelf life of perishable goods, and oxygen levels have been found to be critical to bacterial growth. Although some types will perish in the presence of oxygen the majority react favourably to it and multiply rapidly at higher concentrations of the gas. It is, however, important to the overall freshness of fish meats.

Water and salt High water levels will encourage bacterial growth but its reproduction slows down as these levels decrease. Where the meat has been dehydrated to a level of less than 10 per cent water, the bacterial growth may cease altogether. The presence of salt

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may encourage one type of bacteria and inhibit the growth of another, although those mainly responsible for food poisoning do not grow well in salt concentrations exceeding 10 per cent.

Acidity and toxins Most bacteria thrive in acidity levels of between pH 6.0 and pH 8.0, multiplying more quickly at the higher level. However, at levels higher than pH 8.0 they tend to be discouraged from growth. In general, fish and shellfish have an acidity level of around pH 6.0, while meat is around pH 5.0. This is why shellfish deteriorates so quickly. Toxins in the form of food preservatives, smoke and purifiers have varying effects on bacterial life within shellfish meat. In general, when these levels are increased the bacterial level will decrease but this can be at the expense of overall quality. In its own environment the scallop will support bacteria under fairly constant levels of temperature, oxygen and salt. Once removed from this environment the bacteria often die from shock and those remaining may not start multiplying again for a day or so. External factors will now be variable, with higher temperature being accompanied by a lower salt concentration and a varying oxygen supply. Bacterial growth will be affected by this and may develop in a variety of ways according to the differing combinations of these external factors. The slime build up on the flesh of a dead scallop is a visual indication of bacterial growth, but this is an extreme way of measuring freshness. By using the sensory indicators of appearance, odour and texture, a more accurate assessment can be made and deterioration consequently avoided. Non-sensory freshness tests are a little more complex and the results are not always instantaneous. Bacterial counts can be carried out but may require a couple of days to complete. A problem with this is that not all bacteria cause spoilage, so it is difficult to know what the final count actually represents. Chemical tests have been developed to help obtain more accurate results and the two types have proved to be useful. Certain bacteria form trimethylamine (TMA) when exposed to oxygen, but the fish must contain specific amounts of this chemical to begin with. Scallops have only small amounts of TMA so measurement may not be accurate in their case. As an alternative the measurement of total volatile bases is often used. As the flesh of the fish deteriorates it produces certain bases, which neutralize any acids that are present.These bases become volatile when the flesh is made alkaline, and the amount of acid used to neutralize a distilled quantity, becomes a measure of freshness.

Problems in cold storage Although bacterial activity may have ceased at a storage temperature of −30°C, both chemical and biochemical reactions will still be going on. Texture, appearance, taste and even weight changes will become apparent during prolonged storage, and if

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these are to be avoided distribution of the product should be undertaken as quickly as possible. Poor texture and appearance are accelerated by protein changes, and a dull, soft, tasteless meat is usually the result of prolonged and poor storage. Fat content also alters and this results in the appearance of a bad odour and a discoloration of the meat. Both protein breakdown and fat oxidation are accelerated by dehydration, which also takes place in cold storage. Thus apart from meat deterioration, overall weight loss is also a problem. To reduce dehydration, care must be taken to ensure that the product that has been blast frozen is at approximately the same temperature as the cold store into which it is being placed. A big difference in temperature will result in water vapour coming from the meat to form frost on the walls of the store. Dehydration will be further accelerated by any air movements that may be present, and this can be avoided by ensuring that traffic both in and out of the store is kept to a minimum.

PROCESSING Both large and small farms can benefit financially from processing their own product if the farmers feel it is within the scope of their activities. Bypassing the middle man can bring in extra cash, but not all farmers will want the problems of direct contact with the customer. It need not be thought of as a large-scale undertaking, and for the part-time farmer it may take the form only of shucking meat for the local hotel. However, it cannot be overstressed that environmental health regulations must be met when attempting anything like this. A brief description of the main types of these will demonstrate their application to farmed scallops.

Cut meats In the main the scallop is shucked by hand using a slightly curved blade. Some species, because of their size, may warrant mechanical evisceration but this is usually when their unit price is low. The shucked meat is washed and either sold directly to a retail outlet or blast frozen and glazed for storage. Although some processors soak the meat at this stage to build up the weight, it must be mentioned that customers are becoming aware of this practice. As such, many meats are now sold unsoaked, giving the purchaser a better deal. If the meats are old and discoloured they can be soaked in a bath of water containing a small quantity of acetic acid, but this will be at the expense of flavour loss. Polyphosphate solutions are also used during soakings to prevent the meat from dripping during the next stage of processing, but apart from offering a bad deal to the customer this also results in flavour loss. When using ice for storage both before and after cleaning it can be assumed that there will be some deterioration in the product. Scallops still in their shells will start to lose flavour after 4 days on ice, and the cleaned meat will be good for only 2 days,

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finally becoming tasteless after 7 days. It is therefore recommended that the meat is blast frozen immediately after shucking if there is no alternative.

