Sea Trout: Biology, Conservation and Management

SEA TROUT: BIOLOGY, CONSERVATION AND MANAGEMENT Proceedings of the First International Sea Trout Symposium, Cardiff, July 2004 Edited by

Graeme Harris and Nigel Milner

Central Fisheries Board

Blackwell Publishing

SEA TROUT: BIOLOGY, CONSERVATION AND MANAGEMENT

SEA TROUT: BIOLOGY, CONSERVATION AND MANAGEMENT Proceedings of the First International Sea Trout Symposium, Cardiff, July 2004 Edited by

Graeme Harris and Nigel Milner

Central Fisheries Board

Blackwell Publishing

© 2006 by Blackwell Publishing Ltd Editorial Offices: Blackwell Publishing Ltd, 9600 Garsington Road, Oxford OX4 2DQ, UK Tel: +44 (0)1865 776868 Blackwell Publishing Professional, 2121 State Avenue, Ames, Iowa 50014-8300, USA Tel: +1 515 292 0140 Blackwell Publishing Asia Pty Ltd, 550 Swanston Street, Carlton, Victoria 3053, Australia Tel: +61 (0)3 8359 1011 The right of the Author to be identified as the Author of this Work has been asserted in accordance with the Copyright, Designs and Patents Act 1988. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, except as permitted by the UK Copyright, Designs and Patents Act 1988, without the prior permission of the publisher. First published 2006 by Blackwell Publishing Ltd ISBN-13: 978-1-4051-2991-6 ISBN-10: 1-4051-2991-3 Library of Congress Cataloging-in-Publication Data International Sea Trout Symposium (1st : 2004 : Cardiff, Wales) Sea Trout: Biology, Conservation, and Management : Proceedings of First International Sea Trout Symposium, Cardiff, July 2004/editors, Graeme Harris and Nigel Milner. p. cm. Includes bibliographical references and index. ISBN-13: 978-1-4051-2991-6 (hardback : alk. paper) ISBN-10: 1-4051-2991-3 (hardback : alk. paper) 1. Sea-run brown trout–Congresses. I. Harris, Graeme. II. Milner, Nigel. III. Title. QL638.S2I484 2004 639.3’757–dc22 2006014213 A catalogue record for this title is available from the British Library. Set in 10/13pt Times by Newgen Imaging Systems (P) Ltd., Chennai, India Printed and bound in Singapore by Markono Print Media Pte Ltd The publisher’s policy is to use permanent paper from mills that operate a sustainable forestry policy, and which has been manufactured from pulp processed using acid-free and elementary chlorine-free practices. Furthermore, the publisher ensures that the text paper and cover board used have met acceptable environmental accreditation standards. For further information on Blackwell Publishing, visit our website: www.blackwellpublishing.com

Contents

Foreword

ix

Preface

xi

Opening Address 1. Sea Trout: A Welsh Perspective Carwyn Jones AM

xiii

Opening Address 2. Sea Trout and the Environment Agency Helen Phillips

xvii

1

Setting the Scene – Sea Trout in England and Wales – A Personal Perspective G. Harris and N. Milner

1

Section 1 STOCKS AND FISHERIES 2

Patterns of Anadromy and Migrations of Pacific Salmon and Trout at Sea T.P. Quinn and K.W. Myers

11

3

A Review of the Status of Irish Sea Trout Stocks P. Gargan, R. Poole and G. Forde

25

4

Characteristics of the Sea Trout Salmo trutta (L.) Stock Collapse in the River Ewe (Wester Ross, Scotland), in 1988–2001 J.R.A. Butler and A.F. Walker

5

6

Characteristics of the Sea Trout (Salmo trutta L.) Stocks from the Owengowla and Invermore Fisheries, Connemara, Western Ireland, and Recent Trends in Marine Survival P.G. Gargan, W.K. Roche, G.P. Forde and A. Ferguson Annual Variation in Age Composition, Growth and Abundance of Adult Sea Trout Returning to the River Dee at Chester, 1991–2003 I.C. Davidson, R.J. Cove and M.S. Hazlewood

45

60

76

7

Sea Trout Stock Descriptions in England and Wales G. Harris

88

8

The Rod and Net Sea Trout Fisheries of England and Wales R. Evans and V. Greest

107

9

General Overview of Turkish Sea Trout (Salmo trutta L.) Populations I. Okumu¸s, I.Z. Kurtoglu and S¸ . Atasaral

115 v

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10 The Status and Exploitation of Sea Trout on the Finnish Coast of the Gulf of Bothnia in the Baltic Sea E. Jutila, A. Saura, I. Kallio-Nyberg, A. Huhmarniemi and A. Romakkaniemi 11 Sea Trout (Salmo trutta L.) in European Salmon (Salmo salar L.) Rivers N.J. Milner, L. Karlsson, E. Degerman, A. Johlander, J.C. MacLean and L-P. Hansen

128

139

Section 2 GENETICS AND LIFE HISTORY 12 Genetics of Sea Trout, with Particular Reference to Britain and Ireland A. Ferguson 13 The Genetic Basis of Smoltification: Functional Genomics Tools Facilitate the Search for the Needle in the Haystack T. Giger, U. Amstutz, L. Excoffier, A. Champigneulle, P.J.R. Day, R. Powell and C.R. Largiadèr

157

183

14 Life History of the Anadromous Trout Salmo trutta B. Jonsson and N. Jonsson

196

15 Migration as a Life-History Strategy for the Sea Trout D.J. Solomon

224

16 Life History of a Sea Trout (Salmo trutta L.) Population from the North-West Iberian Peninsula (River Ulla, Galicia, Spain) P. Caballero, F. Cobo and M.A. González

234

17 Review and Perspectives on Molecular Genetic Approaches to Sea Trout Biology M.W. Bruford

248

Section 3 POPULATION DYNAMICS, ECOLOGY AND BEHAVIOUR 18 A 35-Year Study of Stock–Recruitment Relationships in a Small Population of Sea Trout: Assumptions, Implications and Limitations for Predicting Targets J.M. Elliott and J.A. Elliott

257

19 Characteristics of the Burrishoole Sea Trout Population: Census, Marine Survival, Enhancement and Stock–Recruitment Relationship, 1971–2003 W.R. Poole, M. Dillane, E. DeEyto, G. Rogan, P. McGinnity and K. Whelan

279

20 Population Dynamics and Stock–Recruitment Relationship of Sea Trout in the River Bresle, Upper Normandy, France G. Euzenat, F. Fournel and J-L. Fagard

307

Contents

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Section 4 MANAGING STOCKS AND FISHERIES 21 The Spawning Habitat Requirements of Sea Trout: A Multi-Scale Approach A.M. Walker and B.D. Bayliss

327

22 Research Activities and Management of Brown Trout and Sea Trout (Salmo trutta L.) in Denmark G.H. Rasmussen

342

23 Stocking Sea Trout (Salmo trutta L.) in the River Shieldaig, Scotland D.W. Hay and M. Hatton-Ellis

349

24 Is Stocking with Sea Trout Compatible with the Conservation of Wild Trout (Salmo trutta L.)? H. Lundqvist, S.M. McKinnell, S. Jonsson and J. Östergren

356

25 Sea Lice Lepeophtheirus salmonis Infestations of Post-Smolt Sea Trout in Loch Shieldaig, Wester Ross, 1999–2003 M. Hatton-Ellis, D.W. Hay, A.F. Walker and S.J. Northcott

372

26 Comparison of Survival, Migration and Growth in Wild, Offspring from Wild (F1) and Domesticated Sea-Run Trout (Salmo trutta L.) S. Pedersen, R. Christiansen and H. Glüsing

377

27 The Rapid Establishment of a Resident Brown Trout Population from Sea Trout Progeny Stocked in a Fishless Stream A.F. Walker

389

28 Predicted Growth of Juvenile Trout and Salmon in Four Rivers in England and Wales Based on Past and Possible Future Temperature Regimes Linked to Climate Change I.C. Davidson, M.S. Hazlewood and R.J. Cove 29 Sea Trout (Salmo trutta L.) Exploitation in Five Rivers in England and Wales B.A. Shields, M.W. Aprahamian, B.D. Bayliss, I.C. Davidson, P. Elsmere and R. Evans 30 Catch and Release, Net Fishing and Sea Trout Fisheries Management D.J. Solomon and M. Czerwinski

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434

31 A Review of the Statutory Regulations to Conserve Sea Trout Stocks in England and Wales G. Harris

441

32 An Appreciation of the Social and Economic Values of Sea Trout in England and Wales P. O’Reilly and G.W. Mawle

457

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33 Sea Trout Fisheries Management: Should We Follow the Salmon? A.M. Walker, M.G. Pawson and E.C.E. Potter

466

34 Perspectives on Sea Trout Science and Management N.J. Milner, G.S. Harris, P. Gargan, M. Beveridge, M.G. Pawson, A. Walker and K. Whelan

480

Declaration

491

Index

493

Foreword

Fish that spawn in stony rivers tend not to leave many fossils so perhaps we should not be too surprised that the earliest salmonid we know of for certain died a mere five million years ago. Primitive anatomical features, like the wide separation of the pectoral and pelvic girdles and the physostomous swim bladder, suggest that the origins of the group to which Atlantic salmon and sea trout belong lie tens of millions of years earlier when the Atlantic Ocean was much narrower than it is today. Cyto-geneticists tell us that at some point in the early history of the salmonids a ‘mistake’ in cell division led to a doubling up of chromosome numbers. Although there has since been some rearrangement of chromosome arms, especially in the more advanced members of the family, all members of the group still carry clear evidence of their tetraploid ancestry. It is interesting to reflect that, among living fishes closely related to the Salmonidae, the smelt, Osmerus eperlanus (L.), carries a normal diploid complement of chromosomes. This observation tells us that the osmerids and the salmonids separated before the doubling of chromosome numbers characteristic of the latter and it is tempting to speculate that tetraploidy persisted because it had adaptive value in estuarine fishes making increasing use of an environment, the sea, where rapid growth to a large size is possible. We have no direct way of knowing what the life cycles of the first salmonids were like but perhaps among those followed by Salmo trutta (L.), especially the sea running populations, we may see reflections of an archaic life style (also followed by sea running lampreys) in which the benefits of using the comparative safety of fresh water for reproduction, but exploiting the dangerous but much more productive world of estuarine waters and the sea for growth, first established themselves in yet another family of aquatic vertebrates. If fuelling the idle speculations of aged zoologists was the sole justification for studying sea trout, it is highly unlikely that the First International Sea Trout Symposium, of which this book is such a signal celebration, would ever have come about. The fact is that the sea trout is a fish that demands to be studied. Markedly superior to any salmon at table and pound for pound its sporting equal, its high unit value on both counts effortlessly earns it a place in the first division of top quality European fishery resources. Perhaps surprisingly for a commodity which is so highly prized, it is but lightly exploited by directed fishing (apart from certain interception fisheries which also target salmon). Thus, most of the variation we see in the abundance and structure of sea trout resources is driven, not by fishing pressure, but by changes in the growth and survival opportunities provided by the principal environments through which they pass namely, freshwater lakes and rivers, estuaries and coastal waters. Similar to salmon and other anadromous fishes, sea trout are highly sensitive to deterioration in the quality of any of these habitats. However, sea migratory trout have a survival trick up their sleeves. They are often part of more broadly based trout population complexes, some of whose members complete their entire development in their tributaries of origin, some in the main stems and estuaries of rivers and others, especially females, follow the archetypal life cycle by achieving large size and high fecundity at sea. This ix

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flexibility in the life cycle options available to S. trutta has enabled it to survive insults to coastal waters and estuaries which have led to the total loss of salmon populations in many parts of their traditional range. The good news is that, when estuarine conditions once more permit the passage of sea migratory trout, their numbers build up rapidly sometimes, as appears to have happened in the Aberdeenshire Don, outcompeting the river resident trout that hitherto had dominated the system. How lucky we Europeans are still to have the sea trout and how fortunate also that its importance as a biological entity and as a priceless socio-economic resource is at last being accorded the academic recognition (of which this excellent book is the most recent expression) it richly deserves. Richard Shelton

Preface

This volume contains the proceedings of the ‘First International Symposium on the Biology, Conservation & Management of Sea Trout’, held in Cardiff in July 2004. The aim of the Symposium was to assemble and discuss new knowledge and understanding of the biology of sea trout and the science and management of its fisheries. This was required because much has changed since the last scientific workshops on sea trout in Wales and in Scotland in the late 1980s and since ICES started progressing sea trout work on an international level in the mid-1990s. The Symposium attracted contributions from 12 different countries, revealing a wide range of fishery problems and a variety of opportunities and circumstances within which management and science are carried out. The chapters in this book convey this and we have tried through the editorial process to retain the variety of styles and approaches rather than try to apply overly prescriptive structures. The diversity of approaches and data reflects the subject itself. The book structure is straightforward. An introductory section sets the scene historically, identifies some key features of sea trout and raises some of the major topics to be dealt with. The main body of chapters is divided into the four themes of the Symposium: (1) Stocks and Fisheries; (2) Genetics and Life History; (3) Population Dynamics, Ecology and Behaviour and (4) Managing Stocks and Fisheries. A concluding chapter brings together the common threads with recommendations for the future science and management. Finally, the Symposium produced a ‘Declaration’ (always a risky activity) which was drafted by the organising committee and widely circulated at the time. We hope this will offer some milestones against which to judge progress at future Symposia and specialised workshops on sea trout.

Nomenclature In common English parlance, ‘sea trout’ is the name usually given to the adult anadromous (migratory, sea-going) form of Salmo trutta (L). Amongst taxonomists, S. trutta is usually known as the brown trout. However, although by no means universal, common usage has adopted the term ‘brown trout’ as representing the non-migratory form and this can cause confusion. Much time can be spent debating the classification of the phenotypes representing the life history continuum in S. trutta, and the accompanying nomenclature and synonyms (e.g. resident, non-migratory, freshwater, anadromous, brown trout, slob trout, sea trout, sea-trout). We have not attempted to prescribe terminology in this volume, because there is no consensus across the board, but we recognise its desirability for the future. Nigel Milner and Graeme Harris January 2006 xi

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Acknowledgements We wish to thank our colleagues on the Organising Committee, who have in so many ways provided practical ideas, support and encouragement. Alphabetically they are: Steve Barnard (Environment Agency Wales) Mike Bruford (School of Biosciences, Cardiff University) Paddy Gargan (Central Fisheries Board) Graeme Harris (FishSkill Consultancy Services) Tim Hoggarth (Atlantic Salmon Trust) Paul Knight (Salmon and Trout Association) Nigel Milner (Environment Agency) Pat O’Reilly (Environment Agency Wales) Mike Pawson (Centre for Ecology, Fisheries and Aquatic Sciences) Andy Walker (Fisheries Research Services Ken Whelan (Marine Institute) The following comprised the editorial committee: Mike Bruford (School of Biosciences, Cardiff University Paddy Gargan (Central Fisheries Board) Graeme Harris (FishSkill Consultancy Services) Nigel Milner (Environment Agency) Mike Pawson (Centre for Ecology, Fisheries and Aquatic Sciences) Andy Walker (Fisheries Research Services Ken Whelan (Marine Institute) and we thank numerous referees who helped with this task. We are also grateful to Samantha Emmott of the University of Cardiff Conference Office for the overall smooth running of the Symposium and to Bernie Barron, National Fisheries Technical Team, Environment Agency, for her efficient administrative and organisational support.

Sponsorship We gratefully thank the organisations that provided financial support for the Symposium. Such sponsorship demonstrates their commitment to achieve improved understanding and better management of our sea trout resource and we hope that they get value for money from the programme and its outcomes. They are, in alphabetical order: the Atlantic Salmon Trust UK), the Central Fisheries Board (Republic of Ireland), the Centre for Ecology, Fisheries & Aquaculture Sciences (E&W), the Environment Agency (E&W), the Salmon and Trout Association (UK), the Scottish Executive (Scotland) and the Welsh Assembly Government (Wales).

Opening Address 1 Sea Trout: A Welsh Perspective Carwyn Jones AM Minister for Environment, Planning & Countryside, Welsh Assembly Government, Cathays Park, Cardiff CF10 3NQ, Wales, UK

Ladies and gentlemen, I take great pleasure in opening the proceedings of this International Symposium and extend a warm welcome to delegates, especially those who have travelled from overseas. It is encouraging that so many of you are here today. It is appropriate that Wales was selected as the venue for this symposium on ‘The Biology, Conservation and Management of the Sea Trout’ as the sea trout has always been regarded as very special to Wales; where it is still widely referred to as the ‘Sewin’: an old Welsh name that means ‘the silver or shining one’ when loosely translated into English. Indeed Cardiff is one of the few capital cities where, not 400 yards from this venue, sea trout can be caught. It is almost 20 years since the last major scientific meeting on sea trout was held in the British Isles. Since that time there has been an important constitutional change within the UK. We no longer have a centralised structure of Government centred in London. The National Assembly for Wales was set up in 1999. Its executive, the Welsh Assembly Government, now exercises an extensive portfolio. Importantly, matters relating to the management of the coastal and inland waters of Wales are the responsibility of the Welsh Assembly Government. What this means is that we can, and are, shaping policy and actions directly relevant to the needs of Wales and Welsh fisheries. There have also been important changes in England and Wales in recognising the need to ensure that fishery management strategies are under-pinned by robust science. There are many questions yet to be asked, and answered, in relation to the sea trout and the time for this International Symposium is right in bringing these to the fore. The sea trout is of great importance to Wales for several reasons: In terms of its geographical area, Wales is a small part of the British Isles, but it has more than its fair share of sea trout. Following in part from Welsh Assembly funded work, the recovery of the once polluted, over-abstracted and obstructed rivers of south-east Wales from the effects of the Industrial Revolution is well advanced. Almost every river and stream that enters the sea around our 1200 km (750 miles) of Welsh coastline now contains a natural and self-sustaining run of migratory trout. Many of these rivers support productive rod fisheries and, in some instances, commercial net fisheries. In a typical year more than half of the 40 000 or so sea trout caught by anglers xiii

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in England and Wales come from Welsh rivers. The Tywi, Teifi, Dyfi and Mawddach, for example, consistently yield rod catches that are amongst the best in Britain. Compared with the sea trout in most other parts of the British Isles, Welsh sea trout grow faster, live longer and attain a much larger size. Sea trout in excess of 15 lb weight (6.8 kg) are not unusual in most rivers and some, such as the Dyfi, have produced several specimens exceeding 20 lb weight (9.1 kg) in recent years. Unlike other areas in Britain, large amounts of the fishing in Wales are owned or controlled by locally based angling clubs. In effect, they are owned by the community and provide readily affordable fishing for both local and visiting anglers alike. The sea trout has been described as an ‘enigmatic’ and ‘neglected’ species that was often considered to be less worthy of sporting endeavour than its more prestigious cousins – the brown trout and the Atlantic salmon. Sea trout fisheries have not had the attention they deserve. Throughout the British Isles, scientific endeavour and pro-active management action has concentrated on the salmon and brown trout. However, the recent and widespread general decline in salmon stocks has only served to highlight the underlying importance of the sea trout as the mainstay of many fisheries and attract the attention of fishermen in many parts of England and Wales and beyond. Although our sea trout fisheries in Wales appear to be reasonably healthy, we must not be complacent and take our sea trout stocks for granted on the basis of the historical catch record. Recent history shows us that fisheries can be overexploited and that collapsing stocks can lead to both social and economic deprivation. One of the most significant developments in recent years has been the shift towards managing Welsh fisheries in ways that seek to maximise their social and economic value to the community as a whole. This is a goal that is well recognised in Wales and one that is incorporated in our fishing strategies. Studies on the socio-economic value of fisheries have been a recent development in the UK compared with North America and other parts of Europe. However, there have been some, and one of the most recent was the ‘Study into Inland & Sea Fisheries in Wales’ commissioned by the Welsh Assembly Government. This was prepared by Nautilus Consultants Ltd. and published in 2000. It concluded that recreational sport fishing in all its different forms generated an income of some £100 million a year to the economy of Wales. It is clear that angling is an important source of enjoyment, employment and income – especially in those rural areas where most of the fisheries are located. In the context of this Symposium, the ‘Nautilus Report’ also recommended that the sea trout fisheries of Wales should be more actively nurtured and promoted in order to increase the social and economic benefits of angling tourism in Wales. This is also one of our goals. The report of the ‘Salmon and Freshwater Fisheries Review’ published in 2000 also stressed the importance of managing our fisheries to enhance social and economic benefits to the community as a whole: and it further underlined the importance of sea trout in this context. The fisheries legislation in England and Wales was largely formulated in the 1860s when the pressures on our fisheries and their management needs were very different. It has long

Opening Address, Carwyn Jones AM

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been recognised that this legislation needs to be strengthened and updated to address the very different environmental pressures and management needs of today. This seminal Review, commissioned by Parliament in 1998, examined the policies and legislation relating to the management of salmon and freshwater fisheries in England and Wales and made 195 broad and far-reaching recommendations for change. The Welsh Assembly Government has considered these. It is supportive of the need for change along the lines set out in the Review and work is ongoing. As a response to the central recommendations of these two major reports, the Welsh Assembly Government in partnership with the Environment Agency Wales launched the ‘Sustainable Fisheries Programme’ and increased funding by an additional £2.4 million (e3.9 million) over a 3-year period. Early results from the initiative are extremely encouraging with aquatic environments being improved, barriers to fish movement removed or eased and angling participation increased. Furthermore, Wales has been successful in obtaining European Objective 1 funding of £5.3 million (e8.5 million) which has been invested in this Programme and in the ‘Fishing Wales’ Project. The latter is aimed at encouraging angling tourism within Wales and will initially promote sea trout, wild brown trout and bass fishing. These programmes, led by the Environment Agency Wales, involve both other agencies and the angling community. This increased investment in our fisheries is not merely to provide more fish for anglers to catch: although that should be a natural consequence. Instead, the overall objective is to maximise the social and economic value of the fisheries in Wales by making the fishing more attractive to local and visiting anglers alike. The ultimate aim is to increase employment opportunities and incomes within the community as a whole. Another development of potentially enormous significance for the future well being of our migratory fisheries in England and Wales has been the overall reduction in the commercial fishing effort for salmon and sea trout over recent years. Commercial fishing for migratory salmonids is now carefully controlled and regulated to protect and maintain adequate spawning populations. The number of commercial fishing instruments licensed in Wales each year to fish for salmon and sea trout in tidal waters has decreased progressively from 187 in 1981 to the more sustainable level of just 65 in 2003. Most significantly, Wales has now phased out all commercial net fishing in coastal waters that exploited known ‘mixed stocks’ of salmon and sea trout returning to Welsh rivers. Other significant initiatives promoted by the private sector have resulted in the buy-out of the few remaining drift nets on the Usk, Clwyd and Dee. This means that there are now no interceptory fisheries operating off the coast of Wales. Thus, we can say that we have put our own house in order in this particular respect. Although much of the reduction in commercial fishing effort has been driven by the need to protect and conserve Atlantic salmon, these measures do much to increase both the numbers and average size of the sea trout now returning to Welsh rivers. This is making a major contribution to increasing the economic value of our fisheries. Another salutary development over recent years has been the growing awareness within the angling community of the need to conserve fish stocks for the benefit of future generations. Self-imposed ‘Rules and Regulations’ combined with the adoption of voluntary

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‘Codes of Conduct’ by the angling community, have all helped to reduce the number of fish killed and so served to increase the size of the spawning population. Most impressive has been the rapid adoption of catch-and-release as a conservation ethic by sea trout anglers. Whereas less than 10% of the rod catch of sea trout was returned alive to the river after capture in 1993, the corresponding figure across Wales in 2002 was more than 50%; and on some rivers it approached as much as 90% of the total rod catch. In practical terms this has meant that some 13 000 sea trout were voluntarily released to increase the spawning population in 2002 and so strengthen our sea trout stocks in future years. This is a measure that I welcome and would wish to see increase; not only in respect of the sea trout. It is encouraging to think that one of the important outcomes of this International Symposium will be to raise the profile of the sea trout. Given the complex and seemingly opportunistic life history of the fish and the many gaps that appear to exist in our knowledge about its biology, ecology, migration behaviour and genetic status, it is clear that enormous challenges are still faced in attempting to manage this valuable natural resource. Setting ‘egg-deposition targets’ and ‘conservation limits’ for the management of our salmon stocks is difficult. How much more difficult then will it be to manage a species where the proportion of juveniles that may or may not migrate to sea to become sea trout in any year is unknown and can vary widely from river to river and from year to year? This is one of the questions that need to be addressed. The effective management of our sea trout fisheries in the future will require answers to this and many other fundamental questions if this amazing natural resource is to be managed in a sustainable way for the benefit of future generations. That then is the challenge! I wish you all an enjoyable and fruitful meeting. I look forward to seeing a positive outcome from your deliberations over the next 3 days. It is quite clear from the impressive and packed programme that you have a great deal to consider.

Opening Address 2 Sea Trout and the Environment Agency Helen Phillips Regional Director, Environment Agency Wales, Cambria House, 29 Newport Road, Cardiff CF24 0TP, Wales, UK

Ladies and gentlemen, On behalf of the Environment Agency Wales, it is a pleasure to welcome delegates to Cardiff and to address this Symposium which is considering a topic that has substantial significance for the Environment Agency in Wales and in England. Amongst its many other roles in environmental protection, the Environment Agency also has a statutory duty ‘to maintain, improve and develop’ fisheries for salmonids, freshwater fish and eels on behalf of the two nations: and that duty includes sea trout. Fisheries and their successful management are important for two main reasons: first, because fish are icons of environmental quality, people are reassured by their presence in rivers, particularly the big, visible migratory salmonids like sea trout and salmon. The status and well-being of fish stocks is a key bio-indicator of the water quality, water quantity and general well-being of our rivers. The role of fish as bio-indicators is why they will play an important part in helping to define good ecological status in the forthcoming Water Framework Directive. Second, because fish stocks are the basic resource for recreational and commercial fishing, and fishing is a major activity that generates sustainable benefits to rural and urban communities. We have just heard from the Minister the importance that the Welsh Assembly Government attaches to sustainable fisheries management as part of its National strategy for the development of social and economic benefits within the Welsh community as a whole. These two facets of fish stocks, as bio-indicators and in supporting commercial and recreational fishing, determines the Agency’s principal policy aims with respect to fisheries. These are: •

to promote the conservation and maintain the diversity of freshwater fish, salmon, sea trout and eels and to conserve their aquatic environment; • to enhance the contribution that salmon and freshwater fisheries make to the economy, particularly on remote rural areas and in areas with low levels of income; • to enhance the social value of fishing as a widely available and healthy form of recreation. The sea trout has a special place in Welsh fisheries. It has now overtaken salmon as a fish of importance to anglers. Since 1992, when rod catches of both species were the same (at xvii

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about 14 500 fish each year), the total English and Welsh sea trout catch has increased to 45 000 and is now about four times the salmon catch. Of this total approximately 50% come from Welsh rivers; and so we see Wales as a focal point for research and its translation into better management practice. Let me give you a little background to the Agency and its duties. It is a big organisation, having some 2500 employees across England and Wales, with a regulatory and management role across the environment. For example, discharges and waste disposal from industry to air, land and water, are licensed and regulated by the Agency. We manage water resources and flood risk management. We advise planning consultations on most environmental matters and we are the ‘competent authority’ charged with delivering many of the European Directives: such as ‘Nitrates’, ‘Fish’, ‘Urban Waste Water’ and the ‘Water Framework Directive’. Fisheries are just one small, but high profile, part of this activity (with an annual spend of £28 million (e45m) of a revenue budget of £650m (e1 billion). The multifunctional brief of the Agency ensures that fisheries and conservation needs are met within an integrated approach to environmental management and protection. This is a real benefit that facilitates the difficult balancing act of managing conflicting demands on the environment of our rivers, streams and coastal waters where sea trout live. With respect to fisheries, we licence net and rod fisheries, we administer and enforce regulations, we monitor and report on catches, fish stocks, fishing effort and demand, we control fish movements and, most importantly, we facilitate and encourage fishery development in order to promote the high level aim of good fishing that is accessible to all. Sound science is a keystone of the Agency’s business. Modern fisheries management has a strong scientific basis and the fisheries service in Wales has played a leading role in developing and then applying that science. The scientific basis of salmon management has changed considerably over the last 10 years. For example, the methods for carrying out and reporting stock assessment using conservation limits for salmon have introduced a quantitative rigour to the process that was missing before. More effective and better-targeted stock monitoring and assessment methodologies have accompanied this change. Practical methods to protect, enhance and restore fisheries and their aquatic environment have been developed through improved understanding of fish ecology and behaviour. For example, the opening of barriers to fish passage and the protection of bankside habitat by riparian corridor protection schemes will lead to increased production of salmonids. Developments in the techniques and application of fisheries economics and social sciences have enabled better targeting of development and needs to the benefits of management. The science behind sea trout fisheries needs to tackle some tricky problems. During the Symposium we shall hear of the complex links between the non-migratory brown trout and the migratory sea trout: and we shall ponder over the balance between ‘nature and nurture’ in determining migratory behaviour in anadromous fish. The scientific understanding of these contrasting life histories is a formidable scientific challenge. But it will be necessary to meet this challenge, if we are able to develop ‘biological reference points’ for sea trout as has been explicitly required of the Agency by the Governments’ recent ‘Review of Salmon and Freshwater Fisheries’.

