Ecological Aquaculture

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Author: Barry A. Costa-Pierce

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ECOLOGICAL AQUACULTURE The Evolution of the Blue Revolution

ECOLOGICAL AQUACULTURE The Evolution of the Blue Revolution Edited by Barry A. Costa-Pierce

Rhode Island Sea Grant College Program Graduate School of Oceanography Department of Fisheries, Animal and Veterinary Science University of Rhode Island

# 2002 Blackwell Science Ltd, a Blackwell Publishing Company Editorial Offices: Osney Mead, Oxford OX2 0EL, UK Tel: +44 (0)1865 206206 Blackwell Science, Inc., 350 Main Street, Malden, MA 02148-5018, USA Tel: +1 781 388 8250 Iowa State Press, a Blackwell Publishing Company, 2121 State Avenue, Ames, Iowa 50014-8300, USA Tel: +1 515 292 0140 Blackwell Science Asia Pty, 54 University Street, Carlton, Victoria 3053, Australia Tel: +61 (0)3 9347 0300 Blackwell Wissenschafts Verlag, KurfuÈrstendamm 57, 10707 Berlin, Germany Tel: +49 (0)30 32 79 060 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 2002 by Blackwell Science Ltd Library of Congress Cataloging-in-Publication Data Costa-Pierce, Barry A. Ecological aquaculture: the evolution of the blue revolution/Barry A. Costa-Pierce. p. cm Includes bibliographical references (p.). ISBN 0-632-04961-8 (alk. paper) 1. AquacultureÐEnvironmental aspects. 2. AquacultureÐEconomic aspects. I. Title. SH135 .C67 2002 338'71Ðdc21 2001043507 ISBN 0-632-04961-8 A Catalogue record for this title is available from the British Library Set in 10/13pt Times by DP Photosetting, Aylesbury, Bucks Printed and bound in Great Britain by MPG Books Ltd, Bodmin, Cornwall For further information on Blackwell Science, visit our website: www.blackwell-science.com

I dedicate this book to the memory of my beloved father, Edward A. Pierce Sr., who passed away while this book was being completed; to my mother, Thelma Pierce; and to my United Nations family ± Lily Mae Ho-Pierce, Lia Kaiulani Ho Costa-Pierce, Sierra Shaiming Ho Costa-Pierce ± and to the Elders of the Wampanoag Tribe of Massachusetts, USA.

Contents

List of Contributors Foreword Preface Acknowledgments Part 1

The Background of Ecological Aquaculture

1

The History of Aquaculture in Traditional Societies Malcolm C.M. Beveridge and David C. Little

2

The Ahupua'a Aquaculture Ecosystems in Hawaii Barry A. Costa-Pierce

Part 2 3

4

The Methods of Ecological Aquaculture

ix x xii xv 1 3 30

45

Development and Application of Genetic Tags for Ecological Aquaculture Theresa M. Bert, Michael D. Tringali and Seifu Seyoum

47

Aquaculture Escapement, Implications and Mitigation: The Salmonid Case Study C.J. Bridger and Amber F. Garber

77

5

Farming Systems Research and Extension Methods for the Development of Sustainable Aquaculture Ecosystems Barry A. Costa-Pierce

103

6

A Market-driven, Social Ecological Approach to Planning for Sustainable Aquaculture: A Case Study of Tilapia in Fiji Barry A. Costa-Pierce

125

Part 3 7

The Context of Ecological Aquaculture

Village-based Aquaculture Ecosystems as a Model for Sustainable Aquaculture Development in Sub-Saharan Africa Randall E. Brummett and Barry A. Costa-Pierce

143 145

viii

Contents

8

Silvofisheries: Integrated Mangrove Forest Aquaculture Systems William J. FitzGerald, Jr

161

9

An Integrated Fish and Field Crop System for Arid Areas James E. Rakocy

263

10

Sustainability of Cage Aquaculture Ecosystems for Large-Scale Resettlement from Hydropower Dams: An Indonesian Case Study Barry A. Costa-Pierce

11

The Role of Aquaculture in the Restoration of Coastal Fisheries Mark A. Drawbridge

Part 4 12

Conclusion

Ecology as the Paradigm for the Future of Aquaculture Barry A. Costa-Pierce

Index

286 314

337 339 373

List of Contributors

Theresa M. Bert Florida Marine Research Institute,100 Eighth Avenue South, St. Petersburg, Fl 33701, USA Malcolm C.M. Beveridge FK9 4LA, Scotland

Institute of Aquaculture, University of Stirling, Stirling

Christopher J. Bridger College of Marine Sciences, University of Southern Mississippi, 703 East Beach Drive, Ocean Springs, MS 39564, USA Randall E. Brummett International Center for Living Aquatic Resources Management (ICLARM), BP 2008 (Messa), YaoundeÂ, Cameroon Barry A. Costa-Pierce Rhode Island Sea Grant College Program, Department of Fisheries, Animal and Veterinary Science, University of Rhode Island, Narragansett, RI 02882, USA Mark A. Drawbridge Hubbs-Sea World Research Institute, 2595 Ingraham Street, San Diego, CA 92109, USA William J. FitzGerald, Jr

PO Box 6997, Tamuning, Guam 96931

Amber F. Garber Department of Zoology, North Carolina State University, Raleigh, NC 27695-7617, USA David C. Little Scotland

Institute of Aquaculture, University of Stirling, Stirling FK9 4LA,

James E. Rakocy University of the Virgin Islands, Agricultural Experiment Station, Kingshill, VI 00850, USA Seifu Seyoum Florida Marine Research Institute, 100 Eighth Avenue South, St. Petersburg, Fl 33701, USA Michael D. Tringali Florida Marine Research Institute, 100 Eighth Avenue South, St. Petersburg, Fl 33701, USA

Foreword

During the early years of the modern aquaculture era ± which I think of as starting in the 1960s ± practitioners of the art undoubtedly considered themselves to be strong environmentalists. Working with nature to produce food, bait, and ornamental species for the enjoyment of humans was the goal, but the practice involved establishing and maintaining the best possible conditions for production of the target species. Our understanding of pond dynamics, physiological requirements of culture species, and aquatic animal nutrition and disease were just a few among the many topics addressed by researchers. A tremendous amount of information on the relationships between aquatic organisms and their environment, e.g. ecology, was generated and continues to be generated by aquacultural researchers. Yet, by the mid-1980s, at least some forms of aquaculture were being branded as detrimental to the environment. It took a bit of time for the aquaculture community to become sufficiently introspective to recognize that, indeed, some of their practices had negatively impacted the environment. For at least the past decade, a considerable amount of time, money, and effort have been expended by the aquacultural community in addressing both real and perceived problems. The mantra of the aquacultural community became focused on sustainability. Many publications have appeared over that period which address the criticisms and relate how aquaculture has responded to them. Ecological Aquaculture takes a somewhat different approach in that it provides interesting insight into what we would now consider to be primitive culture systems and then ties those activities into modern aquaculture approaches. The book is edited and authored to a considerable degree by Barry Costa-Pierce who has been one of the leaders in the discussion of responsible and sustainable aquaculture development. A prolific author of often thought-provoking articles, he has assembled some of the other leading thinkers in the field to provide a pot-pourri of information spanning the spectrum from artisanal to high technology approaches to producing aquatic animals with an eye on maintaining balanced ecosystems. The approaches advocated in this volume represent the future of aquaculture around the world. Criticisms will continue to be lodged by opponents, but the fact is that if the demand for seafood is to be met in the future, a major source will have to be from aquaculture as capture fisheries are currently being exploited at or beyond maximum sustainable yields. Aquaculture often cannot be practiced without some

Foreword

xi

environmental impact, but that impact can be reduced, hopefully to insignificance, if the proper approaches are adopted. This book helps define those approaches. It should be required reading for anyone interested in producing aquatic organisms in an environmentally responsible manner; which means that it should be read by everyone involved in aquaculture. While the minds of the opposition may not be changed by volumes such as this, those members of society who are interested in the facts concerning how environmentally responsible aquaculture has been practiced in the past, how it is currently being practiced, and where it might be going in the future will find this book to be an excellent primer on the topic. Robert R. Stickney Director Texas Sea Grant College Program Texas A&M University College Station, Texas

Preface

Ìt is the arrogance of the rich to teach the virtue of poverty to the poor.' Dr P.M.S. Blackett, the late Nobel Prize-winning physicist `Don't underestimate the power of a small group to change the World. In fact, that's the only ones who ever have.' Dr Margaret Mead Ecological aquaculture is an integral part of our common planetary wisdom and cultural heritage, and is an essential part of our future evolution as a sophisticated species living in peace with the Earth's complex ecosystems. Traditional aquaculture systems are closely integrated with the management of indigenous land and water food production systems, and rely on intact natural ecosystems. Aquaculture ecosystems evolved as sophisticated forms of agriculture in areas of Asia, the Pacific and Europe where human populations overshot the carrying capacities of the traditional agro- and aquatic ecosystems to support these societies. Aquaculture evolved to take pressure off natural and cultivated land and water ecosystems and ecosystem services. In these `human ecosystems', aquaculture evolved as a part of ± not the dominating feature of ± the wonderful variety of aquatic life, and the evolutionary diversity of cultures that decided to undertake such an extraordinarily specialized art. `Blue revolutions' ± as the natural evolution of societies ± have been happening for over 2000 years. In this regard, the concept of ècological aquaculture' is nothing new ± especially in Asia. In the West, however, the evolution of the `blue revolution', and avoiding the social and environmental blunders of the `green' one, are more recent. Development of an aquaculture ecosystems pedagogy and systems `mentality' began only in the late 1970s and 1980s (MacKay, 1983). The purpose of this book is to stimulate discussion among aquaculture's modern scientific, education, extension communities ± and the larger aquatic resource management community ± about the principles, practices, and policies needed to develop ecologically and socially sustainable aquaculture. It is one of the first primers on ideas of how we are to become twenty-first century stewards of the Earth's cultivated aquatic ecosystems using the singular unifying rubrics of ecological aquaculture and aquaculture ecosystems. However, serious students of aquaculture will recognize that many of the ideas conveyed in this book are nothing new, but have

Preface

xiii

been repackaged in a way to stimulate discussion on how the latest science and outreach advances can assist the evolution of aquaculture into the modern era. The authors of the chapters in this book demonstrate how aquaculture can be a valuable player in the evolution of planning for sustainable aquatic resource management in a more crowded, protein-hungry world. To meet the protein needs for 8 billion people, and at the same time protect the oceans and freshwater ecosystems of the Earth from the uncontrolled exploitation of hunting (capture fisheries), aquaculture must expand dramatically in the twenty-first century. To accomplish expansion, however, aquaculture must be planned as part of, not separate from, a comprehensive management strategy for the restoration of fisheries ecosystems. Fisheries legislation throughout the world, such as the US Magnuson-Stevenson Sustainable Fisheries Act, falls far short of this vision, completely ignoring aquaculture in the planning for sustainable capture fisheries. To accomplish major worldwide expansion, and to ensure its social acceptance, aquaculture needs family and community roots in addition to corporate ones. Thousands of new, ecologically and economically sustainable family farms and progressive start-up companies need to be developed in the twenty-first century. These farms will need to practice ìnput management', recycle water, nutrients and materials, and produce healthy, uncontaminated products without discharges. Farmers incorporating aquaculture into family farms and new companies will internalize, not externalize, plans for more efficient resource recycling and enhance natural ecosystem services as part of their business plans and economic projections ± not neglect their social and environmental responsibilities, as suggested in a classic volume by Ken Boulding some 40 years ago (Boulding, 1962). Aquaculture developments need greater planning in the larger regional and community contexts. In short, aquaculture must become less short-term and less production oriented, and become more ecologically, community, and culturally based. Such approaches make good business sense! If aquaculture doesn't evolve with an environmentally friendly/socially responsible pedagogy in nations where it is new, but evolves principally as a `corporate' undertaking, aquaculture will never bring its full potential benefits. Environmental regulations, management difficulties, and resource and social conflicts coming in the crowded twenty-first century will halt its progress. And it is certain that the public ± worldwide ± will not accept any new forms of food production that exploit people, cause environmental harm, or produce new sources of aquatic pollution. In short, the `blue revolution' will quickly go bust unless it `greens up'. I conclude this book with these concerns about the role of aquaculture in the twenty-first century, contending that aquaculture needs to return to its historical roots ± its ecosystem and community-based roots ± and that ecological aquaculture needs to become the basic level of analysis for development planning for aquaculture worldwide. We contend that in this century, ecological aquaculture needs to emerge as the dominant method not only for smallholder farms, but also for commercial aquaculture. In addition, ecological aquaculture scholarship needs to emerge as a `new' field of applied environmental scholarship throughout the world at the major land and sea universities to assist aquaculture's rapid transition to social and

xiv

Preface

environmental sustainability, and to integrate aquaculture into mainstream planning for sustainable fisheries and coastal zone management. By adopting ecological principles as the basis of development planning aquaculture will play an important role in creating new social constructs that tie together thousands of new, knowledge-based family farmers and companies, producing huge benefits to society. Management of these ècotones' between society, natural ecosystems, and sustainable environmental development is the key to the future of sustainable, ecological aquaculture.

References Boulding, K. (1962) The Reconstruction of Economics. Science Editions, New York. MacKay, K. (1983) Ecological aquaculture, new approaches to aquaculture in North America. Journal of the World Mariculture Society, 14, 704±713.

Barry A. Costa-Pierce University of Rhode Island Narragansett, RI

Acknowledgments

Ideas for this book were planted in the late 1970s while I studied with Murray Bookchin (Bookchin, 1985) and Jim Nolfi at the Institute for Social Ecology, Goddard College in Plainfield, Vermont. Murray and Jim were early pioneers in the study of the social ecology of food systems, alternative energy and social strategies. In addition, I am forever grateful to my teachers, who have helped me (and many others) to formulate the ideas and create the inspiration needed to produce this book, especially: Joseph Kiefer, Roger Pullin, Ron Zweig, Daniel Pauly, John Lyle, Ian Smith, John Bardach, Rich Merrill, Ken MacKay, Ed Laws, Lee Swenson, E.F. Schumacher, Amory Lovins, Eugene Odum, David Brower, Page Nelson, Margaret Mead, Bill McLarney, and John Todd. Special thanks go to all the pioneers at the New Alchemy Institute and the Farallones Institute of the 1970s and 1980s. This book would not be possible without the stimulation from a host of aquatic friends who've been `swimming in these same blue waters' ± special people who have served as examples to me and countless others by dedicating their lives towards giving the next generation a rehabilitated blue-green planet ± Pete Bryant, Bob Stickney, Otto Soemarwoto, Orten Msiska, John Wagner, Randy Brummett, Dave Penn, Arlo Fast, Sutandar Zainal, Reg Noble, Pam Sager, Pepen Effendi, Gelar Wiraatmadja, Jean Davidson, Reg Noble, Joseph Ofori, Jay Maclean, Jim McVey, Gail Work, John Lyle, Glenn Jones, John Munro, Sarvahara Judd, Fredson Chikafumbwa, Chris Bridger, Earl Barnhart, Hilde Maingay Barnhart, Russell Cuhel, Dave Karl, Catalino de la Cruz, Joseph Weinstock, Dan Chodorkoff, Charles Woodard, Calley O'Neill, Dick Jacobs, Daniel Jamu, Don Heacock, Spencer Malecha, Rick Weisburd, Clive Lightfoot, Mark Prein, Jim Rakocy, Les Behrends, Bill Engler, and Anne van Dam. Special thanks to Kay Bruening for all her professional assistance in preparing the book for publication; and to the staff of the Mississippi-Alabama Sea Grant Consortium.

Reference Bookchin, M. (1985) The Ecology of Freedom. Cheshire Books, Palo Alto, CA.