Freezing The purpose of freezing is to seal and maintain the flavour of the meat during long periods of cold storage. The meat of the scallop may be as much as 75% water, and it is this that the freezing process works on. Because spoilage continues in temperatures below 0°C, it is important that the temperature is lowered quickly and this is why the blast freezer is so important to the process. Air blast freezers are an efficient and popular type and are mainly constructed on two basic designs. Continuous systems work on a conveyor belt principle with the air being blasted either along or across the meat, while the batch system relies on air being blasted over a static product. Their main advantage is that they can deal with irregular shapes. Liquid nitrogen freezing is popular where the gas can be easily purchased. With the temperature of the gas at −190°C, the scallop meat is deep frozen in only a few minutes. Once the meat has been frozen, it will need to be stored at a constant temperature both up to and during transportation. This usually takes the form of a large walk-in refrigerated container. It is generally agreed that −30°C is an acceptable storage temperature for cleaned scallop meat, but even at this level it cannot be kept indefinitely and 6 months would be a maximum storage time. Freezing and subsequent cold storage are the most direct means of increasing the scallop’s value, but it is usually only large-scale or cooperative farms that can justify the outlay.

Live in the shell The farmer can offer a product that is most attractive to the catering trade, first, because of its absolute freshness, and, second, because of its overall quality. Where bulk consignments are carried out there is little he can do to enhance his product, but on small consignments he may, if he chooses, present the animals in a more attractive fashion.

Half shell Another attractive way of marketing the scallop is in the form of a half shell. This is accomplished by cutting free the top shell and gut, leaving the adductor and roe exposed (especially appealing when the roe is full).

Smoking Much information is available on exact methods and recipes for smoking all types of meats and the following is merely a guide to show what is involved. Although the

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process does increase the shelf life of the meat, it should not be employed specifically for this purpose. The introduction of salt in the form of brine, and subsequent dehydration during the smoking process, help to reduce bacterial activity. Its main effect, however, is to enhance both the taste and appearance of the meat, which should, therefore, be consumed soon after being smoked. Smoking can be undertaken either hot or cold, and certain shellfish types will be suited to one particular method. Local market research should help determine which is the more popular. In the cold-smoking process the temperature does not rise above 30°C and consequently the meat remains uncooked. Hot smoking, on the other hand, raises the temperature to 70°C and above, cooking the meat during the process.

Procedure There are three stages in the smoking process, preparation (including cleaning), brining and smoking. The correct preparation of the meat is most important because the smoking process will highlight any blemishes that may be present. Washing must be thorough and trimming must not be skimped, even though it may seem that the meat is being whittled away unnecessarily. Once properly prepared, the meat should be encouraged to take up some salt. The aim of either brining or dry salting is to produce a uniform product with a predetermined salt content. By controlling brine strength and time and movement in the solution, some uniformity can be expected. However, as salt intake is not directly proportional to immersion time the intake cannot be doubled by merely doubling the time. The objective is to induce a salt level of between 2 and 5 per cent into the flesh. Most fish are brined in a solution that contains 80–100 per cent of the amount of salt that can be dissolved in water, and an instrument called a brinometer can be used to measure this level. Table 15.1 shows the proportion of salt to water for various brine strengths. Total immersion in brine for anything between 1 and 20 minutes is usual for small meats, but anything larger may be packed in dry salt for a considerably longer Table 15.1 The proportion of salt to water at various brine strengths Brine strength (%)

Grams of salt per litre

10 20 30 40 50 60 70 80 90 100

26.4 52.8 79.2 105.6 132.0 158.4 184.8 211.2 237.6 264.0

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thermometer butterfly

drip tray

door smoke trays

drain plug

heating element

to smoke box

Fig. 15.1 A simply constructed smoker.

period. Once the meat is removed from the brine, it is left to drip and it is at this stage in cold smoking that a pellicle forms. This is a glossy film on the surface, which is made up of swollen protein. The meat is now ready for the smoking process. Smoking has some preservative properties in the form of phenols, which help to limit the activity of fish-spoiling bacteria. Another preservative present is formaldehyde. Phenols and carbonyls combine during smoking to give the meat a distinctive flavour and colour, although in some factories a dye is added to enhance this. Smouldering hardwood chips supply the smoke, the most common being oak. Different types can, however, give their own distinctive flavour. Smoking is usually carried out in a simple kiln (smoker) and the exposure time will depend on the type of meat being smoked. Large meats being cold smoked can spend anything up to 8 hours in the kiln, whereas a hot-smoked queen scallop may only need 25 minutes. Figure 15.1 shows a simply constructed smoker. As a rough guide to the complete process, these are the stages in hot smoking small scallops. The first stage is to clean the external shell and remove any barnacles or weed. The whole shell is then either steamed for 3–4 minutes or simmered lightly for 2 minutes. After being allowed to cool, the scallops are dipped into a 50 per cent brine solution for 1 minute. On removal from the brine they are left to drip dry. The open scallops are laid on trays and the individual meats are lightly brushed with a good quality cooking oil. The trays are then placed into a smoker set at 80°C and left for between 15 and 20 minutes, the time becoming more precise once the exact product requirement is known. On removal from the smoker the shells are left to cool and then packed for either direct dispatch or freezing.