Opening Address, Helen Phillips

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To meet many of these recommendations, the Agency has recently launched its ‘National Trout & Grayling Strategy’ for England & Wales, which naturally includes the interests of migratory sea trout. There has not been a scientific meeting specifically about sea trout in Britain for about 20 years. But, as we shall hear, there have been big changes in our knowledge and understanding and we need to review and harness this knowledge and then to reappraise it in the light of a changing regulatory and management framework. The Agency needs to have this information so that it can more effectively discharge its duties with respect to sea trout fisheries and its stakeholders. We see it as one of our roles to support and encourage such events as this Symposium. The Welsh Assembly Government (WAG) were quick to realise the value of Welsh fisheries, and the contribution to that value made by sea trout. In 2002, it provided the Agency with an additional investment of £2.4 million (e3.8 million) to support the ‘Sustainable Fisheries Programme’ over a 3-year period with which it could undertake a range of enhanced fishery management actions including habitat improvements, fish pass construction and angling participation. Stimulated by the WAG Grant-in-Aid funding for sustainable fisheries, we have secured a further e3.8 million of Objective 1 money over 3 years and, with EU Structural funds, the Agency and its partners have been able to generate a direct investment in our fisheries of over e15.8 million. This investment is crucially important in meeting our strategic aims for the local economy, quality of life and the environment in Wales. It has helped to reduce the impact of barriers to migration, so that upstream access has been created or improved to over 250 km of river in Wales. It has also restored 90 km of degraded fisheries habitat in the past year alone. Much of this work was made possible by the cooperation and support of the landowners and angling clubs, resulting in not only ecological benefits but also in providing ‘exemplar’ demonstration sites that will raise public awareness of the problems being addressed and the practical solutions to those problems. Investment in training for our voluntary and private fishery managers throughout Wales is playing a crucial part in building skills and capability within the fisheries community and so increasing their capacity to identify, fund and deliver projects for themselves. None of this fisheries science, management or development occurs without close partnerships and collaboration between many organisations. I am particularly glad to acknowledge, and pay tribute to, the substantial and wide-ranging works of the fishery associations and angling clubs, the nature conservation bodies (English Nature and The Countryside Council for Wales), the universities and the local authorities. In Wales we are blessed with active and motivated individuals who have had the foresight to take the lead in establishing Angling Federations and Rivers Trusts. The Wye-Usk Foundation and the Pembrokeshire Rivers Trust being two of the best examples having both evolved to a position where they are now able to access £5 million (e8 million) of EU funds for the benefit of their local rivers and communities. So, what of the future? In Wales at least, it seems that sea trout stocks are mostly at historically high levels. But we must not be complacent. The historical problems of gross pollution from domestic and industrial point-sources have been largely overcome: but there are new problems that are more insidious, more complex and with the ability to do as much, if not more, harm to the aquatic environment and its associated flora and fauna. New

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Opening Address, Helen Phillips

challenges lie in the effects of low level diffuse organic pollutants, such as pesticides and low level industrial contaminants. Britain is a small Island and intensive land use has been an increasing problem leading to the degradation and loss of habitat from intensive land use and water demand. These issues will not go away and so we have to repair the damage of the past and find ways to manage them in the future. In Wales we have a landscape dominated by uplands where the issues of high grazing pressure and forestry can exacerbate problems of acidification, soil erosion, siltation and water loss. These are still significant issues that require scientific understanding to develop practical management solutions. Demands for access to water-space for recreational use and the emergence of waterside development in urban regeneration programmes are reasonable expectations by society, but they can bring real problems for fisheries. In Cardiff we have the biggest estuarine barrage development in Europe and another similar development in neighbouring Swansea. The problems of fish passage through a total exclusion tidal barrier, such as that in Cardiff Bay, with a 13 m tidal rise and fall on the downstream side are immense. We hope they have been solved; but this has only been achieved at considerable expense and by using the latest technology and understanding of fish behaviour through fish-passes. All these issues are set in the context of climate change: and its effects on our seas and fresh waters are likely to be considerable. Sea trout use both environments and so we can expect some changes. There may be gains and losses, but more knowledge is needed and the Agency, along with may others, is active in this area. Through our work, such as the Sustainable Fisheries Programme, we will continue to encourage working in partnership with others, developing awareness within our communities of the social and economic value of their fisheries resource, and in enhancing the capacity of the community to manage it in a sustainable way for future generations – of both fish and people. I hope you have a successful Symposium and I look forward to being able to apply its results to better management of fisheries in the future.

Chapter 1

Setting the Scene – Sea Trout in England and Wales – A Personal Perspective G. Harris and N. Milner Symposium Convenors

Introduction Before starting the formal proceedings of this Symposium, we thought that it might help to set the scene by presenting a broad perspective on the sea trout based largely on our experience of the situation in England and Wales. In doing so we are aware that the importance and management needs of the sea trout may vary widely throughout its natural and introduced ranges and that different perspectives may apply in other geographical regions. However, as the aims of this Symposium are to consider ‘perceptions’, to debate ‘conventional wisdom’ and to challenge ‘assumptions’ relating to the sea trout, we make no apologies if this preamble stimulates discussions during the course of the programme. Indeed, it is our intention that it should do so. Keywords: Sea trout, historical neglect, importance, management advantages, uncertainties.

Historical neglect The epithets ‘neglected’, ‘overlooked’, ‘enigmatic’ and ‘taken-for-granted’ have been variously applied to describe the sea trout by commentators in the past. While these descriptions may not be wholly accurate today, they were certainly apposite to sea trout until quite recently compared with the amount of attention given to its more prestigious relatives – the Atlantic salmon and the non-migratory brown trout. The traditional view that sea trout are less worthy of attention is exemplified by ‘Jock Scott’, the pen-name of a well-known Scottish angling author who published Sea Trout Fishing (Scott, 1969) at the end of a long and distinguished career as a salmon angler. He wrote: The sea trout is the Cinderella of the game fish world: authors, government department, fishing owners and all other interested parties pass him by. This is really not so surprising when one considers . . . that a good sea trout river frequently accommodates salmon also, and naturally the latter fish steals all the limelight, attention and money.

When that was written almost 40 years ago, the angling literature contained several hundred books on fishing for salmon and brown trout but only five books had ever been published that were dedicated solely to the sea trout: and almost the only single source of any technical information about the fish itself for managers and scientists was George Herbert Nall’s The Life of the Sea Trout (Nall, 1930) based on his prodigious scale-reading studies throughout the British Isles. Any scientific work up to that time had been largely 1

2

Sea Trout

opportunistic and incidental to work on the salmon and the general attitude of fishery managers appears to have been based on the assumption that if everything was ‘all right’ for salmon and for brown trout then it would be ‘all right’ for the sea trout also. This somewhat complacent approach is illustrated by the fact that while catch records for salmon had been routinely collected on most English and Welsh rivers since at least 1952, it was not until 1976 that sea trout rod catch records began to match those for salmon (Milner et al., 2001). The 1950s and 1960s are now remembered as the ‘golden age’ of salmon angling in the British Isles. Salmon were then abundant almost everywhere and so it is not surprising that most anglers were not particularly interested in sea trout as their main target species: except at a few notable venues where sea trout fishing had become established as a minor cult – such as the Loch Maree in Scotland, the Delphi in Ireland and the Dyfi in Wales. However, things started to change in the late 1960s and early 1970s with the outbreak of the disease ulcerative dermal necrosis (UDN). This pandemic ravaged salmon and sea trout stocks in most rivers throughout the British Isles (and elsewhere) causing massive mortalities among returning adult fish for several years. However, whereas sea trout stocks steadily recovered over the next decade or so to something like their former levels of abundance, salmon stocks continued to decline to their present parlous state on many rivers in England and Wales. While this decline in salmon stocks helped to raise the profile of sea trout as a natural alternative on many fisheries, the growing interest in sea trout by anglers and fishery managers was further increased by three other separate developments that have occurred since UDN. Angler awareness The first development was in the angling literature. In 1962 Hugh Falkus published the first edition of Sea Trout Fishing. It was a slim volume that had very little impact within the angling community at that time because salmon stocks were plentiful (Falkus, 1962). However, its re-publication in a much revised and expanded format in 1975 coincided with the time when salmon stocks were at their nadir following the UDN outbreak and when there was widespread gloom and despondency within the salmon fishing community (Falkus, 1975). As a result of his persuasive writing about the special delights and opportunities of sea trout fishing (especially at night), many new anglers were recruited into the sport and the demand for good sea trout fishing steadily increased in many regions. Subsequent angling authors have developed this theme and have drawn attention to the practical advantages of sea trout as a sport fish when compared with either salmon or brown trout. These are, in brief: •

•

They can be caught in both the largest rivers and in the smallest streams, in lakes with open access to the sea, in estuaries and even in the sea itself. Many good sea trout fisheries have yet to be ‘discovered’ by the angling community. Although generally smaller on average than salmon they are frequently more abundant, and there are probably more salmon-sized sea trout than there are salmon in many of the smaller rivers.

Setting the Scene •

•

•

• •

3

They can be caught using a more extensive repertoire of angling techniques covering fly fishing with the dry fly, wet fly, surface and deep-sunk lures and then by spinning and bait fishing. Not only can they be caught during the day, but they also have the added attraction in that they can also be caught at night. Indeed, throughout Wales and in some parts of England, by far the greatest proportion of the rod catch of sea trout is taken by fly fishing between the hours of dusk and dawn. They will continue to enter the river and move upstream on very low summer flows – when salmon fishing is a normally complete waste of time: and it is often under such conditions that some of the best fly fishing, especially at night, can occur. Access to sea trout fishing is generally less costly than salmon fishing – particularly on those smaller, spate rivers where salmon runs do not appear until late in the season. Quite apart from the popular view that sea trout fight harder and more spectacularly than either salmon or brown trout when compared for size, they can normally be caught in larger numbers than salmon, they come ‘naturally packed’ in a range of more convenient sizes for the dinner table – from about 10 ounces (0.4 kg) to as much as 10 lb (4.5 kg) or more on some rivers and, according to many, they taste better than either salmon or brown trout.

Socio-economic importance The second development stemmed from the late 1970s when the first socio-economic investigations into the value of commercial and recreational fisheries were commissioned in England and Wales. Notwithstanding the decline in salmon stocks, these added to the growing awareness that the sea trout was the mainstay of the rod and net fisheries on many rivers and had a social and economic value equal to or even greater than that of the salmon in many regions (Harris & Winstone, 1990). One of the more important outcomes from these studies was to show that the sea trout was of particular importance in providing recreational opportunities throughout the season on the many minor rivers with small runs of salmon, predominantly grilse, which did not appear until late summer or early autumn. When viewed overall, the value of these minor fisheries was cumulatively greater than that of the smaller number of better-known salmon rivers that had traditionally dominated and driven our management approach and priorities over the years. Events elsewhere The third, and perhaps most important, event that did much to redress the long history of complacency about the active management of the sea trout and ensured that they were no longer taken-for-granted in England and Wales, was the very loud wake-up call provided by the sudden and dramatic collapse of many important and valuable sea trout fisheries in the west of Ireland from the late 1980s and then in some regions of Scotland from the early 1990s. Although the reasons for this collapse were little understood and hotly contested at the time, they generated grave concern that something similar might happen

4

Sea Trout

in England and Wales. This concern triggered a concerted effort to draw together all the disparate information available from past sea trout studies in England and Wales and led to the implementation of the National Sea Trout R&D Programme in a structured endeavour to identify the urgent gaps in our knowledge about the status and well-being of our fisheries and how best to manage them should such a collapse occur. Thankfully it never did, for reasons that eventually became apparent, but it has now placed us in a far better position to manage our sea trout fisheries in a proactive and sustainable way, although there is still much to learn.

Management advantages In addition to its many attributes as a sport fish, the sea trout has certain characteristics that provide several practical management advantages when compared with the salmon and the brown trout. The chief characteristics among these are discussed in the following sections.

Robust life history The pattern of divided smolt migration to the sea when combined with the pattern of divided adult return to fresh water to spawn for the first time as maiden fish and then again as repeat spawners is far more robust than that of the salmon because it is better able to spread the risks to survival across a greater number of year classes and cohorts of fish. It is therefore potentially better able to withstand and recover from any short-term factors affecting survival in the river and in the sea.

Size-range and in-river distribution Sea trout are better able to make use of a greater range of the available spawning and nursery habitat within a catchment than either salmon or brown trout by virtue of the wide range of adult sizes that are likely to occur. The smaller sea trout can penetrate and utilise the smaller tributaries and smaller spawning gravels that would not be suitable for the bigger salmon, whereas the bigger sea trout can utilise the larger spawning gravels that cannot be used by the smaller brown trout.

Total lifetime fecundity Although sea trout are generally much smaller than salmon on their first return to the river as maiden fish, their potential to live to a greater age and to survive to make several spawning trips to fresh water means that the total, or cumulative, fecundity of these multiple spawning sea trout over their lifetime may be several times greater than that of each individual salmon – where repeat spawning, while not unknown, is now a very rare occurrence. Some British sea trout may survive to make as many as 11 (or more) separate spawning visits to fresh water, increasing in size after each visit to the sea.

Setting the Scene

5

Marine movements and ecology Although our information on the marine phase in the life history of the sea trout is very sparse and incomplete for the British Isles, the general picture that emerges is that it is more coastal in its sea feeding habits than salmon. It is therefore less vulnerable to exploitation and interception by high seas fisheries on its return migrations to fresh water and it is less likely to be affected by those factors oceanic affecting the marine survival of the salmon. Return to the river The sea trout is less dependent than the salmon on the occurrence of natural floods and spates to trigger its migration from the sea, through the estuary and into fresh water. Indeed, some fish will migrate upstream on even the lowest drought flows. This characteristic means that sea trout are less exposed to problems of illegal fishing and poor water quality that can affect accumulations of salmon in tidal waters waiting for the next flood to trigger movement into fresh water.

Unknowns and uncertainties So what are the gaps in our knowledge that limit our ability to manage our sea trout fisheries efficiently and effectively? It is difficult to know where to start, so let us begin with the big question. What is a sea trout? This central question was first posed by Lamond (1916). It has yet to receive a definitive answer. Until quite recently, the conventional wisdom was based largely on the conclusions of Regan (1911) that were subsequently reconfirmed and popularised by Trewavas (1953). It was that the sea trout and the brown trout were freely interbreeding fractions of the same single species, Salmo trutta (as first described ‘page-and-line’ by Linnaeus in 1758), and that there were no genetic differences between the many different forms of migratory and non-migratory trout in the British Isles that had previously been accorded species status by assorted naturalists and taxonomists during the nineteenth century on the basis of differences in their external appearance, morphology and anatomy. In essence the popular view was that S. trutta was a highly polymorphic and ‘plastic’ species that was able to exist in many different forms in response to differences in its local environment. However, advances in science can change conventional wisdom: and there is now growing evidence to show the existence of sympatric and reproductively isolated populations of S. trutta that may qualify for recognition as genetically different races or subspecies. It seems that the scientific debate over the relative importance of genetics (nature) or the environment (nurture) in explaining the variable life history of S. trutta, and the occurrence of so many different forms of brown trout and sea trout, has now swung back in favour of accepting that there may well be an important measure of genetic control over the extent to which migratory and non-migratory forms of trout are expressed in different situations.

6

Sea Trout

Natural regeneration Once salmon runs have become locally extinct, for whatever reason, their restoration depends on some form of artificial restocking to kick-start the regeneration of a new founder stock of adult fish. Such stocking programmes are enormously costly. They also pose genetic risks and other practical problems. However, it may be that stocking is not an inevitable consequence when seeking to regenerate sea trout stocks that have been lost or which have been seriously impoverished if, as has been postulated by some workers, the existence of a healthy resident brown trout population within the upstream catchment has the residual potential to produce a proportion of juvenile parr that become smolts and migrate to sea to become sea trout. If this is so, and therein resides the fundamental question, it means that runs of locally adapted sea trout will never be lost permanently provided the local stock of brown trout has not been lost also. All that is required is patience to let the natural sequence of events take place. Is stocking with sea trout a good idea? What are the roles and risks of artificial stocking in sea trout management? Salmon stocking has been a popular management technique for over a hundred years, although it brings risks that need to be managed (Aprahamian et al., 2003; McGinnity et al., 2003) and its efficacy has been regularly questioned (Harris, 1974, 1994). However, sea trout stocking has been much less extensive, partly because of uncertainty over its outcome, attributable to the flexible resident–migratory life-history pattern of S. trutta and partly because of limited demand in England and Wales. Furthermore, the production of sea trout from residual ‘resident’ trout populations in recovering rivers (Champion, 1991) suggests that the natural regeneration capability of sea trout is higher than salmon once limiting factors have been removed. Nevertheless, sea trout stocking is extensive in other countries, but as in the case of salmon, research into its benefits and the consequences for wild fish has been sparse. Given the emergence of sea trout as a popular fishery species, demand for stocking can be expected to increase and so these questions need to be addressed. Climate change If it is genetics rather than environment that determines what proportion of juvenile trout may become either sea trout or brown trout, then what are the implications of climate change likely to be on the abundance and composition of sea trout stocks in the future? Could it be that better conditions for the feeding and subsequent growth of juvenile ‘trout’ parr will occur in fresh water so that fewer sea trout and more brown trout are likely to be produced in accordance with ‘conventional wisdom’? Other issues There are many other issues and concerns about the biology, conservation and management of the sea trout. Some of the more immediate questions that are likely to emerge during the

Setting the Scene

7

Symposium are: •

•

• • • • • • • • •

•

Do any reliable fish counters exist that operate across the range of sizes encountered with most sea trout stocks and can they distinguish reliably between salmon and sea trout of the same sizes? Do the official catch statistics and catch records currently published by various agencies have any meaning as indicators of the strength and structure of our sea trout stocks or the quality of our fisheries? What needs to be done to improve their accuracy and reliability so that valid spatial and temporal comparisons can be made within and across different rivers? What are the rates of exploitation, and the impacts of selective fishing by rod and net fisheries, on sea trout during the marine and freshwater phases of their life history? When will we be in a position to set appropriate conservation limits (CLs) (or their equivalent) for sea trout, and how might this be done? How extensive are sea trout migrations in the sea, and do different stocks and different components of the stock behave differently in this respect? Are there any mixed stock fisheries for sea trout? If so, how vulnerable are their stock components to selective exploitation? Do local races and sympatric sub-stocks of sea trout exist that might require different management approaches for their conservation and development? Does the life-history variation in sea trout have a special biodiversity and conservation value that require stronger protection? Do sea trout tend to smolt as they migrate towards the sea and do a significant proportion of sea trout migrate to sea in autumn? Do sea trout compete with salmon to any significant extent? Could in-stream habitat improvement work to benefit juvenile salmon be detrimental to sea trout by reducing the amount of favourable habitat suitable for juvenile trout and the production of sea trout smolts? How will the recent and emerging European legislation, such as the Habitats and Water Framework Directives, influence future strategies for the protection and sustainable management of sea trout stocks?

The sea trout is a fascinating species that presents a significant challenge to fishermen, managers and scientists alike. Some of the questions raised here will be addressed during the course of the Symposium – and some new ones may emerge. Two key features need to be borne in mind throughout these proceedings. The first relates to the continuum of the migratory habit in S. trutta because recognising and understanding this will ensure that we connect properly across the full range of environmental and ecosystem processes acting on ‘sea trout’. The second is that sea trout management and science are of unusually wide interest and application to a range of stakeholder activities from recreational and commercial fishing, through conservation, to environmental protection. Just as S. trutta is diverse and flexible in its different life-history strategies in response to its widely differing environments, we too must adopt a similarly integrated, cross-cutting and collaborative approach to understanding and managing it for future generations.

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Sea Trout

References Aprahamian, M.W., Martin Smith, K., McGinnity, P., McKelvey, S. & Taylor, J. (2003). Restocking of salmonids – opportunities and limitations. Fisheries Research, 62, 211–27. Champion, A.S. (1991). Managing a recovering salmon river – the river Tyne. In: Strategies for the Rehabilitation of Salmon Rivers (Mills, D., Ed.). Proceedings of the Linnaean Society Joint Conference, November 1990, pp. 63–72. Falkus, H. (1962). Sea Trout Fishing. Witherby, London, 185 pp. Falkus, H. (1975). Sea Trout Fishing, 2nd edn. Witherby, London, 445 pp. Haris, G.S. (1974). Salmon propagation in England and Wales. A Report by the Association of River Authorities/National Water Council Working Party. National Water Council, London, 62 pp. Harris, G.S. (1994). The identification of cost-effective stocking strategies for migratory salmonids. National Rivers Authority, R&D Note 353, Bristol, 150 pp. Harris, G.S. & Winstone A. (1990). The sea trout fisheries of Wales. In: The Sea Trout in Scotland (Picken, M.J. & Shearer, W.M., Eds). Proceedings of a Symposium, 18–19 July 1987, Dunstaffnage, pp. 25–33. Lamond, H. (1916). The Sea-Trout: A Study in Natural History. Sherratt & Hughes, Manchester, 219 pp. McGinnity, P., Prodöl, P., Ferguson, A. et al. (2003). Fitness reduction and potential extinction of Atlantic salmon, Salmo salar, as a result of interactions with escaped farm salmon. Proceedings of the Royal Society of London, B 270, 2443–50. Milner, N.J., Davidson, I.C., Evan, R., Locke, V. & Wyatt, R.J. (2001). The use of rod catches to estimate salmon runs in England and Wales. In: Proceedings of the Atlantic Salmon Trust Workshop (Shelton, R., Ed.). Lowestoft, November 2001, pp. 46–65. Nall, G.H. (1930). The Life of the Sea Trout: Especially in Scottish Waters. Seeley, London, 335 pp. Regan, C.T. (1911). The Freshwater Fishes of the British Isles. Methuen & Co. Ltd., London, pp. 54–72. Scott, J. (1969). Sea Trout Fishing. Seeley, Service & Co. Ltd., London, 216 pp. Trewavas, E. (1953). Sea-trout and brown-trout. Salmon & Trout Magazine, 139, 199–215.

Section 1

STOCKS AND FISHERIES

Chapter 2

Patterns of Anadromy and Migrations of Pacific Salmon and Trout at Sea T.P. Quinn and K.W. Myers School of Aquatic and Fishery Sciences, Box 355020, University of Washington, Seattle, WA 98195, USA

Abstract: This chapter briefly reviews the range of anadromy within the genus Oncorhynchus, using six criteria selected by Rounsefell (1958): (1) spatial extent of marine migrations; (2) duration of stay at sea; (3) state of maturity attained at sea; (4) spawning habitats; (5) post-spawning mortality and (6) occurrence of freshwater forms of the species. We provide updated information on anadromy and marine migration patterns, especially for the iteroparous cutthroat (O. clarki) and rainbow (O. mykiss) trout. These two species display a wide range of anadromy, including truly ‘landlocked’ populations, non-anadromous populations with access to the sea, coastal migrants and fish that migrate extensively at sea (in steelhead, the anadromous rainbow trout). We conclude, as did Rounsefell, that anadromy is best viewed as a suite of life-history traits that vary greatly among species and population. Seen in this light, the Pacific species are not fundamentally different from Atlantic salmon and brown trout but rather all species are along a continuum of anadromy. Brown trout, Salmo trutta L., seem most similar to cutthroat trout in their limited native range, iteroparity, diversity of non-anadromous forms occupying streams, large rivers and lakes as well as the anadromous forms and the limited duration and spatial extent of migrations at sea. Keywords: Onchorhynchus spp., marine migrations, marine residence, maturation, spawning movements, spawning survival, freshwater forms.

Introduction Salmonid fishes have three key life-history traits: (1) anadromy; (2) homing to the natal site for reproduction and (3) semelparity (Quinn, 2005). Homing seems to be essentially universal within the family, but anadromy and semelparity vary considerably among and within species, and these last two traits are often linked. Rounsefell (1958) argued that there are six components of anadromy: (1) extent of migrations at sea; (2) duration of stay at sea; (3) state of maturity attained at sea; (4) spawning habits and habitats; (5) postspawning mortality and (6) occurrence of freshwater forms of the species. This chapter revisits these criteria, providing a brief update on anadromy in Pacific salmon and trout (genus Oncorhynchus) to help place the migration patterns of brown trout (Salmo trutta L.) in the broader context of the life-history variation within the salmonid family. Further details regarding many of these patterns for the Pacific species can be found in Quinn and Myers (2004) and Quinn (2005); the large literature on brown trout will not be reviewed here, as extensive information is available (e.g. Jonsson & L’Abée-Lund, 1993; 11

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Sea Trout

Elliott, 1994; Klemetsen et al., 2003; Jonsson and Jonsson, Chapter 14 and other papers in this volume).

Extent of migration at sea The distribution and migration patterns of salmon in the Pacific Ocean were documented by the International North Pacific Fisheries Commission (coho, O. kisutch: Godfrey et al. [1975]; sockeye, O. nerka: French et al. [1976]; chum, O. keta: Neave et al. [1976]; chinook, O. tshawytscha: Major et al. [1978]; pink, O. gorbuscha: Takagi et al. [1981]; masu, O. masou: Machidori & Kato [1984]; steelhead [the term for anadromous rainbow trout], O. mykiss: Burgner et al. [1992]; juvenile salmonids: Hartt & Dell [1986]) and more recent results were reported by Myers et al. (1996). The most numerous species (pink, chum and sockeye) migrate to sea and feed in offshore epipelagic waters, within about 50 m of the surface. Chum salmon spend a few days or weeks in estuaries but the other species seem to move directly to coastal waters (e.g. sockeye in Bristol Bay: Straty & Jaenicke [1980] and the Fraser River: Groot et al. [1989]). North American populations migrate northward along the continental shelf, or westward along the Alaska Peninsula and across the eastern Bering Sea shelf, until in the fall when they move farther offshore, and they are seldom found in coastal waters until they return at maturity (Fig. 2.1). Variation in the early marine distribution, movements, growth and survival of these species is linked to physical (e.g. sea temperature, water currents) and biological factors, especially the distribution and abundance of their preferred prey (see reviews by Myers et al. [2000]; Beamish et al. [2003]; Brodeur et al. [2003]; Karpenko [2003]; Mayama & Ishida [2003]).