Ecological Aquaculture: The Evolution of the Blue Revolution Edited by Barry A. Costa-Pierce Copyright © 2002 by Blackwell Publishing Ltd

Part 1

The Background of Ecological Aquaculture


Chapter 1

The History of Aquaculture in Traditional Societies Malcolm C.M. Beveridge and David C. Little Institute of Aquaculture, University of Stirling The origins of aquaculture The origins of aquaculture are lost in history and little evidence remains to direct even a serious investigator of the subject. There are, after all, no aquaculturespecific artifacts to guide archaeologists. There is often little to distinguish abandoned ponds, even supposing we were able to find them, from dams of various types or from systems for producing inundated arable crops such as rice. Surface water would be stored to support communities or households in many cultures, and the predominant use for domestic/agricultural purposes may disguise a secondary role of holding or growing fish. Where rainfall is seasonal the focus of communities is around surface water bodies that may have originated as little more than natural depressions but became modified by the dependence these communities had on them. The presence of fish bones and shells in refuse heaps at early human settlements, or representations of fish on cooking pot shards, indicate only that the occupants ate these foods, not how they obtained them. The tools used in aquaculture are common to farmers and fisher folk, and remains of net-like materials or hooks tell us only about how fish met their fate, not whether they were caught from a river or from a fishpond. With few exceptions there is also no genetic record of domestication to draw upon, an important distinction between fish and livestock being that fish didn't need to be domesticated in the way livestock did in order to rear them in captivity. In this chapter, we examine what is known about the origins and development of aquaculture among traditional societies: who practiced it, and why, what distinguishes it from industrial and post-industrial aquaculture and its legacy. We briefly consider agriculture and current theories concerning its origins and development. We draw upon examples from traditional societies in four continents ± Africa, the Americas (with the exception of Hawaii, which is considered in detail in the following chapter), Asia and Europe ± and from various periods in history. Unfortunately, our review is not entirely balanced as there remain enormous gaps in knowledge. We begin with a consideration of what aquaculture is and how it differs from hunting.

4

Ecological Aquaculture

Aquaculture: some definitions It is important at the outset to be able to distinguish aquaculture from fisheries and agriculture. It may be differentiated from fishing because, as in agriculture, some measure of care or cultivation is involved. Reay's (1979) definition of aquaculture as `Man's attempt, through inputs of labour and energy, to improve the yield of useful aquatic organisms by deliberate manipulation of their rates of growth, mortality and reproduction' appeals from a biological perspective. However, it omits the other key component that distinguishes it from hunting: the concept of ownership or the extension of access and exploitation rights. The recently revised definition of aquaculture used by the UN Food and Agricultural Organization states that aquaculture is: `. . . the farming of aquatic organisms including crocodiles, amphibians, finfish, molluscs, crustaceans and plants, where farming refers to their rearing to their juvenile and/or adult phase under captive conditions. Aquaculture also encompasses individual, corporate or state ownership of the organism being reared and harvested . . .' (Rana, 1998). In this definition, both husbandry and ownership are seen as intrinsic. However, many traditional forms of aquaculture are based on the exploitation of multipurpose water bodies in which the organisms themselves are `common property', i.e. òwned' neither by an individual nor by some corporate body or the state. For present purposes we assume the key criteria distinguishing farming from hunting are that: there is some form of intervention(s) to increase yields; and l there is either ownership of stock or there are controls on access to and benefits accruing from the interventions (for parallels in agriculture see Bromley, 1992). l

Another key point in the FAO definition: end purpose is not at issue and fish owned and reared other than for food are regarded as the products of aquaculture. Nevertheless, as is discussed further below, differentiating between hunting and farming in the aquatic environment remains fraught with difficulties, in large measure because comparatively little effort has been expended on documenting and analyzing the range of methods used in exploitation of aquatic environments. A further set of definitions is necessary in order that we can compare aquaculture in traditional societies with contemporary practices from an ecological standpoint: these relate to resource use, or the differences between ìntensive', `semi-intensive' and èxtensive' aquaculture. According to Coche (1982), in extensive aquaculture the aquatic animals must rely solely on available natural food, such as plankton, detritus and seston. Semi-intensive aquaculture involves either fertilization to enhance the level of natural food in the systems and/or the use of supplementary feed. Such feeds are often low-protein (generally 20%), usually based on fishmeal and fish oil. These definitions broadly relate to use of environmental resources ± so-called `goods' ± although they ignore other resources such as land and water and seed. The intensity of production methods also has implications for use of environmental `services'; the more external food that is supplied per tonne production, the greater the wastes and the greater the demands on the environment to disperse and assimilate these wastes. However, the terminology is insufficiently well defined to be any more than a general guide. The term `semiintensive aquaculture', in particular, covers a huge diversity of aquaculture practices and ranges from minimal inputs to fairly substantial inputs of feed.

The origins of agriculture `People did not invent agriculture and shout for joy. They drifted or were forced into it, protesting all the way.' Tudge (1998) Neanderthals, Bandits and Farmers

Introduction The long accepted view of how and why agriculture began and spread has recently undergone some revision (Harris, 1996; Diamond, 1997; Tudge, 1998). While the established view remains that it started some 10 000 to 12 000 years ago, there is a growing recognition that different peoples adopted food production at different times. While some cultures, such as the Chinese, developed agriculture independently, others learned from neighbors or colonizers while a few, such as the Aboriginal Australians, appear never to have acquired agriculture at all (Flannery, 1994). The advantages of farming are readily apparent. Much plant and animal biomass is difficult or dangerous to harvest, labor intensive to prepare or of poor nutritional value. By farming, it is possible to select and grow crops and animals that give high nutritional returns per unit expenditure thereby increasing food supplies. Agriculture also generates food surpluses and food storage, prerequisites to the development of settled, politically centralized, socially stratified, economically complex and technologically innovative societies (Diamond, 1997). However, Tudge (1998) has recently argued that this view still underplays the importance of farming throughout much of our two-million-year history, especially from the late Paleolithic ± some 40 000 years ago ± onwards. He believes that a variety of `proto'-farming activities, a term coined to describe an ad hoc collection of activities that coaxed more food out of the environment, such as crop protection and game management, were part of the repertoire of responses to times when demands for wild foods outstripped supplies. Tudge also contends that when food supplies improved through upturns in abundance of game or more clement weather, or death or emigration of people, they returned to what they enjoyed best: hunting. His contention is that farming was hard work and to be avoided unless absolutely necessary.

6


Although he makes little reference to farming prior to 12 000 years ago, Harris (1996) too believes in the concept of `proto-agriculture' and has elaborated an evolutionary classification of systems of plant and animal exploitation; a simplified, unified history of agriculture (Fig. 1.1a). There is much food for thought in these ideas and we believe that many of the concepts currently being considered by agricultural historians, especially with regard to terrestrial animal production, provide insights into aquaculture and into how it evolved and was practiced among traditional societies.

Fig. 1.1a An evolutionary classification of systems of animal exploitation (modified from Harris, 1996). Long seasonal migrations, examples including permanent winter settlements and summer migrations.

Aquaculture and `proto-aquaculture' Aquaculture too began in different societies, both agriculture- and fishing-based, and followed a pattern of development in many respects similar to that of agriculture. There is good evidence in aquaculture for Tudge's theory of people opting in and out of plant and animal cultivation according to their needs, although as we hope to show these needs were not always related to food. There is also evidence of `protoaquaculture', defined here as activities designed to extract more food from aquatic environments, such as: transplantation of fertilized eggs; entrapment of fish in areas where they could thrive and be harvested as required; l environmental enhancements, such as development of spawning areas, enhancement of food, exclusion of competitors or predators, etc.; l holding of fish and shellfish in systems ± ponds, cages, pens ± until they had increased in biomass or until their value had improved. l l

Each activity might on its own be considered as no more than stock enhancement and thus within the definition of what might be considered as managed fisheries. However, we apply the critical concept of control of access and benefits to draw a line between where managed fisheries end and proto-aquaculture begins. If the effect of such interventions increased supplies sufficiently to satisfy needs and to result in an equitable distribution of benefits, then it may have evolved no further. We propose that the relatively small degree of control over the life cycle of the animal and the low impact of the intervention on fish or shellfish production is used to distinguish proto-

The History of Aquaculture in Traditional Societies

7

aquaculture from aquaculture. The definition of proto-aquaculture is compatible with those of Coche (1982) regarding extensive, semi-intensive and intensive aquaculture and is further characterized by low consumption of energy (see above). The proposed definitions do not neatly distinguish fishing from fish farming, but perhaps this is only to be expected when dealing with something like the transition from hunting to farming. It also ignores some of the more contentious issues, such as ranching, a term used to describe the release of juveniles into the wild, only to be recaptured later as adults. However, it is useful in helping explain how aquaculture might have first developed. It is very much a working hypothesis and others with more detailed and accurate information, more insight and more time for reflection and debate will undoubtedly construct a better framework.

Proto-aquaculture and the origins and pattern of development of aquaculture Why might people in traditional societies have begun farming fish and shellfish? The answer, according to the agricultural historians, would be because it was necessary (Boserup, 1965). It is clear that aquaculture began in various parts of the world and at various points along the aquatic food supply line, between water and plate. The farming of fish and shellfish is by definition an activity of settled societies, originating among both fishing and wetland farming cultures as well as at points of trade. While we may surmise that conditions similar to those favouring the development of agriculture would have usually been necessary, i.e. that foraging and hunting (fishing) were insufficient to satisfy demands for fish, provision of food was not always the most important driver for the development of aquaculture. Stewart (1994) and others believe the importance of fish in early hunter±gatherer societies to have been underestimated. Rudimentary proto-aquaculture techniques would probably have evolved among such societies, although evidence is scant. Native North American peoples living on the Pacific seaboard are believed to have transplanted the eggs of spawning salmon in an attempt to improve fish survival and returns. Many proto-aquaculture activities relied on some sort of holding facility. The simplest to construct would have been earth ponds. In some parts of the world these would have been little more than mud walls constructed to temporarily hold water and fish following the seasonal flooding of a river. Such systems are still in use in some parts of the world today. The whedos or fish holes of Benin are one such example (see Welcomme, 1972, for details). The practice of communal construction of weirs on small rivers and streams in Asia to store water outside of the monsoons principally to ensure adequate irrigation for wet rice cultivation during lulls in the rains and allow early seed bed preparation is also common. Attempts to increase fish yields would have been a logical next step, by affording protection from predators and, perhaps, by feeding fish with household scraps or farm wastes (see Fig. 1.1b). Among fishing-based societies, a number of scenarios in which proto-fish or protoshellfish farming arose are readily envisaged: the short-term storage of catches until there were sufficient fish or shellfish to make the journey to market worthwhile; the transport of live fish to market; the holding of catches until prices improved. These

8


Fig. 1.1b A scenario of how aquaculture may have evolved.

strategies are still seen among fisher folk today: modified traps, netted-off shallow areas of lakes, cages of the sort still seen in parts of Indonesia, traditional floating cages used in the Great Lake area of Cambodia (see Beveridge, 1996). If the theories of the agricultural historians hold true for aquaculture, then we can also expect to see aquaculture wax and wane as the result of changes in supply relative to demand for fish and shellfish.

Africa The earliest evidence of fish culture of sorts purportedly comes from ancient Egypt where fish often had a sacred as well as prosaic role in society. They were strongly associated with the cyclical life-giving forces of the Nile and the New Kingdom Egyptian view of the world, tilapia in particular being strongly linked to the goddess Hathor and the concept of rebirth (Desroches-Noblecourt, 1954). In his account of tilapia in ancient Egypt, Chimits (1957) reproduces a 4000-year-old bas relief figure from the tomb of Thebaine showing what appears to be an artificial, drainable pond being fished by a nobleman (Fig. 1.2). Many New Kingdom tomb scenes also show tomb owners sitting on chairs, fishing tilapias from their ponds, their wives standing behind and assisting with the catches. Although rod and line fishing is believed to have been common among all classes in Egypt at that time, the fishing activities of the

Fig. 1.2 Bas relief from the tomb of Thebaine, showing an Egyptian nobleman catching tilapia from an artificial pond (re-drawn from Chimits, 1957).


9

nobility were limited to their ponds. Their interest in fishing stemmed from religious rituals associated with death and rebirth and not with pleasure or sustenance (Desroches-Noblecourt, 1954; Brewer & Friedman, 1989). This was aquaculture at its most simple, more proto-aquaculture than aquaculture, involving little in the way of inputs or husbandry or pond management. Tilapia would have been transferred from nearby rivers to the ponds where they readily would have bred. While some food may have been provided, it is unlikely to have been important since production of fish for food was not the objective. It is believed that the practice persisted into the New Kingdom until the importance of rebirth in the world view of Egyptians waned. Although Brewer & Friedman (1989) detail many peculiar beliefs and taboos among the priesthood associated with fish, early travelers to Egypt confirm that fish was of tremendous importance in the Egyptian diet. The Roman traveler Diodorus Scullus is quoted as saying that `. . . the Nile contains every variety of fish and in numbers beyond belief: for it supplies the native not only with fish freshly caught but also yields an unfailing multitude for salting.' Herodotus, too, who traveled here some 2500 years ago, reported that `. . . all Egyptians in the Nile Delta possess a net with which, during the day, they fish. . . .' Given the fertility of the river, the abundance of fish and the skills of the fishermen, it is not surprising that these proto-aquaculture activities developed no further and indeed waned with the change in religious significance of fish. Its revival would have to wait several millennia until the early years of the present century.

Asia China and freshwater fish farming Although possibly pre-dated by events in Africa, Asia ± and China in particular ± is widely regarded as the cradle of aquaculture. The chronology is complicated, but is summarized in Tables 1.1 and 1.2. Many factors are thought to have constrained livestock development and predisposed China to develop aquaculture earlier than elsewhere in Asia. The wet rice agro-environment evolved relatively late in China's history, population pressure stimulating colonization of low-lying deltas. Such conditions would have both inhibited any development of mixed farming based on ruminant livestock and crops and supported fish culture and production of livestock such as pigs and poultry that thrived on rice by-products and water-based scavenging respectively. The process of agricultural evolution in southern China, from cropdominated to mixed farming (Grigg, 1974; Little & Edwards, 1997) was, therefore, molded by the limits and potentials of a flood-prone environment. Any diversification from a rice monoculture required a process of `ditching and diking' that produced deeper areas suitable for fish and higher dike areas for horticulture. Although areas of wet rice production were relatively sparsely populated until the Han dynasty (Grigg, 1974), the adoption of increasingly intensive, and irrigated, production in suitable areas prompted a rapid increase in population and demand for aquatic products that would also have been an important factor in stimulating aquaculture. With the development of ditch-dike systems, other crops such as beans, green vegetables and

10


Table 1.1 Chronology of significant aquaculture developments in China, based on written records. Information derived from Lin (1991), Li (1994) and Yang (1994) Date (BP)*

Period

Event

2300

Zhou Dynasty

Publication of monograph by Fan Li, detailing design and layout of ponds, propagation, fry and fingerling production

2200±2100

Han Dynasty

Publication of You Hou Bin, detailing integration of fish with aquatic plant and vegetable production Development of cage, cove and pen culture

1975±1780 1380±1100

Culture of fish in rice paddies Tang Dynasty

1100

Development of polyculture Publication of Lin Biao Lu Yi by Liu Xun, detailing theory of mutualism in rice±fish culture Integration of fish and fruit production

1040±780

Song Dynasty

Increasing collection and distribution of wild fish fry for pond rearing

632±350

Ming Dynasty

The Complete Agricultural Art written by Xu Guangqi and Treatise on Fish Culture by Huang Shenchen detail extensive to intensive fish farming methods in Jiangxi Province, including rotation of fish with aquatic plant production; integration of fish with livestock and effects of manuring on pond fish production

500 360±90

Development of integrated mulberry±dike±fishpond production system Qing Dynasty

40

Detailed written accounts of fry production, sorting and transportation Widespread success in artificial propagation of carps

* BP = Before present.