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Cooked frozen scallops There is a current trend towards high quality, precooked, frozen meals that can be quickly reheated in a microwave oven, and when they are prepared correctly there is little loss in flavour or nutritional value. The main markets for this type of product are restaurants, frozen food retail outlets, and specialist caterers like those supplying airlines and banqueting functions. Cooking methods need not be any different in the preparation of cooked frozen foods as long as it is remembered that reheating will further add to cooking time. It is important to prepare shellfish slightly undercooked and let reheating bring them up to the mark. With some of the more delicate varieties of scallop, reheating may be all that is required for the full cooking process. There are many tried and tested recipes for both fish and shellfish and it is usually the addition of a good sauce that makes them different. The beauty of scallops is that they require little in the way of accompaniment to make them any tastier and usually the only reason for packing them out is to make the portion look larger. There are instances where a cooking process has led to a trade name being established for a particular product, which, in turn, increased its demand. Scampi refers to prawn tails (Dublin Bay prawns) being cooked with a special batter coating. Before scampi came into being, the market for the Dublin Bay prawn was very limited. A move along the same lines was the princess scallop, but this has as yet not met with the same success as scampi.

PACKAGING AND DISTRIBUTION Where there is a local market there should be no need to invest in expensive types of packaging. There are, however, advantages in presenting the final product in a professional manner. There will, of course, be certain standards imposed by local health agencies that will have to be adhered to. Scallops delivered in an old sack may not seem very enticing, yet it is very cheap and easy to present them in an attractive manner. Packaging them in a ‘netted pineapple’ is a form of marketing often used on Continental Europe. Figure 15.2 demonstrates the process, and Figure 15.3 shows the finished product. This makes for an eye-catching presentation. Good packaging will help to prevent drying out when in cold storage and should reduce damage from poor handling. An attractive outer covering will also help to catch the eye of the consumer. Speciality packaging allows the consumer to cook the scallop enclosed in its wrapping (boil in a bag), and this allows thawing without the usual flavour loss through leaching. There are many types of packaging available to the processor and each may have a specific purpose. The requirement may be to insulate, to protect from damage, to allow final cooking or to market the processed scallop.

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inverted bucket

mussel stocking

tie wrap

Fig. 15.2 The process of forming the ‘pineapple’.

Packaging materials Hydrocarbon polymers The hydrocarbon polymers include polythene, polypropylene and polystyrene. They are excellent where a moisture barrier is required and are fairly inexpensive. Being heat sealable gives them much versatility, but being permeable to some gases prevents them from being used for vacuum packing. Condensation polymers Both nylon and terylene come into the category of condensation polymers and both have excellent packaging properties. They are relatively impermeable to gases, good in low temperatures, give excellent clarity and can be heat sealed.

Marketing, Handling and Processing

303

Fig. 15.3 Scallops presented in a pineapple type of packaging.

Chlorinated polymers The best known chlorinated polymer is PVC, but others include polyvinylidene chloride, and hydrochlorides of rubber. All are good barriers to gas and water and can be used for low-temperature storage; another application being shrink wrapping. Laminates and waxed cardboard Most laminates are a polythene base with one other material to give the overall requirements of the product. Waxed cardboard also uses polythene as a coating and this provides a water barrier and a heat-sealing property. Aluminium foil Aluminium foil offers a barrier to almost everything in the external environment. However, it is expensive and requires a coating of polythene to make it heat sealable. Combinations Combinations of the above materials can meet the needs of most packaging requirements, although it must be said that new and improved materials appear on the market very regularly. With the objective of sealing in flavour and prolonging shelf life, various packaging techniques have been developed and have proved to be of great use to the industry.

Vacuum packing By removing all the gas from the package, deterioration of the product can be reduced and flavour can be sealed in. Vacuum machines work in two ways. The first

304

Scallop Farming

requires the meat to be put into plastic bags, then placed in the machine for gas removal and sealing. The second is more mechanized and carries out the whole packaging process automatically.

Gas packaging Gas packaging is a fully automated process, which has proved to be a big step forward in prolonging shelf life and retaining product flavour. Its principle is to seal the meat in a gas environment made up of oxygen and carbon dioxide. The oxygen level is high enough to keep the meat fresh and the carbon dioxide is present to keep bacterial growth to a minimum. However, it is an expensive process because the machines must be capable of the combined actions of package moulding, gas blending and sealing. Consequently, they are usually only cost effective when large quantities of meat are to be processed.