Arctic Ocean

N

Yana River

Lena River

70° Kotzebue Anadyr Sound River

Kolyma River

ALASKA (USA) Yukon River

Norton Sound

RUSSIA

Kuskokwim River Copper River

Bering Sea Bristol Bay

Kamchatka River

Sea of Okhotsk Amur River

Aleutian Islands

Prince William Sound Kodiak Queen Island Charlotte Islands Gulf of Alaska

Mackenzie River CANADA 60° Nass River Skeena River Fraser River 50°

Vancouver Island

CHINA Yalu River

Kuril Islands Sea of Japan

Columbia River

Kamchatka Peninsula North Pacific Ocean

Hokkaido

Sacramento River

Honshu KOREA

140°

40° USA

JAPAN

160°E

180°

160°W

140°

120°

Fig. 2.1 Pacific Rim showing the region (shaded) from which Pacific salmon and trout migrate to sea (from Quinn, 2005).

Anadromy and Migration Patterns

13

In contrast to these species, juvenile coho and chinook salmon seem to migrate more slowly along the coast, and are common in coastal and inland waters during their period at sea, though they also occur offshore. Coho and chinook salmon entering the ocean off California and Oregon are largely limited to the coastal zone where upwelling brings cool, nutrient rich water to the surface. In this region the offshore waters are warm, less productive and dominated by other fishes. North American coho salmon in coastal waters tend to be caught (generally in their second summer at sea) near their area of origin (Weitkamp & Neely, 2002). Offshore, Asian and North American coho salmon overlap south of the central Aleutians (Myers et al., 1996). Interestingly, northern coho salmon stocks are found farther offshore (averaging four times as far from tag recovery sites), compared with the more coastal distribution of southern stocks (Walker et al., 1992). From south central Alaska to California, there are progressively fewer recoveries from offshore tag releases and more recoveries from releases in coastal waters. Travel rates also reflect this difference; Asian and western Alaska fish travel over 40 km/day compared with about 10 km/day for coho salmon from south-eastern Alaska and southwards. North American chinook salmon range across almost the entire Bering Sea (Myers et al., 1996), and in the North Pacific from the coastal waters off California west to the central Aleutian Islands. Chinook salmon are classified as ‘ocean-type’ (migrating to sea in their first year of life) and ‘stream-type’ (migrating to sea after a full year in fresh water; Healey [1991]). Ocean-type chinook, most prevalent towards the southern end of the species’ range, migrate downstream over a protracted period and then reside in estuaries much longer than stream-type chinook (Healey, 1991). As with coho, the tendency of chinook to migrate to the open ocean is not completely known, but stream-type chinook seem more inclined to do so than ocean-type. The vast majority of anadromous salmonids in the Pacific Ocean are from one of the five semelparous Oncorhynchus species but interesting patterns are found in other species. In most North American populations of steelhead, the smolts migrate rapidly through estuaries (e.g. Dawley et al., 1986), leave coastal waters early in the summer and range at sea across almost the entire North Pacific, in some cases over 5000 km from home. Steelhead from coastal Oregon and California may have more restricted westward migrations than more northern stocks, consistent with patterns in coho and chinook salmon. Masu salmon are exclusively Asian and their marine distribution is largely limited to the Sea of Japan and Sea of Okhotsk (Machidori & Kato, 1984). Cutthroat trout (O. clarki) are exclusively North American, and also have restricted (but poorly known) marine migrations. Presumably, the presence of these two species on only one continent (reminiscent of brown trout) results in part from their limited movements at sea, whereas steelhead or stream-type chinook salmon are most similar to Atlantic salmon (Salmo salar) in migration patterns.

Duration of stay in the sea and in fresh water The length of time that individual fish spend at sea, relative to time in fresh water, was Rounsefell’s second criterion for anadromy, and the information he presented needs little revision. Pink salmon, at one end of the continuum (Table 2.1), migrate seaward immediately

14

Sea Trout Table 2.1 Characteristic (++) and less common (+) ages at seaward migration (i.e. winters in fresh water after hatching) of different salmonids. Age Species Pink salmon Chum salmon Chinook salmon Coho salmon Sockeye salmon Masu salmon Steelhead trout Cutthroat trout Dolly Varden Brown trout Atlantic salmon

0 ++ ++ ++ + +

1

2

3

++ ++ ++ ++ + +

+ ++ ++ ++ ++ ++ + ++ ++

+ + + ++ ++ ++ ++ ++

+ +

4

5

6

7

8

+ + + +

+ + + +

+

+

+ + ++ ++ + ++

Source: From Randall et al., 1987; Quinn, 2005, and references therein.

Table 2.2 Generalised duration of marine residence (winters at sea) before first maturation among salmonid species, expressed as characteristic (++) and less common (+) patterns. Age Species Chum salmon Chinook salmon Sockeye salmon Steelhead trout Masu salmon Coho salmon Pink salmon Cutthroat trout Dolly Varden Atlantic salmon Brown trout

0

+ + + ++ ++ ++

1 + + ++ ++ ++ ++ + + ++ ++

2 ++ ++ ++ ++ + +

3 ++ ++ ++ ++

4 ++ ++ + +

++ ++

++ +

+ +

5 or more + +

after emerging from redds, and some populations actually spawn within the intertidal zone, especially in south-east Alaska. Virtually without exception, pink salmon in their natural range return to spawn after one winter at sea (1SW), for a total age of 2 years (Table 2.2). Chum salmon show the next least reliance on fresh water for rearing, commonly spending a few days or weeks in streams, then rearing in estuaries before migrating through coastal waters and out to the sea where most spend 2–4 years. Seaward migration in the first year of life also occurs in chinook, coho and sockeye salmon. At the southern end of the range and at lower elevations, chinook salmon typically migrate to sea as either newly emerged fry or after residing for a few months in rivers. Northern populations and many in the interior are yearling migrants (Healey, 1991), reflecting slower growing conditions. Chinook salmon also vary in duration of marine

Anadromy and Migration Patterns

15

residence, with 2–4 years being typical (Table 2.2; Roni & Quinn, 1995). Most sockeye salmon spend 1 or 2 years in a lake and then 2 or 3 years at sea but river-type juveniles reside for a year in a river and ocean-type sockeye migrate to sea in their first year of life (Wood, 1995). The great majority of coho salmon smolts are also 1 or 2 years, with more 2-year-old fish in the north (Weitkamp et al., 1995). However, fry are often caught in downstream traps and in many coastal systems, they enter the ocean shortly after emergence; little is known about the fate of these fry. Regardless of freshwater age, most coho salmon spend one winter at sea but some males (jacks) spend only the summer at sea before returning. Japanese masu salmon smolts typically migrate in spring and the adults return the next spring. However, some populations in Miyagi and Fukushima prefectures migrate to sea in the fall and return the following spring (Masahide Kaeriyama, Hokkaido University, pers. comm.). In Russia, there are four life-history types of masu salmon (Tsiger et al., 1994; Anton Ulatov, KamchatNIRO, pers. comm.): (1) the typical anadromous form, most of which spend one winter at sea; (2) a neotenic form (almost always males but rarely females) that matures as parr in their first or second fall of life; (3) males that mature once or twice as parr that then undergo smolt transformation, migrate to sea for 2–3 months, and then return to spawn and (4) fully resident populations. Pacific salmon spawn in the fall (though this may be as early as July or as late as February, depending on species and region) whereas the Pacific trout species spawn in spring. The evolutionary and ecological aspects of this are unclear; perhaps it reflects a niche shift to avoid competition. Atlantic salmon and brown trout spawn in the fall, as do charr, so this characterises the family in general. The Pacific trout have somewhat smaller eggs than sympatric salmon with which they compete (notably coho). Perhaps because of these traits the trout tend to spend more time in fresh water before migrating to sea than the salmon. Most North American steelhead go to sea at age 2 or 3 (older smolts predominate in the northern end of the range, Busby et al. [1996]) and spend 2 or 3 full years at sea, but some (mostly males) spend only a single year at sea. Moreover, some populations from northern California and southern Oregon have fish that return after only a summer at sea and do not spawn. Owing to their small size, these fish are locally known as half-pounders (Kesner & Barnhart, 1972), and share some attributes with the sea trout, known as finnock or whitling, that spend only a summer at sea. Western Kamchatka steelhead are more diverse in life-history patterns than those in North America, showing four patterns: (1) typical anadromous fish that migrate far offshore to the North Pacific Ocean to feed; (2) fish that stay near the coast and probably feed in the Sea of Okhotsk (including half-pounders); (3) a river-estuarine group, that enters saltwater lagoons and (4) river fish that do not migrate to the ocean, consisting mainly of males (Savvaitova, 1975; Savvaitova et al., 2003). The typical, anadromous pattern predominates in northern populations and especially in small rivers, whereas the coastal and river strategies are more common in the south and in larger rivers. Cutthroat trout may go to sea at ages 1–6 (Table 2.1) but 2, 3 and 4 are most common (Trotter, 1989; Johnson et al., 1999). Johnston (1982) noted that cutthroat smolts in protected waters such as Puget Sound are smaller and younger than those on the open coast. He hypothesised that in benign inland waters they forage in the littoral zone (where they are

16

Sea Trout

also caught by anglers) whereas the heavy surf of the ocean beaches forces them to forage farther from shore and so larger size is needed for survival. Unlike salmon or steelhead, cutthroat trout characteristically spend only a summer at sea. During this time, their growth is modest and they reach a much smaller final size than steelhead.

State of maturity attained at sea The maturity state attained by salmonids at sea varies enormously. The great majority of pink and chum salmon return to fresh water in a nearly or completely mature state and spawn only a short distance inland within a few days or weeks, though some chums migrate far inland (e.g. in the Amur and Yukon rivers) and they enter in a much less advanced state of maturity. Coho salmon often enter fresh water in a less advanced state of maturity and spawn at least a month later, though they do not necessarily migrate very far inland. However, all of these species generally spawn in the same season in which they left the ocean but other salmonids show more complex patterns. ‘Fall’ chinook salmon enter fresh water in the fall and spawn within about a month but large rivers draining the interior plateau such as the Sacramento, Klamath, Columbia and Fraser rivers have ‘spring’ chinook that enter from March to June in a relatively immature state, migrate much of the way to their natal spawning grounds, hold during the summer and spawn in the fall (e.g. September). The Sacramento River also has unique ‘winter’ chinook that migrate in late winter and spawn in late spring (Fisher 1994). Some sockeye salmon populations also enter as early as March or April and then spawn in the fall. These are not populations with long migrations; rather, they are coastal populations in the southern end of the range. These sockeye avoid warm fall temperatures by entering early and remaining below the thermocline in lakes until they enter tributaries to spawn in the fall (Hodgson & Quinn, 2002). Even more extreme variation is seen in steelhead (Burgner et al., 1992; Busby et al., 1996). Ocean-maturing steelhead tend to occur in coastal rivers in the central and southern part of their range, entering fresh water in March or April and spawning in April or May and leaving thereafter. Stream maturing steelhead may enter large rivers such as the Columbia, Fraser and Skeena in late summer or early fall (Robards & Quinn, 2002), migrate part of the way home, then hold in suitable winter habitat and ascend to the spawning sites in spring. Some rivers have both forms of steelhead, and their migration timing is strikingly different. For example, the ocean-maturing steelhead migration into the Kalama River begins in late fall, peaks in April and most spawning is in mid-April (Leider et al., 1984). In contrast, the migration of stream-maturing fish peaks in July but continues into the winter, with a mean spawning date in early February. This migration pattern probably results where suitable areas for adults to spawn and juveniles to rear are inaccessible for reasons of flow or temperature in the months shortly before spawning. Therefore, the only option is to leave the ocean early, get past the hazardous area and then minimise energy losses until it is time to spawn. Having said this, it is not always possible to identify the barrier to migration, and this subject needs further study. According to Johnston (1982), cutthroat from coastal Oregon and Washington rivers tend to be sexually mature at first return to fresh water, whereas many from the Columbia River,

Anadromy and Migration Patterns

17

Puget Sound, British Columbia and Alaska do not spawn after their first return to fresh water, and in this regard are similar to sea trout, much as Atlantic salmon seem more similar to steelhead and chinook salmon. In addition, the timing of cutthroat trout migration, and hence the state of maturity, varies among areas (Johnson et al., 1999). For example, in Eva Lake, Alaska, they migrated to sea in May and June and returned in September (Armstrong, 1971). Sand Creek, on the coast of Oregon, showed a longer period of marine residence, from April–May to October–December (Sumner, 1962). In Washington, there seem to be two patterns. In large rivers the cutthroat enter relatively early, in September and October (Johnston, 1982) but in smaller streams they enter later (January–March), shortly before spawning, and leave primarily in April (e.g. Big Beef Creek: Wenburg [1998]).

Spawning habits and habitat Rounsefell (1958) noted that spawning in streams is typical of all Oncorhynchus and Salvelinus species except lake trout, S. namaycush, but other habitats are also used. In terms of anadromy, intertidal spawning, chiefly displayed by pink and chum salmon in small streams of south-east Alaska, is the greatest shift from the stream habitats (Helle, 1970; Thorsteinson et al., 1971). The shortness of the streams in this area and the high densities at which these species typically spawn may have contributed to the evolution of intertidal spawning. On the other hand, many lakes support sockeye salmon populations that spawn on beaches. Sockeye fry typically rear in lakes, so this seems to be a natural expansion of the breeding habitat for them. The spawning beaches are commonly at the outwash of a river, or the margins of the lake where groundwater flows down a hillside and wells up to irrigate the embryos (Wood, 1995). However, sockeye can spawn on lowlying islands with no groundwater. At these beaches the water is circulated through the gravel by wind-driven currents, and the substrate is very large (Kerns & Donaldson, 1968). Interestingly, coho salmon commonly rear in lakes and ponds, especially in winter, but we do not know of any beach spawning coho salmon populations. Indeed, it is noteworthy that salmonids as a group have taken little advantage of lakes for spawning. There have been many studies on the physical habitat features used by stream spawning salmonids. Some of these differences may arise from differences in size among the species (Kondolf & Wolman, 1993) and some from the rearing requirements of juveniles. However, most studies have been conducted on one species in a limited range of streams, so our holistic understanding of the roles of interspecific competition and species-specific habitat choice is still quite limited. There are species that are absent from streams that appear suitable and that support other species, and also cases of species with different habitat use patterns in different parts of their range. Perhaps the most puzzling is the distribution of pink salmon (Heard, 1991). They all spawn at 2 years of age, so even-year and odd-year lines are genetically distinct. At the southern end of their distribution, they are present almost exclusively on odd-numbered years, and many rivers have none at all or very few on evennumbered years. Streams in the middle of the range tend to have runs on both cycles but in the northern part of the range even-year runs tend to be more numerous. In addition to this very peculiar distribution pattern, pink salmon tend to use different habitats for spawning

18

Sea Trout

in the different parts of their range, and consequently different patterns of segregation and sympatry with other salmon species. This highlights the fact that there is still much to be learned before we can extrapolate from details of redd site features to explain the overall distribution of the species.

Mortality after spawning Mortality after spawning is not, strictly speaking, a component of anadromy but the two traits are linked to some extent. Rounsefell (1958) stated that all members of the genus Oncorhynchus (the Pacific trout species were classified in the genus Salmo when his paper was written) die after spawning, and this is true with two exceptions. First, male masu salmon that mature in fresh water as parr are capable of surviving, migrating to sea and spawning in a subsequent season (Ivankov et al., 1977; Tsiger et al., 1994), though anadromous males and females are semelparous. Second, under experimental conditions male chinook salmon can mature as parr, survive spawning, grow and spawn again the following year and even a third year (Unwin et al., 1999). The mature parr had very large gonads and depleted energy reserves and so the likelihood of their surviving the winter in rivers would be low. Nevertheless, post-spawning survival in this species indicates that the separation between semelparous and iteroparous salmonids may not be as great as was once thought. Indeed, the life-history patterns of salmonids are much more variable than the discrete terms ‘semelparous’ and ‘iteroparous’ suggest. ‘Iteroparity’ refers more to the possibility rather than the likelihood of repeat breeding. The frequency of repeat spawning is higher in non-anadromous populations of both steelhead/rainbow trout and cutthroat trout (Fleming, 1998; Fleming & Reynolds, 2004). Steelhead are technically iteroparous but sampling indicates that most (sometimes nearly all) spawn only once. In 26 North American populations, first time spawners comprised 92% of the adults in British Columbia and Washington, 94% in the Columbia River, 85% in Oregon and 81.5% in California (Busby et al., 1996). In addition, sampling on the high seas produced primarily steelhead that had never spawned (Burgner et al., 1992). The proportion of repeat spawners is both a natural attribute of populations and a consequence of fishing; highly exploited populations would be expected to have a lower proportion of individuals surviving to spawn repeatedly. In addition, post-spawning survival is usually lower in males than in females, even though females have much larger gonads than males. In iteroparous species, females abandon their redd shortly after spawning whereas males remain on the spawning grounds longer, and this may deplete their energy and reduce survival. The morphological changes at maturity are also more extreme in males, and this energetic cost may be reflected in lower survival as well. Ocean-maturing steelhead should have a higher proportion of successful repeat spawners because they spend much less time in fresh water than the stream maturing ones, and data from the Kalama River (Leider et al., 1986) support this hypothesis. There has not been a comprehensive review of iteroparity in anadromous cutthroat trout, and the subject is complicated by the fact that some fish return to fresh water but do not spawn, especially on their first time back, a trait that they share with sea trout. However,

Anadromy and Migration Patterns

19

data from four populations (Sand Creek, Oregon: Sumner [1962]; Snow and Salmon creeks and the Stillaguamish River, Washington: Michael [1989]; Big Beef Creek, Washington: Wenburg [1998]) indicated that few fish spawned more than once and most of the repeat spawners were females, consistent with the general pattern of higher post-breeding survival in females.

Occurrence of freshwater forms Pacific salmonids vary widely in the occurrence of freshwater forms within their native range. Pink and chum salmon apparently have no natural non-anadromous populations, and this is consistent with their being the strongest anadromous salmonids. To our knowledge there are no naturally occurring non-anadromous populations of chinook salmon in their native range, though some have become established within this century. More fundamentally, some stream-type chinook salmon populations have mature male parr (Taylor, 1989; Myers et al., 1998). Coho salmon are essentially always anadromous, though there are a few reports of ‘residual’ populations (Sandercock, 1991). It is not clear whether these populations are truly self-sustaining (the bodies of water were all connected to the ocean, so the fish were not landlocked), and they have received little research attention. Interestingly, the residual coho salmon populations have been associated with lakes. Streams are the ‘classic’ coho salmon habitat but many populations spend a significant amount of time in lakes. Given the abundance of non-anadromous sockeye salmon, it is unclear why non-anadromous coho salmon are so rare. Sockeye salmon commonly form non-anadromous populations called kokanee. Wood (1995) reviewed the ecological and evolutionary aspects of this life-history pattern and noted that anadromy prevails in systems with short migrations and unproductive rearing lakes whereas more productive lakes with more arduous migrations tend to have kokanee that are polyphyletic, having evolved from sockeye salmon on numerous independent occasions (Taylor et al., 1996), and the two forms can remain genetically distinct even in sympatry despite some interbreeding (Wood & Foote, 1996). Rainbow and cutthroat trout also commonly occur as non-anadromous forms, and in large parts of their range only this form exists (Behnke, 1992, 2002). Steelhead are rare or absent from Alaska, north of the Alaska Peninsula, despite numerous robust rainbow trout populations with easy access to the ocean. Non-anadromy in these trout seems to be determined more by opportunities for growth than difficulty of migration. At the southern end of their range, rainbow trout exist in northern Mexico, where migration to sea may be impossible or the conditions at sea may be unsuitable for trout, so they persist in fresh water. In between, there are examples of sympatric rainbow and steelhead trout populations, existing with some degree of genetic isolation (e.g. Docker & Heath, 2003). Resident trout tended to spawn later in the season and used shallower, lower velocity spawning sites (Zimmerman & Reeves, 2000) consistent with their smaller size than sympatric steelhead. Cutthroat trout have an even longer and more complex history of non-anadromy, as there are sub-species in drainages that do not connect with the Pacific Ocean (Behnke, 1992, 2002). Some coastal cutthroat trout populations are truly landlocked by waterfalls but in other cases the non-anadromy is facultative.

20

Sea Trout

In addition to the non-anadromous populations of rainbow and cutthroat trout, a fraction of the males mature as parr in anadromous populations. This phenomenon has been closely studied in Atlantic salmon (Fleming, 1998; Hutchings & Jones, 1998) and brown trout (L’Abée-Lund et al., 1990); in these species rapid growth in fresh water is associated with a higher proportion of males maturing as parr. However, the reports for Pacific trout species (e.g. Shapovalov & Taft, 1954; reviewed by Busby et al., 1996) are rather anecdotal and there does not seem to be a systematic survey of the proportion of male parr in steelhead or anadromous cutthroat trout populations. However, sea run cutthroat populations often show a predominance of females, and we might infer that the balance of the males remained in fresh water (Johnson et al., 1999).

Salmo trutta in comparison Scientists working on either Atlantic or Pacific salmonids often seem to view the species in the other ocean as fundamentally different, sometimes ignoring those species when reviewing the pertinent literature for their papers. However, as Rounsefell (1958) noted, anadromy is really a series of interrelated traits, and salmonids can be arrayed along a continuum rather than falling into two discrete modes. Steelhead are more similar to Atlantic salmon than they are to pink, chum or sockeye salmon, and cutthroat trout are more similar to brown trout than they are to most species in their own genus. Cutthroat and brown trout share apparently limited migrations at sea in terms of distance (though very little is known about the distances travelled by cutthroat trout), and also in many cases spend only a summer at sea. Overwintering at sea (and especially for multiple years) is apparently much more common in sea trout (Jonsson & L’Abée-Lund, 1993; Knutsen et al., 2004) than in cutthroat trout. Sea trout commonly reach a larger maximum size (Jonsson & Jonsson, this volume) than is typical of anadromous cutthroat trout but have a wider range than is routinely seen in steelhead. Similar to cutthroat trout, brown trout show a wide range in smolt ages, a predominance of females among the smolts and return migration by immature as well as mature fish. Both cutthroat trout and brown trout are naturally distributed on only one side (in both cases, the eastern) of their respective oceans. Transplants have shown brown trout to be adaptable to many habitats, including those in eastern North America (MacCrimmon & Marshall, 1968), so we must infer that it was limited migration rather than narrow habitat suitability patterns that determined their distribution. Among the more pressing issues, from both the perspectives of basic science and also conservation, is the extent of genetic control over anadromy in the different salmonid species. Various lines of evidence have been presented indicating the plasticity of anadromy within polymorphic populations of brown trout (e.g. Jonsson, 1985; Jonsson & Jonsson, Chapter 14 this volume) and species of charr as well. On the other hand, genetically distinct anadromous and resident populations have been reported in sympatric populations of Atlantic salmon (Verspoor & Cole, 1989) and sockeye salmon (Wood & Foote, 1996). It would be very informative to learn whether changes in growing conditions (e.g. regional warming, increased forage fish populations, density-dependent growth, eutrophication, etc.) or selective fisheries cause shifts in migration patterns. A thorough understanding of the

Anadromy and Migration Patterns

21

genetic basis for migratory patterns will also help determine whether the loss of one form in the presence of a healthy population of the other (e.g. declining sea trout but abundant resident brown trout) constitutes a transient and reversible or a permanent loss. Such information can help guide our efforts to conserve and restore populations of these fishes, and especially the anadromous life-history pattern.

Acknowledgements The support provided by H. Mason Keeler Endowment to TQ during the preparation of this chapter, and by NOAA Contract 50-ABNF-1-0002, NPAFC Research Coordination to KM is gratefully acknowledged.

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Hartt, A.C. & Dell, M.B. (1986). Early oceanic migrations and growth of juvenile Pacific salmon and steelhead trout. International North Pacific Fisheries Commission Bulletin, 46, 1–105. Healey, M.C. (1991). Life history of chinook salmon (Oncorhynchus tshawytscha). In: Pacific Salmon Life Histories (Groot, C. & Margolis, L., Eds). University of British Columbia Press, Vancouver, pp. 311–93. Heard, W.R. (1991). Life history of pink salmon (Oncorhynchus gorbuscha). In: Pacific Salmon Life Histories (Groot, C. & Margolis, L., Eds).University of British Columbia Press, Vancouver, pp. 119–230. Helle, J.H. (1970). Biological characteristics of intertidal and freshwater spawning pink salmon at Olsen Creek, Prince William Sound, Alaska, 1962–63. United States Fish and Wildlife Service, Special Scientific Report, Fisheries 602, Washington, DC, 1–19. Hodgson, S. & Quinn, T.P. (2002). The timing of adult sockeye salmon migration into fresh water: adaptations by populations to prevailing thermal regimes. Canadian Journal of Zoology, 80, 542–55. Hutchings, J.A. & Jones, M.E.B. (1998). Life history variation and growth rate thresholds for maturity in Atlantic salmon, Salmo salar. Canadian Journal of Fisheries and Aquatic Sciences, 55 (Suppl. 1), 22–47. Ivankov, V.N., Padetskiy, S.N. & Chikina, V.S. (1977). On the postspawning neotenic males of the masu, Oncorhynchus masu. Journal of Ichthyology, 15, 673–8. Johnson, O.W., Ruckelshaus, M.H., Grant, W.S. et al. (1999). Status review of coastal cutthroat from Washington, Oregon and California. NOAA Technical Memorandum NMFS-NWFSC-37, Seattle. Johnston, J.M. (1982). Life histories of anadromous cutthroat with emphasis on migratory behavior. In: Salmon and Trout Migratory Behavior Symposium (Brannon, E.L. & Salo, E.O., Eds). University of Washington, School of Fisheries, Seattle, pp. 123–7. Jonsson, B. (1985). Life history patterns of freshwater resident and sea-run brown trout in Norway. Transactions of the American Fisheries Society, 114, 182–94. Jonsson, B. & L’Abée-Lund, J.H. (1993). Latitudinal clines in life-history variables of anadromous brown trout in Europe. Journal of Fish Biology, 43 (Suppl. A), 1–16. Jonsson, B. & Jonsson, N. Life history of anadromous trout Salmo trutta. In: Sea Trout: Biology, Conservation and Management (Harris, G.S. & Milner, N.J., Eds). Proceedings of the 1st International Sea Trout Symposium, July 2004, Cardiff, Wales, UK. Blackwell Publishing, Oxford, pp. 196–223. Karpenko, V.I. (2003). Review of Russian marine investigations of juvenile Pacific salmon. North Pacific Anadromous Fish Commission Bulletin, 3, 69–88. Kerns, O.E., Jr. & Donaldson, J.R. (1968). Behavior and distribution of spawning sockeye salmon on island beaches in Iliamna Lake, Alaska. Journal of the Fisheries Research Board of Canada, 24, 485–94. Kesner, W.D. & Barnhart, R.A. (1972). Characteristics of the fall-run steelhead trout (Salmo gairdneri gairdneri) of the Klamath River system with emphasis on the half-pounder. California Fish and Game, 58, 204–20. Klemetsen, A., Amundsen, P.-A., Dempson, J.B. et al. (2003). Atlantic salmon Salmo salar L., brown trout Salmo trutta L. and Arctic charr Salvelinus alpinus (L.): a review of aspects of their life histories. Ecology of Freshwater Fish, 12, 1–59. Knutsen, J.A., Knutsen, H., Olsen, E.M. & Jonsson, B. (2004). Marine feeding of anadromous Salmo trutta during winter. Journal of Fish Biology, 64, 89–99. Kondolf, G.M. & Wolman, M.G. (1993). The sizes of salmonid spawning gravels. Water Resources Research, 29, 2275–85. L’Abée-Lund, J.H., Jensen, A.J. & Johnsen, B.O. (1990). Interpopulation variation in male parr maturation of anadromous brown trout (Salmo trutta) in Norway. Canadian Journal of Zoology, 68, 1983–7. Leider, S.A., Chilcote, M.W. & Loch, J.J. (1984). Spawning characteristics of sympatric populations of steelhead trout (Salmo gairdneri): evidence for partial reproductive isolation. Canadian Journal of Fisheries and Aquatic Sciences, 41, 1454–62. Leider, S.A., Chilcote, M.W. & Loch, J.J. (1986). Comparative life history characteristics of hatchery and wild steelhead trout (Salmo gairdneri) of summer and winter races in the Kalama River, Washington. Canadian Journal of Fisheries and Aquatic Sciences, 43, 1398–409. MacCrimmon, H.R. & Marshall, T.C. (1968). World distribution of brown trout, Salmo trutta. Journal of the Fisheries Research Board of Canada, 25, 2527–48. Machidori, S. & Kato, F. (1984). Spawning populations and marine life of masu salmon (Oncorhynchus masou). International North Pacific Fisheries Commission Bulletin, 43, 1–138. Major, R.L., Ito, J., Ito, S. & Godfrey, H. (1978). Distribution and origin of chinook salmon (Oncorhynchus tshawytscha) in offshore waters of the North Pacific Ocean. International North Pacific Fisheries Commission Bulletin, 38, 1–54.