Table 1.2 Schema showing the evolution of farming systems for livestock and fish. It illustrates the probable evolution of farming systems from traditional, crop-dominated systems (Settled Agricultural Phase I) through mixed farming in which the importance of livestock was enhanced through their integration with crops (Settled Agricultural Phase II), to industrial agriculture characterized by monoculture (Settled Agricultural Phase III). (From Little & Edwards, 1997.) Category System definition

Evolutionary stage/trend Traditional crop dominated

Mixed farming

Agro-industrial

Intensity level

Extensive

Semi-intensive

Intensive

Descriptor

Settled Agricultural Phase I

Settled Agricultural Phase II

Settled Agricultural Phase III

Livelihood

Part of a complex of activities

Specialized activity

Knowledge

Indigenous

Scientific

Resource use

Land, water*

Cash, fossil fuel energy intensive

Market

Rural, subsistence, local

Urban, cash, export

Cultured species

Polyculture

Monoculture

* Based on pond fish culture.


11

tobacco could also be grown alongside (Bray, 1984). As today, fish would have been a common component of seasonally inundating rice paddies. Given the lack of animals and the prevalence of wetlands it is thus not surprising that fish was a prominent component of the diet in many areas. The development of irrigation in China and elsewhere was driven by the fact that rice grows best when provided with water of the right quality and in the right quantity at the right time. While there is no neat chronology of evolution of irrigation systems in China, it is clear from the widespread existence of clay models of irrigated agriculture systems recovered from graves throughout southern China that by the Han Dynasty (2300±1700 BP) ponds were being widely employed for water storage (Bray, 1984; Li, 1994). To some this indicates the earliest that aquaculture might have been developed. In a single grave over 18 varieties of aquatic plants and animal, that are still used by the Chinese today, were found within an intact rice-field model. These included lotus flowers, seeds and leaves, water chestnuts, soft-shelled turtles (Trionyx sinensis), grass carp (Ctenopharyngodon idella) and goldfish Carassius auratus (Guo, 1985, in Li, 1992). These areas of southern China had high densities of people culturally dependent on aquatic foods. As population densities increased, demand for fish and other aquatic foods would have increased and the practice of holding and growing fish would become increasingly attractive compared with reliance on increasingly exploited and inconsistent wild stocks. In the floodplains of China and elsewhere in Asia, soil is excavated to construct elevated, better-drained areas for establishing homesteads and raising crops. Although the resultant excavations may be referred to as fishponds by aquaculturists, farmers refer to them simply as ponds, an indication of their multipurpose nature. Others, however, including the Fisheries Society of China, refer to the short treatise published by the statesman Fan Li some 2500 years ago (2500 BP). It describes common carp (Cyprinus carpio) farming in sufficient detail to provide incontrovertible evidence that fish culture had developed well beyond a proto-aquaculture activity and that aquaculture was well established by this time (Li, 1994). The monograph details the design and layout of fishponds, carp breeding, and fry and fingerling rearing techniques. Fan Li's account is of `semi-intensive' monoculture of carp, although there remains some debate as to the species (see Balon, 1995). The integration of fish ± presumably carp ± culture with that of aquatic plants and vegetables is apparent from written records dating from 2200 to 2100 BP while written records of rice-fish culture date from the period 1975±1780 BP (Yang, 1994). Despite the long history of freshwater fish farming in China, there are few documentary accounts and details are fragmentary at best (see Table 1.1). According to Li (1994) fish culture expanded from rice paddies and ponds to lakes ± this implies the use of cages, pens and/or enclosures ± during the Han Dynasty (206 BC±AD 220). Provided herbivorous species were used, culture could have relied on semi-intensive or even extensive methods. If, however, omnivores were farmed, then there would have been a greater reliance on supplementary feed. There is strong evidence that small dams, constructed by farmers primarily for water storage purposes, were also used to produce lotuses, water chestnuts, fish and turtles (Bray, 1984). A milestone for aquaculture in China seems to have been reached at the beginning of the Tang

12


Dynasty in AD 618 with the culture of combinations (polyculture) of carps (Ling, 1977; Li, 1994). However, while we might expect that this would have been promoted as a means of increasing yields from semi-intensively managed systems, historians claim polyculture to have been less due to an appreciation of ecology and the synergies of growing together species with complementary feeding habits than to the fact that the word for common carp in Chinese ± `Li' ± sounded the same as the emperor's surname. As a result, the catching, selling and eating of this species was banned for the next 300 years or so. Availability of suitable wild seed was critical to China's aquaculture development, and the same was true for Indian carp polyculture in the subcontinent and culture of Vietnamese silver carp (Hypophthalmichthys harmandi ), mud carp (Cirrhinus molitorella) and common carp (Cyprinus carpio) in the Red River Delta, Vietnam (Chevey & Lemasson, 1937). There is also evidence that there were traditional methods of producing seed that pre-date the now widespread use of hypophysation in hatcheries. Dry `bundhs', seasonal ponds that fill quickly at the time of the first rains, were used to stimulate spawning of Indian major carps in West Bengal over a hundred years ago (Sharma & Rana, 1986). Other key events in Chinese aquaculture include the gradual integration of fish ponds with various crop and livestock production systems (see Table 1.1), leading to what is widely regarded as the most complex integrated aquaculture system of all, the fishpond±dyke±mulberry system of Zhujiang, southern China (Ruddle & Zhong, 1988). The fishpond±dyke±mulberry system was strongly output orientated to meet both local demand for a variety of products ± live fish, fruit, etc. ± and distant markets for products such as silk. Until recent decades the yields of Chinese carp polycultures are likely to have remained low (100 years; recent is 55% of the daily litter production (Lee, 1988). Tidal gei wai ponds act as sediment traps and accelerate accretion, leading to progressive increase in elevation of the mangrove stands. Less inundated sites allow more litter accumulation to be processed by crabs (Perisesarma spp. and Parasesarma spp.) in the stands, thus leading to little export (Li & Lee, 1998). Fauna that graze on or shred the litter increase the rate of breakdown of detritus (Tenore et al., 1982). Jones (1984) noted a number of species of crabs that are abundant in tropical Asia± Pacific mangroves that consume significant quantities of litter. Lee (1989b) found that crab (Chiromanthes spp.) consumption of mangrove leaves was a major factor in forming an energy sink and limiting litter export within shrimp tidal ponds (a type of silvofishery) in Hong Kong. Crabs fragmented leaf litter and returned the nutrients as fecal pellets or shredded pieces, which facilitated further degradation. In a study by Emmerson & McGwynne (1992) on consumption of mangrove (Avicennia marina) leaf litter, they found the crab Sesarma minerti consumed 44% of the annual leaf litter, resulting in feces production, and facilitating the leaf turnover an estimated four-fold. Robertson & Daniel (1989) estimated that leaf processing by crabs turns over litter at more than 75 times the rate of microbial decay alone. Similarly Lee (1993) found a selective preference by the mangrove crabs Chiromanthes bidens and C. maipoensis for senescent leaves in the order of Avicennia marina > Kandelia candel > Aegiceras corniculatum which correlated with a preference for leaves with lower C:N ratios (greater nutritive value). In addition A. marina had the lowest tannin level of the three mangrove trees. Lee (1989b) reported that sesarmine crabs were capable of

204


consuming >57% of the daily leaf litter. Such in situ consumption by crabs reduces tidal export and may also initiate further processing of mangrove-derived organic carbon by way of coprophagous food chains based on crab feces (Li & Lee, 1998). Mangrove litter dynamics in the New World tropics (Ecuador) were also found to be influenced by mangrove crabs, Ucides occidentalis, that were able to remove daily additions of leaf litter material within one hour except during a limited period (August±October) of crab inactivity (Twilley et al., 1997). Robertson (1986) demonstrated that leaf-consuming crabs (Sesarma spp.) played a significant role in litter turnover of mangrove ecosystems in the Indo-West Pacific. In a study of leafconsuming crab Sesarma messa consumption of leaves of Rhizophora stylosa, consumption amounted to 28% of the annual leaf fall (Robertson, 1986). Robertson (1986) documents the important link sesarmid crabs make between mangrove primary and secondary production with the consumption and retention of a large proportion of the annual leaf fall within mangroves. This represents an important pathway of litter processing not accounted for in previous mangrove food chain models, particularly in the Indo-Pacific mangroves. In a study of a low-lying Rhizophora mucronata mangrove stand in East Africa, litter removal was mainly attributed to the crab Sesarma guttatum and not tidal action, while in an elevated Ceriops tagal area, which is flooded only during spring tides, the detritivorous snail Terebralia palustris served as the major macrobenthic organism responsible for litter removal (Slim et al., 1997). Water availability from either rain or tidal inundation was a determining factor in the amount of litter consumed by T. palustris, since potential desiccation of the snail restricted its foraging movements. In both locations diurnal fluctuation had a significant impact on the litter removed (under favorable conditions 25.2% by day and 41.6% by night for T. palustris, and 40.3% by day and 21.7% by night for S. guttatum). Decomposition rate is influenced by the species-specific characteristics of the vegetation. Tam et al. (1990) found the rate of leaf decomposition and the amount of nutrients released to be species specific and related to the chemical composition of the leaves. Decomposition rates in descending order were Kandelia candel > Avicennia marina > A. corniculatum with 85% to less than 50% of the leaf matter lost in an 8week incubation period. Varying concentrations of C and N occurred over the initial 4 weeks and stabilized at approximately 24:1, mainly due to an increase in %N (Tam et al., 1990). Twilley (1982) found that decomposition and organic carbon leaching rates were much higher in Avicennia than Rhizophora leaves. Twilley et al. (1986a) also noted the effect on litter dynamics from species differences in leaf decomposition rate with Rhizophora mangle decomposing more slowly than Avicennia germinans. Other studies that examined the rate of decomposition similarly found Avicennia to decompose in half of the time or less compared with other mangrove vegetation (Albright, 1976; Boonruang, 1978; Goulter & Allaway, 1979; Steinke et al., 1983). The following relative decomposition rates for species have been identified as Avicennia marina > Rhizophora apiculata (Boonruang, 1978); A. marina >Bruguiera gymnorrhiza (Steinke & Ward, 1987); A. marina > R. stylosa > Sonneratia alba > B. gymnorrhiza (Angsupanich et al., 1989); and A. marina > Ceriops tagal > R. stylosa (Robertson, 1988a). A. marina consistently had the fastest rate of decomposition of

Silvofisheries: Integrated Mangrove Forest Aquaculture Systems

205

the species considered and this was up to a factor of approximately three-fold faster decomposition. This would provide an advantageous characteristic (along with low C:N and low tannin content) in the use of A. marina as the main litter source in a silvofisheries system, since it would accelerate the incorporation and utilization of the detrital material into the food web. This has a significant advantage in shortening the period of time to make the nutrients available for use by heterotrophs and the eventual recycling; thereby accelerating the energy turnover. The initial availability and the subsequent role of microbes depend on the detritus source (Tenore, 1988). For example, seaweed-derived detritus is typically high in available calories and nitrogen content that can be directly utilized by macroconsumers while those from vascular plants are typically low in both available caloric and nitrogen content and require an extended time period before becoming available for utilization by macroconsumers. During the latter stages of the slow decay of refractory material, the microbial biomass, and more importantly their nitrogen-rich exudation products, accumulate and can increase the absolute nitrogen mass of the detritus (Hobbie & Lee, 1980; Rice & Hanson, 1984). The physical structure and chemical composition influence the rate of degradation of mangrove litter. For example, leaves covered with a thick cuticle would impede the entry of water and degradative organisms. Avicennia leaves are thin and sink in water while Rhizophora or Sonneratia leaves are thicker and are buoyant initially in water; thereby, contributing to the more rapid decomposition of Avicennia (Wafar et al., 1997). Plant materials high in crosslinked celluloses and lignins resist decay while those high in soluble ash, organic nitrogen and other hydrolyzable components are easily degraded (Twilley et al., 1986b). The level of tannin content in leaves similarly has been associated with impeding microbial activity and grazing by macrofauna which hinders degradation (Alongi, 1987; Alongi et al., 1989; Emmerson & McGwynne, 1992) as well as inhibiting microbial activity in sediments with high concentrations of tannins (Boto et al., 1989). Tannin levels in mangrove leaves of Avicennia marina and Bruguiera gymnorrhiza show significant decreases after 48 h of submergence with a 74±85% reduction after 14 days (Steinke et al., 1993). The physical structure, the nutrient level reflected in the C:N ratio, and the level of tannin in the litter products influence their food value and the decomposition of the materials into the detrital pool of energy. Table 8.5 provides a comparison of selected mangrove species C:N and tannin levels. A. marina has the most rapid rate of decomposition and recycling compared with other mangrove tree leaf litter (Van der Valk & Attiwill, 1984; Steinke & Ward, 1987; Robertson, 1988a; Angsupanich et al., 1989; Lee, 1993). Cundell et al. (1979) found the C:N ratio of senescent Rhizophora mangle leaves to decrease from 90.6 to 40.7 over a 70-day period of immersion. This was attributed to the loss of readily leachable carbohydrates and the increase in nitrogen from microbial activity. The microbial population slowly increased on the leaf with leaching of the tannin compounds. Tannin content in R. mangle senescent leaves was recorded at 5.2% initially, which declined to less than 1% after 35 days of water immersion (Cundell et al., 1979). The antimicrobial and enzyme inhibitant characteristics of tannin are assumed to delay colonization of senescent leaves by bacteria

206


Table 8.5 Carbon, nitrogen and tannin content (based on dry weights) of selected mangrove species (Cundell et al., 1979; Robertson, 1986; Lee, 1993; Wafar et al., 1997) Species Avicennia marina Kandelia candel Aegiceras corniculatum Rhizophora stylosa R. mangle R. apiculata R. mucronata Sonneratia alba Avicennia officinalis

% Organic carbon

% Organic nitrogen

C:N

% Soluble tannins

34.5 36.7 54.6 ± 46.2 43.4 43.8 42.4 41.9

1.26 0.75 0.79 ± 0.51 0.98 0.66 1.15 0.95

27.4 49.1 69.1 70.0 90.6 44.3 66.4 36.9 44.1

0.86 2.35 1.95 17.00 5.20 ± ± ± ±

and fungi. In the decomposition of R. apiculata leaves, Raghukumar et al. (1994) similarly observed a sequence in colonization by fungal species and fungi and bacteria biomass peaking at 21 and 35 days respectively. The sequence of events in the decomposition process of Rhizophora mangle and R. apiculata leaves is identified in Table 8.6. The caloric content fell during day 28 through 49 and then increased as microbial biomass accumulated.

Recycling of nutrients/biochemical cycles There is a continuous process of exchange and assimilation of energy fixation, accumulation of biomass, decomposition of dead organic material and mineral cycling within the mangrove ecosystem. There is also a recycling of the nutrients into new growth of the mangrove trees. The nutrient flux through a mangrove ecosystem is illustrated in Fig. 8.23. Holguin et al. (2001) provide an overview of the role of microorganisms in the mangrove ecosystem and conclude that there is a close microbe±nutrient±plant relationship that functions to recycle and conserve nutrients and consequently plays an important role in the productivity and sustainability of the ecosystem. There is a beneficial relationship with plant-growth-promoting bacteria and nutrient recycling, which supports production of plant-root exudates that serve as a food source for

INORGANIC NUTRIENT INPUT • Rainfall • Freshwater runoff • Nitrogen fixation • Mineralization • Tidal borne • Chemical release from fixed states in soil • Man-made influences (agriculture, sewage, etc.) • Upland input

MANGROVE SYSTEM Recycling

NUTRIENT OUTPUT • Tidal transport • Leaching • Denitrification and volatization • Immobilization of inorganic nitrogen • Leaching of soils by freshwater • Active transport by temporary inhabitants of mangroves (e.g., penaeid shrimp, fish, etc.)