Distribution A fresh product must be transported to the customer as quickly as possible and in a condition that will prevent deterioration. With careful handling there is no reason why the consumer should not be able to eat a scallop in as fresh a condition as it was when it left the water. Frozen meat requires different handling, and distribution must be such that little or no heat differences occur during the process. Assuming that most retailers will carry on freezing the product for the short term, the most deterioration that can occur will be if there is a build up of heat during transportation. Refrigerated transportation is therefore essential.

SUMMARY •

•

• •

•

The level and intensity of marketing may vary with the size of the operation. To maximize a small output, a one-man farm may put much effort into display and promotion in the hope of attracting local markets. On a larger scale a farmer may put all his efforts into scallop production and rely on others to create the markets. Marketing is not considered as being restricted to the point of sale but as covering all aspects of handling from when the scallop leaves the lantern to when it arrives on someone’s dinner plate. Any marketing strategy should be considered as a recipe, the ingredients being price, promotion, product and place. Although a farm may be able to almost guarantee a steady supply of scallops, it must be borne in mind that this will only make up a small proportion of the total scallops landed, fishing being the main contributor to the market. Changes in demand are mainly controlled by consumer spending power, the prices of other shellfish, the scarcity or not of the prime product, the prices of competing foods and the effects of marketing on consumer choice.

Marketing, Handling and Processing • •

• • •

• •

• • • •

• • •

• •

305

Large businesses have an advantage in that they can seek outlets that require larger volumes of the product. By marketing with other farmers the small unit should at least be able to compete on equal terms, and will also have the benefit of being able to concentrate just on production and leave the selling to someone else. Anyone belonging to a marketing group must show trust and commitment, and be prepared to give up much of his independence. Processors are usually concerned with bulk consignments and will either blast freeze the meat or ship the whole animal live to larger markets. When a processor buys scallops for live distribution he will want the farmer to be more careful in his handling of the product. This request is usually accompanied by a premium on the price. Quality control for the scallop farmer, although important, is basically a question of commonsense, good handling and sensory assessment. The consumer is more aware now than ever before about the quality of produce, and legislation is moving quickly in his favour, especially in the perishable food market. In its own environment the scallop will support bacteria under fairly constant levels of temperature, oxygen and salt. Poor texture and appearance are accelerated by protein changes, and a dull, soft, tasteless meat is usually the result of prolonged and poor storage. Both large and small farms can benefit financially from processing their own product if the farmers feel it is within the scope of their activities. Freezing and subsequent cold storage are the most direct means of increasing the scallop’s value, but it is usually only large-scale or cooperative farms that can justify the outlay. The farmer can offer a product that is most attractive to the catering trade, first, because of its absolute freshness, and, second, because of its overall quality. Another attractive way of marketing the scallop is in the form of a half shell. There is a current trend towards high quality precooked frozen meals, which can be quickly re-heated in a microwave oven, and when they are prepared correctly there is little loss in flavour or nutritional value. Where there is a local market there should be no need to invest in expensive types of packaging. A fresh product must be transported to the customer as quickly as possible and in conditions that will prevent deterioration. With careful handling there is no reason why the consumer should not be able to eat a scallop in as fresh a condition as it was when it left the water.