Anadromy and Migration Patterns

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Mayama, H. & Ishida, Y. (2003). Japanese studies on the early ocean life of juvenile salmon. North Pacific Anadromous Fish Commission Bulletin, 3, 41–67. Michael, J.H., Jr. (1989). Life history of anadromous coastal cutthroat trout in Snow and Salmon creeks, Jefferson County, Washington, with implications for management. California Fish and Game, 75, 188–203. Myers, J.M., Kope, R.G., Bryant, G.J. et al. (1998). Status review of chinook salmon from Washington, Idaho, Oregon and California. National Marine Fisheries Service, NOAA Technical Memorandum NMFS-NWFSC35, Seattle. Myers, K.W., Aydin, K.Y., Walker, R.V., Fowler, S. & Dahlberg, M.L. (1996). Known ocean ranges of stocks of Pacific salmon and steelhead as shown by tagging experiments, 1956–1995. North Pacific Anadromous Fish Commission Document 192, School of Aquatic and Fishery Sciences, University of Washington, Seattle. Myers, K.W., Walker, R.V., Carlson, H.R. & Helle, J.H. (2000). Synthesis and review of U.S. research on the physical and biological factors affecting ocean production of salmon. North Pacific Anadromous Fish Commission Bulletin, 2, 1–9. Neave, F., Yonemori, T. & Bakkala, R.G. (1976). Distribution and origin of chum salmon in offshore waters of the North Pacific Ocean. International North Pacific Fisheries Commission Bulletin, 35, 1–79. Quinn, T.P. (2005). The Behavior and Ecology of Pacific Salmon and Trout. University of Washington Press, Seattle. Quinn, T.P. & Myers, K.W. (2004). Anadromy and the marine migrations of Pacific salmon and trout. Reviews in Fish Biology and Fisheries, 14, 421–42. Randall, R.G., Healey, M.C. & Dempson, J.B. (1987). Variability in length of freshwater residence of salmon, trout, and char. American Fisheries Society Symposium, 1, 27–41. Robards, M.D. and Quinn, T.P. (2002). The migratory timing of adult summer-run steelhead trout (Oncorhynchus mykiss) in the Columbia River: six decades of environmental change. Transactions of the American Fisheries Society, 131, 523–36. Roni, P. & Quinn, T.P. (1995). Geographic variation in size and age of North American chinook salmon (Oncorhynchus tshawytscha). North American Journal of Fisheries Management, 15, 325–45. Rounsefell, G.A. (1958). Anadromy in North American Salmonidae. Fishery Bulletin, 131, 171–85. Sandercock, F.K. (1991). Life history of coho salmon (Oncorhynchus kisutch). In: Pacific Salmon Life Histories (Groot, C. & Margolis, L., Eds). University of British Columbia Press, Vancouver, pp. 395–445. Savvaitova, K.A. (1975). The population structure of Salmo mykiss in Kamchatka. Journal of Ichthyology, 15, 876–88. Savvaitova, K.A., Kuzishchin, K.V., Gruzdeva, M.A., Pavlov, D.S., Stanford, J.A. & Ellis, B.K. (2003). Long-term and short-term variation in the population structure of Kamchatka steelhead Parasalmo mykiss from rivers of western Kamchatka. Journal of Ichthyology, 43, 757–68. Shapovalov, L. & Taft, A.C. (1954). The life histories of the steelhead rainbow trout (Salmo gairdneri gairdneri) and silver salmon (Oncorhynchus kisutch) with special reference to Waddell Creek, California and recommendations regarding their management. California Department of Fish and Game, Fish Bulletin, 98, 1–375. Straty, R.R. & Jaenicke, H.W. (1980). Estuarine influence of salinity, temperature and food on the behavior, growth and dynamics of Bristol Bay sockeye salmon. In: Salmonid Ecosystems of the North Pacific (McNeil, W.J. & Himsworth, D.C., Eds). Oregon State University Press, Corvallis, pp. 247–65. Sumner, F.H. (1962). Migration and growth of the coastal cutthroat trout in Tillamook County, Oregon. Transactions of the American Fisheries Society, 91, 77–83. Takagi, K., Aro, K.V., Hartt, A.C. & Dell, M.B. (1981). Distribution and origin of pink salmon (Oncorhynchus gorbuscha) in offshore waters of the North Pacific Ocean. International North Pacific Fisheries Commission Bulletin, 40, 1–195. Taylor, E.B. (1989). Precocial male maturation in laboratory-reared populations of chinook salmon, Oncorhynchus tshawytscha. Canadian Journal of Zoology, 67, 1665–9. Taylor, E.B., Foote, C.J. & Wood, C.C. (1996). Molecular genetic evidence for parallel life-history evolution within a Pacific salmon (sockeye salmon and kokanee, Oncorhynchus nerka). Evolution, 50, 401–16. Thorsteinson, F.V., Helle, J.H. & Birkholz, D.G. (1971). Salmon survival in intertidal zones of Prince William Sound streams in uplifted and subsided areas. In: The Great Alaska Earthquake of 1964: Biology. (Nybakker, J., Ed.). National Academy of Science Publication, vol. 1604, pp. 194–219. Trotter, P.C. (1989). Coastal cutthroat trout: a life history compendium. Transactions of the American Fisheries Society, 118, 463–73.

24

Sea Trout

Tsiger, V.V., Skirin, V.I., Krupyanko, N.I., Kashlin, K.A. & Semenchenko, A.Y. (1994). Life history form of male masu salmon (Oncorhynchus masou) in South Primoré, Russia. Canadian Journal of Fisheries and Aquatic Sciences, 51, 197–208. Unwin, M.J., Kinnison, M.T. & Quinn, T.P. (1999). Exceptions to semelparity: postmaturation survival, morphology and energetics of male chinook salmon (Oncorhynchus tshawytscha). Canadian Journal of Fisheries and Aquatic Sciences, 56, 1172–81. Verspoor, E. & Cole, L.J. (1989). Genetically distinct sympatric populations of resident and anadromous Atlantic salmon, Salmo salar. Canadian Journal of Zoology, 67, 1453–61. Walker, R.V., Davis, N.D. & Myers, K.W. (1992). High seas distribution of coho and chinook salmon. In: Proceedings of the 1992 Chinook and Coho Workshop, Boise, Idaho, September 28–30, 1992, American Fisheries Society, Bethesda, MD, pp. 120–34. Weitkamp, L. & Neely, K. (2002). Coho salmon (Oncorhynchus kisutch) ocean migration patterns: insight from marine coded-wire tag recoveries. Canadian Journal of Fisheries and Aquatic Sciences, 59, 1100–115. Weitkamp, L.A., Wainwright, T.C., Bryant, G.J. et al. (1995). Status review of coho salmon from Washington, Oregon and California. National Marine Fisheries Service, NOAA Technical Memorandum NMFS-NWFSC24, Seattle. Wenburg, J.K. (1998). Coastal cutthroat trout (Oncorhynchus clarki clarki): genetic population structure, migration patterns and life history traits. PhD Thesis, University of Washington, Seattle, WA. Wood, C.C. (1995). Life history variation and population structure in sockeye salmon. American Fisheries Society Symposium, 17, 195–216. Wood, C.C. & Foote, C.J. (1996). Evidence for sympatric genetic divergence of anadromous and nonanadromous morphs of sockeye salmon (Oncorhynchus nerka). Evolution, 50, 1265–79. Zimmerman, C.E. & Reeves, G.H. (2000). Population structure of sympatric anadromous and nonanadromous Oncorhynchus mykiss: evidence from spawning surveys and otolith microchemistry. Canadian Journal of Fisheries and Aquatic Sciences, 57, 2152–62.

Chapter 3

A Review of the Status of Irish Sea Trout Stocks P.G. Gargan1 , W.R. Poole2 and G.P. Forde3 1 2 3

Central Fisheries Board, Dublin, Ireland Marine Institute, Newport, Co. Mayo, Ireland The Western Regional Fisheries Board, Galway, Ireland

Abstract: The status of Irish sea trout stocks has been reviewed by the Sea Trout Working Group, 1991–94, and the Sea Trout Review Group, 2002, but little has been published since the collapse of the stocks in the mid-west region in 1989–90. This chapter presents the historical data, updates the national trap census and rod catch data from 1989 to 2003 and provides an assessment of the national current status of Irish sea trout stocks. Accurate sea trout rod catch statistics are available from the majority of the fisheries in the midwestern zone (Connemara–South Mayo area) and rod catch per unit effort (CPUE) data for the Burrishoole, Owengowla, Invermore and Delphi fisheries. Annual Connemara sea trout rod catch was about 10 000 fish between 1974 and 1986, a decline over the 1987–88 period followed by a collapse to 646 sea trout in 1989 and 240 sea trout in 1990. A progressive, but modest, improvement in rod catch occurred during the 1990s until 2001, after which catches decreased again. Catches have not recovered to the levels seen before 1988. Rod catches are presented for each of the fisheries regions outside the mid-west from 1993 to 2003. Data from these regions indicate that appreciable numbers of sea trout have been captured on rod and line in the 1990s and indications are that stocks remain relatively good in most areas. Summary information is also presented on trap census of sea trout, including smolt output and marine survival from upstream and downstream trapping facilities on four key west of Ireland fisheries, Burrishoole, Owengowla, Invermore and Tawnyard (Erriff catchment). Marine survival indices for mid-western fisheries confirm that the collapse in the rod catch was linked to a collapse in the stock and that unprecedented low marine survival of sea trout has been observed for most years since then. The chapter concludes that stock levels and marine survival in the majority of mid-western sea trout stocks are low, relative to historical records. Urgent management action is required if these sea trout stocks are not to be lost and the elimination of lice on and in the vicinity of marine salmon farms must be a constant priority of management and regulatory practice. Keywords: Sea trout, rod catch, commercial catch, stock census, marine survival.

Introduction Sea trout are to be found in most estuaries or bays around the Irish coast. The ancestors of our present sea trout stocks first entered fresh water after the last Ice Age, some 14 000 years 25

26

Sea Trout

ago. Sea trout are essentially fish of acid, oligotrophic waters flourishing where freshwater growth rates are poor, where survival in fresh water is difficult and where there is easy access to the sea. Since the nineteenth century a modest, but locally important, tourism industry developed around the summer and autumn runs of these fish. This was particularly true in the Connemara, Ballinakill, Cork, Kerry and Donegal districts where there were extensive areas of blanket bog feed acid, nutrient-poor lough systems. Few accurate long-term data are available on Irish sea trout catches outside the Connemara region. During the 1970s and 1980s there was evidence of a slow decline in sea trout stock from the Burrishoole, north of Connemara, partly attributed to factors such as illegal fishing, afforestation and hillside erosion because of overgrazing by sheep (Poole et al., 1996). Rod catch data from 15 Connemara fisheries for the period 1974–86 showed no evidence of a decline, but catches had begun to decrease over the 1986–88 period. In 1989 both catch and stocks in many mid-western and Connemara sea trout fisheries collapsed (Anon., 1992). The history of the sea trout stock collapse and subsequent events has been well documented (Whelan, 1993a, b; Poole et al., 1996; Gargan, 2000). In 1989, when sea trout stocks collapsed in western fisheries, sea trout were observed in the lower pools of the Delphi fishery in Connemara in late May with heavy infestations of juvenile sea lice (Lepeophtheirus salmonis). Sampling of rivers began in 1990 to determine whether this phenomenon was widespread and sea trout post-smolts and some sea trout kelts were recorded in all rivers sampled with infestations of sea lice, predominantly juvenile lice, indicating recent transmission (Tully et al., 1993). This has been linked with the development of marine salmon farming in the mid-west zone at that time (Gargan et al., 2003). Information on the status of Irish sea trout stocks was published by the Sea Trout Working Group in its annual reports for each year over the period 1991–94 (Anon., 1992, 1993, 1994a, 1995) and by the Sea Trout Task Force (Anon., 1994b). This chapter reviews the national sea trout catch and stock information as collected using rod catch statistics (Central and Regional Fisheries Boards) for 26 mid-western fisheries from Clew Bay to Galway Bay (1985–2003), rod catch data from selected fisheries in other areas around the coast (1993–2003) and summary data on stock from traps (Central and Regional Fisheries Boards, Marine Institute). Summarised sea trout stock numbers, including marine survival, are presented from four key west of Ireland fisheries, Owengowla, Invermore, Burrishoole and the Tawnyard Lough trap. More detailed information on these fisheries is presented elsewhere by Poole et al. (2006) and Gargan et al. (2006).

Sea trout life history Brown trout (Salmo trutta L.) occur in both fresh water (resident) and anadromous (sea trout) forms in Ireland. Sea trout smolts migrate to sea from March to June each year. Some of these fish return to fresh water in the summer following migration, and in Ireland these fish are known as finnock, harvesters, whitling, juniors or post-smolt. A further component may not return to the natal river to spawn for the first time for at least 1 year; these are known as maidens and are an important component of the spawning stock. Sea trout migrate back to sea

Review of Irish Stock Status

27

after the winter, both as spawned kelts and fish which have overwintered without spawning. Sea trout are often multiple spawners, and there is a variation in smolt age and the time of first return to fresh water. Many different life-history strategies have been observed (Fahy, 1985).

Materials and methods Rod-fishery statistics Sea trout rod catch statistics were available for 26 mid-western fisheries (Connemara– South Mayo area) for the period 1985–2003, along with historical data for 16 Connemara fisheries since 1974, as individual fishery owners and/or fishery managers were in place on most fisheries (Fig. 3.1). Rod catch data were divided into Category 1 and Category 2 data depending on the source and accuracy of the information. Fisheries included in Category 1 report accurate catch data collected by fishery owners or fishery managers in their own fisheries. Data for Category 2 rivers are less accurate, having only reports by district fishery inspectors gathered from individuals or angling club records. Rod catch data from areas in Ireland other than the mid-western zone represent Category 2 data. Since 1990, a bye-law prohibiting the retention of rod caught sea trout has been in place in the mid-western zone from Galway Bay to Achill. Numbers reported for the 1990–2003 period refer to fish captured and returned to the water. These may be overestimates in some fisheries as sea trout below the 1990 size limit of 25 cm and resident brown trout may have been included and there is also the possibility that some fish may have been captured on more than one occasion. Rod effort has also declined in many sea trout fisheries over the period.

Sea trout CPUE rod catch data Catch per unit effort (CPUE) data were available for the Burrishoole, Owengowla, Invermore and Delphi fisheries. Effort was calculated in rod days (∼8 h) and CPUE data are calculated as number of trout caught per rod day.

Commercial catches Sea trout are taken commercially in all fishery districts, both by drift and draft nets, normally as a by-catch in the salmon fishery, although in the mid-western region fishermen are obliged, since 1990, under the commercial bye-law to return all trout to the water. The Eastern Regional Fisheries Board collected the most complete annual data on total commercial sea trout catch. The collection of this data has been superseded since 1 January 2001 by a wild salmon and sea trout tagging and logbook scheme (Fisheries [Amendment] Act, 1999 [Number 35 of 1999]) and therefore the total catch data was only available for the period 1990–99. Fish trapping facilities Information was available on various aspects of the biology of sea trout from upstream and downstream traps on the Burrishoole, Owengowla, Invermore and Erriff (Tawnyard) systems (Fig. 3.1).

28

Sea Trout

1

2 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

3

4 5

Killary 6 8

7

9

12

10 11

13

Burrishoole Newport Belclare Bunowen Carrowniskey Delphi Erriff Culfin Kylemore Clifden Ardbear Doohulla Ballinahinch Gowla Carna Invermore Inverbeg Screebe Furnace Lettermuckoo Costello Crumlin

14 16

17

18

Bertraghboy Bay 15

19 20

Kilkieran Bay

Connemara Fishery District Boundary

21 22

Fig. 3.1

Mid-western sea trout fisheries and trapping location (•).

The Burrishoole system discharges to the north-east corner of Clew Bay on the midwestern coast of Ireland. Fish trapping facilities in Burrishoole in operation since 1958, with full trapping on both rivers flowing out of lake Feeagh since 1970, have enabled a full census to be made of all migratory fish movements upstream and downstream since 1970 (see Poole et al., 1996; Poole et al., Chapter 19). The Owengowla system discharges into Bertraghboy Bay in Connemara. A downstream smolt and kelt trap and an upstream trap were installed by the Fisheries Board in 1991 and upgraded in 1994 and 2002 (see Gargan et al., Chapter 5).

Review of Irish Stock Status

29

The Invermore river discharges into Kilkerrin Bay in Connemara. In 1992 an upstream trap was installed on the Invermore system approximately 500 m from the sea and a smolt and kelt trap was installed in 1993 and upgraded in 2002 (see Gargan et al., Chapter 5). A downstream Wolf-type trap has operated since 1985 on the Black River downstream of Tawnyard Lough, a sub-catchment of the Erriff fishery, which discharges into Killary Harbour. This consists of a fish fence barrier which diverts downstream migrants, smolts and kelts, into a wolf trap with sloped grids with 12-mm spacing leading into a box trap. Traps were generally monitored at least daily and more frequently during runs of fish or periods of high water. Fish in the Tawnyard traps were fin-clipped and pan-jet marked. Assessment of the number of downstream migrating kelts was made on the basis of previous clips, or on fish length and condition. Both spawned kelts and unspawned overwintered finnock were recorded as sea trout kelts. Upstream migrating fish judged to be less than 32 cm were classified as finnock.

Results National rod catch statistics

Mid-western zone Annual sea trout rod catches for the period 1985–2003 for 26 mid-western fisheries (Fig. 3.1, Table 3.1a,b) display an overall trend for the period of catches decreasing until 1988, followed by a collapse in 1989–90. Some improvement in catches was seen in the Delphi, Erriff and Kylemore fisheries in 1991 and 1992. A notable increase in sea trout catches was recorded in the Costello fishery in the 1993–94 period while in 1994 the Delphi and Erriff sea trout rod catch continued to improve. These fisheries recorded a reduced catch in 1995 while the catches on the Ballynahinch fishery showed an increase. Over the 1991–95 period the total sea trout rod catch for Category 1 fisheries remained low in comparison with catches recorded before the stock collapses of 1989–90 (Table 3.1a). In 1995, the overall catch for Category 1 fisheries decreased below that recorded for the previous 2 years. The overall catch rose in 1996 and decreased back again in 1997. Highest overall recorded sea trout catches since the 1989–90 collapse were recorded over the 1998– 2000 period, largely reflected by good catches in the Delphi, Erriff, Kylemore and Costello fisheries. By the end of the 2003 season, catches had decreased considerably in these four fisheries and very poor sea trout rod catches continued to be recorded in the Burrishoole, Newport, Screebe and Crumlin fisheries. Sea trout catches in Category 2 fisheries have closely (correlation coefficient = 0.856, d.f. = 16) followed those in Category 1 fisheries (Fig 3.2), have fluctuated since the 1989–90 collapse and still remain low in comparison with pre-1988 data (Fig. 3.2, Table 3.1b).

Long-term trends in Connemara sea trout catches Accurate rod catch data were available from 16 Connemara fisheries covering the period 1974–2003 (Fig. 3.3). Data show a sea trout rod catch of about 10 000 fish over the

Table 3.1a Fishery Burrishoole Newport Delphi Erriff Kylemore Ballynahinch B’hinch Up. B’hinch Mid B’hinch Lr. Inagh Athry Gowla Invermore Inverbeg Screebe Costello Crumlin Total

Rod catch figures for Category 1 rivers in the mid-western region of Ireland. 1985

1986

1987

1988

1989

1990a 1991a 1992a 1993a 1994a 1995a 1996a 1997a 1998a 1999a 2000a 2001a 2002a 2003a

497 1155 2150 770 2411

614 1485 1281 433 1099

237 783 832 450 543

245 1049 675 308 1116

41 135 309 120 198

39 N/A 112 60 10

106 N/A 437 219 450

24 30 494 293 200

159 109 660 217 320

166 112 709 318 362

200 47 181 202 181

125 90 412 263 675

136 61 446 466 296

150 58 753 520 862

47 48 653 637 862

40 52 346 321 826

48 36 519 359 676

12 50 568 282 732

16 61 124 142 549

378 202 2300 2316 218 1035 1481 254 665 2745 328

398 150 2000 1104 283 867 1345 220 337 2316 222

306 224 1500 1369 153 266 325 67 346 1698 261

173 75 850 824 89 210 199 18 396 1851 26

10 5 20 29 0 0 48 0 55 462 0

N/A 0 90 10 0 0 0 0 0 140 N/A

N/A 30 200 7 0 0 0 10 0 234 N/A

N/A 45 50 45 N/F N/F 0 50 2 375 25

N/F N/A 100 N/F N/F N/F N/F N/A 10 1041 20

15 10 208 185 N/F N/F N/F 5 40 1064 N/A

59 40 334 297 N/F N/F N/F N/A 118 634 N/A

5 0 304 650 N/F N/F N/F 0 0 1281 0

25 13 59 203 N/F N/F N/F 10 0 679 13

10 36 91 87 N/F N/F N/F 0 20 1744 0

14 15 123 195 N/F N/F N/F 0 30 1381 0

14 0 350 411 N/F N/F N/F 0 45 1604 0

105 105 300 600 N/F N/F N/F 0 56 1778 0

19 0 166 256 N/F N/F N/F 0 47 598 0

6 0 256 245 N/F N/F N/F 0 35 693 0

18 905

14 154

9360

8104

1432

461

1693

1633

2636

3194

2293

3805

2407

4331

4005

4009

4582

2730

2127

Category 1: Statistics collected from local sources by private fishery owners. N/A = Not Available; N/F = Not Fished. a post catch & release bye-law; Burrishoole – (Only L.Furnace fished, 1999–2003).

Table 3.1b Fishery

Rod catch figures for Category 2 rivers in the mid-western region of Ireland. 1985

Carowniskey N/A Bunowen 475 Belclare 95 Culfin 298 Clifden 95 Ardbear 86 Doohulla 200 Carna 60 L’muckoo 74 Furnace 426 Total Cat. 1 & 2 combined

1986

1987

1988

1989

1990a 1991a 1992a 1993a 1994a 1995a 1996a 1997a 1998a 1999a 2000a 2001a 2002a 2003a

97 110 70 173 70 75 150 180 50 525

90 146 98 222 98 36 100 100 100 165

160 340 400 235 20 27 20 60 30 200

45 88 0 36 4 5 1 3 2 6

N/A 10 6 8 N/A N/A N/A N/A 0 0

65 120 60 175 6 15 N/A N/A 0 0

10 25 20 60 N/A N/A N/A N/A N/A 0

60 100 76 120 N/A 30 N/A 15 40 0

42 65 25 47 62 N/A N/A 45 2 3

28 55 35 20 22 25 N/A 26 0 30

21 42 35 26 25 0 0 0 0 0

28 70 40 0 17 0 50 20 0 10

65 170 90 76 130 0 0 0 0 0

70 120 35 90 35 0 0 0 3 6

90 150 110 156 73 0 0 0 0 0

18 19 12 102 70 0 0 0 0 0

60 98 96 65 83 0 10 0 0 0

0 50 63 70 71 0 40 0 0 0

1809

1500

1155

1492

190

24

441

115

441

291

241

149

235

531

359

579

221

412

294

20 714

15 654

10 515

9596

1622

485

2134

1748

3077

3485

2534

3954

2642

4862

4364

4588

4803

3142

2421

Category 2: Statistics collected from local sources by District Fishery Inspectors. N/A = Not Available; N/F = Not Fished. a post catch & release bye-law.

32

Sea Trout

Standardised annual rod catch

4

Category 1 rivers

Category 2 rivers

3

2

1

2003

2002

2001

2000

1999

1998

1997

1996

1995

1994

1993

1992

1991

1990

1989

1988

1987

1986

1985

0

Year Fig. 3.2 Annual rod catches for Category 1 and Category 2 rivers for the mid-western region, standardised to their long-term mean, 1985–2003.

Connemara sea trout rod catch 1974–2003 14 000

Number of fish

12 000 10 000 8000 6000 4000 2000 2002

2000

1998

1996

1994

1992

1990

1988

1986

1984

1982

1980

1978

1976

1974

0

Year Fig. 3.3 Annual sea trout rod catch from Connemara District between 1974 and 2003, with a 3-year moving average.

period 1974–86, a decline over the 1987–88 period followed by a rod catch collapse to 646 sea trout in 1989 and 240 sea trout in 1990. While there has been a progressive small improvement in rod catch since 1990, largely contributed to by an improvement in Costello– Fermoyle, Ballynahinch Lower and Inagh between 1998 and 2001, catches decreased again in 2002 and 2003 and have not recovered to the levels before the collapse in 1988 and 1989.

Review of Irish Stock Status

33

Northern region

North-western region

Western region

Eastern region

Shannon region Southern region

South-western region

Fig. 3.4

Location of the Irish Regional Fisheries Boards.

Other areas in Ireland Rod catch data for each of the six other fisheries board regions (Fig. 3.4) are shown in Table 3.2 and summarised in Fig. 3.5.

Eastern region The reported sea trout catch has ranged from 6125 to 11 492 over the 1993–2003 period. Good catches were made in most years on the Castletown, Fane, Boyne, Slaney and Dee. A reduced sea trout rod catch was reported for the Slaney in 2000. Available information does not suggest the same sea trout stock collapse experienced in mid-western fisheries, although there appears to be some decline in catches over time (r 2 = 61; P = 0.005), possibly linked to poor water quality and low summer flows.