Fig. 8.23 Nutrient flux through mangrove forest (after Boto, 1982).


207

Table 8.6 Sequence of events in the decomposition of Rhizophora mangle and R. apiculata

Time 1±14 days

Events Rhizophora mangle Cundell et al., 1979 Rapid leaching of reducing sugars and tannin

Caloric content, cal (ash-free)/g

Events Rhizophora apiculata Raghukumar et al., 1994

5200

0±28 days

Initial leaching period followed by rapid microbial decomposition. Species of fungi specific to initial colonization. Rapid cellulose decrease during first 21 days

14±28 days

Depletion of leachable reducing sugar. Leaching of tannin. Initial colonization by micro-organisms especially bacteria

5351

28±49 days

Colonization of outer leaf surface by bacteria, fungi, pennate diatoms, and stalked protozoa

5254

28±60 days

A shift in fungal species to Hyphomycete XVII. Maximum growth of `late colonizer' fungi. Increased growth of thraustochytrids. A more rapid degradation of xylem

49±70 days

Erosion of leaf surface. Rich microflora, cellulolytic bacteria and fungi, stalked diatoms and tube worms

4217

70+ days

Fragmentation of the leaves

5429

microorganisms and production of other plant material serving as a food source for larger organisms (e.g. crabs). The magnitude and direction of net material flux are determined by a combination of physical parameters, such as geomorphology, tidal inundation regime and topography, and biotic factors such as the species and growth form of vegetation, seasonal growth patterns and rates of primary production, and the development stages of the wetland±estuarine system (Odum, 1969; Dame & Lefeuvre, 1994). The nutrient pool of the mangrove ecosystem is regulated by five interacting processes (Saenger et al., 1983). The last process is concerned with the recycling and conservation of the nutrient pool and is of particular interest in the management of silvofisheries systems. These processes are as follows: Freshwater or tidal flooding introduction of organic material and inorganic mineral ions. l Sedimentation-introduced inorganic mineral ions. l

208


Wind-introduced inorganic mineral ions. Depletion of nutrient pool with the flooding of freshwater and tidal action. l Microbial decay of organic material providing for internal cycling of mineral ions. l l

Mangroves have been considered as a significant universal exporter of organic matter to coastal waters. However, more recent studies indicate that this role is not nearly as great as previously considered. Estimates of organic carbon from intertidal wetlands range from 45% (Teal, 1962; Twilley, 1985) to less than 1% (Heinle & Flemer, 1976) of their net production, while some intertidal wetlands may even import organic carbon (Woodwell et al., 1977; Lee, 1990a). Mangrove production contributed only 1.8% to the total carbon available in Deep Bay, Hong Kong (Li & Lee, 1998). Heinle & Flemer (1976) found that fluxes of detritus from stable tidal marshes subjected to modest tidal flooding are less than 1% of the maximum areal standing crops and the tidal marsh serves mainly as a nutrient sink. In a study of a South China mangrove it was found to be in equilibrium with no net import or export of N and P (Li, 1997). In Deep Bay, Hong Kong, the outer mangrove is a net exporter of organic carbon while the landward gei wai, a semi-enclosed tidal pond, acts as a net importer. This difference is attributed mainly to the tidal inundation regime (Li & Lee, 1998). Therefore, the energy flow in mangroves is mainly contained within the various subsystems in the mangroves. In a silvofisheries pond the litter and nutrient dynamics can approach that of a closed system. The traditional silvofisheries pond (i.e. no fertilizer or supplemental feed inputs), with modified and controlled tidal flushing along with harvesting of cultured products from the system, is normally a very low exporter or net energy importer with an influx of inorganic nutrients from the adjacent environments and juveniles of species cultured (natural stocking). Gong & Ong (1990) identified the macronutrient levels of N, P, K, Ca, Mg, and Na that are released annually from a managed Malaysian mangrove forest (Matang Mangrove Forest, 40 800 ha). A total of 656 kg dry wt/ha of macro-nutrients with 46% from litter, 44% from dead trees, and 10% from slash are released annually. In Table 8.7 these values have been calculated based on an annual per hectare basis. Table 8.7 The amount of nutrients and organic matter (dry wt) released from small litter (leaves, twigs and fruit), dead trees, and slash (cuttings of trees harvested) from the Matang Mangroves, Malaysia (after Gong & Ong, 1990)

Litter contribution (kg/ha/yr) Biomass N P K Ca Mg Na Organic matter

9 726 54.2 6.3 28.0 132.5 39.9 38.3 *9 050.0

Dead tree contribution (kg/ha/yr) 13 713 73.9 3.8 17.5 36.9 41.8 117.0 12 787.9

* Estimation based on similar percentage for dead trees and slash.

Slash/cuttings contribution (kg/ha/yr) 1 462 11.1 1.6 9.7 10.0 15.7 17.8 1 349.2

Total (kg/ha/yr) 24 901 139.3 11.7 55.1 179.4 97.3 173.1 23 187.0

Per cent of Total

100 0.56 0.05 0.22 0.72 0.39 0.70 93.12


209

In general, nitrogen is considered to be the major nutrient limiting production in the marine environment. The nitrogen cycle similarly has a functional role in the food web as a major building component of organic matter. Nitrogen is usually considered a limiting growth factor for primary producers. In enriched waters the primary producers grow much more abundantly and the food chain is contracted (multiplicative effect with higher productivity 6 higher ecological efficiency) so that more of the primary production ends up in the upper level consumers. The main source of nitrogen is through the breakdown of organic matter and the oxidation of inorganic forms of nitrogen. In addition, in coastal land based transitional zones, such as the mangroves, a major source of nitrogen is also introduced through the runoff from the land. There has been found (Potts, 1984) to be a significant input of nitrogen from benthic microbial populations in mangroves associated with periods of high tide, since the tidal cycle is a major factor impacting on the desiccation of communities of cyanobacteria (activation of nitrogenase activity after wetting with the incoming tide). Similarly, Twilley et al. (1986a) noted that nitrogen fixation may be a major source of nitrogen in mangroves and is influenced by desiccation (tidal inundation duration) reducing the nitrate reductase enzyme activity. In tropical conditions with year-round warm temperatures, N fixation by bluegreen algae in fishponds is considered to be a significant factor in aquaculture pond fertilization (Egna & Boyd, 1997). Commonly nitrogen limitation has been found throughout the intertidal zone and phosphorus limitation was also evident at the higher elevation areas within the mangroves (Boto & Wellington, 1983). Boto & Wellington (1983) found a highly significant correlation between mature Rhizophora leaf nitrogen and phosphorus levels with soil ammonium and extractable phosphorus; therefore suggesting the use of mangrove leaves as indicators of mangrove forest nutritional status. It was further noted in this study that there was significant mangrove growth response after ammonium enrichment at a lower intertidal site and at an upper site with the addition of phosphate enrichment. Kristensen (1988) found benthic fauna to have a significant role in nutrient cycling. Below the oxic zone a decline in the nutritional quality of the organic matter with depth and age in the sediment slows the rate of mineralization by anaerobic processes (e.g. fermentation, denitrification, and sulfate reduction). However, the exchange of nitrate between the sediment and the overlying water is affected considerably by the burrow-dwelling infauna. Burrows serve as an extension of the sediment±water interface. Ventilation of burrows and tubes is a major factor controlling biogeochemical processes occurring in sediments (Kristensen, 1984, 1985). In addition, during feeding (i.e. deposit or filter feeding) the majority of infaunal animals selectively concentrate organic rich material into fecal pellets and these pellets are sites of high microbial activity. Microenvironments, such as fecal pellets and intermittently ventilated burrows, create a close spatial and temporal coupling of both the nitrification and denitrification processes. Therefore, the benthic animals can increase the nutrient turnover in coastal ecosystems and improve primary production through stimulation of the mineralization process. The role of benthos fauna in cycling nitrogen is influenced by the basic nutritional

210


needs of the benthos, the food resources, and the feeding strategies that the benthos organisms use to exploit the available resources. The benthos includes a variety of feeding types consisting of suspension and deposit feeders and scavenging/carnivorous organisms. The potential food sources of benthic deposit feeders include benthic microalgae, detritus, fecal pellets and microbenthos (i.e. bacteria, fungi, and protozoa). However, refractory detritus (e.g. vascular plant material ± mangroves, seagrass), which is typically low in nitrogen and composed of structural materials not directly assimilable by detritivores, must be depolymerized by microbial decomposition with the resultant microbial biomass or transformation products being available to deposit feeders. The microbial decomposition of fecal pellets (coprophagy) and detritus from vascular plants' refractory nature is necessary before the nutrients become available to macroconsumers as part of the detritus food chain. The process increases the nutritional value and particularly the relative nitrogen content of the detritus (Tenore, 1988). In addition to being an essential part of the food web, bacteria are important mineralizers of organic detritus and recyclers of essential nutrients (e.g. carbon, nitrogen and phosphorus), which are particularly important functions in mangroves. Sedimentary bacteria populations play a significant role in energy flows and cycles of tropical mangroves, and are mainly controlled by temperature and tidal inundation frequency (Boto et al., 1989). Bacteria account for a disproportionate share of nutrient uptake to the extent that bacterial communities act as a sink for carbon, processing most of the energy and nutrients in tropical aquatic systems, thereby serving as a basic driving force for aquatic food webs (Alongi, 1994). This function is heightened in the tropics. Bacteria enrich the protein content of detrital plant material and fecal pellets by decomposing refractory components over time. Detritivores derive a significant amount of their nutrition from digestion of this enriched material with bacteria and their mucus. Bacterial abundance is usually controlled by the carrying capacity of the system, nutrient supply and environmental conditions with the microbial food web serving as a sink for energy and major nutrients (Alongi, 1994).

Selection of appropriate mangrove species There are six recognized major groups of mangrove species based on geographical regions with different degrees of speciation; however, Rhizophora and Avicennia are considered pan-world (Chapman, 1984). Not only are species differentiated by habitat preference and tolerances, but there are also characteristics of the various species that are important to a silvofisheries system. Selection of the most appropriate mangrove species is particularly important in replanting projects as part of a silvofisheries system where a greater degree of control can be exercised. Some of the desired characteristics in selecting appropriate mangrove tree species include: l l

tolerance of trees to extended submergence; rapid growth and high litter production (i.e. high value of the litter/production ratio);


211

high nutrient value of litter products; rapid decomposition of litter; l mixed population of vegetation to maximize production; and l openness of canopy to allow light penetration to the mangrove floor ± enhancing algae production. l l

Lugo et al. (1988) identified a few environmental core factors (hydrological and nutritional) that are responsible for the productive characteristics of wetland forests (fresh and saltwater) and a grouping of wetland forests in three types, which consist of riverine, basin and fringe types. However, the effect of the core factors can be modified by cumulative secondary environmental factors. This serves as a helpful guide in identifying characteristics of potential silvofisheries sites. The core factors that define the fundamental niche are classified as: kinetic energy of water flow (e.g. waves, tides, water runoff); l predominant direction of water flows (whether water flows through the wetland unidirectionally as in river floodplains, bidirectionally as in fringe forests, or fluctuating vertically as in basin forests); l hydroperiod (duration and frequency); and l nutrient supply (nutrient quality of site's sediments and waters). l

In summary, structural complexity and rate of ecosystem processes usually follow the order riverine > fringe > basin. General biotic responses of freshwater and saltwater wetland environments in relation to the basic core factors consist of the following: Forest structure ± The average number of tree species decreases as follows: riverine > basin > fringe. The number of tree species decreases with increasing intensity of hydroperiod and hydrologic energy. Salinity also decreases species richness (mangroves having fewer species than freshwater wetlands). Tree density is higher in basin forests than riverine. Younger stands have higher tree densities (hurricane/typhoons maintain younger forests). Increasing hydrologic energy affects tree density. l Primary productivity and evapotranspiration ± Net primary productivity is higher (lower respiration) in saltwater forested wetlands. Riverine forests are always more productive (up to twofold). l Litter dynamics ± Average rate of litter fall is higher in saltwater than in freshwater wetlands. The rates of saltwater wetland forests follow the ranking of riverine > fringe > basin based on hydrologic energy and nutritional factors. Rates of litter decomposition are much higher in saltwater than in freshwater forests. Litter fragmentation and transport by tidal forces is partly responsible. Mangrove forests have higher total organic carbon and higher rates of carbon export than freshwater-forested wetlands. l Nutrient dynamics ± The ratio of mass of organic matter to mass of nutrients in litter fall provides insight into how much carbon is returned to the forest floor per l

212


unit of nutrient mass. Mangroves return more organic matter to the forest floor per unit of N and Ca nutrient return than do freshwater wetland forests. Nutrient use efficiency by litter fall and litter turnover is higher in tidal saltwater wetlands than in freshwater wetlands. The ratio utilized of mangrove to open water area in silvofishery ponds varies substantially among the countries practicing silvofisheries. Table 8.8 illustrates this variation. Table 8.8 Comparison of the predominant ratio used of mangrove to open water area in silvofishery ponds Mangrove area

Open water area

80% 80% 30% 70% 20%

20% 20% 70% 30% 80%

Indonesia Philippines Thailand Vietnam China, Hong Kong

These predominant ratios by country vary within the countries also. This ratio is a critical factor in the basic energy dynamics of the extensive silvofishery pond system, since the mangroves are normally the major source of nutrients and organic matter supporting the pond's food web. Therefore, it will have a significant impact on aquaculture production from the system. There needs to be further research into this ratio to determine an optimum range under different conditions. It has been reported (Soewardi et al., 1996; Takashima, 1999) that productivity of shrimp increased with the increase in mangrove area within the pond (Table 8.9). However, these values are based on a production area limited to the open water portion of the total silvofishery pond (i.e. 20% in an 8:2 silvofishery pond) and then projected to a production value reflecting an area that is completely open water (100% of the pond). Furthermore, this does not account for the utilization during periods of flooding of the mangrove area by the aquaculture species. This extrapolated value can be misleading in terms of total actual production from a given land area. Production values, as well as other pond area related values (e.g. stocking density) should be based on the total land area Table 8.9 Productivity of shrimp ponds with different levels of mangrove area within the pond (Soewardi et al., 1996; Takashima, 1999)

Amount of pond area with mangroves (%) 0 40±60 70±80 80

Production projectedbased on open water area (kg/ha/yr)

Reported value adjusted to reflect production based on actual land area of silvofishery pond ± inclusive of mangrove and open water area (kg/ha/yr)

171.2 181.0 335.0 413.5

171.2 72.4±108.6 67.0±100.5 82.7


213

utilized in the pond system (including mangrove area). Since this will allow for a comparative analysis of different systems (e.g. silvofisheries, extensive, semi-intensive, and intensive aquaculture systems), it is essential for a realistic evaluation of the system's comparative economic values as well as a benefit/cost analysis comparison. The silvofisheries system can also have the addition of integrated products (e.g. construction material, honey, alcohol, vegetables, fruits, etc.) to those produced by the aquaculture component that would contribute to the total economic value of the system and therefore should be reflected in the total quantity of land utilized by the system. A comparison of production from silvofisheries ponds of two categories of mangrove density and age and stocking practice (natural ± with tidal influx of wild stock, and purchased ± supplemental stocking of seedstock) resulted in net revenue differing by a factor of approximately 1.8-fold increase in ponds with the lower mangrove density and stocked milkfish (Rusdi & Jasin, 1994). This further reflects the importance of the mangrove area to open water area ratio and density along with the management practices applied to the ponds' operation on the level of financial return the farmer obtains. There needs to be a balance in the diversity, area and density of mangroves that addresses not only the requirements of the silvofishery pond system, but also the broader management of the mangrove forest so as to maintain its functions and biodiversity. Caution needs to be exercised in the development of silvofishery activities, particularly in large developments, that utilize monospecies planting (e.g. Rhizophora sp.) on the overall viability of the mangrove forest. As in managed timber forests that cultivate large tracts of single tree species, this can impact on the diversity and survival of plant and animal species that are dependent on the forest system directly and indirectly.