Bibliography

Aitken A., Mackie I.M., Merritt J.H. & Windsor M.L. (1982) Fish Handling and Processing. Ministry of Agriculture, Fisheries & Food, Torry Research Station, Aberdeen. Amirthalingam C. (1928) On lunar periodicity in reproduction of Pecten opercularis near Plymouth in 1927–28. J. Mar. Biol. Ass. UK, 15, 605–641. Ashley C.W. (1944) The Ashley Book of Knots. Faber, London. Baird R.H. (1958) On the swimming behaviour of escallops (Pecten maximus L.) Proc. Malac. Soc. Lond., 33, 67–71. Baird R.H. & Gibson F.A. (1956) Underwater investigations of escallops (Pecten maximus L.) beds. J. Mar. Biol. Ass. UK, 35, 555–562. Barrow C. (1982) The Small Businessman’s Guide. Pitman Press, London. Bayne B.L. (ed.) (1976) Marine Mussels Their Ecology and Physiology. Cambridge University Press, Cambridge. Beaumont A.R. & Le Pennec M. A Key to the Larvae of British Bivalve Molluscs Based on Hinge Structure and Shell Shape. Department of Marine Biology, University College of North Wales, Bangor. Bourne N., Hodgson C.A. & Whyte J.N.C. (1988) A Manual for Scallop Culture in British Columbia. Canadian Technical Report of Fisheries and Aquatic Sciences, No. 1694, Fisheries and Marine Services Canada. Caldwell B. (1980) Sea Lawyer. Granada Publishing, London. Campbell A.C. (1976) The Hamlyn Guide to Seashores & Shallow Seas of Britain and Europe. The Hamlyn Publishing Group, London. Charton B. & Tietjen J. (1988) Marine Science. Facts on File Publications, New York. Cox I. (ed.) (1957) The Scallop. Shell Transport and Trading Company Ltd, London. De Hass W. & Knorr F. (1966) Marine Life. Burke, London. Desouter D.M. (1978) The Boat Owner’s Practical Dictionary. Hollis and Carter, London. Duncan P. (1989) Spawning and Flesh Weight Variations of the Scallop Pecten maximus on the West Coast of Scotland, DAFS Marine Laboratory, Aberdeen and Aberdeen University M.Sc Thesis. Fell H.B. (1975) Introduction to Marine Biology. Harper and Row, New York. Fraser D.I. (1983) Observations on the settlement of Pectinid spat off the West Coast of Scotland. ICES Cm K. Gree A. (1984) Anchoring and Mooring. Adlard Coles Nautical, London. Hardy D. (1981) Scallops and the Diver Fisherman. Fishing News Books. Hardy D. & Walford A. (1994) The Biology of Scallop Farming. Aquaculture Support, Scotland. Hardy D. & Walford A. (1995) Northern Adriatic Scallop Research Project (1995). Aquaculture Support, Scotland. Hazeltine B. & Bull C. (2003) Field Guide to Appropriate Technology. Elsevier Science Publishers, New York.

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Herriot N. Mussel Farmers Manual. Irish Board of Science and Technology. Le Pennec M. (1980) The larval and post larval hinge of some members of bi-valve molluscs. J. Mar. Biol. Ass. UK, 60, 601–617. Mason J. (1958) A possible lunar periodicity in the breeding of the scallop, Pecten maximus (L.). Ann. Mag Nat. Hist., 37, 601–602. Mason J. (1983) Scallop and Queen Fisheries in the British Isles. Fishing News Books. Minchin D. & Duggan C.B. (1989) Biological control of the mussel in shellfish culture. Aquaculture, 81, 97–100. Milne P.H. (1972) Fish and Shellfish Farming in Coastal Waters. Fishing News Books. Paul J.D. (1983) Potential for Scallop Culture in the UK. SFIA Technical Report No 224. Paul J.D. (1987) An Introductory Guide to the Cultivation of the Queen Scallop. SFIA Technical Report No 297. Paul J.D. (1988) Cultivation of the Scallop Pecten maximus using the techniques of ear hanging. SFIA Technical Report No 326. Seafish Report. (1988) Scottish Marine Farming Strategic Study. SFIA Report No 335M. Shumway S.E. (1989) Scallops: Biology, Ecology & Aquaculture. Elsevier Science Publishers, New York. Sisman D. (1982) The Professional Divers Handbook. Submex, London. Spencer B. (2002) Molluscan Shellfish Farming. Fishing News Books. Ventilla R.F. (1982) The Scallop Industry in Japan. Adv. Mar. Biol., 20, 309–382.

Index

access, choice of site, 63 adductor muscle, toxin build up, 17 algae blooms, 17, 44 growth, 17 production, hatcheries, 53 toxins, 20 amnesic shellfish poisoning ASP, 17–8 choice of site, 63 anaerobic conditions, 13 anchoring, marking, 103–5 anchors breaking strain, 168–9 diving work, 225–6 fluke angles, 183–4 holding power, 167–8 placement, 179 secondary, 105 self construct, 184–5, 202–4 spring, 168, 169 terminology, 174 types, 176–6 weight, 168 Archimede’s principle, moorings, 181–2 Argopecten irradians, China, 15 Argopecten purpuriatus, Chile, 15 Australia, farming, 16 automatic sorting equipment, 233–4 bacteria, fish flesh, 295, 296 balance, scallop growth, 42 barnacles, 44 bathyplankton, 24 beam trawl, scallops fishing, 283 benthic, scallop food, 41 benthos, seabed, 24 boat deck layout, 125 durability, 120 electronics, 123 engines, 122 farm requirement, 120

hull types, 123–5 hydraulics, 123 machinery, 123 manoeuvrability, 121 rigging, 127 running costs, 123 safety regulations, 128 size and displacement, 120 stability, 120 use of, 109–10 boat work, see moorings boring worms, predation, 43 bottom culture choice of site, 64 diving, 217–8 Japan, 11–13 predation, 43, 44 varieties, 163–61 breakwaters, 211 buoyancy adjustable, 112 collector bags, 71 explanation, 239 fouling, 267 frequency, 256–7 longline, 110, 233 oyster cage and frame, 153, 155 pearl nets, 139 requirement, 240–7 size and lifting capacity, 256 variation, 256–7 work rates, 249–50 bureaucratic anomalies, 18–19 business structure associations, 132 co-operatives, 132 equipment pools, 133 partnerships, 132 byssus, larval growth, 51, 52 Canada, farming, 16 capital outlay, costs, 263–4 capstan, boat, 126