Southern region Information collected from angling clubs indicates that sea trout angling has been good on the Colligan and Bride rivers over the 1993–2003 period. Angling on the Colligan was

34

Sea Trout

Table 3.2

Estimated sea trout rod catches by fisheries region, 1993–2003. 1993

1994

1995

1996

1997

1998

1999

2000

2001a

2002

2003

Northern Erne Estuary Murvagh Eske Eany Clonmany Glen Glengannon Owenea Gwebarra Clady Ray Tullaghobegley Lackagh Swilly Leannan Trawbreaga Bay Crana Total

1400 N/A N/A N/A N/A N/A N/A N/A N/A 350 N/A N/A 800 N/A N/A N/A N/A 2550

1200 134 190 469 N/A 202 N/A 656 705 100 383 N/A 440 N/A N/A N/A 70 4549

1200 250 200 430 N/A 550 N/A 183 181 490 380 N/A 78 N/A N/A N/A 180 4122

N/A N/A N/A 100 N/A 168 N/A 60 746 307 505 N/A 400 89 153 N/A 400 2928

N/A N/A N/A 100 N/A N/A 77 105 N/A N/A N/A 195 N/A 122 172 195 154 1120

1300 N/A 20 100 71 300 93 100 800 350 N/A 230 400 452 176 230 350 4972

2000 N/A 20 105 68 150 114 115 N/A N/A 52 421 336 558 80 421 344 4784

600 140 75 80 50 140 52 100 200 200 50 100 300 150 69 176 74 2556

1000 150 100 150 50 85 40 200 600 200 50 100 1000 130 100 200 255 4410

800 100 200 80 20 70 18 50 250 80 20 40 400 100 60 150 120 2558

2000 50 180 50 N/A 140 N/A 70 200 50 N/A N/A 1000 80 110 140 80 4150

Eastern Castletown Fane Boyne Ballymascanlon Dargle Vartry Slaney Dee South Wicklow Glyde Total

500 400 3250 300 700 200 3000 N/A N/A N/A 8350

400 400 3500 350 258 200 1800 N/A N/A N/A 6908

350 250 3800 200 489 250 3500 300 N/A N/A 9139

300 350 2500 250 250 150 2250 400 N/A N/A 6450

400 300 2500 250 150 125 1800 600 N/A N/A 6125

500 500 2000 150 330 150 2000 500 N/A N/A 6130

400 500 3000 200 242 150 4000 3000 N/A N/A 11 492

500 500 1900 300 180 80 1200 3000 N/A N/A 7660

1000 750 1300 400 50 70 1300 2000 N/A N/A 6870

200 200 2000 100 150 60 1500 300 300 50 4860

200 250 1200 100 150 70 1200 150 200 N/A 3520

Southern Colligan Bride Total

1800 1800 3600

1700 2000 3700

1600 1500 3100

1700 1650 3350

1550 1600 3150

2500 2000 4500

2100 1500 3600

1500 1100 2600

1600 1000 2600

1800 1200 3000

1850 1230 3080

South-Western Bandon Argideen Ilen Currane Inny Owenmore Total

N/A 573 224 345 120 500 1762

986 530 375 1655 N/A 470 4016

1450 265 388 5410 N/A 250 7763

1800 400 185 6899 100 100 9484

600 150 142 3820 20 60 4792

1015 200 215 4583 110 200 6323

2000 700 350 6073 120 250 9493

2000 700 200 4440 125 260 7725

600 220 85 3500 100 150 4655

1400 1200 400 3300 170 150 6620

1200 650 80 2500 400 200 5030

North-Western Newport Burrishoole Owenduff Owenmore

109 159 528 1062

112 166 800 850

47 200 273 1180

90 125 163 370

61 136 363 2211

58 150 634 889

48 47 277 805

52 40 362 968

36 18 357 494

50 12b 470 608

61 16 343 267c

Continued

Review of Irish Stock Status Table 3.2

35

Continued. 1993

1994

1995

1996

1997

1998

1999

2000

2001a

2002

2003

Glenamoy 300 Palmerstown 150 Moy Estuary 3036 Easky 40 Drumcfiffe 221 Total 5605

115 150 2800 N/A 392 5385

225 30 1100 50 500 3605

42 25 796 350 88 2049

34 70 2852 200 26 5953

150 270 1980 100 650 4881

37 150 4000 110 254 5728

30 115 3450 240 300 5557

150 50 1200 90 350 2745

65 30 800 280 400 2703

60 0 3500 302 350 4899

a Reduced angling effort due to Foot & Mouth Restrictions. b Burrishoole Fishery closed in August 2002 (only L. Furnace fished since 1999). c Carrowmore lake section of Owenmore closed.

2001

2002

2003

2002

2003

2000

North-western region

4000

5000 Rod catch

6000

3000 2000 1000

4000 3000 2000

Year

2000

1999

1998

1997

1996

1995

1994

0

1993

2003

2002

2001

2000

1999

1998

1997

1996

1995

1994

1000 1993

Rod catch

Southern region

Fig. 3.5

1999

Year

5000

0

2001

Year

1998

2003

2002

2001

2000

1999

1998

1997

1996

1995

1994

0

1993

2000

1997

4000

1996

6000

1995

Rod catch

Rod catch

8000

1994

South-western region 8000 7000 6000 5000 4000 3000 2000 1000 0

1993

Eastern region 10 000

Year

Regional rod catches for fisheries with complete data (see Table 3.2).

particularly good over the 1998–99 period with sea trout up to 6 lb taken regularly and some individual catches of up to 30 sea trout per day being taken. An electro-fishing survey of sea trout stocks in the Colligan carried out in 1999 by the Central Fisheries Board indicated a good stock of sea trout with a full representation of age classes in the population structure.

South-western region A very low sea trout rod catch was recorded for Lough Currane in 1993 and 1994. The recorded catch rose significantly in 1995 and has ranged from 3820 to 6899 over the 1996– 2000 period. Good sea trout rod catches have been recorded from the Bandon in recent years, and recent sea trout catches from the Argideen have been among the highest over the time period.

36

Sea Trout

Shannon region No accurate sea trout rod catch data were available from the River Feale, the most important sea trout fishery in the region. However, anecdotal information indicates that good catches are taken annually. In the Feale estuary over 1000 sea trout have been taken annually in the draft-net fishery in recent years. Good angling is also reported from a number of small rivers in the Clare area.

North-western region Sea trout catches have remained low in the Burrishoole and Newport systems, the two main fisheries entering Clew Bay in the north-western region, since the stock collapse experienced in 1989–99. Catches in 1999 and 2000 were particularly poor and the Burrishoole fishery has been closed to angling for the latter half of the previous two seasons. Sea trout catches in the Owenmore and Owenduff, situated north of Clew Bay, have fluctuated over the 1993–2003 period but there is no indication that the stock is in decline and sea trout in all the age classes previously recorded are still represented in the recent catches. The Owenmore catch was low in 2003, partly because of an intense algal bloom in Carrowmore lake which resulted in angling being suspended that year. Sea trout angling has been very good in the Moy estuary in recent years and a bag limit of six sea trout per day has been imposed. Despite this daily bag limit, an estimate of 4000 sea trout was recorded for 1999 and 3500 sea trout recorded in 2003.

Northern region The availability of rod catch data is variable from year to year and it is difficult to follow definite catch trends in many fisheries. The Eske, Eany, Ray, Gweebarra, Swilly and Crana have all recorded poorer catches in recent years. Unlike other regions outside the midwestern zone, it is difficult to generalise from the catch data available regarding the state of sea trout stocks in the northern region.

Sea trout CPUE effort data It is acknowledged that the Catch and Release Bye-Law introduced in the mid-1990s may have affected angling effort on some fisheries and has made the collection of accurate data more difficult. Sea trout CPUE data available for the Burrishoole, Owengowla, Invermore and Delphi fisheries (Fig. 3.6) demonstrates that catch collapse between 1988 and 1990 was not related to reduced angling effort but to an actual collapse in stock, indexed by CPUE.

Sea trout commercial catch data Sea trout were taken commercially in all fishery districts, both by drift and draft nets, normally as a by-catch in the salmon fishery. The most accurate data on commercial sea trout catches came from the eastern region where detailed data on number and weight

Review of Irish Stock Status

37

6 Delphi Burrishoole

5

Owengowla Invermore

Rod CPUE

4 3 2 1

2003

2001

1999

1997

1995

1993

1991

1989

1987

1985

1983

1981

1979

1977

1975

1973

1971

1969

1967

1965

1963

1961

1959

1957

1955

0

Year

Fig. 3.6 Catch per unit effort (CPUE) for rod fishery data for the Delphi, Invermore, Owengowla and Burrishoole fisheries. Table 3.3 Total numbers of sea trout captured over the 1990–1999 period in commercial fisheries in the Eastern Region. Eastern

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

Dublin Wexford Drogheda Dundalk Total

2605 975 710 80 4370

1134 864 254 179 2431

2274 1214 511 142 4141

2829 2553 1034 668 7084

2893 5670 1697 2964 1084 1246 320 413 5994 10293

4982 1533 1068 56 7639

4154 1394 982 281 6811

2552 1792 2032 426 6802

2158 3090 1646 956 7850

of sea trout taken per district are recorded annually. The total number of sea trout taken commercially in the eastern region has ranged from 2431 in 1991 to 10 293 in 1996 with an overall increasing trend for the period (r 2 = 0.45; P < 0.05) (Table 3.3). Catches recorded over the 1996–99 period were substantial and have averaged over 6000 fish annually. Since the introduction of the logbook and tagging scheme for salmon and sea trout (>40 cm) in 2001, returns for sea trout greater than 40 cm are available for all fishery districts (Table 3.4). The total declared catch in 2001 was 4225 trout and this has decreased to 1945 in 2003 (Anon., 2003). The majority of large trout were taken on the east and south coasts with fewer fish being taken north of Limerick on the west coast. No sea trout were declared in Galway, Connemara, Ballinakill and relatively few were declared in Ballina, Bangor and Sligo. Table 3.4 also shows the number of draft and drift net licences granted in each fishery district. There is a close association between the distribution of draft-net licences and the catches of sea trout. It is notable that the draft nets in Ballinakill have not recorded sea trout over 40 cm in the past 3 years where traditionally a large proportion of trout would have been taken in, for example, Killary Harbour. The sea trout conservation bye-law may also have affected catch returns in these mid-western districts.

38

Sea Trout

Table 3.4 Commercial sea trout catch for 2001–03 determined from logbook returns and presented by district, and number of commercial licences (drift net and draft net). District

2001 Total

Dundalk Drogheda Dublin Wexford Waterford Lismore Cork Kerry Limerick Galway Connemara Ballinakill Ballina Bangor Sligo Ballyshannon Letterkenny Total

374 180 609 574 787 365 653 220 285 0 0 0 9 34 3 61 71 4225

% by district 8.9 4.3 14.4 13.6 18.6 8.6 15.5 5.2 6.7 0 0 0 0.2 0.8 0.1 1.4 1.7 100

2002 Total 280 86 362 233 376 195 340 65 84 0 0 0 1 10 0 8 43 2083

% by district 13.4 4.1 17.4 11.2 18.1 9.4 16.3 3.1 4 0 0 0 0 0.5 0 0.4 2.1 100

Total 134 88 213 310 482 168 243 100 51 0 0 0 4 0 0 41 111 1945

2003

Number of licences

% by district

Draft net Drift net

6.89 4.52 10.95 15.94 24.78 8.64 12.49 5.14 2.62 0 0 0 0.21 0 0 2.11 5.71 100

42 51 11 75 3 6 33 50 95 4 0 17 3 31 1 84 43

0 0 16 0 172 80 106 39 86 37 29 39 83 25 10 28 127

549

877

National trap census data

Smolt output Summary trap data up to 2003 are presented for the Burrishoole, Owengowla, Invermore and Erriff traps in Table 3.5. In spite of wide variation, there was no significant change in smolt output from the Burrishoole between 1970 and 1989. However, after the collapse in spawning stock, smolt output has decreased significantly (P < 0.005). The highest smolt counts in the Owengowla were in 1991 (7540) and 1992 (5999) and in the Invermore in 1993 (4837) and 1996 (4643), with a significant downward trend for Owengowla (P < 0.05) but not for Invermore. Smolt numbers in the Erriff trap declined over the 1991–93 period, with the recorded run for 1993 being the lowest over the entire time series (Table 3.5). These smolts, primarily 2-year-old fish, would have been derived from the 1991 kelt run of 78 sea trout. Sea trout smolt numbers improved steadily over the 1994–96 period and ranged from 2659 to 4149 over the 1997–2003 period. The release of sea trout fry into streams entering Tawnyard Lough since 1994 may have contributed to the sea trout smolt run recorded from 1996 onwards, along with an unknown contribution from resident trout.

Adult migrations Upstream migrations of trout were low since 1989, although a recovery was seen in the Tawnyard sub-catchment of the Erriff, as demonstrated by the downstream kelt numbers

Review of Irish Stock Status

39

Table 3.5 Sea trout smolt numbers, total upstream counts and downstream kelts (Erriff), and proportions of finnock (0+ sea age) at the four trapping stations in the west of Ireland. Data summarised from Poole et al. (this meeting) & Gargan et al. (this meeting). Year

Burrishoole

Owengowla

Invermore

Smolt Total % 0+ Smolt Total % 0+ Smolt Total output upstream sea age output upstream sea age output upstream 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003

3228 2961 5465 6071 4527 3587 5207 3889 3167 5676 2337 6710 3907 4852 2383 4238 3454 3371 4290 3719 2063 2520 1936 1720 1127 1821 1289 817 1608 1260 769 530 1272 787

1244 1407 2225 2844 2929 3348 3302 2212 1830 2430 2004 1896 1624 1572 1501 1465 1387 950 863 224 155 342 151 173 210 180 197 137 106 264 111 89 115 78

50.0 50.0 50.0 50.0 50.0 33.0 44.9 32.7 21.0 26.6 31.0 44.8 48.4 56.5 36.9 46.8 50.7 48.8 42.4 24.6 73.5 62.3 45.7 68.8 49.5 48.3 58.9 55.5 70.8 76.5 59.5 49.4 69.6 75.6

Erriff–Tawnyard % 0+ Smolt Total sea age output kelts

2877

7540 5999 4090 3962 3517 4800 3045 4831 2762 3614 F&M 4027 Flood

13 1 6 637 322 117 24 16 117 57 489 61 157

84.6 0.0 0.0 98.1 58.4 14.5 62.5 75.0 99.1 57.9 100.0 68.9 89.7

— 31 4837 87 4332 53 1570 137 4643 76 2262 13 3527 23 2654 32 — 48 F&M 152 3249 19 1391 69

80.6 44.8 20.8 56.2 100.0 84.6 47.8 100.0 70.8 100.0 100.0 94.2

2448 3534 1841 416 1475 2900 3468 3020 3339 3915 2659 2270 4149 3481

412 510 489 633 no trap 60 78 313 332 354 518 478 582 690 740 640 370 647 962

Data excludes premature returning finnock before 1st June. Incomplete trapping periods for Owengowla & Invermore 1991–93. F&M: Foot & Mouth Restrictions affected access.

with numbers since 1995 similar or higher than those recorded between 1985 and 1988 (Table 3.5). It is also evident that there has been a change in the proportion of finnock (0+ sea age) returning with fewer older fish in the stock. The proportion of finnock in the Burrishoole system before 1989 averaged between 32% and about 50%; but after 1989 the proportion increased to more than 60%, although the numbers returning had decreased by

Sea Trout 1985–88

80 70 60 50 40 30 20 10 0

No. of kelts

No. of kelts

40

80 70 60 50 40 30 20 10 0

18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58

18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58 Length (cm)

1990–91

No. of kelts

80 70 60 50 40 30 20 10 0

1996–97

18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58

18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58

Length (cm)

Length (cm)

1992–93

80 70 60 50 40 30 20 10 0

No. of kelts

No. of kelts

No. of kelts

Length (cm) 80 70 60 50 40 30 20 10 0

1994–95

80 70 60 50 40 30 20 10 0

1998–99

18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58

18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 58

Length (cm)

Length (cm)

Fig. 3.7 Length–frequency distribution of sea trout kelts in the Tawnyard trap on the Errif fishery, 1985–99.

a factor of about 20. This is because of a marked reduction in the abundance of older age classes. Over the 1985–88 period, the Erriff Tawnyard sea trout kelt population structure comprised a finnock peak (small sea trout kelts), a peak of one and two sea winter (SW) maidens and some older previous spawners (Fig. 3.7). This would represent a normal population structure for a Connemara sea trout stock. The 1990 and 1991 kelt trapping data revealed a complete collapse in population structure with only 60 sea trout captured, the great majority being small fish. Over the 1992–95 period there was an increase in the number of small sea trout kelts recorded and some fish in the 35–45 cm length range were also present. Since 1995 there has been a progressive improvement in the numbers of small sea trout kelts, although their length distribution has not fully recovered to that recorded before 1989, with a dearth of sea trout larger than 35 cm.

Marine return In the Burrishoole system, the percentage of smolts that return as finnock in the same year historically ranged from 11.4% to 32.4% (Fig. 3.8) with a historical mean of 21%. In 1988 it decreased below the previous recorded minimum to 8.5% and in 1989 to a minimum of 1.5%. There has been a see-saw pattern of finnock return rates in the 1990s increasing to

Review of Irish Stock Status Burrishoole

Percentage marine survival

35

Gowla

41

Invermore

30 25 20 15 10 5

01

99

03 20

20

19

95

93

91

89

97 19

19

19

19

19

85

83

81

79

87 19

19

19

19

19

75

77 19

73

19

19

19

71

0

Fig. 3.8 Trends in smolt to finnock survival for three Irish fisheries: Burrishoole, Gowla and Invermore.

16.7% in 1999 – the highest return rate since 1986. The mean for the 1990s, excluding 1999, was 6.8%, three times lower than the historical average. Poor sea trout finnock returns were also recorded for the Owengowla since 1991, with the exception of 1994 (when whole bay spring fallowing of marine salmon farms took place in Bertraghboy Bay, into which the Owengowla discharges) (Fig. 3.8). Returns of finnock ranged from zero in 1992 and 1993 to a maximum of 625 in 1994. The marine return rate as finnock was equal to or below 1% for 8 of the 11 years examined. There was a marked increase in return rates in 1994 to 15.8%. The marine return rate to Invermore as finnock was also low since 1992 with a highest recorded value of 4.9% in 1995 (Fig. 3.8). The higher return observed in the Owengowla in 1994 was not observed in the Invermore.

Discussion Few accurate data on the status of Irish sea trout stocks have been published since their collapse in the mid-west region in 1989–90. It is now 15 years since the collapse and all available data have been compiled here to assess current stock status nationally. Rod catch figures alone may not be a useful indicator of stock in individual years because of the many variables influencing the catch, particularly fishing effort (Mills et al., 1986) and the methods of collection of the statistics. However, if rod catch figures are collected systematically and consistently over a number of years in each fishery they can be useful in indicating possible trends in the population rather than absolute stock numbers (Anon., 1995). The most reliable rod catch estimates in Ireland are for those fisheries in the midwest and these may be treated as indicative of the trend in that region (Anon., 1994b). Detailed marine survival and stock data from Burrishoole and the Erriff before 1989 and

42

Sea Trout

Owengowla and Invermore after 1991 support the trends observed in rod catch. The overall picture presented here showed that catch, CPUE and trap data all indicated a stock collapse in sea trout stocks in the mid-west in 1988 and 1989. Over the 1993–2001 period, rod catch data indicated a gradual increase in numbers of trout captured in some fisheries, such as Delphi, Erriff, Kylemore and Costello. However, rod catches never approached the levels recorded before the 1989–90 collapse and catches decreased again in recent years. Marine survival data from three fisheries in the mid-west also demonstrate that sea trout stocks remain in a much depleted state with a change in population structure. Sea trout length–frequency data for the Tawnyard sub-catchment of the Erriff fishery (this chapter) and the Burrishoole system (Poole et al., 1996) demonstrate that a breakdown of population structure can occur over a very short period and that consistent improvements in marine survival are required over a number of years in order to rebuild the stock structure. Data from the fisheries regions outside the mid-west zone indicate that appreciable numbers of sea trout have been captured on rod and line in the 1990s and the sea trout stock collapse documented in the mid-west was not generally apparent elsewhere. While appreciable numbers of sea trout were taken on rod and line in the eastern region, a downward trend in catch may be linked to deterioration in water quality (McGinnity et al., 2003). In the period 1990–99, there has been a significant increase in the commercial catch in the same region. However, without basic information on the origins of the stocks available to the commercial fishery it is difficult to draw firm conclusions on its impacts. A period of poor angling was observed in the south-west, particularly the Currane fishery in the early 1990s, but since that time there has been a marked improvement in rod catch. A significant increase in tourist angling has emerged for sea trout fishing in estuarine and sea areas in recent years, particularly in the Moy and Erne estuaries. This may have implications for the management of neighbouring sea trout stocks. Tully et al. (1999) have demonstrated that the presence of marine salmon farms significantly increased the level of sea lice infestation on sea trout post smolts in those areas in Ireland. Similar findings have been reported from Norway (Grimnes et al., 2000) and Scotland (Mackenzie et al., 1998; Butler, 2002). Gargan et al. (2003) demonstrated a statistical relationship between lice infestation on sea trout in Ireland and the distance to the nearest salmon farm over a 10-year-period with highest infestations seen close to fish farms and concluded that sea lice from marine salmon farms were a major contributory factor in the sea trout stock collapses observed in aquaculture areas in western Ireland. This study has demonstrated a sea trout stock collapse in the mid-west region. This coincided with the introduction and location of marine salmon farms. Stocks have not recovered in these areas, and fisheries remain vulnerable, if present trends in marine survival continue in the short term. As stated by the Sea Trout Task Force (Anon., 1994b): ‘if these stocks are to be saved and restored, both the elimination of lice on and in the vicinity of sea farms, … as the factor most closely associated with the marked incidence of adverse pressure on sea trout stocks …, must be a constant priority of management and regulatory practice’. This must

Review of Irish Stock Status

43

be achieved on a consistent annual basis for successful recovery of sea trout population structure. This should also be accompanied by protection and improvement of the freshwater environment and habitat. The sea trout life-cycle is complex and the indications from unpublished electro-fishing surveys are that in some systems juvenile salmon may have now filled the niche previously occupied by trout. Thus, the time period for a full recovery of the population structure of these stocks may be considerable and this will only be achieved through sustained improvements in marine survival. Sea trout stocks in the remainder of the country are under increasing pressure and, here also, protection of the freshwater environment is paramount. As noted above, there is increasing interest in the marine exploitation of sea trout by anglers and the effects of these fisheries need to be quantified and management action needs to be taken, if damage to individual local stocks is to be avoided. This review confirms earlier conclusions that statistics on sea trout stocks and catch outside the mid-western region still require improvement if the status of those stocks is to be accurately monitored and protected on a countrywide basis.

Acknowledgements The authors are indebted to the staff of the Central and Regional Fisheries Boards for providing information for this report. The provision of sea trout CPUE data for the Delphi fishery is gratefully acknowledged. The authors would also like to thank the staff of the Western Regional Fisheries Board and the Marine Institute, Newport, for the dedicated work in the various fish trapping facilities.

References Anon. (1992). Report of the Sea Trout Working Group, 1991. Department of the Marine, Dublin, 49 pp. Anon. (1993). Report of the Sea Trout Working Group, 1992. Department of the Marine, Dublin, 109 pp. Anon. (1994a). Report of the Sea Trout Working Group, 1993. Department of the Marine, Dublin, 127 pp. Anon. (1994b). Report of the Sea Trout Task Force, Department of the Marine, Dublin, 80 pp. Anon. (1995). Report of the Sea Trout Working Group, 1994. Department of the Marine, Dublin, 254 pp. Anon. (2003). Wild Salmon And Sea Trout Tagging Scheme; Fisheries Statistics Report 2001–2003. Central Fisheries Board, Dublin. Butler, J.R.A. (2002). Wild salmonids and sea louse infestations on the west coast of Scotland: sources of infection and implications for the management of marine salmon farms. Pest Management Science, 58, 595–608. Fahy, E. (1985). The Child of the Tides. The Glendale Press, Dublin, 188 pp. Gargan, P.G. (2000). The impact of the salmon louse (Lepeophtheirus salmonis) on wild salmonids in Europe and recommendations for effective management of sea lice on marine salmon farms. In: Aquaculture and the Protection of Wild Salmon (Gallaugher, P. & Orr, C., Eds). Workshop Proceedings, July 2000. Simon Fraser University, Vancouver, British Columbia, Canada, pp. 37–46. Gargan, P.G., Tully, O. & Poole, W.R. (2003). The relationship between sea lice infestation, sea lice production and sea trout survival in Ireland, 1992–2001. In: Salmon at the Edge (Mills, D., Ed.). Proceedings of the Sixth International Atlantic Salmon Symposium, July 2002, Edinburgh, UK, Chapter 10. Atlantic Salmon Trust/Atlantic Salmon Federation, pp. 119–35. Gargan, P.G., Roche, W.K., Forde, G.P. & Ferguson, A. (2006). Characteristics of sea trout (Salmo trutta L.) stocks from the Owengowla and Invermore fisheries, Connemara, western Ireland, and recent trends in marine survival. In: Sea Trout: Biology, Conservation and Management (Harris, G.S. & Milner, N.J., Eds). Proceedings of the First International Sea Trout Symposium, July 2004, Cardiff, Wales, UK. Blackwell Publishing, Oxford, pp. 60–75.

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Sea Trout

Grimnes, A., Finstad, B. & Bjorn, P.A. (2000). Registrations of salmon lice on Atlantic salmon, sea trout and charr in 1999. NINA Oppdragsmelding (In Norwegian with English abstract), 634, 1–34. Mackenzie, K., Longshaw, M., Begg, G.S. & McVicar, A.H. (1998). Sea lice (Copepoda: Caligidae) on wild sea trout (Salmo trutta L.) in Scotland. ICES Journal of Marine Science, 55, 151–62. McGinnity, P., Gargan, P., Roche, W., Mills, P. & McGarrigle, M. (2003). Quantification of the freshwater salmon habitat asset in Ireland using data interpreted in a GIS platform. Irish Freshwater Fisheries Ecology and Management Series Number 3, Central Fisheries Board, Dublin, Ireland, 132 pp. Mills, C.P.R., Piggins, D.J. & Cross, T.F. (1986). Influence of stock levels, fishing effort and environmental factors on anglers’ catches of Atlantic salmon, Salmo salar L. and sea trout, Salmo trutta L. Aquaculture and Fisheries Management, 17, 289–97. Poole, W.R., Whelan, K.F., Dillane, M.G., Cooke, D.J. & Matthews, M. (1996). The performance of sea trout, Salmo trutta L., stocks from the Burrishoole system western Ireland, 1970–1994. Fisheries Management and Ecology, 3(1), 73–92. Poole, W.R., Dillane, M., deEyto, E., Rogan, G., McGinnity, P. & Whelan, K. (2006). Characteristics of the Burrishoole sea trout population: census, marine survival, enhancement and stock recruitment, 1971–2003. In: Sea Trout: Biology, Conservation and Management (Harris, G.S. & Milner, N.J., Eds). Proceedings of the First International Sea Trout Symposium, July 2004, Cardiff, Wales, UK. Blackwell Publishing, Oxford, pp. 279–306. Tully, O., Poole, W.R. & Whelan, K.F. (1993). Infestation parameters for Lepeophtheirus salmonis (Krøyer) (Copepoda: Caligidae) parasitic on sea trout (Salmo trutta L.) post smolts on the west coast of Ireland during 1990 and 1991. Aquaculture and Fisheries Management, 24, 545–57. Tully, O., Gargan, P., Poole, W.R. & Whelan, K.F. (1999). Spatial and temporal variation in the infestation of sea trout (Salmo trutta L.) by the Caligid Copepod Lepeophtheirus salmonis (Krøyer) in relation to sources of infection in Ireland. Parasitology, 119, 41–51. Whelan, K.F. (1993a). Historic overview of the sea trout collapse in the west of Ireland. In: Aquaculture in Ireland – Towards Sustainability (Meldon, J., Ed.). Proceedings of a Conference held at Furbo, Co. Galway. 30th April–1st May, 1993, An Taisce, Dublin, pp. 51–3. Whelan, K.F. (1993b). Decline of sea trout in the west of Ireland: an indication of forthcoming marine problems for salmon? In: Salmon in the Sea and New Enhancement Strategies (Mills, D., Ed.). Proceedings of the Fourth International Atlantic Salmon Symposium, June 1992. St. Andrews, N.B. Canada, Chapter 9, Fishing News Books.