Survival (submergence/emergence) Tolerances of mangrove species to submergence will be of particular interest in the management of the silvofisheries system, since in ponds designed with a single control of water level the mangrove trees will be exposed to extended periods of submergence when the ponds are maintained at their upper water capacity for the benefit of the cultured aquatic species. Limited research has been done on specific duration tolerance to submergence for different species of mangrove trees. However, general information can be drawn from the natural distribution of the different species within the land to seaward transition in species, which would reflect increasing exposure to periods of submergence. Waston (1928) delineated five classes based on frequency of inundation: (1) (2) (3)

species growing on land flooded at all high tides (Rhizophora mucronata); species growing on land flooded by medium high tides (Avicennia alba, A. marina and Sonneratia griffithi); species growing where they are flooded by normal high tides (majority of mangroves but dominated by Rhizophora);

214

(4) (5)


species growing on land flooded by spring tides only (Bruguiera gymnorrhiza and B. cylindrica); species on land flooded by equinoctial or other exceptional tides only (Bruguiera gymnorrhiza, dominated by R. apiculata and Xylocarpus granatum).

Dagar et al. (1991) identified three conspicuous zones (proximal, middle and distal zones) within mangroves from seaward to landward. The proximal zone (seaward zone) consisted mainly of Rhizophora spp., Avicennia spp. and Sonneratia spp. However, this classification was too broad with excessive overlap of species to be useful in identifying the most appropriate species for silvofisheries other than the genera of species in the proximal zone. Por (1984) suggested further delineation of the zones to a total of 11 zones based on a linear progression from total submergence to emergence quantified in hours per day and days per month. Untawale (1987) identified five zones of mangrove distribution based on salinity: (1) (2)

(3)

(4) (5)

euhaline zone (30±40 ppt, high wave action, rocky and sandy substratum): absence of mangroves; polyhaline zone (18±30 ppt, low wave action and sandy clay substratum): Sonneratia alba, Rhizophora mucronata, R. apiculata, Avicennia marina, A. officinalis, Bruguiera gymnorrhiza, B. parviflora and Acanthus officinalis; mesohaline zone (5±18 ppt, silty clay bottom, feeble wave action); Kandelia candal, Avicennia officinalis, Rhizophora spp., Aegiceras corniculatum and Sonneratia alba; oligohaline zone (0.5±5 ppt, silty substratum): Sonneratia caseolaris, Acrostichum aureum, Scirpus sp., Cyperus sp., Fimbristylis sp.; limnetic zone (42 (75% or more of possible points); suitable is between 28 and 42 (50%); not suitable is 150

50±150

25

25±10

0.05)

An Integrated Fish and Field Crop System for Arid Areas

271

Table 9.2 Summary of three greenwater tank culture experiments for the production of Nile tilapia fingerlings (Oreochromis niloticus), giving stocking rate, stocking size, growth rate, final biomass, feed conversion ratio (FCR) and survival over a 12-week production cycle. Stocking rate (number/m3)

Stocking size (g)

Final size (g)

Growth rate (g/d)

Final biomass (kg/m3)

FCR

Survival (%)

1

200 400 600

0.7 0.7 0.7

58.6 35.1 21.0

0.69 0.41 0.24

9.8 12.9 11.7

1.04 1.04 1.04

83.7 91.7 93.1

2

177 355 532

7.3 7.4 7.3

137.2 90.4 59.2

1.55 0.99 0.62

18.6 19.6 20.6

1.45 1.69 1.65

76.4 61.3 65.5

3

300 400 500

1.2 1.1 1.1

75.1 64.3 49.4

0.88 0.75 0.57

21.0 23.0 21.7

1.06 1.09 1.12

94.7 91.2 89.4

Experiment

The feeding rates were gradually reduced to 0.8±1.4% at the end of production cycle. In experiments 5 and 6, the fish were fed ad libitum twice daily with an amount of feed they could consume in one hour. In the Virgin Islands there are two desired final fish sizes. They are 500-g red tilapia for the West Indian market, which prefers whole fish after scales, guts and gills are removed (Fig. 9.12). The other market is for 900 g or larger Nile tilapia from which skinless fillets are produced (Fig. 9.13).

Fig. 9.12 Red tilapia produced in a greenwater tank system. (Photograph by J.E. Rakocy.)

The results of the experiments were far from conclusive in determining the optimum stocking rates because too many variables changed from one experiment to the other and the greenwater culture technology was continually being refined and improved. However, some general observations and goals can be given. Being situated in the tropics where year-round production is feasible, greenwater systems should be designed to give two crops per year for simplicity of management planning.

272


Fig. 9.13 Nile tilapia produced in greenwater tank system. (Photograph by J.E. Rakocy.)

Assuming a 1-week turnaround time for harvesting, marketing, refilling and stocking, the culture period would be 25 weeks or 175 days of feeding. For red tilapia, none of the stocking densities in experiments 1 (20 weeks) and 2 (24 weeks) affected growth. The length of the culture period and the initial size did affect growth rate between the experiments. Starting with 46-g fingerlings, the highest stocking rate (16 fish/m3) resulted in an average growth rate of 2.8 g/day during 20 weeks. Assuming that the experiment had run for 25 weeks and the average daily growth rate increased to 3.0 g/day (as tilapia become larger the daily growth rate increases), the fish would have reached an average size of 571 g. Starting with 50-g fingerlings, a growth rate of 2.57 g/day will produce 500-g fish in 175 days. In later experiments, final densities of 17 kg/m3 were obtained for Nile tilapia with improved management techniques. Assuming that red tilapia can reach this density at a 500-g average size, then the optimum stocking rate would be 34 fish/m3. An experiment is needed for verification. Several densities between 16 and 34 fish/m3 will be tested in future experiments, always starting with advanced fingerlings weighing approximately 50 g. Nile tilapia reached the 900 g to 1 kg size range in experiment 5 at a stocking density of 17.8 fish/m3, a growing period of 25.6 weeks and an advanced fingerling size of approximately 200 g. This is not a practical fingerling size for conditions in the Virgin Islands. As with red tilapia, an initial size of 50 g is more appropriate. Nile tilapia would have to grow at an average rate of 4.86 g/day to reach 900 g in 25 weeks. A growth rate of 4.86 g/day was not approached in experiments 3,4 or 6


273

at densities of 24, 26 and 24 fish/m3, respectively. Only in experiment 5 with the large fingerlings and a stocking rate of 17.8 fish/m3 were the growth rates in the range of 4.35±4.66 g/day. Knowing that a final density of 17 kg/m3 is feasible, a stocking rate of 18.9 fish/m3 would produce 900-g fish if the desired growth rate could be obtained. An experiment needs to be conducted at densities ranging from 16 to 20 fish/m3 (e.g. 16, 18 and 20 fish/m3). Although improved management procedures should lead to higher growth rates, a fingerling size of 50 g may be too small, and therefore experiments will be conducted testing 75- and 100-g fingerlings.

Fingerlings In trial 1, the aeration system was inadequate to sustain optimum feeding rates at the high densities, and DO levels were often < 2.0 mg/liter during the last month of the trial. This initial aeration system consisted of 13 air stones (4.5 cfm total) around the tank perimeter. Not only were DO levels insufficient for fish metabolism, they affected nitrification and high levels of ammonia and nitrite developed. Under these conditions only the lowest stocking density (200 fish/m3) exceeded the desired final size (Table 9.2). In trial 2, the aeration system was upgraded to 25 air stones with 9.65 cfm total air volume. As DO levels increased, final size, growth rate and final biomass increased. The results were confounded by having by a much higher initial stocking size (>7.0 g) and much lower survival, which contributed to the high feed conversion ration (1.45±1.69). The cause of high mortality at 177 fish/m3 is unknown but may have been due to bird mortality as no dead fish were found (the tanks were covered by nets, but some holes were noticed in the nets after the experiment). At 355 fish/m3, massive mortality occurred 2 days before the end of the experiment due to bacterial disease, possibly resulting from excessive organic matter in the water column. It is speculated that the density was approximately 30 kg/m3 when the die-off occurred. This density exceeded the capacity of the system's waste treatment process. At 532 fish/m3, massive mortality occurred due to one incidence of nitrite toxicity, which was brought under control by adding calcium chloride. In spite of the problems, the final biomass reached their highest levels (18.6±20.6 kg/ m3), and all treatments exceeded the target fingerling size (50 g) by a wide margin (59.2±137.2 g). In trial 3, stocking rates of 300, 400 and 500 fish/m3 were tested under a new set of management procedures (see feeding and water quality management sections). The initial stocking size (1.1±1.2 g) was appropriate for fry coming off a 28-day sexreversal procedure. Growth was rapid and fish stocked at 300 and 400 fish/m3 exceeded the target size (Table 9.2). There were no replications of stocking rate treatments for advanced fingerling production as only three systems are available (Table 9.2). When best management practices are determined and stocking rates appear to bracket the optimum rate, experimental treatments will be replicated over time.

274


Feeding Grow-out All fish in the grow-out phase are fed a complete diet (32% protein, 3% fat) delivered as an 8-mm floating pellet. The daily ration was initially determined by using a feeding rate schedule based on the percentage of body weight, which was determined every month by sampling. The daily ration was divided into two allotments, which were delivered at approximately 0900 hours and 1600 hours. The initial feeding rate of 3±4% of body weight declined to 0.8±1.4% by the end of the growing cycle, which was low for fish ranging from 400 to 500 g in experiments 1±3 (Table 9.1). Daily feed consumption varied and often the fish were overfed as indicated by the relatively high feed conversion ratios (1.6±1.9) in experiments 1 and 2. If the fish could not finish their ration, it remained floating for most of the day, causing cancellation of the afternoon feeding. Although nitrification in a suspended greenwater system proved to be less stable than fixed-film nitrification, water quality variables such as DO, ammonia and nitrite could not always explain the fluctuation of appetite. Starting with experiments 5 and 6, the fish were fed ad libitum. Initially a feeding rate was determined for the week by one day of ad libitum feeding, as determined by all the feed the fish could finish in 1 hour per feeding twice a day. Later the feeding period was reduced to 30 min. Eventually feed rates were adjusted on Mondays, Wednesdays and Fridays. The feeding rate determined that day was used for the next day or the next 2 days after the Friday determination. Feed conversion rates came down dramatically in experiments 5 (1.79±1.87 for fish ranging from 947 to 1002 g) and 6 (1.55±1.56 for fish ranging from 629 to 744 g). Management time increased, but feed costs declined. During the 3 hours required for weekly feed adjustments, other tasks can be performed.

Fingerlings Similar to grow-out feeding, fingerling feeding procedures went through a period of adjustment until a suitable system was developed. The current procedure is to feed a complete diet (50% protein, 17% fat) of sinking granules (1.2 mm) at 10% of body weight daily for the first 2 weeks. The feeding rate is adjusted daily based on a hypothetical (1:1) feed conversion ratio. The daily ration is divided into four feedings at 0800, 1100, 1400 and 1700 hours. A standpipe with a fine-mesh screen is used during the first 2 weeks to draw effluent from the top of the tank and prevent feed loss to the clarifier. After 2 weeks, a complete diet (44% protein, 15% fat) of floating pellets (1.6 mm) is fed ad libitum for 30 min four times daily for 4 weeks. From this point on, the standpipe is removed and effluent to the clarifier is drawn off the bottom of the tank. A medium-mesh plastic screen retains the fingerlings in the rearing tank. During the last 6 weeks of the grow-out period, a complete diet (32% protein, 5% fat) with 4.8-mm floating pellets is used. The fish continue to be fed four times daily ad libitum for 30 min. A maximum feeding rate of 550 g/m3/day has been obtained with the fingerling production system.


275

Water quality management Grow-out Continuous aeration and twice-daily solids removal are essential to the operation of the grow-out system. The aeration system has maintained DO levels in the range of 5±6 mg/liter at final densities of 17 kg/m3 and average daily feeding rates for treatments that ranged from 100 to 153 g/m3 in experiments 5 and 6. The maximum daily feeding rate exceeded 200 g/m3. This rate is less than the maximum feeding rate of 360 g/m3/day reported by Avnimelech (personal communication) and by Kahle (personal communication), who was president and general manager of Solar Aquafarms in Niland, California. However, their systems employed substantially more water exchange (Avnimelech) or aeration (Kahle). Diurnal measurements of DO during one day in experiment 4 showed that the DO concentrations reached a peak value (7.8 mg/liter) at 1200 hours and the lowest value (3.7 mg/liter) at 1800, 2000 and 2200 hours (Cole et al., 1997). This diurnal cycle does not occur during a period of algal die-off when the water turns brown in color. During these periods, the system depends totally on mechanical aeration, and the elevated biochemical oxygen demand (BOD) of decaying algal cells decreases DO concentrations temporarily until another algal bloom develops. The fish respond by consuming less feed during these periods. The system depends on continuous aeration. A disruption in aeration during the day does not lead to immediate stress in the fish. However, failure of the aeration system at night will lead to mortality. On two occasions, partial mortality occurred when the vertical-lift pump failed during the night even though diffused aeration via the 13 air stones continued. The clarifiers were very effective in removing solid waste and improving water quality. Over the course of experiment 4, for every 1000 g of feed input, based on dry weight, the clarifiers removed 357 g of total solids, 20 g of total nitrogen, 5.5 g of total phosphorus and 42 g of biochemical oxygen demand (BOD) (Cole et al., 1997). For each 1 kg of net fish production 33 liters of sludge were generated, although the sludge was quite dilute, averaging 1.1% dry weight of solids. Daily production of sludge averaged 65 liters or 0.23% of the rearing tank volume. In addition to feces and detritus, much of the sludge consisted of senescent algal cells, as indicated by its dark green appearance and a 37-fold increase in chlorophyll a concentrations in the sludge compared with the concentrations in the water column. In experiments 3 and 4, the treatments consisted of twice-daily sludge removal compared with no sludge removal. In each experiment, final fish size, growth rate and final biomass were all significantly higher when the sludge was removed (Table 9.1). However, sludge removal did not affect survival in either experiment or feed conversion ratio in experiment 3. The effect of sludge removal on water quality from experiment 4 is shown in Table 9.3. Sludge removal did not significantly affect concentrations of DO, total ammonia nitrogen (TAN) or nitrite nitrogen, variables that are critical to good fish production. Sludge removal did significantly decrease the concentrations of nitrate nitrogen, dissolved orthophosphate, chemical oxygen

276


Table 9.3 Mean values of water quality parameters (mg/l) in greenwater tank systems with sludge removal twice daily and no sludge removal, and in the sludge removed from the tanks in experiment 4. The systems were used for the production of Nile tilapia (Oreochromis niloticus) over a 24-week period. Values in each row followed by the same letter are not significantly different (p>0.05)* Parameter Dissolved oxygen Total ammonia nitrogen Nitrite-nitrogen Nitrate-nitrogen Dissolved orthophosphate Chemical oxygen demand Total suspended solids Settleable solids (ml/l)

Sludge removal

No sludge removal

Sludge

6.7a 0.87a 2.69a 109.3a 7.9a 200.3a 168a 6.9a

6.3a 0.77a 3.29a 137.0b 17.3b 337.0b 492b 54.7b

± 1.61 6.10 89.1 10.5 793.8 10 957 644.1

* From Cole et al. (1997).