309

310

Index

carnivores, plankton, 26, 32, 52 cash flow, 264 cement blocks, see moorings Chains moorings 183–4 types, 184 Chile, farming, 15 China, farming, 15 Chlamys asperrima, Australia, 16 Chlamys farreri, China, 15 Chlamys opercularis, see scallops Chlamys purpurta, Peru, 15 circular search, diving, 219–20 classification, scallops, 24 collector bags, 66 attachment, 70 constructing, 67–69 diving, 218 hanging, 70–2 mesh size, 67 monitoring, 79 quantities, 79 setting, 69 spat collection, 66–74 transporting, 162 compass search, diving, 220–1 convection, water movement, 35 Co-operatives, 20, 292 Copepods, 26, 28 corner posts grid systems, 105 replacement, 108 costs depreciation, 264–5 examination, 262–6 fixed, 264 variable, 264 crabs fishing, 287–8 predation, 43 Crown commissioners, several orders, 19, 59 cultch, settlement material, 54 dehydration, scallop meat, 297 Department for Transport, 60 depreciation, cost, 264–5 depth, site choice, 63 Diarrhoetic shellfish poisoning DSP, 18 choice of site, 63 diatoms, 25, 28, 37 digestive tract, Iarval growth, 50 dinoflagellates, 25 disposable netting, 195 dissoconch, shell growth, 49 distribution, marketing, 304 diversification, 270, 272

diving anchors, work, 216, 225–6 boat maintenance, 218 bottom culture, 217 broken lines, 218 fishing, 285, 286 gear, 215 general view, 214 grid search, 220 harvesting, 157 HSE, 215 line tangles, 217 marine fouling clearance, 216–7 moorings, 195 predator spotting, 217 propeller clearing, 226 qualifications, 214 rafts, 155 representatives, 215 salvage, 218 seabed searches, 219–21 seabed surveys, 216, 226 shackle replacement, 222–3 supervisors, 215 team composition, 214 work practice, 215 work, scope, 216 worksite, 221–222 domoic acid, toxins, 17 dredge, scallop, 13, 284 dredge, venturi, 285–6 D-shaped larvae, 47, 48–9, 54, 76–7, 86–90 ear hanging attachments, 146, 147 buoyancy, 146 Japan, 14 mortalities, 266 production alternatives, 266 techniques, 145–7 E. coli, water purity, 64 ecology, 10 economic multiplier, 5 electron microscope, photos, 9 environment epiplankton, 24 regulations, 60 respect for, 5, 6, 134 equipment levels of, 261 repair and maintenance, 262 transporting, 262 escalop, France, 4 euphotic zone, photic, 22 euryhaline, salinity, 30 exposure, site choice, 62

Index feeding, larval growth, 51 fertilization, hatcheries, 54 filler, cultch, collector bags, 66 filters, monitoring, 85–6 Fishermen’s associations, 60 fishing, diversity, 4 Food Standards Agency, regulations, UK, 63 food supply choice of site, 62 filtering, 3 scallop growth, 62 scallop reproduction, 46 foot, larval motion, 51 varieties, 22 formalin, buffering, 81, 82 fouling buoyancy, 267 collector bags, 162 gear handling, 250 lanterns, 163, 164 scallop shells, 160 suspended culture, 163 France, farming, 15 freezing, scallop meat, 298 gametes presence of, 46, 47 roe content, 44 water temperature, 29 geoids, tidal movement, 33 geology, see moorings gills, larval growth, 51 gonad analysis, 89–93 index, 93 scallop reproduction, 45, 46, 47 states, 46–47, 91–2 government agencies, 60 GPS, anchor marking, 103, 285 grading, lantern changes, 243 grapnel, 204 grapnel creeper, 204 graticule, microscope work, 83–4 grazing, plankton, 26 grid search, diving, 220 grid system, jumbo longline, 107 harvesting diving, 223–4, 225 equipment, 285, 286 mussels, 281 spat collector bags, 72–74 hanging culture, 137 hatcheries manila clams, 279 oysters, 273 spawning, 53