Chapter 4

Characteristics of the Sea Trout Salmo trutta (L.) Stock Collapse in the River Ewe (Wester Ross, Scotland), in 1988–2001 J.R.A. Butler1 and A.F. Walker2 1

CSIRO Sustainable Ecosystems, c/o Faculty of Science, Engineering & IT, James Cook University, PO Box 6811, Cairns, QLD 4870, Cairns, Australia 2 Fisheries Research Services Freshwater Laboratory, Faskally, Pitlochry, PH16 5LB, UK

Abstract: Rod catches of sea trout Salmo trutta L. from the River Ewe system collapsed in 1988 and have not recovered since. Data from the Ewe fishery, including Loch Maree, collected before and after the collapse demonstrated changes in the sea trout population structure. Between 1980 and 1997–2001 maximum sea age decreased from 11 to 5 years, and marine growth rates declined. This was reflected in River Ewe rod catches, with changes in the weight distribution of fish between 1971–80 and 1992– 2001, and mean weights decreased from 0.54 to 0.34 kg. The mean frequency of spawning migrations also declined from 2.3 in 1980 to 1.3 in 1997–2001. These changes coincided with shifts towards earlier run timing: in 1971–80, 53% of the River Ewe catch was taken in July, but in 1992–2001 61% were caught in June. The mean date of first entry of fish .0+), 3–6 scales are removed for age determination purposes. In addition, a lesser number of fish (approx. every third fish sampled) are weighed (to the nearest 25 g). After tagging and measuring, fish are allowed to fully recover in a holding pool before release. Further details on trapping, fish handling and other aspects of the Dee programme are given in Davidson et al. (1996). Note that since 1994, fine mesh screens (20 mm × 20 mm) have been secured to the upstream bars of the trap in July and August in order to retain all sizes of whitling. Before 1994, sampling was biased towards larger whitling and so estimates of mean length or weight before 1994 are excluded from subsequent analyses. Sampling bias before 1994 may also have resulted in a tendency to underestimate the run of .0+ fish – although the degree to which this might have occurred is uncertain. Back-calculated freshwater growth Back-calculated lengths at each river annulus were derived from the scales of .0+ and .1+ maidens using the method described by Friedland et al. (2000). Measurements were obtained from cleaned scales viewed under magnification (×30 or ×50) with radii distances recorded from a single scale. In most years, scale measurements were taken from 150 to 200 fish. To avoid sub-sampling bias, fish were selected in proportion to the number available in each sea-age group per month.

Results Run size, timing and age composition Run estimates for .0+ (whitling) and older sea trout (>.0+) at Chester Weir for the past 12 years are shown in Fig. 6.2 (run estimates for salmon are also shown for comparison). Estimates for whitling showed an increasing trend over the time series, rising from a minimum run of 2537 in 1992 to a maximum of 14 680 in 2001 (overall mean = 7207). In contrast, run estimates for older (>.0+) sea trout remained relatively stable (mean = 2069; range = 1424–2776), as have those of salmon (Fig. 6.2). The combined average run for all sea trout at 9275 was more than 1.5 times that for salmon (5625) over the equivalent period. In all years, peak monthly trap catch rates for whitling occurred in July with an average of 90% of the total catch rate taken within a 3-month period centred on this month. The equivalent peak in catch rate for older sea trout occurred in June (except in 1994 when catch rates peaked in July). As with whitling, catch rates were intense around the peak month with 85% of the total catch rate taken in the peak month and one month before or after. Whitling sea trout were rarely caught at Chester before May but could still be present in

Variation in Age Composition and Growth

79

20 000 .0+ Sea trout >.0+ Sea trout Salmon (all ages)

Run size

15 000

10 000

5000

0 91

92

93

94

95

96

97

98

99

00

01

02

03

Return year

Fig. 6.2 Annual run estimates for sea trout (and salmon) at Chester Weir, 1991–2002 (error bars indicate 95% confidence limits).

(a)

S4 0.2%

(b) 2+ 5.8%

Other 8.1%

0+SM+ 31.7%

S3 8.2%

S1 1.5%

1+SM+ 7.3%

0+2SM+ 6.3% 1+ 40.9%

S2 90.2%

Fig. 6.3 Age composition of Dee sea trout run, 1991–2003: (a) sea age (>.0+ fish only) and (b) smolt age (all adult fish).

December. Older fish appeared as early as February, but also persisted in catches to the end of the year. The sea and river age composition of the Dee sea trout run is summarised in Fig. 6.3. Maiden .1+ (41%) and .0+SM+ fish (32%) were the dominant age groups among the older sea trout (Fig. 6.3a). The remainder was made up of other previous spawners and a few maiden .2+ fish (6%). (Other previous spawners include individuals that appeared to have spawned for up to eight consecutive years.)

80

Sea Trout 2.4

Mean smolt age (years)

.0+ fish .1+ fish

2.2

2.0

1.8 89

90

91

92

93

94

95

96

97

98

99

00

01

02

03

Smolt year

Fig. 6.4 Annual variations in MSA (aligned by smolt year) for .0+ and .1+ sea trout 1990–2003 (error bars indicate 95% confidence limits).

Based on readings from adult scales, around 90% of fish appeared to have emigrated as 2-year-old smolts (S2s) (Fig. 6.3b). S2s were present in similar proportions in both whitling and .1+ maiden sea trout groups (both close to 90%), but the proportion of S1s was larger than expected among .1+ fish (4%) and smaller than expected among whitling (1%), the opposite being true for S3s and S4s (a combined figure of 7% in .1+ fish and 10% in whitling) (χ 2 = 110.6; P < 0.001). Mean smolt age (MSA) of whitling and .1+ maiden sea trout declined over the period of the study (Fig. 6.4), significantly so in the case of the latter (log10 transformed data: r = −0.583; P = 0.037). Annual estimates of sea-age composition among sea trout greater than .0+ have been used to assign the total run for this group to separate sea-age components. These are aligned by smolt year in Table 6.1 along with run estimates for whitling. Estimates of .1+ abundance from Table 6.1 show a significant declining trend over the time series (r = −0.589; P = 0.044) – the opposite trend to that observed for whitling (r = 0.862; P = 0.003) (Fig. 6.5). Abundance of whitling was positively correlated with that of .0+SM+ fish from the same smolt year class (r = 0.766; P = 0.027). In contrast, no significant correlation was evident between abundance of .1+ maidens and that of .1+SM+ fish (r = −0.002; P = 0.995) (Fig. 6.5). These relationships exclude .0+ run estimates before 1994 which are shown as open symbols in Fig. 6.5.

Post-spawner survival Post-spawner survival rates, estimated from Table 6.1, are shown in Fig. 6.6. Annual survival rates increase progressively across all maiden groups for the first four post-smolt years (i.e. equivalent to sea ages .0+4SM+; .1+3SM+ and .2+2SM+), and then decline. (Survival

Table 6.1

Abundance estimates for individual sea-age groups aligned by smolt year class, 1982–2002. Smolt year class

Sea age

1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992

1993

1994

1995

1996

1997

1998

1998

2000

2001

2002

5202 2537

11 505

.0+ .0+SM+ .0+2SM+ .0+3SM+ .0+4SM+ .0+5SM+ .0+6SM+ .0+7SM+ .1+ .1+SM+ .1+2SM+ .1+3SM+ .1+4SM+ .1+5SM+ .1+6SM+ .1+7SM+ .1+8SM+ .2+ .2+SM+ .2+2SM+ .2+3SM+ .2+4SM+ .2+5SM+

0

0

0 0

0 0 0

0

0 0

0 0 0 0

0 0

9 0 0

0 0 0 0 0

9 4 3

9693

3897

6673

4645

5509

7877

6763

7502

14 680

89 89 14 14 2 0 0

406 106 23 7 6 0 0

457 74 13 9 8 3 0

483 59 28 16 6 0 3

576 146 107 23 25 7 8

520 222 15 11 13 4

983 132 63 36 8

597 222 108 46

758 210 34

774 92

1351

810

9 14 0 0 0

85 43 17 0 0 0

530 115 31 11 0 0 0

782 155 11 0 2 3 0 0 0

822 90 23 7 0 8 0 0 0

951 242 22 12 12 3 4 0 4

1391 106 44 36 12 4 0 0

588 159 79 3 4 7 0

676 238 18 39 10 15

744 64 53 30 11

469 194 85 46

695 73

43 0 3 3 0 0 0

1656 180 41 11 9 0 0 0 0

574 121 46

26 7 0 0 0 0

179 22 10 0 3 0 0 0

120 28 5 3 0 0

81 5 0 0 0 0

166 17 2 0 0 0

373 13 9 4 0 0

51 12 12 0 4 0

105 12 0 0 7 0

80 9 11 0 0

71 53 13 8

75 23 0

40 4

9 4 0 0

197 29 7 5 0 2

81

26 25 10 3 0

0 0 0 0

82

Sea Trout 10 000

10 000 r = 0.862 P = 0.003 1000 1990

1995

2000

.1+ abundance

.0+ abundance

100 000

1000

r = –0.589 P = 0.044 100 1985

2005

Smolt year

1990

1995

2000

2005

Smolt year 1000

1000

r = 0.766 P = 0.027 100 1000

.1+SM+ abundance

.0+SM+ abundance

10 000

100

r = –0.002 P = 0.995 10

10 000

.0+ abundance

100 000

100

1000

10 000

.1+ abundance

Fig. 6.5 Correlations between (i) abundance of .0+ and .1+ sea trout and smolt year and (ii) abundance of .0+ and .1+ fish and that of .0+SM+ and .1+SM+ fish of the same smolt year class (log10 scales used; trend lines indicated; open symbols indicate .0+ estimates from 1991, 1992 and 1993).

rates have been averaged across age groups older than four post-smolt years as very few individuals reach this age.) Average survival rates peaked between the third and fourth post-smolt years at 57% to age .0+4SM+, 52% to age .1+3SM+ and 41% to age .2+2SM+. Maturation of whitling Tag recoveries and scale readings indicate that, among the .0+ sea trout captured at Chester Weir, some will go on to spawn in the year of their first return (i.e. are recaptured as .0+SM+ fish) while the rest remain maiden fish (most recaptured aged .1+ with a few aged .2+). It was not possible to judge the maturation state of whitling from external characteristics and no fish were killed for internal examination. For all years combined (1992–2003), 329.0+ fish were recaptured aged .0+SM+, 109 aged .1+ and 2 as .2+ fish (Table 6.2). These totals indicate a maturation rate in the first year of return of 75%, although on an annual basis (1994–2002) this rate has varied from 58% to 95% and appears to have increased gradually over the time series (the latter figures exclude the first 3 years when too few recaptures were made for meaningful comparison).

Variation in Age Composition and Growth

83

0.80

0.60

Survival rate

0.40

0.20

0.00 .2+3SM+ to .2+5SM+

.2+2SM+

.2+SM+

.1+4SM+ to .1+8SM+

.1+3SM+

.1+2SM+

.1+SM+

.0+5SM+ to .0+7SM+

.0+4SM+

.0+3SM+

.0+2SM+

–0.20

–0.40 Post-spawner age

Fig. 6.6 Average annual survival rates to post-spawner age for fish from the 1986–2002 smolt year classes (error bars indicate 95% confidence limits).

Table 6.2 Estimated maturation rates for whitling sea trout based on recaptures of .0+SM+, .1+ and .2+ fish, 1991–2003. Recapture age

Tagging year 91

.0+SM+ .1+ .2+ Total % Maturation

92

93

94

95

96

97

98

99

00

01

02

All

4 0 0

8 4 0

5 9 0

42 30 0

34 11 1

38 16 0

47 19 1

35 7 0

28 4 0

18 5 0

40 2 0

30 2 0

329 109 2

4

12

14

72

46

54

67

42

32

23

42

32

440

66.7

35.7

58.3

73.9

70.4

70.1

83.3

87.5

78.3

95.2

93.8

100.0

74.8

These rates ignore any differential mortality between maturing and non-maturing groups; for example, they will underestimate the true maturation rate if mortality among previous spawners is greater than in maiden fish. Among the 440 recaptures identified in Table 6.2, 324 had retained their tags and so could be traced as individual .0+ fish. The remaining fish with missing tags were assigned to the tagging year based on the presence of a permanent mark made by the removal of a small disc of tissue from the adipose fin at the time of tagging. The permanence of this fin clip was confirmed by its presence in all recaptured fish which had retained their tags. In the group of 324 fish which had retained their tags, 239 (74%) were recaptured as .0+SM+ fish, 83 (26%) as .1+ fish with only two fish recovered aged .2+. Based on these recaptures, whitling that returned as .0+SM+ fish were significantly larger than those

84

Sea Trout

returning as .1+ maidens (mean lengths 322 and 309 mm, respectively; ANOVA: F = 8.95; P = 0.003) and arrived earlier in the year (mean capture date of the 20th July compared with the 14th August; ANOVA: F = 58.23; P = .0+) sea trout has remained relatively stable, numbers of .1+ maiden fish (which normally comprise around 41% of this group) seem to have been in decline. Recaptures at Chester Weir indicate that most whitling entering the freshwater Dee spawn in their first ‘post-smolt’ winter. These mature fish tend to be larger and arrive earlier than non-maturing contemporaries, which delay maturation for a further 1 or occasionally 2 years. There is no reliable information from this study on the sex composition of mature and immature whitling. It is also unclear as to whether immature whitling overwinter in fresh water or return to estuarine or coastal waters. However, as few whitling have been recaptured at Chester Weir (at head-of-tide) in the same year they were tagged it seems there is no tendency for fish to circulate between estuarine and fresh waters. Back-calculation studies (Davidson et al., 2001) suggest that mature whitling appear to be not only larger than immature fish on their return to fresh water but also show similar size

86

Sea Trout

log10 length increment (mm)

2.70 2.50 2.30

log10 Y = 15.4575 + 0.0090 X r = 0.789; P = 0.002

2.10 1.90

log10 Y = 11.520 + 0.0068 X r = 0.699; P = 0.036

1.70

.0 + fish .1+ fish

1.50 90

92

94

96

98

00

02

Smolt year

Fig. 6.9

Trends in post-smolt growth increment for .0+ and .1+ sea trout, 1990–2002 smolt years.

differences as 2-year-old smolts (although at river age 1 no size differences were apparent). These differences in smolt size are in keeping with observations on MSA – where all fish returning as whitling (a sample which includes immature as well as mature individuals) were also of consistently greater MSA than sea trout returning aged .1+ (see Fig. 6.4). A decline in MSA among .0+ and .1+ maidens over the period of this study (Fig. 6.4) suggests that fish may be growing faster to reach the size required to emigrate at a younger smolt age. However, back-calculated ‘smolt’ lengths (taken as the length when the previous river annulus was formed) for .0+ and .1+ fish of all smolt ages showed no evidence of increasing size over the time series (Fig. 6.8). This is consistent with the lack of a trend in trout growth rates predicted using the model of Elliott et al. (1995) and based on river temperature records for the Dee over the equivalent period (Davidson et al., 2006). It would seem then, that the increase in whitling abundance on the Dee has not arisen as a result of faster ‘pre-smolt’ growth. However, ‘post-smolt’ growth increment has increased significantly for both .0+ and .1+ fish (Fig. 6.9) (where post-smolt growth increment is defined here as the size difference between the back-calculated length at the previous river annulus and length at first return for the same group of fish). This may be indicative of more favourable growth conditions in the marine environment, although the extent to which these two groups of fish coexist in the sea or estuarine waters is unknown. Improved growth rates in the post-smolt stage may be linked to an increased tendency for fish to return as whitling, although the size of whitling at return shows no significant trend over time. If this were the case it might also explain the decline in .1+ abundance, presumably because a smaller proportion of outgoing smolts return as .1+ fish. However, the picture is only a partial one as no information is available on the numbers of smolts emigrating to sea each year or their subsequent survival to return as whitling or older maiden fish. Whatever mechanism is at work, if marine growth rates are increasing then inverse-weight hypotheses, such as that of Doubleday et al. (1979), suggest that survival rates should also

Variation in Age Composition and Growth

87

be improving – with larger fish being less susceptible to predation and other sources of mortality. This should benefit smolt survival (e.g. Friedland et al. [2000] reported a positive correlation between post-smolt growth increment in 1SW salmon and smolt return rate), but may also improve the survival of post-spawners – assuming that larger individuals are better placed to withstand the rigours of spawning.

References Bagenal, T. (1978). Methods for Assessment of Fish Production in Fresh Waters. IBP Handbook No. 3. Blackwell Scientific Publications Ltd., Oxford. Chapman, D.G. (1952). Some properties of the hypergeometric distribution with applications to zoological sample censuses. University of California Publication on Statistics, 1, 131–60. Davidson, I.C., Cove, R.J., Milner, N.J. & Purvis, W.K. (1996). Estimation of Atlantic salmon (Salmo salar L.) and sea trout (Salmo trutta L.) run size and angling exploitation on the Welsh Dee using mark-recapture and trap indices. In: Stock Assessment in Inland Fisheries (Cowx, I.G., Ed.). Fishing News Books, Blackwell Science, Oxford, pp. 293–307. Davidson, I.C., Hazlewood, M.S., Cove, R.J. & McIlroy, J.T. (2001). Analysis of growth and survival of sea trout from the Welsh Dee, Atlantic Salmon Trust Project Ref 99/7. Environment Agency Wales (internal report). Davidson, I.C., Hazlewood, M.S. & Cove, R.J. (2006). Predicted growth of juvenile trout and salmon in four rivers in England and Wales based on past and possible future temperature regimes linked to climate change. Proceedings of Biology and Management of Sea Trout Conference, 6–8 July 2004, Cardiff, Wales. Doubleday, W.G., Rivard, D.R., Ritter, J.A. & Vickers, K.U. (1979). Natural mortality rate estimates for North Atlantic salmon in the sea. ICES C.M. 1979/M:26. Elliott, J.M., Hurley, M.A. & Fryer, R.J. (1995). A new, improved growth model for brown trout, Salmo trutta. Functional Ecology, 9, 290–98. Friedland, K.D., Hansen, L.P., Dunkley, D.A. & Maclean, J.C. (2000). Linkage between ocean climate, post-smolt growth and survival of Atlantic salmon (Salmo salar L.) in the North Sea area. ICES Journal of Marine Science, 57, 419–29. Nall, G.H. (1930). The Life of the Sea Trout. Seeley Service, London, 335 pp. Shields, B.A., Bayliss, B.D., Davidson, I.C., Elsmere, P. & Evans, R.E. (2006). Sea trout exploitation from five rivers in England and Wales. Proceedings of Biology and Management of Sea Trout Conference, 6–8 July 2004, Cardiff, Wales. Solomon, D.J. (1994). Sea trout investigations. Phase 1 – Final Report. R&D Note 318, National Rivers Authority. Went, A.E.J. (1962). Irish sea trout, a review of investigations to date. Scientific Proceedings of the Royal Dublin Society, 1A (10), 265–96.

Chapter 7

Sea Trout Stock Descriptions in England and Wales G. Harris FishSkill Consultancy and Resource Management Services, Greenacre, Cathedine, Bwlch, Brecon, Powys LD3 7PZ, Wales, UK

Abstract: The results of a major scale-reading investigation to provide baseline descriptions of the structure and composition of adult sea trout stocks from 16 rivers in four geographical regions of England and Wales from 1996 to 1998 are summarised. The sampling programme was synchronised over the same 3-year period with material collected only from rod-caught fish (15 rivers) or only from trap-caught fish (1 river). This standardised sampling procedure overcame many of the problems of selective sampling bias associated with previous investigations using samples obtained from multiple sources and provided results that were more directly comparable across rivers and regions. Potential sources of bias in the scale collections from the rod fishery affecting the reliability of the stock descriptions are considered. A comparison of key life-history features (age at smolt migration, age at first return as maiden fish and frequency of spawning) indicated the presence of at least three distinct groups of sea trout in different geographical regions. Some of the principal management applications of the investigation are discussed. Keywords: Salmo trutta L., sea trout, stock structure, smolt age, maiden sea age, spawning frequency, stock groupings.

Introduction and background The dramatic collapse of regional sea trout stocks that occurred in the west of Ireland from the late 1980s (Gargan et al., 2003) and then in some parts of Scotland from the early 1990s (Anon., 2005) raised serious concerns about the risks of a parallel situation developing in England and Wales. This led to the implementation of an R&D programme for sea trout in England and Wales to draw together all the available data on the structure and composition of sea trout stocks and to address any deficiencies in the nature and scope of those data so that the early symptoms of any existing or future stock collapse might be recognised and the appropriate management response identified. The programme had three phases. Phase 1 entailed a major desk-study to draw together all the available information about the biology, ecology, genetics and behaviour of sea trout in England and Wales from relevant sources, both published and unpublished. Much of that information related to disparate scale-reading investigations undertaken opportunistically by various workers between 1925 and 1995 that described the principal life-history characteristics of sea trout stocks in various 88

Stock Descriptions in England and Wales

89

rivers. The final reports (Solomon, 1994, 1995) concluded that while past scale-reading studies provided a basic qualitative description of the structure and composition of sea trout stocks for 23 of the 100 or so sea trout rivers in England and Wales, minimal information of variable quality existed for some of those rivers, and for many others none was available. Phase 2 of the programme was commissioned to address deficiencies in the quality and scope of the historical database on adult stock structures identified by Solomon (1994). The overall objective was ‘to design a sampling programme to provide reliable data on sea trout stock characteristics in England and Wales and to allow those stocks to be monitored and managed in a cost-effective way’. The final report (Harris, 1995) confirmed many of the reservations expressed by Solomon (1994). It concluded that few of the previous studies were directly comparable, either spatially or temporally, because of (1) the multiplicity of different sampling strategies used to obtain scale samples; (2) the different and unknown extent of any selective sampling bias inherent within each of those methods; (3) the long period often taken to assemble the scale collections; (4) concern about the accuracy of the scale readings in some investigations; (5) doubts about the relevance to the present of stock descriptions obtained many years ago and (6) problems arising from the presentation of results in a variety of non-comparable formats. It was proposed that any future sampling strategy should accommodate four basic requirements: (1) generate robust and reliable information that allowed direct comparisons on a like-for-like basis among different rivers at any time and for any one river at different times; (2) provide as much information as practicable within a fixed cost to describe the range of variability in different stocks; (3) allow the database to be expanded by the inclusion of directly comparable information from other rivers and (4) enable the database for any one river to be interrogated in future years by replication with the same sampling method so that any temporal changes in the stock structure and composition could be identified. It was accepted that the most complete, accurate and reliable stock descriptions were likely to be obtained with samples collected from fixed trapping stations operating throughout the year on the lower reaches of rivers. However, the lack of such installations, both now and in the future, on all but a very few rivers effectively excludes this as a standard sampling strategy. The use of commercial net fisheries licensed to fish for salmon and sea trout in tidal waters as a standard means for collecting samples was also discounted because (1) some net fisheries were thought to exploit mixed stocks originating from an unknown number of different rivers; (2) the restricted netting season meant that fish entering a river before or after the end of the netting season could not be sampled; (3) the restrictions on the size of the mesh used in the construction of the nets would have resulted in the collection of unrepresentative samples biased against fish of less than 35 cm in length (Evans et al., 1995) and (4) net fisheries operated on relatively few rivers and their number and distribution was likely to decrease even further in subsequent years. Therefore, because the only single source of material available on all rivers at that time, and likely to be so in the future, was from sea trout caught by the recreational rod-and-line fishery, it was recommended that this source of material should form the basis of a future, long-term sampling strategy. This recommendation was accepted and the Phase 3 study was commissioned ‘to implement a sampling programme to provide a baseline of reliable data

90

Sea Trout

on sea trout stock characteristics in England and Wales which will enable sea trout stocks to be managed in a cost-effective way’. This chapter summarises the main findings of the final report of that study (Harris, 2000).

Method and materials The sampling programme was based on material obtained from rod-caught fish on 15 rivers located in four different geographical regions, where scale samples were collected by volunteers recruited from within the local angling community (Fig. 7.1). The selection

Coquet North-east Esk Wear

Kent

Lune

North west

Ribble Clwyd Dwyfor Dee Wales Teifi

Dyfi

Tywi

Taw

Camel

Teign

South-west Tamar

Fig. 7.1

Names and geographical locations of the 16 rivers studied.

Stock Descriptions in England and Wales

91

of each river took into account an a priori assessment of whether the historical rod catch and the extent of cooperation by the angling community towards the sampling programme on each river were likely to yield the predetermined targets set for a statistically robust sample size of either 250 or 500 fish (Keating in Harris, 2000). Samples were collected also from fish captured in the permanent fixed trap operating in the tideway of the River Dee, where there was an ongoing programme of monitoring runs of salmon and sea trout which commenced in 1992. This had established that although the declared annual catch of sea trout by the rod fishery was insufficient to yield an adequate sample of scales, very large numbers of sea trout (4000–10 000) entered the river each year (Davidson et al., 1996). The historically low level of exploitation by the rod and net fisheries on this river, indicated by the declared average annual catches of only 149 for the rod fishery and 75 for the net fishery in the preceding years, suggested that this particular river was of special interest in establishing the composition of a relatively ‘pristine’ stock. Volunteers recruited from within the local angling community on each river by various means (Harris, 2000) undertook the collection of scale samples from rod-caught fish. Experienced fishery workers engaged in the routine trapping programme undertook the collection of samples from the Dee. Every angler engaged in the scale collection programme was issued with specially designed scale packets for storing samples and recording the details of each individual fish. Clear instructions were given about the importance of taking a representative sample of their entire catch and, in particular, avoiding any non-random and selective sampling bias for a particular size of fish. The scale collection sampling programme on all 16 rivers was synchronised over a 3-year period from 1996 to 1998. The standard scale-reading procedures recommended by Shearer (1992) for salmon and by Elliott & Chambers (1996) for sea trout were adopted. For the immediate purposes of this investigation, life-history determination was restricted to the interpretation of (1) parr age in winters at the time of smolt migration; (2) maiden sea age in winters at the time of first return to fresh water after smolt migration and (3) the number of spawning marks present.

Terminology The terminology used to describe the life-history characteristics of sea trout follows the International Standard Nomenclature proposed by Allan & Ritter (1997). The term ‘whitling’ refers to those sea trout that return to fresh water in the same year that they migrated to sea as smolts. It is synonymous with the terms ‘finnock’, ‘herling’ and ‘schoolpeal’ used elsewhere. The term ‘maiden’ refers to any adult fish that has yet to spawn for the first time, and the term ‘previous spawner’ refers to any fish that has spawned on at least one previous occasion. The conventions used in the scale formulae to denote the smolt age, sea age and spawning history of sea trout are based on those adopted by both Nall (1930) and Went (1962) – with the notable exception of the whitling stage being shown as .0 (instead of .+) on the logic that everything after the decimal point denoting smolt migration in the formula should record the number of complete winters spent in the sea after smolt migration.