demand (COD), total suspended solids (TSS) and settleable solids (Fig. 9.13). It is possible that the high levels of suspended solids affected fish growth in the treatment where sludge was not removed daily. The final TSS concentration was 1250 mg/liter in the treatment without sludge removal compared with 368 mg/liter in the sludge removal treatment. The accumulation of organic matter and its decomposition may have produced more intermediate organic breakdown products, possibly decreasing fish growth. When sludge was removed daily, algal populations appeared to be healthier, as dead or clumped algal masses were quickly removed from the system and water clarity was better, which increased the depth of the photic zone. In the treatment without sludge removal, there was more nitrification, as indicated by higher nitrate-nitrogen levels, and more mineralization, as indicated by the high levels of dissolved orthophosphate. The effectiveness of the clarifiers can be assessed from their solids levels, which were 65 times higher for TSS and 93 times higher for settleable solids when compared with levels in the water column. Other means of improving water quality and fish growth were investigated. In experiment 2, in addition to daily sludge removal, daily water exchange of 5% was performed in one treatment. Water exchange did not affect any of the fish production parameters. However, final densities (6.5±6.8 kg/m3) in this experiment were well below the maximum density of 17 kg/m3. At higher densities and feeding rates, water exchange rates may have a positive impact on fish production by reducing excessive levels of nitrates and organic matter. In experiments 5 and 6, alum (aluminum sulfate) was tested as a means of improving water quality by flocculating and increasing the removal of suspended particulate organic matter. To counteract the acidic reaction of alum in water, 0.37 mg/liter of Ca(OH)2 were added for each 1.0 mg/liter of alum addition after total alkalinity decreased to less than 100 mg/liter as CaCO3. Sludge production and water clarity did increase after the addition of alum. Alum reduces phosphate, which forms a precipitate with aluminum. A reduction in phosphate can decrease algal growth if phosphorus becomes a limiting nutrient. In experiment 5 (unpublished data), which was a non-replicated preliminary trial to assess the effect of


277

three levels of alum (per week) on tilapia production, it appeared that increasing levels of alum addition did exert a positive effect on growth rate, final size and final biomass (Table 9.1). As alum addition increased, there was an increase in daily sludge production (72, 78 and 106 liters/day of sludge at 25.8, 38.7 and 51.5 mg/liter/week of alum, respectively). Experiment 6 (unpublished data) employed replicated treatments to determine if weekly additions of 50 mg/liter of alum affect tilapia production. The results showed that there was no significant difference (P>0.05) in any of the production parameters (Table 9.1). Comparing the nonalum and alum treatments, there were no significant differences in daily sludge production (62 and 67 liters/day), TAN (2.7 and 3.8 mg/liter) and nitrite nitrogen (2.0 and 4.6 mg/liter), respectively. Nitrate nitrogen was significantly (P50 g) during a 12-week production cycle Parameter

300 fish/m3

400 fish/m3

500 fish/m3

Dissolved oxygen Total ammonia nitrogen Nitrite nitrogen Nitrate nitrogen Sludge

6.0 3.7 19.7 195 50

5.0 2.1 16.6 188 54

5.1 6.7 24.3 175 51

In trial 3 another important consideration became apparent. It is possible that during periods when sludge production is high and sedimentation of organic matter is optimal for some unknown reason, the sludge removed from the system represents a good portion of the biofilter and water quality may deteriorate. This concept requires further study.

Water consumption Total water consumption was 0.15 m3/kg of tilapia production in experiment 6 where a final standing crop of 17.0 kg/m3 was obtained in the non-alum treatment. In the `Dekel' system of Israel, tilapia are intensively cultured in 500-m2 concrete tanks aerated with two or three 1.5-hp paddlewheel aerators and the water is recycled through a 1.2-ha earthen pond stocked with carp at 1 fish/m2. This system achieves total yields (tilapia and carp) of 2.4 kg/m2 and consumes 1.2 m3 of water per kg of

280


production (Mires et al., 1990). A pond that produces 5 mt/ha consumes approximately 2±4 m3 of water per kg of production, depending on mean depth and evaporation and seepage rates. In experiment 5, the daily water exchange (make-up) rate was 0.58%, a rate that compares favorably with rates of 13 cages

No.

Village

R

N

R

N

R

N

R

N

1 2 3 4 5 6 7 8 9 10

Cipicung Tegal datar Patok beusi Ciputri Janggari Nyalempet Neundeut Kebon coklat Bongas Calincing

38 67 11 19 22 30 8 8 21 25

18 22 4 14 9 31 27 12 17 22

50 112 15 24 33 61 17 24 23 48

30 41 29 32 23 83 46 32 27 43

45 87 10 10 10 48 6 14 20 37

26 42 34 30 16 78 21 30 18 35

29 82 10 14 9 56 9 12 9 28

Total families

249

176

407

386

287

330

258

Total of families R

N

44 42 34 31 11 121 17 23 12 44

162 348 46 67 74 195 40 58 73 138

118 147 101 107 59 313 111 97 74 144

379

1 201

1 271

Total cages 3 105 5 190 1 682 1 653 1 054 5 946 1 272 1 546 1 227 2 883 25 558

Notes: R (resettled) = families that lost land flooded by reservoir impoundment; N (newcomers) = immigrants from outside reservoir shore line.

(2)

(3)

(4)

persons as managers or laborers in the cage industry in return for `shadow ownership'. The aquaculture permit was in the name of a displaced person but the owner was an absentee `waterlord' in the city. Consolidation of the aquaculture industry into the hands of the rich puts into question any long-term social benefits of the project (Zerner, 1992). Multidisciplinary nature of the efforts. While commendable, such multidisciplinary environmental efforts require more administration than traditional, disciplinary ones. Such extra administrative efforts must be funded. In this case, they were not. It was difficult to coordinate all the professionals needed for project implementation. Many persons had difficulty seeing beyond the narrow bounds of their professional training. It was felt, however, that the developmental situation would have been even worse if the project had been led by a conventional fisheries or aquaculture research organization, rather than by an ecology institution. Ecologists, in general, have a more `generalist' training, and overall were more sensitive to interactions and interfaces. Vague nature of institutional agreements and responsibilities. The institutional framework for project implementation between electric company, university, fisheries, and regional and village political institutions had to be created by the project, necessitating the above-mentioned larger than anticipated administrative load. In addition, each institution occasionally (and repeatedly) had their own interpretation of what the project agreement actually said. And in some cases, these separate institutions actually carried out their interpretations of the agreements without communicating with others, causing duplication and disagreements. Self-pollution. IOE & ICLARM (1989) calculated that the aquaculture carrying capacity of the two reservoirs was 16 400 cages (5800 in Saguling and 10 600 in Cirata). Depending on the availability of adequate numbers of fingerlings, each

Aquaculture Ecosystems for Resettlement from Hydropower Dams

303

cage could produce, conservatively, 1±3 mt fish/year, or a final carrying capacity of 16 400±49 200 mt of fish per year (Costa-Pierce & Hadikusumah, 1990). IOE & ICLARM (1989) also included a dispersal of cages throughout most of the suitable sites for cages (deep, sheltered, and well-flushed bays) (Figure 10.2).

Fig. 10.2 Aquaculture development plan for the Cirata reservoir (Effendi, 1988). The plan apportions water-based aquaculture systems (floating cages, net pens) and land-based aquaculture systems (hatcheries, rice-field fish nurseries and intensive running water systems) in and around the 6200 ha reservoir. Effendi (1988) forecast aquaculture production from floating cages in Cirata to be 1597 mt by 1992. Fish aquaculture production in Cirata actually grew much more rapidly ± annual fish production reached 3880 mt by 1992 (Table 10.3). Administratively, the reservoir was located in two regions (Bandung and Cianjur; kab. = kabupaten) and four districts (kec. = kecamatan) of kabupaten Cianjur.

304

(5)


This areal distribution of cages did not occur. Farmers crowded into a very few select bays of the Saguling reservoir (southern Bongas region) and Cirata reservoir (Janggari region) due to better availability of the village and economic infrastructures, and better access to large fish markets in Sukabumi, Bandung, and Jakarta. This crowding led to `self-pollution' by the cages due to waste feed and nitrogen discharges from the cages (and the wastes from an increasing number of residents on the surface of the water) (Soemarwoto et al., 1990). The result has been development of nuisance algal blooms and more frequent oxygen depletions, leading to large fish kills. Industrial pollution. In the 1990s Indonesia experienced high rates of industrial growth, especially in the manufacturing sector. In the Saguling±Cirata reservoir region, there has been an especially rapid growth in the textile industry. Some of these textile mills discharged untreated wastes into the Saguling reservoir, and were cited by residents as causing fish kills. Industrial wastes discharged to the reservoirs threaten the very basis of the entire cage aquaculture developments and are a principal concern to the public and product safety now and into the future.

The lack of social sustainability: aquaculture's role in equity and the rural poor Aquaculture development has often promised the rural poor in developing countries increased access to rural jobs, and better incomes in an environmentally sensitive, non-polluting business. In this case study, however, even strong government laws and other regulations controlling access, the number of cages (4 per family), and a permitting system reserved only for displaced persons could not stop the new aquaculture industry from being usurped and consolidated into the hands of the urban rich. In addition, planning could not stop the haphazard crowding of cages into a very few areas of the reservoirs where the wastes caused self-pollution and economic losses. Benefits of the new reservoir aquaculture enterprises in Indonesian reservoirs have accrued increasingly to those with adequate capital and power who are not displaced persons (Table 10.4). The poorest of the displaced residents have been resigned to laboring in the industry, rather than controlling it. The institutional will to enforce control over access has evaporated when cage numbers exceeded the guidelines and problems appeared. The fisheries department is the authority responsible for the cages, the water resources directorate owns the water, and the State Electric Company the dam and the reservoir bottom, but none of these agencies is willing to restrict new cage development or enforce their own laws (T. Walton, personal communication, 1997). In addition, there is a new problem because, in the drive for privatization, the reservoirs are now operated not by the State Electric Company (PLN), but by wholly owned subsidiary companies of PLN. However, there have been a number of positive, `trickle-down' type of benefits for the rural poor. It has been estimated that the new aquaculture industry created many new jobs in a rural area of severe underemployment (22 new types of rural jobs have


305

been documented; Costa-Pierce, 1997). These new jobs were higher paying (it has been estimated that cage aquaculture workers earned about Rp 56 000 per month more than rice field workers in the same area); and the new work was less rigorous than hard labor in rice paddies (Costa-Pierce, 1997). In 1992, it was estimated that 7527 persons were employed either full- or part-time in the reservoir aquaculture industry in the two reservoirs: 1162 directly and 6365 indirectly (Costa-Pierce, 1997). More difficult to discern is whether or not any of the trickle-down benefits were due to these new and high paying aquaculture jobs or were simply due to the increased economic opportunities that have been available to most of Java in the 1990s.

The lack of environmental sustainability: how to ensure sustainability of cage aquaculture production in tropical reservoirs The West Java Provincial Fisheries Agency led the drafting of two 5-year plans for reservoir aquaculture development in Saguling (1985±89) and Cirata (1988±92) (Effendi, 1985, 1988). Plans called for a stepwise development of cage aquaculture with 3195 mt of fish to be produced from cages in Saguling and Cirata in equal amounts by 1992 (6390 mt total), along with development of other land- and waterbased aquaculture support systems (Table 10.5). Cage aquaculture developed much more rapidly and in a much more haphazard fashion. Instead of 6390 mt by the end of 1992, fish production was estimated at 7933 mt (Table 10.3). The IOE & ICLARM (1989) reservoir fisheries and aquaculture development plan estimated a carrying capacity of 5800 cages for Saguling and 10 600 for Cirata, or 16 400 total fish cages distributed throughout the reservoirs (Fig. 10.2). There are an estimated 25 558 cages in Cirata in 1996 (Table 10.4), and these are crowded into very few areas. As a result, more frequent oxygen depletions have occurred since 1993, leading to large fish kills in Saguling (> 500 mt in 1994±95). There is a significant role for an ecosystems approach to developing aquaculture, by designing non-polluting aquaculture ecosystems and closing biogeochemical nutrient cycles as an alternative approach to the `feedlot' aquaculture scenarios (Folke & Kautsky, 1992; Costa-Pierce, 1996). High nutrient inputs enter the reservoirs from surrounding urban areas making a high biomass of plankton available year round. Plankton could be cropped by fish in cages in èxtensive', or no feed, cage culture of the tilapias and Chinese carps (Hai & Zweig, 1987; Costa-Pierce, 1997). In addition, `condominium' cages having one insert cage suspended above another with fish that are fed, and an outer cage having a crop of fish that is unfed, could increase fish production from the same area of water surface, increase feed efficiency, and decrease self- and external environmental pollution (CostaPierce, 1997). It is recommended that an expansion of `no feed' cage aquaculture systems for Chinese carps and tilapias be developed and that more emphasis be placed on development of land-based hatcheries and rice±fish nursery systems. Emphasizing an ecosystems approach and developing ecosystems technologies would also better concentrate aquaculture's local economic development and multiplier effects.

306

Activity

Unit

1985

1986

1987

Floating net cages Pens Hatcheries

7 6 7 6 2.5 m 1 ha 1500 m2

75 35 52

230 20 2

340 15 2

Activity

Unit

1988

1989

1990

Floating net cages Pens Hatcheries Running water Rice±fish

7 6 7 6 2.5 m 1 ha 1500 m2 100 m2 1 ha

75 27 20 5 115

230 24 18 4 15

340 15 16 2 10

Year

Year

1988

1989

Total

1985

1986

Production (kg) 1987 1988

340 15 2

355 15 2

1 340 100 60

337.5 63 24 128

1 035 36 928

1 530 27 928

1991

1992

Total

1988

1989

Production (kg) 1990 1991

340 15 14 2 10

355 15 12 2 10

1 340 96 80 15 160

337.5 156.6 9 280 25 40.3

1 035 1 392 8 352 20 53

1 530 87 7 424 10 3.5

1 530 27 928

1 530 87 6 496 10 3.5

1989

Total

1 597.5 27 928

6 030 180 27 840

1992

Total

1 597.5 87 5 568 10 3.5

6 030 556.8 37 120 75 56.1


Table 10.5 Five-year step-by-step development plan for the development of aquaculture systems for resettlement in the Saguling and Cirata reservoirs (Effendi, 1985, 1988)


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Due to uncontrolled population growth and increased demands for water and power, there has been a boom in hydropower construction since the 1950s, especially in Asia. New methods are needed to manage reservoirs for sustainable food production and restore the livelihoods of displaced peoples. In these studies, an interdisciplinary, `social ecological' approach was used to develop aquaculture as a means of local population resettlement and income restoration. Village participatory research methods were used to develop a `basket of low cost aquaculture systems', and encourage development of intimate societal interactions with the new land± water aquatic ecosystems in villages most impacted by hydropower reservoirs, as opposed to moving people far away from these new environments. There are numerous situations in the developing countries of Asia where this paradigm may be of interest. Aquaculture's role in sustainable rural development must be determined by the agenda of the intended beneficiaries. Sophisticated traditional methods of aquatic ecosystems management exist in numerous developing nations, especially in Asia. By involving the target group from the outset to develop a step-by-step technology and social adaptation program, we have evolved a set of appropriate technologies based on traditional aquaculture ecosystems in the Saguling±Cirata reservoir region that present a exciting new model of large-scale protein food production for proteinhungry Asia. It is argued that social and environmental restoration of damaged watersheds from dam construction can only be accomplished through such active involvement of displaced people who have an investment in rehabilitation. In this case an integrated program using the principles of farming systems research and extension methods allowed the necessary flexibility of choices to be made by the people themselves on the best component technologies they could capitalize on and manage. Reservoirs offer unique opportunities to educate people about their new environments and for formulating innovative, flexible, and evolutionary ownership patterns and agreements between electric companies, research institutions, nongovernmental organizations, and communities to meet a common set of restoration goals. Few reported aquaculture development experiences in any country have met with such remarkable success in as short a period of time as the reservoir cage aquaculture developments in Saguling and Cirata in Indonesia. But success of the fish cage aquaculture industry cannot only be measured by tons of fish. These aquaculture systems are fragile, and presently are unsustainable both environmentally and socially. This study shows clearly that sustainability of aquaculture requires government support in the form of technical extension inputs, strict enforcement of its own regulations on access permits, systems numbers, and pollutant discharges, and clear institutional commitments to equity. If a means could be found to ensure the more equitable distribution of long-term benefits to the target group, this notion of developing floating cage aquaculture in artificial reservoirs as a new source of aquatic protein could, in the future, represent a new, globally important food resource. The development scenario reviewed here is characterized by rapid, dynamic and constant change. For this reason, it is recommended that comprehensive, long-term studies of the fish cages and the people be accomplished. These people have made a

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huge social leap from being principally highland rice farmers to fish farmers, transiting in a few short years from being land farmers to water farmers. They are a remarkable group of people, a unique living laboratory of new indigenous knowledge. These people could teach us a great deal about the global and localized factors contributing to success, and provide more accurate forecasts in order for scientists and policy-makers to better judge the applicability of the aquaculture resettlement option to other developing countries.