herbivores, plankton, 26 hermaphrodites, scallop reproduction, 44 hog ringing, collector bags, 149, 150 holoplankton, 24 hypoplankton, 24 identification, larvae, 86–90 Japan predators, 14 production costs, 14 spat collection, 13–14 Japanese Efficiency Model, 11, 12 jetties, 129 jumbo longline, 107 kati-ami dredge, 13 king scallop, 6, 40 knots attachment to longline, 100 long splice, 101 langmuir circulations, 33 lanterns alternate rigging, 144 build criteria, 190–1 costs, 143–5 dimensions and logistics, 243–4 employed, explanation, 239 emptying, 194–5 equipment logistics, 240–7 grading, 243 handled, explanation, 239 Japan, 11, 140–2 management, 268 mesh sizes, 243 permanent covers, 144–5 production alternatives, 265 removable stocking, 140–2 requirement, 251–2, 258–9 rigging, 193 self construct, 191–4 sorting tray, 195 underwater cleaning, 217 Walford loading system 142–3 weights, 257 work rates (handling), 249–50 larval growth, feeding, 51 larval identification D-shaped larvae, 49 law, farms, 133 lifting bags, diving, 223, 224 light compensation depth, 31 light photosynthesis, 31 scallop reproduction, 46 lifting bags, 223, 224

311

312

Index

line search, diving, 220 lobsters, fishing, 288 local authorities, regulations, 60 locking, scallop shells, 247 locomotion, larval growth, 52 longlines anchoring, 98–100 attachment knots, 100 boat positioning, 117 breaking, 109, 226 buoyancy, 110 diving, 218 employed, explanation, 239 grid system, 105–8 lantern hanging, 110 length, 255 management, 266, 268 marking (information), 266, 7 motion transmitting, 112–3 mussels, 279, 280 oysters, 274 production alternatives, 265, 266 requirement, 251–2, 258–9 setting, 97–99, 110–12 shell wear, 114 sinking, 267 spacing (equipment), 256 spat settlement, 266 tensioning, 100–03 weights, 111 macroplankton, 22 Magdalen Islands, farming, 16 manila clams, 277–8 manpower requirement, 261–2 mantle, scallop growth, 41, 42, 50 marine activity, 76 marketing groups, 292–3 Japan, 15 manila clams, 278 mix, 227 oysters, 276 promotion, 291 sales, 260, 293 scallops, 290–3 match/mismatch, food supply, 26 meat yield hanging culture, 161 seabed, 161 meroplankton, 24 metamorphosis, larval growth, 50, 51, 52 micronekton, 24 microplankton, 22 microscopes, 82–3 Mimachlamys australis, Australia, 16 mollusca, 3

monitoring data recording, 86 equipment, 77 programmes, 80, 93–95 science, 75–86 moorings Archimede’s Principle, 181–2 attachments, 171 boat work, 187 boulders, 186 cement blocks, 185 cement keys, 186–7 chains, 183–4 chandlery, 170 component protection, 180 depth, 173 four point, 178 geology, use of, 185–6 longline, 179–80, 186–7 maintenance and inspection, 186, 188 markers, self build, 210–11 mechanical advantage, 182–3 mousing, 172 navigation, 128–9, 210 rafts, 119, 180–1, 199 ropes, 183 running, 131 seabed, 174 shelter, 173 shore points, 186 single point, 176, 177 three leg, 177 tide, 173 two point, 176, 178 water purity, 174, 175 mortalities ear hanging, 266 hanging culture, 161–2 production logistics, 244–6 seabed, 161–2 stocking densities, 241 mousing, see moorings multiplier, economic, 5 musculature, larval growth, 50 mussels byssus thread, 281 farming, 279–81 identification, larvae, 88 predation, 248 raft cultivation, 280 scallop predation, 44, 74 spat collection, 279–80 spawning, 279 Mytilids, see mussels

Index navigation self construct markers, 209–10 special markers, 128–9 net riddles, scallops, 204–5 neurotoxin shellfish poisoning choice of site, 63 NSP, 18 neuson, 24 New Zealand, farming, 15 Notovola fumata, Australia, 16 nursery tanks, hatcheries, 54 nutrients autumn, 38 dispersal, 34 ocean zones, 23 opportunity cost, 263 optimum factor combination, 264 organs, scallop, 45 oxygen, shelf life, 295 oysters bottom culture, 277 cage construction, 152 collection, 273 hatcheries, 273 packaging gas, 304 materials, 302–3 meats, 301–4 vacuum, 303–4 paralytic shellfish poisoning, PSP, 18, 25, 63 Patinopecten yessoensis, Japan, 10 pearl nets buoyancy, 139 cleaning, 217 description, 138–9 handling, 139 Japan, 11, 14 rigging, 196 self made, 195–6 sizes, 139 Pecten fumatus, Australia, 16 Pecten jacobaeus, Italy, 164, 165 Pecten maximus, see scallops Pecten novazealandair, New Zealand, 15 Pectinides, see scallops Pediveliger, D-shaped larvae, 49 percent cover, see stocking densities Peru, farming, 15 photosynthesis, 31–32 phytoplankton diatoms, 25 food, 30 Plactopecten magellanicus, Magdalen Islands, Canada, 16