92

Sea Trout

Results Scale collections The number of scales collected from each river over the 3-year period is given in Table 7.1. This also shows the declared rod catch for each year of the study and the a priori target set for obtaining a statistically robust sample for each river. The number of samples obtained for each river exceeded or approximated the set target on all rivers with the notable exception of the Lune. However, the Lune data have been included here because they do not differ markedly from the results of other recent scale-reading investigations on this river given by Solomon (1995) and Harris (2000). Age at smolt migration A total of 6578 sets of readable scales were obtained, which showed the number of years each fish had spent in the rivers as a juvenile parr before migrating to the sea as a smolt. The results are given in Table 7.2. It should be noted that these data may not reflect the actual age composition of the smolt run at the time of migration because of differential rates of survival of different smolt age groups in the sea (Solomon, 1995). Table 7.1 The numbers of fish sampled in each river (1996–98) in relation to declared catches and target sample size. Region and river

Declared catch for rods and actual catch in the Dee trap each year

Total no. of fish in sample (1996–98)

Sample no. as percentage of catch (1996–98)

Target sample size (no. of fish)

Sample no. as percentage of set target

1996

1997

1998

Total

North-east England Wear 781 Coquet 417

914 423

1064 909

2759 1749

235 249

8.5 14.2

250 250

94.0 99.6

North-west England Border Esk 1357 Kent 450 Lune 1601 Ribble 686

1135 299 1701 952

1671 576 2730 1635

4163 1325 6032 3273

726 226 251 348

17.3 17.1 4.2 10.6

250 250 500 250

290.4 90.4 50.2 139.2

(1210) (1622) (1748) (4580) 528 717 1730 2975 775 389 1787 2951 752 1316 1337 3405 2325 2146 3605 8076 1838 2462 4539 8893

1579 176 235 658 314 570

34.4 5.9 8.0 19.3 3.9 6.4

500 250 250 500 250 500

315.6 70.4 94.0 131.6 125.6 114.0

206 659 411 612

10.3 26.0 33.0 26.9

250 250 250 250

82.4 259.6 164.4 248.8

Wales Dee – trapa Clwyd Dwyfor Dyfi Teifi Tywi

South-west England Taw 510 Camel 818 Tamar 428 Teign 553

613 1077 344 705

869 658 475 1017

1992 2533 1247 2275

a Catches (in parenthesis) represent the actual number of fish trapped.

Stock Descriptions in England and Wales Table 7.2

Smolt age: the number and proportion of fish in each smolt age group.

Region and river

Age at smolt migration (winters) S1 No.

S2 %

No.

S3 %

No.

93

No. of fish sampled

S4 %

No.

%

North-east England Wear 6 Coquet 3

2.6 1.3

207 200

89.6 84.0

18 35

7.8 14.7

0 0

NR NR

231 238

North-west England Border Esk 20 Kent 5 Lune 2 Ribble 1

3.9 2.6 0.9 0.3

445 169 206 283

87.5 86.2 88.4 90.4

44 22 24 29

8.6 11.2 10.3 9.3

0 0 1 0

NR NR 0.4 NR

509 196 233 313

Wales Dee Clwyd Dwyfor Dyfi Teifi Tywi

35 7 7 37 3 24

2.6 4.2 3.2 6.1 1.0 4.6

1191 152 201 542 267 452

88.8 91.0 92.6 88.5 92.1 85.5

112 8 9 33 20 51

8.4 4.8 4.1 5.4 6.9 9.7

2 0 0 0 0 1

0.2 NR NR NR NR 0.2

1340 167 217 612 290 528

South-west England Taw 3 Camel 6 Tamar 0 Teign 0

1.6 1.0 NR NR

176 418 283 347

92.2 71.6 75.9 62.4

12 156 88 209

6.2 26.7 23.6 37.6

0 4 2 0

NR 0.7 0.5 NR

191 584 373 556

NR = not relevant.

All smolts migrated after 1–4 years in the river, but there were variable proportions of fish in each smolt age group from different rivers. Between 93.9% and 100.0% of all fish became smolts at 2 and 3 years of age, with 2 year-old smolts forming the dominant age group in all rivers, at 62.4–92.6% of all age groups. Although they were present in all rivers, the proportion of 3-year-old smolts was relatively small, at 4.1–14.7%, in Wales and north-east England, but they represented between 23.6% and 37.6% of the sample in three of the four rivers in south-west England. Smolts aged 4 years were not found in 11 rivers and represented less than 0.7% of the sample in the other 5 rivers. Smolts aged 1 year were absent from two rivers and generally scarce in all other rivers, where they did not exceed more than 6.1% of the sample. Sea-age structure Adult sea trout stocks contain two distinct groups of fish based on their spawning history: (1) those fish that return to the river to spawn for the first time (maidens) and (2) those other fish that have spawned on at least one previous occasion (previous spawners). A total of 7113 sets of scales were readable for both maiden sea age and previous spawning history (Table 7.3). Although the proportion of previous spawners exceeded that of

94

Sea Trout Table 7.3 Sea age: the number and proportion of maiden and previously spawned sea trout. Region and river

Sea-age group All maiden fish

All spawned fish

No.

No.

%

Total no. of fish

%

North-east England Wear 184 Coquet 209

79.3 83.9

48 40

20.7 16.1

232 249

North-west England Border Esk 385 Kent 125 Lune 148 Ribble 164

72.6 59.0 60.7 48.5

145 87 96 174

27.4 41.0 39.3 51.5

530 212 244 338

Wales Dee Clwyd Dwyfor Dyfi Teifi Tywi

1066 135 214 485 250 410

67.5 80.4 93.5 75.1 82.0 73.6

513 33 15 161 55 147

32.5 19.6 6.5 24.9 18.0 26.4

1579 168 229 646 305 557

South-west England Taw 136 Camel 519 Tamar 242 Teign 367

68.3 82.7 61.0 60.7

63 109 155 238

31.7 17.3 39.0 39.3

199 628 397 605

maiden fish in the Ribble (51.5%), maiden fish were dominant on all other 15 rivers (range 59.0–93.5%). These data are broken down into separate maiden and previously spawned stock components for further analysis in the following sections. Maiden sea age Table 7.4 shows the number and proportion of fish in each maiden sea-age group. Although .3 sea-winter (SW) maidens were not recorded from any river, .2SW maidens, while scarce, were identified in nine rivers, where they represented 0.3–6.0% of the samples. At least 94% of all maiden fish in any single river were from the .0SW and .1SW sea-age groups. The .1SW maiden fish were the single most dominant group in seven rivers (range = 60.0–94.7%), while .0SW maidens were the most dominant maiden group in the other nine rivers. The relative importance of these two maiden groups varied across regions. The .1SW maiden group was dominant in the north-east and north-west of England but, with the single exception of the Dyfi, the .0SW maiden group dominated the samples from Wales and south-west England. The scarcity of .0SW fish in the two rivers of north-east England, at only 1.1% and 2.9% of the sample, is notable.

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Table 7.4 Maiden fish: the number and proportions of sea trout in each maiden sea-age group. Region and river

Maiden sea-age group (sea winters) .0SW No.

.1SW

%

Total no. of fish

.2SW

No.

%

No.

%

North-east England Wear 2 Coquet 6

1.1 2.9

171 198

92.9 94.7

11 5

6.0 2.4

184 209

North-west England Border Esk 152 Kent 48 Lune 49 Ribble 33

39.5 38.4 33.1 20.4

231 77 98 129

60.0 61.6 66.2 79.6

2 0 1 0

0.5 NR 0.7 NR

385 125 148 162

Wales Dee Clwyd Dwyfor Dyfi Teifi Tywi

751 111 184 124 227 233

70.4 82.2 86.0 25.6 90.8 56.8

293 24 30 355 23 168

27.5 17.8 14.0 73.2 9.2 41.0

22 0 0 6 0 9

2.1 NR NR 1.2 NR 2.2

1066 135 214 485 250 410

South-west England Taw 83 Camel 464 Tamar 190 Teign 219

61.0 89.4 78.5 59.7

52 55 52 147

38.2 10.6 21.5 40.1

1 0 0 1

0.8 NR NR 0.3

136 519 242 367

NR = not relevant.

Spawning frequency Table 7.5 shows the number of spawning marks identified on the scales of 2076 fish that had spawned at least once. The maximum number of such marks recorded was x6, but this was limited to a single fish in each of the two rivers. The proportions of fish that had spawned on one or more previous occasions varied within wide limits for the individual rivers; the maximum number of spawning marks was x2 for 16 rivers, x3 for 15 rivers, x4 for 14 rivers, x5 for 8 rivers and x6 for 2 rivers. There were only four rivers where the proportion of fish that had spawned on at least two previous occasions exceeded 15% and only four rivers where more than 5% of the sample had spawned on at least three previous occasions. Adult life tables The data in Tables 7.3–7.5 were reproduced in a standard, readily comparable format as a series of adult life tables showing the structure and composition of each adult stock. These were supplemented with information on the length of each sea-age category (Harris, 2000). Table 7.6 for the River Dee and Table 7.7 for the River Dwyfor illustrate the extremes of variability encountered across the stock structures for the 16 rivers.

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Table 7.5 Spawning frequency: the number and proportion of sea trout in each group of previously spawned fish. Region and river

Number of spawning marks detected on scales x1 No.

x2 %

North-east England Wear 42 87.5 Coquet 34 85.0

No.

x3 %

No.

x4 %

x5

Total no. of fish

x6

No.

%

No.

%

No.

%

6 4

12.5 10.0

0 1

NR 2.5

0 1

NR 2.5

0 0

NR NR

0 0

NR NR

48 40

North-west England Border Esk 105 Kent 56 Lune 56 Ribble 112

72.4 64.3 60.4 65.5

32 16 19 37

22.1 18.4 19.8 21.6

6 8 12 18

4.1 9.2 12.5 10.5

1 5 8 3

0.7 5.8 8.3 1.8

0 2 1 0

NR 2.3 1.0 NR

1 0 0 1

0.7 NR NR 0.6

145 87 96 171

Wales Dee Clwyd Dwyfor Dyfi Teifi Tywi

71.9 84.9 86.6 69.1 57.8 59.8

99 1 1 8 42 38

19.3 3.0 6.7 14.6 26.1 25.9

27 3 1 7 13 11

5.3 9.1 6.7 12.7 8.1 7.5

11 1 0 2 12 9

2.1 3.0 NR 3.6 7.5 6.1

7 0 0 0 1 1

1.4 NR NR NR 0.6 0.7

0 0 0 0 0 0

NR NR NR NR NR NR

513 33 15 55 161 147

60.3 74.3 79.4 71.0

15 18 23 48

23.8 16.5 14.8 20.2

6 5 7 12

9.5 4.6 4.5 5.0

3 3 2 7

4.8 2.8 1.3 2.9

1 2 0 2

1.6 1.8 0 0.8

0 0 0 0

NR NR NR NR

63 109 155 238

369 28 13 38 93 88

South-west England Taw 38 Camel 81 Tamar 123 Teign 169 NR = not relevant.

Key features summary The data in Tables 7.2, 7.4 and 7.5 were used to generate a series of arithmetic values representing key features of the age structure and spawning history of each stock, namely: • • • • •

mean smolt age (MSA) – the average number of years that juveniles spent in fresh water before migrating to sea as smolts; mean maiden age (MMA) – the average number of years (winters) that the post-smolts spent in the sea before returning to the river to spawn for the first time as maiden fish; mean spawning frequency (MSF) – the average number of spawning marks detected on the scales of individual fish that had spawned on at least one previous occasion; mean adult age (MAA) – the average number of years (winters) as an adult after migrating to sea as a smolt (=MMA + MSF); mean total age (MTA) – the average age from birth to capture (=MSA + MAA).

The results of this summary are shown in Table 7.8.

Table 7.6

Adult life table: the structure and composition of the adult sea trout stock of the River Dee (sample size = 1579 fish). Maiden sea-age group

Sea age (SW)

First return as .0SW maidens Frequency

.0+ .1Sm+ .2Sm+ .3Sm+ .4Sm+ .5Sm+ .6Sm+ .7Sm+ NR = not relevant.

Sea age (SW)

Length (mm)

No.

%

Mean

Range

751 246 66 22 9 4

47.56 15.58 4.18 1.39 0.57 0.25

322 422 506 589 632 634

225–437 322–700 322–700 421–655 498–742 609–717

First return as .1SW maidens Frequency

.1+ .1 + 1Sm+ .1 + 2Sm+ .1 + 3Sm+ .1 + 4Sm+ .1 + 5Sm+ .1 + 6Sm+

Sea age (SW)

Length (mm)

No.

%

Mean

Range

293 113 29 5 1 2

18.56 7.16 1.84 0.32 0.06 0.13

468 539 614 673 677 722

323–624 422–671 489–777 623–734 NR 674–769

First return as .2SW maidens Frequency

.2+ .2 + 1Sm+ .2 + 2Sm+ .2 + 3Sm+ .2 + 4Sm+ .2 + 5Sm+

Length (mm)

No.

%

Mean

Range

22 10 4

1.39 0.63 0.25

619 671 687

533–768 623–761 642–757

1 1

0.06 0.06

825 793

NR NR

Table 7.7

Adult life table: the structure and composition of the adult sea trout stock in the Afon Dwyfor (sample size = 226 fish). Maiden sea-age category

Sea age (SW)

First return as .0SW maidens Frequency

.0+ .1Sm+ .2Sm+ .3Sm+ .4Sm+ .5Sm+ .6Sm+ .7Sm+ NR = not relevant.

Sea age (SW)

Length (mm)

No.

%

Mean

Range

184 9

81.42 3.98

329 451

267–483 368–660

First return as .1SW maidens Frequency

.1+ .1 + 1Sm+ .1 + 2Sm+ .1 + 3Sm+ .1 + 4Sm+ .1 + 5Sm+ .1 + 6sm+

Sea age (SW)

Length (mm)

No.

%

Mean

Range

30 4 1 1

13.3 1.8 0.4 0.4

490 584 775 768

343–584 559–635 NR NR

.2+ .2 + 1Sm+ .2 + 2Sm+ .2 + 3Sm+ .2 + 4Sm+ .2 + 5Sm+

First return as .2SW maidens Frequency

Length (mm)

No.

Mean

%

Range

Table 7.8 Key features summary: mean (±SD) of smolt age, maiden sea age, spawning frequency, total sea age and total age for each of the 16 stocks along with their derived length–weight relationship. Region and river

MSA Mean

MMA

MSY

MAA

MTA

Length–weight relationship SE

Slope

SE

R2

−8.91 −9.04

0.45 0.52

2.61 2.62

0.07 0.08

0.84 0.82

0.85 0.99 1.18 0.89

−8.87 −9.22 −10.12 −9.14

0.41 0.22 0.26 0.31

2.59 2.64 2.79 2.63

0.07 0.04 0.04 0.05

0.87 0.88 0.93 0.89

2.80 2.46 2.23 3.16 2.43 2.95

1.00 0.83 0.56 1.00 0.85 1.05

−10.50 −9.30 −8.95 −9.82 −9.16 −8.52

0.07 0.52 0.30 0.18 0.28 0.21

2.87 2.66 2.60 2.74 2.63 2.55

0.01 0.09 0.05 0.03 0.05 0.03

0.97 0.86 0.92 0.94 0.91 0.91

2.94 2.60 2.89 3.21

1.06 0.81 0.88 1.00

−10.35 −9.49 −9.94 −8.86

0.27 0.27 0.25 0.24

2.83 2.67 2.75 2.58

0.04 0.05 0.04 0.04

0.96 0.84 0.91 0.87

SD

Mean

SD

Mean

SD

Mean

SD

Mean

SD

Intercept

North-east England Wear 2.13 Coquet 2.05

0.38 0.32

0.98 1.03

0.26 0.26

0.20 0.23

0.51 0.48

1.18 1.26

0.54 0.51

3.31 3.31

0.63 0.59

North-west England Border Esk 2.05 Kent 2.09 Lune 2.10 Ribble 2.09

0.35 0.36 0.34 0.30

0.57 0.52 0.65 0.58

0.51 0.51 0.53 0.51

0.37 0.67 0.68 0.77

0.71 1.04 1.07 0.96

0.94 1.19 1.33 1.35

0.84 1.08 1.20 0.94

2.98 3.21 3.41 3.38

Wales Dee Clwyd Dwyfor Dyfi Teifi Tywi

2.06 2.01 2.01 1.99 2.06 2.05

0.33 0.30 0.27 0.34 0.28 0.38

0.33 0.20 0.16 0.75 0.12 0.48

0.52 0.40 0.36 0.46 0.34 0.53

0.46 0.26 0.08 0.42 0.27 0.43

0.81 0.62 0.33 0.87 0.68 0.85

0.79 0.46 0.24 1.17 0.40 0.91

0.97 0.80 0.54 0.99 0.83 1.05

South-west England Taw 2.05 Camel 2.27 Tamar 2.25 Teign 2.38

0.28 0.48 0.44 0.48

0.43 0.10 0.17 0.31

0.52 0.30 0.37 0.47

0.52 0.25 0.50 0.56

0.93 0.64 0.73 0.85

0.94 0.34 0.66 0.87

1.10 0.70 0.78 0.88

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North-east – Coquet North-east – Wear North-west – Ribble North-west – Kent North-west – Lune South-west – Taw Wales – Tywi North-west – Esk Wales – Dee Wales – Dwyfor Wales – Clwyd Wales – Teifi Wales – Dyfi South-west – Tamar South-west – Camel South-west – Teign

Fig. 7.2

Key feature analysis: dendrogram of stock groupings.

Stock groupings A cluster analysis was undertaken to compare the features in Table 7.8 that were thought most likely to indicate the biological similarities and differences between individual stocks that were least likely to be affected by local factors and were independent of any other feature. The three stock features used were (1) mean smolt age; (2) mean maiden sea age and (3) mean number of spawning years. The results of this analysis are shown in Fig. 7.2.

Discussion Stock descriptions for the 16 rivers were obtained using a single source of material for each river for the same time frame; scale readings were obtained by the same worker and the results were produced in a standard format. These constants have reduced many of the uncertainties associated with earlier studies (Solomon, 1994; Harris, 1995) and provided results that are now more directly comparable on a like-for-like basis than was possible hitherto. However, three criteria must be met before each stock description can be accepted as an accurate representation of the qualitative structure and quantitative composition of the total run of sea trout into any river: (1) the entire run of fish entering the river over any year should be sampled; (2) each stock component should be equally vulnerable to capture and (3) the fish caught should be sampled at random with no selective bias in terms of fish size. The large sample obtained from the fixed trapping station in the tideway of the River Dee fulfilled the first two criteria and, as far as was practicable and cost effective, broadly achieved the third. All stock components were equally liable to capture. The trapping programme operated regularly throughout each month of the year. All fish entering the trap were sampled at random by experienced fishery workers. The spacing between the screens

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101

in the trap was such that 90% of all fish less than 35 cm in length were retained for sampling (Davidson, pers. comm.). It is therefore probable that the stock description for the River Dee is unprecedented (at least for England and Wales) in providing an accurate representation of both the qualitative structure and the quantitative composition of the annual runs of sea trout into that river. The accuracy of the stock descriptions for the 15 rivers where anglers collected the samples from their individual catches is less certain and more variable because of the extent to which these criteria might have been fulfilled on individual rivers. An important source of sampling bias will occur if different age groups of fish enter the river in significant numbers after the end of the angling season. Such fish would be unavailable for capture and sampling by the rod fishery. In broad terms, the timing and duration of the angling season coincide with the pattern of the adult runs into most rivers in north-west England, Wales and south-west England. However, there is evidence that a significant proportion of sea trout entering the rivers of north-east England do so in November and December, after the end of the rod-fishing season in late October (Champion in Le Cren, 1985; Solomon, 1995). As no sample could be obtained from these late-running fish in the Coquet and Wear, the qualitative stock descriptions for these two rivers should be viewed with some initial caution. Solomon (1995) drew attention to the general lack of good data on the rates of exploitation on sea trout stocks by rod-and-line fishing. Shields et al. (2006) have since provided detailed information on total exploitation rates for five rivers and differential exploitation rates on sea trout above or below 1 lb weight (0.45 kg) from two rivers over a 14-year period. However, the results are contradictory in that the average rod exploitation rate (all methods) was positively correlated with stock size on two rivers but negatively correlated in two other rivers, and the level of exploitation was higher on smaller fish in one river but higher for larger fish in another river. Notwithstanding this confusion, there is as yet no published information to judge (1) whether some stock components are more vulnerable to capture by angling than others; (2) whether the different methods of angling (i.e. fly, spin and bait fishing) selectively exploit different stock components and (3) whether the often very different fishing rules and regulations determining where, when and how anglers may fish within different sections of a river affect the relative rates of exploitation on different stock components for that river. It is therefore impossible to state whether samples obtained from the rod-and-line fishery on any river provide a representative sample of the structure and composition of the actual stock that is potentially available for capture during the fishing season. The adoption of catch-and-release by the angling community as a voluntary code of conduct to conserve adequate spawning stocks has increased in recent years to the point where some 50% of all sea trout taken by rod-and-line fishing in England and Wales are now returned alive to the water immediately after capture (Anon., 2003). All anglers engaged in the sampling programme were clearly asked to ensure that their total catch on any occasion was sampled at random and that any selective sampling bias in terms of fish size was avoided. A significant number of anglers expressed reluctance to increase the risks to survival of released fish because of the damage and increased handling stress caused by taking scale

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Sea Trout

samples and measuring length and/or weight. As those sea trout most likely to be released are the smallest fish caught, it is likely that the relative proportions of .0SW whitling are underestimated in the stock descriptions. Notwithstanding these caveats, the stock descriptions obtained from the 15 rivers sampled by the rod fishery represent a considerable improvement in the reliability and accuracy of the database when compared with previous studies. They now provide a reasonably robust characterisation of each stock in qualitative terms and a pragmatic description of each stock in semi-qualitative terms. It will be essential to monitor any changes in the fishery rules and regulations on each river during the period between any initial survey and its replication on the same river in subsequent years to allow valid judgements about the significance of any temporal changes in the stock structure. The analysis of key features (Table 7.8) for each of the 16 stocks suggests the occurrence of at least three different geographical groups of sea trout in England and Wales based on similarities and differences in their smolt age, maiden sea age and spawning frequency (Fig. 7.2). These groups cover (1) north-east England; (2) southwest England and (3) Wales and north-west England. This broadly corresponds to a more subjective and wider appraisal based on earlier scale-reading studies and supplementary information on run-timing and growth rates that indicated that the sea trout stocks of England and Wales could be grouped into four categories based on combinations of their longevity (long versus short living) and feeding conditions in the sea (fast versus slow growing). The sea trout of the rivers in north-east England (including the adjacent River Tweed) are characterised by stocks that contain very few .0SW whitling, which rarely survive to spawn more than once, run later in the year than most other stocks and attain a very large size by rapid growth in the sea over their short lifespan. In contrast, the sea trout stocks of south-west England are characterised by stocks that live longer, contain higher proportions of older smolts, .0SW whitling and fish that have spawned more than once, and grow more slowly in the sea and enter fresh water earlier in the season. The large and amorphous group of sea trout in Wales and north-west England was generally intermediate between these two extremes and exhibited a wide range of variability in most key features. They generally lived longer and spawned more frequently than the fish of north-east England and attained a large size because of their greater longevity and reasonably rapid rate of growth in the sea between multiple spawning visits to fresh water. The somewhat curious position of the Taw (south-west England) and Border Esk (northwest England) within the third group of 11 rivers around the west coast of England and Wales requires comment. While the Taw is grouped alongside the Tywi (South Wales), both rivers flow into the Bristol Channel and have estuaries that are geographically close. The characteristics of sea trout in rivers along the north coast of Devon are different from those of sea trout in south Devon and Cornwall. The close similarity of the Taw fish to the longer living and faster growing sea trout of the Tywi may reflect similar marine feeding conditions and a common ancestry. The grouping of the Border Esk as remote from its neighbouring rivers in north-west England may be a reflection of the intensive commercial fishing pressure

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103

in its near-coastal waters and estuary. The Border Esk exhibited an appreciably lower mean spawning age than the three other rivers in the north-west of England (Table 7.8), and this may reflect the impact of the commercial fishery on the survival and abundance of repeat spawning fish. Nall (1930) was sceptical about attempts by Day (1887) and Regan (1911) to describe different ‘races’ of sea trout in the British Isles solely on differences in their morphology, anatomy and assumed migratory behaviour. However, he was able to draw on greater knowledge about their life history from his pioneer scale-reading investigations to propose that British sea trout were divided into two different forms (designated ‘east-coast’ and ‘west-coast’ types) based on their stock characteristics. While this study broadly confirms that view, it is probable that this broad classification contains further additional groups and sub-groups. In the absence of parallel information about the genetic composition of individual stocks of sea trout in England and Wales, it is not known whether the observed variability in the structure of individual stocks has an underlying genetic basis or whether the observed differences among regional stocks are merely a manifestation of differences in their local marine and freshwater environments and in how and how much they are exploited in those environments. However, recent significant advances in our understanding of the genetic composition of different populations of migratory and non-migratory forms of Salmo trutta (Laikre, 1999; Fergusson, 2006) suggest that at least some of the differences may have a genetic basis linked to the postglacial recolonisation of the rivers in England and Wales by sea trout from one or more of four different evolutionary lineages (Fergusson, 2006). Most of the investigations to date on stock structure have concentrated on the larger, more important and valuable fisheries. Further studies are now required to extend the scope of the database to cover the rivers of southern England and include adequate representation from the many other minor rivers that collectively represent a significant part of the total resource in England and Wales. The stocks of many of these minor rivers frequently appear to have sea trout that differ in such features as run timing from the stocks of the larger rivers in their vicinity, which may reflect an important expression of the overall diversity exhibited within the sea trout/brown trout complex. The sea trout of southern England are of particular interest as they may form a further distinct group with characteristics that are different from or intermediate between those stocks in north-east and south-west England. Rivers from this region were excluded from this investigation because it was thought that an adequately sized sample could not be obtained from the rod-and-line fisheries. Stock descriptions of the type produced by this study have a range of different management applications. First, they provide a snapshot of the structure and composition of each stock at a particular point in time. Their main value, and the original reason for this work, is that they provide a permanent historical baseline of information against which the results of replicate studies can be compared to determine the nature and extent of any changes that might have occurred over the intervening period. There are various reasons why managers might wish

104

Sea Trout

to interrogate stock descriptions of this type: • • • •

•

to undertake a periodic health check as part of a routine monitoring programme to determine the status and well-being of any stock; to determine the impact of changes in management practice intended to maintain, improve and develop a fishery; to investigate the substance of any allegations about a decline in the quality of a fishery by anglers, netsmen or fishery owners; to monitor the impact of any developments within a catchment that may be detrimental to the quality of the fishery (e.g. estuary barrage construction, hydropower generation, water abstraction schemes); to study long-term trends in stock composition and abundance.

The ability of any stock of sea trout to withstand and recover rapidly from any adverse factors in its freshwater and marine environments will depend initially upon its basic structure and composition. Sea trout stock structures are generally more robust and resilient than those of salmon because sea trout exhibit a less risk-averse life history in the pattern of divided smolt migration to the sea (1–4-year classes) and adult return to the river to spawn for the first time (1–3-year classes) and because of the often high incidence of repeat spawning in some stocks. The potential significance of this extended pattern of divided smolt migration and adult return is that it reduces the impact on future stock abundance of deleterious factors affecting survival in any 1 year because a proportion of the stock would remain unaffected, either in fresh water or in the sea, to cushion the stock from collapse and expedite its rate of recovery. Consequently, a stock that was ‘robust’ would contain a wide spread of smolt and maiden age groups and a large number of categories of previously spawned fish so that no single smolt age group or maiden sea-age group or year class was totally dominant. In contrast, a ‘fragile’ stock would be one where all fish from any spawning year class migrated to sea at the same smolt age, returned to spawn for the first time at the same sea age and rarely survived to spawn more than once. The River Dee is an example of a robust stock (Table 7.6). It contains 17 different categories of fish derived from all three maiden sea-age groups. There are five different categories of previous spawners in each maiden group, of which 41% had spawned at least once and 6.6% at least twice. The maiden whitling component represented 47.5% of the sample. By contrast, the River Dwyfor is an example of a fragile stock (Table 7.7). It contains only six categories of fish derived from two maiden sea-age groups. There are only three categories of previous spawners, of which 6.6% had spawned at least once and 0.8% at least twice, .1SW maiden fish were uncommon and the entire stock was dominated by .0SW maiden fish, at 81.4% of the sample. The robust structure of the sea trout stock in the River Dee may reflect the low rates of exploitation recorded from the declared catches by the rod and net fisheries and, therefore, the greater rate of escapement of .1SW and .2SW maidens and previous spawners. The fragile nature of the sea trout stock structure on the Dwyfor is a cause for concern. The fact

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105

that this stock is almost exclusively dominated by 2-year-old smolts (Table 7.3) derived from a single spawning year class that migrated to sea and returned to fresh water to spawn in the same year, rarely surviving to spawn a second time, suggests that it is seriously at risk of collapse if adverse conditions affecting the survival of the smolts or .0SW whitling occur at any stage over this short life history. Until quite recently the traditional management of sea trout stocks in England and Wales was very largely driven by the numbers of fish caught in the recreational and commercial fisheries. However, much greater importance is now attached to managing both the quantitative and qualitative features of individual stocks (Harris, 2006). In practice, the broad aims of sea trout management should be to increase its strength in both ‘breadth’ (defined as the number of maiden sea trout groups represented) and ‘depth’ (defined as the number of categories of previous spawners within each maiden sea-age group). However, the wide variability in stock composition revealed by the 16 rivers in this study and the possibility that they represent at least three heterogeneous groups that may be genetically distinct suggests that a ‘one-size-fits-all’ approach to the management of the resource in England and Wales is inappropriate.