Conclusions From 1985 to 1988 the Saguling and Cirata hydropower reservoirs in the densely populated highlands of West Java, Indonesia, displaced over 40 000 families. As part of a comprehensive resettlement plan, an attempt to resettle 3000 families in waterbased, floating fish cage aquaculture and land-based aquaculture support was initiated. Over a 4-year period, aquaculture research, demonstration, extension, and training programs were conducted and study tours to other Asian nations with relevant experiences arranged. By the end of 1992, water- and land-based aquaculture ecosystems in and around the Saguling and Cirata reservoirs employed 7527 persons. At the end of 1996, total fish production was 24 496 metric tons (approximately 95% common carp, Cyprinus carpio and 5% hybrid red tilapia, Oreochromis spp.), an amount equal to about 20% of the fish entering the Bandung district (estimated population 3 million persons). Total 1996 gross revenue from fish was over US$24 million, over twice the estimated annual revenue (US$10.4 million adjusted for inflation to 1996) from the 5783 ha of ricelands lost to the reservoirs. However, from 1994 to the present, aquaculture developments in the Saguling and Cirata reservoirs are neither environmentally nor socially sustainable. The benefits of floating cage aquaculture, which were guaranteed originally to the displaced people by provincial legislation and were designed to give them exclusive ownership over the production and marketing sectors of the industry, were usurped by the politically powerful, and consolidated into the hands of the urban rich from Bandung and Jakarta. Survey of fish cage ownership in 1996 in Cirata showed only 48% of cage owners were resettled persons (1201 out of 2480 total aquaculture families). Most of the displaced people were involved as employees of absentee owners. Guidelines set on the numbers of cages (10 600 in Cirata and 5800 for Saguling) to protect the reservoir environments were not enforced, causing environmental degradation and self-pollution (at the end of 1996, Cirata had 25 558 cages and Saguling 8199 (1997 survey)). Fish cages were developed haphazardly in very few areas of the reservoirs where market access was good, rather than where the environments were suitable, degrading water quality. As a result of overcrowding and water-column turnovers, there were numerous fish kills in the upstream Saguling reservoir (aquaculture production dropped from 6666 mt in 1993 to 4405 mt in 1996). Numerous Saguling farmers moved downstream to the Cirata and Jatiluhur reservoirs, where they crowded cages in the waters beyond sustainable levels (Cirata's fish production


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increased from 6556 mt in 1993 to 24 496 mt in 1996). Thus, while the reservoir cage aquaculture developments were successful from a fish production viewpoint, aquaculture has not been sustainable socially or environmentally over the long term. Cage aquaculture in reservoirs can be an important new means of large-scale population resettlement from hydropower dam construction and protein production in tropical developing countries only if: (1) (2) (3) (4) (5)

adequate government planning for fisheries is included before dam construction (too often fisheries are viewed as another `simple engineering problem'); adequate financial compensation for lost assets is given; there is rigid enforcement of institutional regulations guaranteeing the long-term benefits of the new lakes for the exclusive use of the displaced people; there is enforcement of regulations on cage numbers to prevent environmental degradation; and adequate government subsidies are provided for aquaculture job creation, training, long-term extension support, and active monitoring.

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Chapter 11

The Role of Aquaculture in the Restoration of Coastal Fisheries Mark A. Drawbridge Hubbs-SeaWorld Research Institute Introduction When aquaculture is used as a vehicle to help restore fisheries, it is referred to as `sea ranching' or `stock enhancement'. These terms are often used interchangeably, especially as they pertain to marine programs, but they have been appropriately and separately defined (Bannister, 1991). Sea ranching involves marking and releasing organisms so they can later be identified and harvested by the releasing organization. Salmon are often ranched in this fashion, while the ranching of branded cattle offers a good land-based analogy. Unlike sea ranching programs, stock enhancement is typically initiated and implemented for the public good ± no single user group is rewarded (Bannister, 1991). The commonality between sea ranching and stock enhancement is that organisms are released into an ecosystem from an external source. It should be noted that the broader definition of stock enhancement involves not only culture-based activities, but also habitat protection and modification. Specific examples are the creation of protected areas (e.g. refugia), artificial habitats (e.g. reefs), and nursery areas. These categories of enhancement are not necessarily directed toward any one species or age class, as is often the case for stocking programs. Interest in establishing stocking programs in the marine environment has developed from a variety of circumstances. The most compelling of these has been the plight of fisheries resources during the past century. According to recent statistics, among 200 marine fisheries for which data are available, approximately 60% are either fully or over-exploited (FAO, 1997). Since 1985, worldwide fish landings have stabilized at approximately 80 million metric tons (mt) with 75% of that total being food fish (New, 1997). In 1995, aquaculture production of fish and shellfish added another 21 million mt to this total. Unlike capture fisheries, which showed no increased yield, aquaculture production almost doubled between 1990 and 1995. New (1997) estimated that fishery production needs to reach 52 million mt by 2025, taking into consideration the current level of seafood consumption (approximately 13.5 kg/ caput/yr in 1995) and increasing human populations. Since production by capture fisheries is not expected to increase significantly, if at all, aquaculture must play a large role in meeting this deficit. Because the goal of stock enhancement is to use

Role of Aquaculture in the Restoration of Coastal Fisheries

315

cultured organisms to complement fishery production, it represents a bridge between capture and culture-based fisheries that will likely have some impact on the future availability of seafood. Like commercial fishermen, recreational fishers are often powerful stakeholders in fishery conservation programs. The balance of political power between recreational and commercial fishers often dictates the focus of stock enhancement programs. In the United States, the total economic impact of recreational fishing is estimated to be $108 billion ± 23% of that being attributed to saltwater fishing activity (Maharaj & Carpenter, 1996). Bartley (1999) reported that among stock enhancement programs that were not classified as experimental, approximately 12% were directed toward recreational species, 60% toward commercial species, and the remaining 28% toward species that were both recreationally and commercially valuable.

Stock enhancement ± past and present Historical perspective Surprisingly, concerns about depletion of wild fishery resources, disputes between recreational and commercial fishers, and plans to establish hatcheries for stock enhancement were reported as early as 1870 in the United States (Bowen, 1970). During this period marine hatcheries were also established in Canada, France, Great Britain, New Zealand, and Norway. Stocking programs of this era involved stripspawning of adults from the wild and releasing fertilized eggs or newly hatched larvae into coastal waters. In addition to a number of anadromous species, early stocking programs focused on cod (Gadus morhua), haddock (Melanogrammus aeglefinus), pollack (Pollachius virens), winter flounder (Pseudopleuronectes americanus), herring (Clupea harengus), tautog (Tautog onitis) and Atlantic mackerel (Scomber scombrus) (Shelbourne, 1964; Richards & Edwards, 1985). Although biologists released millions of eggs and fry, they found no conclusive evidence to indicate that target populations were being enhanced as a result. Even without validation of success, stocking programs continued into the early 1950s. At this time, funding was eliminated and programs shut down under mounting criticism regarding the lack of evidence of efficacy. The failure of these early stocking efforts was due to two primary factors. First, technological limitations prevented culturists from growing large numbers of fish to metamorphosis, so that only eggs and larvae were released. Post-release mortality was likely very high, either from predation or from starvation. Secondly, the efficacy of the stocking efforts was not rigorously assessed. To a certain extent, this failure was again a technological limitation. To accurately evaluate the success of releases, it was necessary to mark hatchery fish so that they could be distinguished from wild fish. At that time techniques were not readily available to mark or otherwise identify released eggs and larvae. Led by Japanese scientists working with red sea bream (Pagrus major), culture of marine fishes progressed quickly from 1965 onwards. By the 1980s, British and French scientists were successful in establishing the techniques required for

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large-scale production of sea bass (Dicentrarchus labrax), gilthead sea bream (Sparus aurata), and turbot (Scophthalmus maximus) (Sorgeloos et al., 1993). With the scientific achievements in marine fish culture, particularly in larval nutrition, came a revived interest in marine stock enhancement. This interest was bolstered by the fact that the depletion of marine resources recognized in the previous century had not been corrected by traditional management strategies. Quite the contrary, technological advances in the commercial fishing industry increased harvests, and development of coastal areas severely impacted critical nursery and spawning habitats.

Modern techniques While modern science has overcome the primary technological hurdles experienced by early investigators, the potential pitfalls associated with the improper application of stock enhancement are still present and new concerns have emerged. The notion that `more is better' or `quantity over quality' is still a political reality in some areas. Some programs continue to fail in evaluating the effectiveness of hatchery releases adequately, even though numerous techniques for marking fish and other marine organisms are now available (Parker et al., 1990). A more stringent regulatory environment has impeded program development in some areas, including hatchery production. In cases where enhancement hatcheries are capable of the mass production of juveniles, new concerns have emerged about the potential genetic and ecological impacts of releasing so many hatchery-produced individuals. Notwithstanding these concerns, the revival of marine stock enhancement is moving quickly, as scientists and managers are eager to test its potential and evaluate the true concerns regarding its application. From the early controversy, and recent pilot-scale feasibility studies, guidelines for establishing a responsible, comprehensive approach to marine stock enhancement are being developed. The guidelines outlined by Blankenship & Leber (1995) include: (1) (2) (3) (4) (5) (6) (7) (8) (9) (10)

prioritizing and selecting species for enhancement; developing a comprehensive species management plan; defining qualitative measures for success; applying genetic resource management; applying disease and health management; forming stock enhancement objectives and strategies using all available ecological, biological, and life-history information; identifying hatchery fish and assessing the effects of stocking; using an empirical process to define optimal release strategies; identifying economic and policy objectives; and using adaptive management.

Because of their relevance to this discussion, many of these points are covered in this chapter.


317

Program planning and review Prior to stocking, careful consideration and evaluation should be given as to how and why the organism will be released, the potential impacts of stocking, the goals for the stocking program, and how success will be measured. A step-wise strategy for developing and implementing a stocking program is illustrated in Fig. 11.1. The stock enhancement plan should be integrated within a more general species management plan that includes other resource management tools, as well as contingency procedures for modifying the plan as new data become available. Another important component to consider early in the planning phase is a review process that will allow an unbiased evaluation of the performance of each component of the species management plan, including releases of juveniles.

Selection of species Developing and evaluating a list of candidate species is one of the first steps in the planning process. To do this, a thorough review of the history and current status of local stocks should be conducted. The species on this list are then ranked using criteria that are developed a priori. The process of prioritizing or ranking potential species for stock enhancement is often based on a combination of economic, sociopolitical and biological factors. Given the uncertain success associated with new enhancement programs for marine species, and the costs associated with both culture operations and post-release assessment, it is not surprising that economic considerations (i.e. the economic value of the species) weigh heavily in this process. Similarly from a biological standpoint, species with a known culture potential may be favored over species that have not been cultured in order to reduce the risk of failure. Sociopolitical factors become important when multiple user groups (e.g. recreational and commercial fishers) advocate enhancement of different depleted resources. Blankenship & Leber (1995) describe a step-wise process of workshops, surveys and interviews that is designed to reduce conflict frequently associated with the species selection process. They recommend using a numerical index derived from pre-established criteria to reduce bias, as well as using a trained facilitator.

Ecological criteria for success As part of the planning and species-selection process, it is important to understand the reason for the decline in the resource, because this will have a direct impact on the success of the stocking program. Similarly, while difficult to measure, an understanding of the carrying capacity of the system is necessary in order to optimize enhancement programs. Munro & Bell (1997) point out that two basic ecological conditions must exist in order to successfully enhance fish populations through stocking. First, following natural recruitment, sufficient habitat of appropriate quality must be available to accommodate stocked juveniles. Secondly, prey abundance associated with these habitats must be sufficient to support the growth and survival of the stocked fish.

318 Ecological Aquaculture

Fig. 11.1 Suggested strategy for planning, implementing and evaluating a stocking program in order to minimize risks and maximize benefits (adapted from Cowx, 1994, and Howell, 1998).


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It is often reported that habitat and trophic resources of marine ecosystems are rarely fully exploited. This statement is supported by historical patterns of recruitment where peak years (well above the average recruitment) still result in successful colonization (Munro & Bell 1997). If the species to be enhanced has been overexploited, as is often the case, then it would seem intuitive that habitat and trophic resources once occupied by wild fish would be available to support stocked fish. However, it may also be that other species in the community that were not similarly exploited now utilize these resources, making it less likely that stocking will be effective. This phenomenon of alternating species abundance has been well documented between sardines and anchovies (Lluch Belda et al., 1992). Certainly if critical habitats have been reduced or significantly altered, it may not be possible to reach historical production levels again. The challenge for stock enhancement programs is to try to understand the complexities of carrying capacity and make the best use of underutilized spatial or trophic resources. As hatchery technology improves, and greater numbers of juveniles are available for release, the potential for overstocking or saturating an environment will increase. In cases where the carrying capacity is reached because of stocking, cultured animals may displace wild ones or fail to survive (Hume & Parkinson, 1987). Densitydependent factors such as reduced growth or condition have also been reported as the carrying capacity is approached (Peterman, 1991).

Establishing objectives and measures of success The objectives and measures of success for stocking should be clearly defined before fish are released. The objectives for stocking typically fall into one of four categories: stocking to restore, mitigate, augment, or create new fisheries (Cowx, 1994; Fig. 11.1). In restoration-oriented stocking programs, the first step is to identify the factor responsible for limited population growth, and then correct it. The bottleneck may be related to anthropogenic impacts such as poor water quality or restricted migratory access. Once the bottleneck is eliminated, stocking is used to rebuild the population but is not necessary over the long term (see Richards & Rago, 1999, for case study). Mitigation programs involve a known anthropogenic impact that limits productivity but is not corrected because of sociopolitical factors. The negative impact of hydroelectric dams on salmon populations is a classic example where mitigation hatcheries are utilized. In this case, stocking is required as long as the bottleneck exists. Stocking programs with an enhancement or augmentation objective are the most common, especially in the marine environment. In this case, the goal is to enhance or supplement an existing stock for which numbers are below the carrying capacity of the system. Unlike restoration programs, in this case the limitation to population growth may not be clearly identified. The use of stocking to create new fisheries was widely practiced in the past, particularly in freshwater systems, but is becoming less common today because of the potential for negative ecological impacts. The indicators used to measure the success of a stocking program will vary according to the specific objectives described above. Regardless of the objective, three

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pieces of information are required to fully evaluate the success of enhancement. This information includes: (1) the cost to produce fish to release size; (2) the number of stocked fish surviving to harvest; and (3) the value of the harvested fish. During the planning phase, the specific indicators and techniques used to quantitatively assess success should be identified and stated precisely for each objective. For example, one objective might be to attain a specific percentage increase in landings within a specified period of time (Blankenship & Leber, 1995).