plankton D-shaped larvae, 28 food supply, 30 grazing, 26, 27 hauls, nets, 76–8, 81 levels, 6 mortality, 29 nutrients, 31 oxygen levels, 30 photosynthesis, 25 reproduction, 26 scallop food, 3 seasonal variations, 35 size, 22, 24 water temperature, 29 plastic trays construction, 150 weights, 257 pleuson, 24 pocket nets, scallop culture, 148–9 pollution, scallop mortality, 44 polydora, predation, 44, 248 polystyrene blocks, rafts, 198 pots, crabs, lobsters, prawns, 287 prawns, fishing, 288 predation boring worms, 43 scallop spat, 232, 235 spat collection, 74 pressure washers, 123, 207, 248 processing, scallops, 297–301 production levels, 257–9 profitability, farm, 269–70 propeller, clearing, 226 protoplankton, 24 pycnocline, 28, 29 quality control, 294–7 queen scallop, see scallops rafts adjustable buoyancy, 155–6, 200–2 breakwaters, 211 buoyancy, 197–8 choice of site, 63 culture, 118 design criteria, 196–7 effective use of, 268 lantern hanging, 110 moorings, 119 mooring points, 199 mussel cultivation, 280 production alternatives, 265 safety, 119 self build, 196–200 steel pontoons, 200 work, 118

313

314

Index

red tides, toxins, 17, 25 Regulating Orders, 19, 20 regulatory factors, 19, 59, 60 rents, farm, 131 reproduction, plankton, 26 research, scallops, 8 riddles, scallop culture, 206–7 rope culture, scallops, 147–8 ropes, moorings, 183 running moorings, endless rope, 131 safety, 119, 131 salinity, 30, 40, 62 salvage, 133–4, 218 saturated systems, spat transportation, 75 scallop academic interest, 8 buying in, 260 Chlamys opercularis, 6 economic multiplier, 5 environment, 5 fishing, 283–6 food, 3, 22, 46, 62 grading, 255 grading equipment, 205–7 growth, 41, 241–2, 250–1, 255 habitat, 6, 40 handling, 393–7 king scallop, 6 mortalities, 247–8, 258, 294 organs, 50 Pecten maximus, 6 Pectinides, 6 predators, 42, 248 processing, 297–301 queen scallop, 6 religious connections, 4 reproduction, 44–52 research, 8 storage, 294 swimming, 3 tide flow, 40 world interest, 10 yield, meat, 251–2, 260 scallop spat buying in, 231–2 collection, 231 growth, 51 handling, 74 monitoring, 75–9 mortalities, 232 photos, 9–10 quantities, 232–3 research, 8 sorting, 232–6 scientific equipment, monitoring, 81–6

seabed choice of site, 63 grid, wild ranching, 158–9 Sea Fish Industry Authority, 264, 272 sea grass, barrier, 160 senses, scallop growth, 41 Several orders, 19, 20 shock rings, shell growth, 41 silicate, diatom growth, 31 site selection, spat levels, 61 slide preparation, 84–85 smoking, scallops meat, 298–300 sorting equipment, scallops, 205–7 Spanish windlass, tensioning, 108, 182, 222 special markers, see navigation species, choice of, 259 species identification, 86–91 splice, long splice, 101 spring, anchoring systems, 168–9 stag’s horns, 116 starfish, 43, 248 star wheel roller, 114–15, 126, 164, self build, 207–9 stenohaline, salinity, 30 stocking densities, spat, 75, 240–1 stoppers, anchor work, 102–3 stratification, 29 striae, shell growth, 41 supply and demand, 291–2 surface buoys, longlines, 114 techopelagic, 24 temperature bacteria, 295 choice of site, 62 scallop reproduction, 45 sustaining plankton life, 28 thermal shock, scallop reproduction, 46, 54 thermocline description, 28–9 summer, 38 tide choice of site, 62 effect on longline, 114 explanation, 32–4 mortalities, 247–8 toxins choice of site, 63 effect on sales, 291 Japan, 14 problems with, 17–8 trestles, oysters, 274 trial collectors, 77, 78–9 trochophore, scallop reproduction, 47 tubeworms, scallop mortality, 44

Index ultraplankton, 24 United Kingdom, farming, 16 upwellings, water movement, 30, 34 velum larval growth, 50 scallop reproduction, 47 virus, scallop mortality, 44 water movement, 32 purity, 64 weather, management, 247 weed, scallop predation, 44, 159, 161 weights, self build, 212–3 wet well, rafts, 118

wild ranching large scale, 156 manmade barriers, 158, 159 natural barriers, 157 predation, 259 seabed grid, 158–9 small scale, 156–61 wind dispersal of nutrients, 32 windrows, tides, 32 work rafts, 201 work rates, gear handling, 249–50 World symposia, scallops, 32 yields, shell meat, 260–1 zooplankton, 26–8 zygote, reproduction, 47

315