Pre-release evaluations and feasibility assessment The targeted population and its native habitat must be well understood before initiating a culture program and releasing fish. Knowledge of historical patterns of distribution (habitat use) and abundance for different life stages, as well as interactions with predator, prey and competitor species, is necessary in the planning process. This information will help the evaluation of feasibility, program implementation (e.g. broodstock collection and management, designing release strategies), and impact assessment (e.g. positive or negative interaction with native species).

Genetic considerations The potential impact cultured fish impose on the genetic integrity of native populations is one of the greatest concerns associated with stocking programs, especially those programs involving small populations (see Bert et al., Chapter 3). Concerns related to genetic quality assurance in stocking programs have been reviewed and evaluated by a number of investigators (Brannon, 1993; Joerstad et al., 1994; Naevdal, 1994; Bartley et al., 1995; Shaklee & Bentzen, 1998; Tringali & Bert, 1998). The rapid growth and improvement of genetic identification techniques is resulting in a corresponding increase in this body of literature. Because the importance of genetic quality assurance is now clear, guidelines for maintaining genetic integrity among enhanced populations have been developed (Kapuscinski & Jacobson, 1987; FAO, 1992). A good understanding of the genetic population structure for each species is important because the seed for enhancement programs typically comes from captive adults. Broodfish should be collected from within the population that is targeted for enhancement. This approach facilitates local adaptation and survival of the progeny and promotes genetic integrity among interbreeding wild and hatchery-reared fish (Brannon, 1993; Conover, 1998; Utter, 1998). In cases where the targeted population no longer exists, geneticists recommend using adults from as similar an environment as possible (Travis et al., 1998). The genetic population structure of marine animals tends to be more homogenous than freshwater or anadromous species. The lack of genetic differentiation is primarily attributed to patterns of egg and larval dispersal. Marine organisms often have relatively long planktonic stages of development. Ocean currents and a lack of physical barriers facilitate the dispersal of these planktonic stages in the ocean (Bartley et al., 1995; Conover, 1998). However, clinal differences in gene frequency


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have been observed in some marine species, making it necessary to evaluate each target species independently (King et al., 1995; Tringali & Bert, 1998). Responsible stocking practices require a thorough understanding of the genetic characteristics of the fish being released. The size of the breeding population must be evaluated on a species-by-species basis, and the relative contribution of each potential parent must be assessed. Allendorf & Ryman (1987) recommend a minimum broodstock population of 100 males and 100 females when information regarding genetic diversity and spawning habits is limited but adult fish are plentiful. Geneticists also recommend that culturists encourage single pair matings among their broodstock and that eggs be collected equally from all females in the population. Using empirical data from both wild and hatchery-reared white seabass, Bartley et al. (1995) recommended a minimum broodstock population size of 150 adults. These investigators implemented a broodstock management plan that included 200 adult fish and provisions for rotating males among maturation pools and integrating new stock into the captive-breeding program (Figs 11.2, 11.3). A similar broodstock management plan was established in Texas for red drum (McEachron et al., 1995).

Bioeconomic modeling A bioeconomic model is a useful tool for evaluating enhancement programs before, during and after implementation of stocking. As the name suggests, this type of model

Fig. 11.2 Schedule of broodstock rotation and replacement as part of an overall broodstock management plan. Cylinders represent mass spawn pools maintained on controlled temperature and day length cycles with 25 males and 25 females (adapted from Bartley et al., 1995).

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Fig. 11.3 Researchers work on a sedated seabass broodfish collected from the wild. Prior to being added to the breeding stock, each fish is biopsied to determine its sex, weighed and measured to assess growth, passive induced transponder tagged for physical identification, and fin clipped for genetic analyses.

combines biological criteria (growth, survival, etc.) with economic ones (cost to culture, harvest product value, etc.). Before stocking is initiated, a bioeconomic model can help evaluate the likelihood of success in economic terms. Once an enhancement program is initiated, bioeconomic models can be used as a simulation tool to identify specific areas within the stocking program where improvements will result in a higher rate of return. Bioeconomic models can be used to set goals (i.e. specific targets for cost to benefit) and should be refined as new data is available. Outputs from the model in the form of cost-to-benefit ratios represent an excellent measure of the program success (Sproul & Tominaga, 1992; Ungson et al., 1993; Hilborn, 1998). It should be emphasized that the output from any model is only as good as the information entered into it. Care must be taken to select a model that is sufficiently detailed and that represents the components of the stocking program accurately. A model that does not have these features can produce very misleading results.

Pilot-scale studies to optimize post-release survival Marking techniques A thorough review of marking techniques used to evaluate stocking success is beyond the scope of this work. However, it is important to note that a wide variety of tools have been developed in recent years that allow researchers to mark individuals within the full range of life history stages for almost any species (Parker et al., 1990). Access to and implementation of these tools is critical to understanding and evaluating stocking efforts, and to assure optimum success of the releases. The choice of marking technique is dictated by the age, size and species involved, as well as the specific objectives of the stocking program. Chemical markers, including oxytetracycline and calcein, can be used effectively to mark animals as early as the egg and larval stages (Wilson et al., 1987; Monaghan, 1993; Brooks et al., 1994; Secor et al., 1995; Mohler, 1997). The primary advantages to this technique are its ability to mark small life stages, and its ease of application as a bath or in the feed. Genetic


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marking techniques are also being developed for stocking programs (Murphy et al., 1983; Joerstad et al., 1991; Gaffney et al., 1996; Kristiansen et al., 1997; Wilson et al., 1997). The primary benefit of this technique is that it allows assessment of the reproductive contribution of stocked fish, as genetic markers are passed down to subsequent generations. As illustrated in Fig. 11.4, a variety of physical tags and marking techniques have been developed for larger fish, including those that are applied internally such as coded wire, passive induced transponder, or visible implants; or externally such as fin clipping, anchor-type, or branding (Bergman et al., 1992; Guy et al., 1996). The specific objectives of the study will dictate which type of tag is most appropriate. Tags differ in the degree of invasiveness to the organism and the longevity as a mark. Consideration must also be given to the techniques and costs associated with implanting and later identifying the mark, the amount of information the tags encode, and any bias associated with results.

Hatchery techniques ± fitness considerations Successful, responsible stocking practices require that the organisms being released are of the highest quality possible. Individuals whose behavior or health is compromised will likely starve or be eaten, or may transmit diseases to wild fish. Therefore, hatchery managers must consider factors that will affect post-release performance, and develop techniques to minimize their impact. Culture techniques used in hatcheries that produce animals for market sale may not be adequate for those that will be released into the ocean.

Fish health and nutrition Good husbandry practices that result in vigorous, healthy animals are required to produce maximum post-release survival of stocked fish and to minimize potential impacts to native species. The goal of any stocking program should be to release organisms that are as similar to wild conspecifics as possible. The similarities should include physical, physiological, and biochemical characteristics, and parasite load. This is obviously a difficult goal and although deviations from `normal' are commonly reported in the literature, the implications of these differences are not always clear. Physical differences range from subtle deviations in meristics, morphometrics and color patterns, to the grossly abnormal (Fig. 11.5). The latter have obvious relationships to decreased fitness (Balbontin et al., 1973; Blaxter, 1976; Fukuhara, 1990; Stoner & Davis, 1994; Ellis et al., 1997a). Physical malformations are most often attributed to improper nutrition or sub-optimal holding conditions (e.g. stressful lighting regimes, high stocking densities, poor water quality). Reduced fitness of stocked fish has also been attributed to low stress tolerance caused by improper nutrition and chemical imbalances (Howell, 1994; Olla et al., 1994, 1998; Wallin & Van den Avyle, 1995). Reduced tolerance to stress is particularly important at the time of release when stress levels are high due to handling and transport conditions.

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Fig. 11.4 Different tags used historically on fish and their attachment sites. Approximate minimum tag sizes are given for scaling (adapted from Guy et al., 1996, with permission, from the original image by Wydoski & Emery, 1983).


Fig. 11.5 Two species of organisms being evaluated for enhancement, demonstrating clear differences between hatchery and wild individuals. (a) Cultured conch on the left has poorly developed shell compared with wild counterpart on the right (photo with permission from A.W. Stoner, National Marine Fisheries Service). Note streamer tags used for marking. (b) Cultured California halibut on the left has natural pigmentation compared with abnormal pigmentation on the right. In both cases, animals released with these abnormalities would have reduced predator avoidance capacities and therefore limited stocking effectiveness.

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(a)

(b)

A number of cases have been reported in which diseases associated with hatcheryreared fish spread to native fish, sometimes with devastating results (Heggberget et al., 1993; Hindar & Jonsson, 1995). Transfer of disease can occur through the release or escape of unhealthy hatchery stock, or from cage and farm effluents. Conversely, the transfer of disease from wild to hatchery-reared organisms is also possible, especially in cases where animals are transferred from a relatively sterile, hatchery environment into the natural environment. In this case, the danger may not be immediate for the wild population, but the stocked or caged animals may act as a reservoir for the proliferation of the particular pathogen (Cowx, 1994). Disease outbreaks occur when typically stable but delicate relationships among the host animal, pathogen and the environment become imbalanced. For example, poor water quality (environment) may lead to stressed animals (host) and increased susceptibility and proliferation of disease (pathogens). Within this triangle, pathogenic organisms can often be isolated and identified, and therefore they receive a great deal of attention. However, a thorough understanding of the interrelationships between the host and its environment is generally lacking, especially for wild populations (Hedrick, 1998). Diseases occur in natural populations of aquatic organisms, but are

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poorly documented. A better understanding of disease processes is required to effectively and responsibly manage disease interactions within culture-based fisheries (Coutant, 1998). High quality seed animals can be produced by applying sound genetic principles, using modest stocking densities, and providing a high-quality diet. It may also be advantageous to modify larval rearing techniques in order to cull out genetically inferior groups of individuals early in the culture process, similar to what would occur naturally in the wild. Promoting survival among only the hardiest larvae would likely reduce the incidence of disease outbreaks in later life-history stages and allow maximum post-release survival among stocked fish. These modifications might include reducing the use of antibiotics in larval rearing systems (Coutant, 1998), modifying filtration systems so the water is not completely sterile, and purposefully exposing larvae to natural bacteria or `probiotics' that are carefully selected (Kennedy et al., 1998). To minimize the risk of releasing inferior or compromised organisms, a certified professional should inspect each batch of fish prior to transfer or release.

Fish behavior, conditioning and performance Behavioral differences between hatchery-reared and wild organisms have been reviewed by a number of investigators (Blaxter, 1976; Howell, 1994; Olla et al., 1994, 1998). Variations in behavior related to feeding (Ersbak & Hasse, 1983; Iglesias & Rodriguez-Ojea, 1994; Steingrund & Fernoe, 1997), migration (Jonsson et al., 1991), schooling, and predator avoidance (Schiel & Welden, 1987; Stoner & Davis, 1994; Ellis et al., 1997b) have been reported. Because behavioral processes are complex, the effects that behavioral differences impose on the fitness of stocked organisms are not always clear. For example, differences in feeding may involve the mode of prey capture (Steingrund & Fernoe, 1997), the diurnal pattern of feeding (Howell, 1994), or the type and quantity of prey captured (Nordeide & Salvanes, 1991; Kristiansen & Svasand, 1992). Deficits in any one of these facets of behavior will negatively impact the fitness of stocked fish by either increasing the expenditure or decreasing the intake of energy, or by increasing the risk of predation due to poor foraging skills. Because behavioral deficits are often a by-product of traditional culture practices, there is a need to better evaluate the impacts and, if possible, mitigate them. The performance of stocked animals may be improved by using more extensive rearing techniques and by conditioning animals prior to release. For example, Olla et al. (1994) demonstrated that fish exposed to predators in the laboratory (experienced) survived better upon release than fish with no prior exposure (naõÈ ve). While many predator avoidance and feeding behavioral characteristics are innate, a controlled learning period often is required to successfully implement them (Ellis et al., 1997b; Steingrund & Fernoe, 1997). There is a growing body of evidence to suggest that culturing organisms under more natural conditions for at least a short period prior to release will have a significant, positive impact on post-release survival and the ability of cultured fish to integrate with wild conspecifics. More `natural' culture conditions include lower stocking densities, more variable water quality, and exposure to natural substrates or


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structure, prey and predators. The combination of these modifications will increase feeding success, and reduce stress and predation (Howell, 1994; Olla et al., 1994; Maynard et al., 1995; Tanaka et al., 1998; Berejikian et al., 2000). In California, white seabass destined for stocking are acclimated to natural conditions for 5±6 months prior to release by growing them in net cages in protected embayments (Kent & Drawbridge, 1999; Fig. 11.6).

Fig. 11.6 Cage system used to grow-out and acclimate white seabass prior to release. Cage is located in Marina del Rey, California, and is owned and operated by volunteers from a local fishing club.

Release strategies ± biological and ecological considerations After the culture protocols are developed, strategies for releasing the animals must be evaluated. While the principal goal of the culture program is to produce animals of the highest quality, release programs are designed to achieve the highest rate of recruitment possible. The size and numbers of organisms to release, and the season and habitat in which to release them are the primary factors that can be manipulated to optimize recruitment success. It is important to note that there may be strong interactive effects among these components, so release strategies must be developed accordingly. Similarly, interspecific differences require that each species be evaluated separately.

Fish size at release The most appropriate or òptimum' size to release fish should be empirically defined prior to full implementation of any stocking program. Leber (1995) defined the òptimum release size' as the size of fish at which stocking results in the greatest rate of return or recruitment. Intuitively one would think that the larger the organism is at release, the greater its chance of survival. In fact, this has been demonstrated empirically for a number of different species but may not always be the case when interactive effects of release season or habitat are considered (Tsukamoto et al., 1989; Ray et al., 1994; Yamashita et al., 1994; Leber, 1995; Willis et al., 1995). In addition to the size-specific aspects of growth on survival, the optimum release size is also commonly evaluated in relation to the economic considerations associated with

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raising organisms to a larger size. That is, the benefits of releasing fish at a larger size (i.e. increased post-release survival) are typically weighed against the added costs of the extended growout (Kent et al., 1995). In addition to the optimum release size, Leber et al. (1995) also define a `critical release size' as `the size at release below which the probability of survival to reproductive size approaches zero'. In that study involving striped mullet, the critical size was 70 mm total length (TL) for summer releases. While this is only one example, it is not difficult to understand why early marine stocking programs, releasing eggs and larvae, were likely to be very ineffective.

Season of release The season or timing of release is another important factor to consider when refining release strategies. Stocking of organisms is possible year-round for many species, even at the same target size, because spawning can be induced artificially and out of phase with wild populations. Similarly, growth rates in the hatchery environment can be manipulated to bring the development of organisms into or out of phase with wild counterparts. Stocking success is often dictated not only by the size of the animal at release, but also by the timing of the release. In fact, these two parameters are usually highly correlated (Hume & Parkinson, 1988; Willis et al., 1995; Leber et al., 1997, 1998). Return rates for organisms released during different times of year can vary widely. For example, Willis et al. (1995) reported a rate of return greater than 800% for red drum stocked in phase with wild fish compared with similar sized individuals stocked six months out of phase. Leber et al. (1997) demonstrated that the timing of releases can have a dramatic effect on recapture rates among groups of fish released at different sizes. While few small mullet (

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