References Allan, I.R.H. & Ritter, J.A. (1977). Salmon terminology. Part 2. A terminology list for migratory trout (Salmo trutta L.). Journal du Conseil International pour l’Exploration de la Mer, 37(3), 293–99. Anon. (2003). Salmonid and Freshwater Fisheries Statistics for England & Wales, 2002. Environment Agency, Bristol, 28 pp. Anon. (2005). Statistical Bulletin. Scottish Salmon and Sea Trout Catches, 2004. Fisheries Series No. Fish/2005/1. Davidson, I., Cove, R.J. & Milner, N.J. (1996). Dee Stock Assessment Programme. Annual Report 1994, Environment Agency, Bristol, 51 pp. Day, F. (1887). British and Irish Salmonidae. Williams & Norgate, London, 298 pp. Elliot, J.M. & Chambers, S. (1996). A Guide to the Interpretation of Sea Trout Scales. National Rivers Authority, Bristol, ISBN 1 873160 29 1. R&D report 22, 54 pp. Evans, D.M., Mee, D.M. & Clarke, D.R.K. (1995). Mesh selection in sea trout, Salmo trutta L., Seine net fishery. Fisheries Management and Ecology, 2, 103–11. Gargan, P.G., Tully, O. & Poole, W.R. (2003). The relationship between sea lice infestations, sea lice production and sea trout survival in Ireland, 1992–2001. In: Salmon at the Edge (Mills, D., Ed.). Proceedings of the Sixth International Atlantic Salmon Symposium, Edinburgh, UK. Blackwell Science Ltd, Oxford, pp. 119–35. Harris, G.S. (1995). The Design of a Sea Trout Stock Description Sampling Programme. National Rivers Authority, Bristol, R&D Project 559, R&D Note 418, 94 pp. Harris, G.S. (2000). Sea Trout Stock Descriptions: The Structure and Composition of Sea Trout Stocks from 16 Rivers in England & Wales. Environment Agency, Bristol. R&D Technical Report W224, 93 pp. Harris, G.S. (2006). A review of the statutory regulations to conserve sea trout stocks in England & Wales. In: Sea Trout: Biology, Conservation and Management (Harris, G.S. & Milner, N.J., Eds). Proceedings of the Ist International Sea Trout Symposium, July 2004, Cardiff, Wales. Blackwell Publishing, Oxford, pp. 441–56. Laikre, I. (Ed.) (1999). Conservation and Genetic Management of Brown Trout (Salmo trutta) in Europe. Report of the concerted action on identification, management and exploitation of genetic resources in the brown trout (Salmo trutta). (‘Trout Concert’: Eu Fair CT97-3882), 91 pp. Le Cren, E.D. (1985). The Biology of Sea Trout. Synopsis of a Symposium at Plas Menai, 24–26th October 1984. Atlantic Salmon Trust Ltd, Pitlochry, 42 pp. Nall, G.H. (1930). The Life of the Sea Trout: Especially in Scottish Waters. Seeley, Service & Co., London, 335 pp. Regan, C.T. (1911). The Freshwater Fisheries of the British Isles. Methuen & Co., London, 267 pp. Shearer, W.M. (1992). Atlantic Salmon Scale Reading Guidelines. International Council for the Exploration of the Sea, Cooperative Research Report No. 188, 446 pp.

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Shield, B.A., Aprahamian, M.W., Bayliss, B.D., Davidson, I., Elsmere, P. & Evans, R. (2006). Sea trout (Salmo trutta L.) exploitation of five rivers in England and Wales. In: Sea Trout: Biology, Conservation and Management (Harris, G.S. & Milner, N.J., Eds). Proceedings of the Ist International Sea Trout Symposium, July 2004, Cardiff, Wales, UK. Blackwell Publishing, Oxford, pp. 417–33. Solomon, D.J. (1994). Sea trout investigations – phase 1. National Rivers Authority, R&D Note 318, Bristol, 104 + 62 pp. Solomon, D.J. (1995). Sea trout stocks in England and Wales. National Rivers Authority, R&D Report 25, Bristol, 102 pp. Went, A.E.J. (1962). Irish sea trout: a review of the investigations to date. Scientific Proceedings of the Royal Dublin Society, Series A, 10, 265–96.

Chapter 8

The Rod and Net Sea Trout Fisheries of England and Wales R. Evans and V. Greest National Fisheries Technical Team, Environment Agency, Cambria House, Cardiff, CF24 0TP, UK

Abstract: Socially and economically important sea trout (Salmo trutta L.) fisheries exist in many of the rivers and coastal areas of England and Wales. Licensed fishermen are required by law to submit a full and accurate catch return to the Environment Agency at the end of each fishing season. Declared annual rod and net catches during the period investigated (1978–2003) ranged from 14 742 to 55 863 and 27 159 to 97 206, respectively. Since 1978, rod catches have increased significantly (P < 0.05) on 29% of the main river fisheries (n = 67), whilst significant declines have been recorded on 21% of these rivers. Catch and release rates in the rod fisheries have increased from 35% in 1994 to 55% in 2003. Differences in mean monthly catches and weights recorded in the fisheries highlight the differences in sea trout life-history strategies around the country. Rod and net catches were not synchronous between 1978 and 2003 (F = 1.82; P = 0.074). Rod catches generally remained stable throughout the period investigated. In contrast, net catches have declined steadily since the late 1970s, partly in response to a decrease in the number of net licences issued (from 1060 in 1978 to 417 in 2003). Keywords: Sea trout, rod fishing, net fishing, catches, trends, regional variation, conservation limits.

Introduction The rivers and coastal areas of England and Wales support many sea trout (Salmo trutta L.) rod and net fisheries, for which the Environment Agency collects data on the rod and net catches via licence holders’ catch returns (Environment Agency, 2003). In 2003, there were 110 rod and 38 net fisheries for which sea trout catches were reported, although numbers were small in the Thames rod fishery (1 kg) spawners in the coastal rivers, natural sea trout populations have been weak for almost 50 years (Kaukoranta et al., 2000), and they are now only found in three river systems: the Tornionjoki, the Lestijoki and the Isojoki (see Fig. 10.1). In addition, regular reproduction was generally found in two rivers and three brooks, but this was based on a mixed stock or dependent on supportive stocking. Electrofishing surveys in the other rivers revealed that they had lost their natural populations of sea trout. The disappearance of these populations has happened gradually since the nineteenth century by damming, dredging, pollution and the silting of rivers or by various combinations of these (Ikonen, 1984). The Tornionjoki River is over 500 km long and is a border river between Finland and Sweden. The water quality in the river has been assessed as good. Sea trout mainly spawn in several tributaries of the main stem. These streams have a total of over 250 ha of rapids that are suitable nursery areas for sea trout. Electrofishing carried out in the 1980s revealed the highest parr densities in the tributaries Äkäsjoki and Pakajoki. Regulation of fishing, restoration of dredged rapids and stocking with hatchery-reared parr and smolts

Fig. 10.1 The Baltic Sea showing the existing and most important potential sea trout rivers on the Finnish coast of the northern (ICES subdivision 31) and southern (30) Gulf of Bothnia. Existing rivers: (1) Tornionjoki; (2) Kangosjoki; (3) Pakajoki; (4) Äkäsjoki; (5) Naamijoki; (6) Lestijoki and (7) Isojoki. Potential rivers: (1) Kiiminkijoki and (2) Merikarvianjoki.

Status of Sea Trout in the Gulf of Bothnia

131

Table 10.1 Mean density of sea trout parr 0+ and greater than 0+ (individuals per 100 m−2 ) in the electrofishing sites in the Äkäsjoki (a tributary of the Tornionjoki River) and Lestijoki rivers (1990–2003) and in the Isojoki River (1993–2003). The density of parr greater than 0+ includes both wild and reared parr. Year

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003

Lestijokia

Äkäsjoki

Isojoki

0+

>0+

0+

>0+

0+

>0+

5.5 3.4 1.1 1.7 4.6 0 0 0.7 0.8 4.8 2.1b 6.8b 4.9b 15.4b

2.2 2.6 9.1 11.0 16.2 13.8 10.2 14.8 8.0 13.6 23.0b 11.9b 20.6b 17.0b

0.1 0.2 0.4 1.1 0.1 0 35 12 14 16 18 20 35 Width (m) Fig. 11.5 The occurrence of salmon as a percentage of the total salmonid (salmon + trout) fry (summer 0+) in streams of three NEAC countries.

and catchment areas ranging between 930 and 1793 km2 . The correction factor would be smaller for smaller rivers, which typically have smaller total catches of both species and smaller sea trout, leading to lower sea trout egg deposition. Relative abundance of juveniles A limitation of using rod catch data is that, because catch returns are normally based on whole rivers, it gives no information on the distribution or relative abundance of the two species within catchments. Notwithstanding uncertainties about the true relationship between catch and escapement or egg deposition, the simple assumption of uniform distribution around catchments, in proportion to catches, is certainly flawed in most cases. No systematic surveys of spawning distribution of the two species were found for any catchment. Examination of within-river spatial patterns was therefore based on the abundance of juveniles, derived from electro-fishing surveys, usually in late summer (July–September). Three data sets, for Sweden, England and Wales together and Scotland demonstrated the same result that the proportions of the two species varied systematically with stream width (Fig. 11.5). Trout were dominant (>50% of total juvenile salmonids) in streams narrower than 6 m in all data sets. In order to translate this result in terms of total catchment salmonid production, it was necessary to know what proportion of nursery areas lie within different channel width categories. The starting hypothesis was that stream widths vary predictably around catchments (Ferguson, 1981), such that narrow, low-order streams contribute most to total catchment stream length whereas most wetted area is contributed by higher order, wider channels. It follows that in smaller streams having higher proportions of low-order channels

148

Sea Trout 100

Percentage of area at width Ireland > Scotland > Norway. It should be noted that sea trout also occur in

Sea Trout in European Salmon Rivers

149

100

Cumulative % area

80

60

40

20

0 0

5

10

15

20

25

30

35

40

Width (m) Fig. 11.7 The relationship between cumulative proportion of total stream area and stream width, in 39 English and Welsh streams (total area = 9269 ha).

other countries and regions, where salmon are less abundant (see ICES, 1994). In some of these, sea trout are found at very high abundance. For example, large sea trout (mean weight 2.25 kg) are abundant in the Normandy rivers of France, giving egg depositions up to 1300 per 100 m2 (Euzenat et al., 2006). Iceland, Finland, Poland, Denmark and northern Spain also have significant sea trout stocks (ICES, 1994), but were not included in the SALMODEL analysis because of the limited information on or the absence of coexisting significant salmon stocks. Relative abundance of both species, based on rod catches, increased with catchment size, but sea trout were increasingly numerically dominant in smaller catchments and this pattern of adult abundance fitted qualitatively with observed patterns of juvenile abundance. The latter were characterised by increasing dominance of trout as channel size (width) decreased below 6 m. It was shown that such smaller channels (e.g. width 0.05) in annual smolt numbers, but since 1991 there has been a significant reduction in smolt output (Mann–Whitney U; P < 0.005). The age composition of the smolt run was similar in 1958–60 and 1980–84 and averaged 68% 2+ and 32% 3+ years (Table 19.4). No samples were taken between

Features of Burrishoole Trout Population

289

Table 19.2 Stock composition derived from length measurements of rod-caught (L. Feeagh 1986) and upstream migrants through the traps in Burrishoole, 1985, 1987 and 1990–2003. Year

n

1985 1986a 1987 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003

Percentage sea age

n/a n/a 920 210 370 211 207 248 235 262 271 191 382 166 129 170 114

0+

1+

2+

3+

50.0 56.0 56.0 82.9 71.6 60.2 79.7 62.9 59.6 64.9 64.2 68.1 77.2 60.8 53.5 74.1 80.7

33.0 39.0 33.0 10.5 27.8 32.7 15.9 32.7 37.4 28.2 29.5 21.5 19.1 33.7 39.5 19.4 17.5

15.0 5.0 11.0 5.7 0.5 7.1 2.9 4.4 3.0 5.3 5.5 8.9 3.1 4.8 4.7 5.3 0.9

2.4 0.0 0.5 1.0 0.0 0.0 1.4 0.0 0.0 1.5 0.7 1.6 0.5 0.6 2.3 1.2 0.9

a L. Feeagh rod catch sample. 1985–86 data from Mills et al., 1990, 1987 data from Ann. Rep. SRTI (1987).

% Return as finnock 35.00

% Return

30.00 25.00 20.00 15.00 10.00 5.00 2003

2000

1997

1994

1991

1988

1985

1982

1979

1976

1973

1970

0.00

Year

Fig. 19.6

Annual percentage return of smolts returning to the Burrishoole traps as finnock.

1984 and 1990. The age composition of smolts in 1990 showed a slight increase in the number of 3-year-old smolts on the 1980–84 average; but a significant change (χ 2 = 175.7; P < 0.0001) in the proportions of ages was found in 1991, with 43.2% 2+, 49.4% 3+ and 7.4% 4+ year-old smolts (Poole et al., 1996). Sampling in 1992 showed a continuing, but not significant change, towards the older age groups, which may have been a result of

290

Sea Trout 8000

Smolt number

7000 6000 5000 4000 3000 2000 1000 2003

2000

1997

1994

1991

1988

1985

1982

1979

1976

1973

1970

0

Year Fig. 19.7

Annual numbers of smolts counted migrating downstream, 1971–2003.

Table 19.3 Summary data for number of smolts and juvenile autumn trout counted migrating downstream through the traps. Migration year

Smolt

Autumn trout

Percentage 0+ autumn trout

Total recruitment

1970–74 1975–79 1980–84 1985–89b 1990–94 1995–99 2000–03

4450 (607) 4305 (484) 4038 (820) 3814 (193) 1873 (228) 1361 (171) 840 (153)

2836 (253) 3116 (327) 1907 (228) 1765 (185) 491 (134) 739 (93) 1162 (377)

35.0a 35.0 37.7 33.9 30.9 30.7 46.2

5943 (841) 6373 (530) 5413 (874) 4877 (165) 2149 (286) 1860 (174) 1455 (320)

Total recruitment is the total of smolts and 1+ age autumn trout from the preceding year. Standard errors are given in parentheses. a Autumn trout were not categorised into age class in the traps between 1970 and 1979. An average from 1980 to 2003 was used as an estimate to calculate 1+ recruitment. b No autumn trout count in 1989.

Table 19.4 smolts.

Percentage age composition of Burrishoole sea trout

Year

1958–60 1980–84 1990 1991 1992 1993 1994

Percentage age class 2+

3+

4+

68–70 68.0 60.0 43.2 36.9 54.9 74.6

28–31 32.0 38.7 49.4 53.1 42.5 25.4

1–2 — 1.3 7.4 10.0 2.6 —

n

Source

599 — 75 419 211 195 122

Piggins (1961) Mills et al. (1990) Poole et al. (1996) Poole et al. (1996) Poole et al. (1996) Poole et al. (1996) Poole et al. (1996)

Features of Burrishoole Trout Population

291

the spawning collapse in 1988 and 1989. In 1993 and 1994, the proportions of 2+ and 3+ smolts reverted back to the ratios observed prior to 1990 where up to 70% of the run was 2-year-old smolts. There was a significant downward trend in numbers of unsilvered juvenile trout migrating in autumn over the entire study period (y = −132.7x + 12899.7; r = −0.88, P < 0.0001) (Table 19.3). This contrasts with smolt abundance, which has shown a decline only since 1991. The age composition of the autumn trout ranged from 0+ to 3+ years, the percentage of 0+ trout varied from 16.1% to 60.9% in the period 1982–2003. It is not known if the 0+ age fish are true migrants or if they are displaced downstream as a result of population pressure or, possibly, floods. Whilst 0+ trout are not old enough to become sea trout smolts in the following spring, tagging studies (Mills et al., 1990; Poole et al., 1996) show that the remainder, predominantly 1+ age fish, could contribute to the overall recruitment of smolts in the following year.

Enhancement According to Mills et al. (1990), the majority of reared sea trout released into the Burrishoole River system between 1962 and 1988 were 2+ smolts, and they gave return rates of 0–10%, averaging 4%, compared with means of 22% and 16% for wild smolt returning as finnock in the 1970s and 1980s, respectively (Table 19.5a). Most first time sea-run recaptures in the

Table 19.5a Details of sea trout enhancement programmes from 1964 to 2002, showing the numbers of fish released, recaptured, their age class at recapture and an estimate of possible ova deposition from surviving adults. Year

No. released

No. recaptured

10% estimate rod catch

% 0+

No. 0+

No. older

Total ova

1964 1970 1971 1974 1982 1983 1984 1985 1986

485 500 1 517 1 949 2 844 1 300 2 761 3 527 12 030

5 0 3 3 188 8 235 38 149

4.5 0 2.7 2.7 169.2 7.2 211.5 34.2 134.1

42.5 0 42.5 42.5 34.9 42.5 33.4 42.5 59.2

2 0 1 1 66 3 78 16 88

3 0 2 2 122 5 157 22 61

1 267 1 267 86 803 3 380 110 323 16 054 50 106

1994 1995 1996 1997 1998 1999 2000 2001 2002

976 1 532 3 170 1 950 1 690 465 58 0 0

101 92 103 272 136 64 6 2 0

0 0 0 0 0 0 0 0 0

68.9 44.6 74.8 72.7 90.3 51.6 16.7 0.0 0.0

70 41 77 198 123 33 1 0 0

31 51 26 74 13 31 5 0 0

28 907 37 871 26 815 75 438 24 845 24 033 3 966 1 600 0

2 112

292

Sea Trout

Table 19.5b Number and age of smolts produced from 1+ parr stocked into L. Feeagh along with the percentage return as silver finnock, percentage total return as 0+ age (silver and brown) and total return of trout from stocked progeny between 1993 and 2000. Smolt migration year

Number of parr released

Total no. of autumn trout the previous year

No. of smolt

Total recruitment

% age 1/2/3/4 year olds

% Return as 0+ sea age silver

% Return as 0+ sea age total

Total return of trout all ages

1993 1994 1995 1996 1997 1998 1999 2000

6 463 9 234 23 914 4 705 4 250 1 578 — —

— 64 74 418 453 515 246 48

202 912 1458 2752 1497 1175 219 10

202 976 1532 3170 1950 1690 465 58

100/0/0/0 2/98/0/0 46/54/0/0 5/88/7/0 28/37/35/0 17/65/12/6 0/77/16/7 0/0/80/20

0.5 7.2–7.7 1.3–1.4 2.3–2.7 5.8–7.5 2.0–2.9 2.4–5.0 1.7–10.5

1.0 9.4–10.1 3.4–3.6 3.4–3.9 11.2–14.6 4.0–5.8 6.6–14 1.7–10.5

— 101 92 103 272 136 64 6

angling catch in L. Furnace and in the upstream traps were made as finnock within nine months of release. Though these fish were the progeny of sea trout, a large proportion of recaptures (e.g. 64% in 1984) had not migrated to sea, but had adopted a brown trout-like existence in L. Furnace and the estuary. Between 1994 and 2000, a total of 8225 marked spring smolts migrated seaward through the traps (Table 19.5b). This represented a mean smolting rate from released parr to 2+ and 3+ smolt of 16.4%. As a total of 8702 wild smolt also migrated through the traps during the same period, this programme effectively doubled the smolt output from the catchment. Similar to the wild fish, a downstream migration of marked trout was also recorded in the autumn. These were predominantly immature fish up to 3+ age, although some older maturing fish were also recorded. The total numbers recorded have been included in Table 19.5 and, when added to the smolt run in the following year, give an estimate of total recruitment downstream. From these releases, a total of 324 reared trout, or 3.9% of the smolts, returned as silvered finnock, compared with 9% for wild smolt, and a further 249 as unsilvered trout, giving a total return of 7.0% of the smolts, compared with 16% for their wild counterparts. The corresponding return rates for the total recruitment were 3.2% and 5.7% respectively. A total of 774 adult trout counted through the traps between 1994 and 2000 originated from the released parr.

Stock and recruitment Table 19.6 gives the main parameters used in the construction of the stock and recruitment relationship, including spawning escapement and percentage age class of upstream migrating trout, estimated ova deposition and subsequent downstream recruitment as 0+

Table 19.6 Spawning escapement, sea-age class and number of ova deposited along with the subsequent number of recruits as autumn-migrating trout (Aut) and smolt for individual year classes of the Burrishoole sea trout stock, 1971–2003. Usptream migration (stock) Year Spawn % 0+ % 1+ % >1+ Total ova Escape sea age sea age sea age deposited

1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003

1249 1883 2391 2519 3118 3117 1898 1486 2226 1846 1794 1519 1531 1422 1308 1274 905 820 224 249 412 223 236 276 249 265 278 220 431 174 143 183 118

50.0 50.0 50.0 50.0 33.0 44.9 32.7 21.0 26.6 31.0 44.8 48.4 56.5 36.9 46.8 50.7 48.8 42.4 24.6 75.3 62.4 54.1 71.1 56.1 56.9 61.8 65.9 71.3 77.4 60.4 54.8 70.8 79.7

44.0 38.0 38.0 38.0 38.0 38.0 38.0 35.9 38.0 28.5 25.6 26.2 23.3 55.5 46.8 43.4 44.0 50.6 63.8 11.2 37.1 36.0 22.5 38.4 40.6 30.6 27.6 21.8 18.7 34.1 37.7 20.9 18.6

6.0 12.0 12.0 12.0 29.0 17.1 29.2 43.1 35.4 40.5 29.6 25.4 20.2 7.6 6.4 5.9 7.2 7.0 11.6 13.4 0.5 9.9 6.4 5.5 2.4 7.6 6.5 6.9 3.8 5.5 7.5 8.2 1.7

Downstream migration (recruitment) Est. ova Tot. ova dep. by enhanced

490 891.6 1 267 758 588.8 962 928.1 1 014 229.5 1 267 1 613 761.5 1 363 536.9 985 380.8 894 172.4 1 247 436.6 1 007 884.3 820 925.7 656 584.8 86 803 585 091.4 3 380 658 895.9 110 323 537 135.3 16 054 496 329.5 50 106 362 965.1 355 833.8 119 499.8 68 244.9 132 190.1 84 431.4 67 221.7 99 614.0 28 907 87 584.5 37 871 88 745.1 26 815 86 655.7 75 438 62 657.2 24 845 106 968.9 24 033 58 921.3 3 966 52 999.1 1 600 52 927.7 0 27 533.9 0

492 158.6 758 588.8 962 928.1 1 015 496.5 1 613 761.5 1 363 536.9 985 380.8 894 172.4 1 247 436.6 1 007 884.3 820 925.7 743 387.8 588 471.4 769 218.9 553 189.3 546 435.5 362 965.1 355 833.8 119 499.8 68 244.9 132 190.1 84 431.4 67 221.7 128 520.9 125 455.9 115 559.8 162 093.3 87 502.6 131 001.7 62 887.2 54 599.1 52 927.7 27 533.9

No. 0+ No. 1+ No. 2+ No. 3+ Aut Smolt Smolt & 1+ Tot. Recruit. Aut Aut Smolt Smolt Equivalent Equivalent Equivalent Equivalent

1231 722 886 919 1418 1002 1192 885 799 895 430 1109 374 773 640 331 518 866 236 356 82 124 175 57 114 264 165 325 259 200 1174 476 408

2389 1402 1720 1784 2753 1945 2314 1718 1552 1736 1300 1109 1200 611 1472 1726 949 556 634 655 234 183 306 282 336 513 717 644 358 218 910 976 426

2013 3716 4128 3078 2439 3541 2645 2154 3860 1589 4563 2657 3299 1620 2882 2349 2292 2917 2529 1238 1260 716 946 845 1382 611 664 1144 896 547 186 282 438

948 1749 1943 1449 1148 1666 1244 1013 1816 748 2147 1250 1553 763 1356 1105 1079 1373 1190 825 1260 1220 774 282 439 678 153 464 364 222 345 990 349

2442 2670 3672 3363 3316 2910 2437 2536 2195 1539 2309 985 2245 2366 1280 1074 1500 891 590 265 430 457 393 627 981 809 683 477 1110 2150 902

4226 4105 4785 3658 3970 4608 3736 5813 4209 4062 2977 3987 3427 3665 4107 3354 2498 2480 1490 1228 1284 2060 764 1128 1508 1118 892 1175 632

5946 5889 7538 5603 6284 6326 5288 7550 5509 5171 4177 4598 4899 5391 5056 3910 3132 3135 1724 1411 1590 2342 1100 1641 2225 1762 1250 1393 1542

6668 6775 8457 7021 7286 7518 6173 8349 6404 5601 5286 4972 5672 6031 5387 4428 3998 3371 2080 1493 1714 2517 1157 1755 2489 1927 1575 1652 1742

294

Sea Trout

and 1+ age juvenile trout and 2+ and 3+ smolt. The following text box indicates the sources of the data or the basis on which estimates were made.

Sources of data used in Table 19.6. Spawning escapement from trap and rod fishery records, summarised in Table 19.1. No attempt was made to quantify natural mortality. % sea age: 1971–88 from Mills et al. (1990). 1989–2003 from trap records based on lengths, verified by scale reading. Numbers of ova deposited, see Section Materials and methods. Estimated number of ova deposited by enhanced fish. 1971–89 fecundity from Mills et al. (1985), and using estimates of exploitation (10%) and sea age. Information on enhanced fish was incomplete and considered to be overestimates. 1990–2003 similar criteria used for wild fish were applied to returns from enhanced fish, but this was considered to be an overestimate as many fish were trapped migrating downstream before spawning, were immature or may not have spawned effectively. 0+ & 1+ autumn trout aged by length, confirmed by sporadic scale reading; 0+ 20%). Stock–recruitment relationship The stock–recruitment data (Fig. 20.6) were not well matched to either the Ricker or Beverton and Holt models, though their parameter estimates were similar (Table 20.5). The Ricker model was considered to provide the best fit to the data, and gave a spawning stock SM (for maximum recruitment) of 955 fish, equivalent to 2.4 million eggs laid, that is 875 eggs per 100 m2 and a maximum production RM of around 7000 smolts or 2.6 smolts per 100 m2 . At this level, the river survival was 0.30%. The stock required for replacement, SR , was 1550 spawners, laying 3.4 million eggs, whilst the stock level that provided maximum surplus production, SG , was 605 spawners (1.5 million eggs), which is 63% of SM . However, it is apparent that the Bresle sea trout stock shows a high variability without detracting from its stability. Numbers of returning adults were directly proportional to smolt output (Fig. 20.6b, d). The regression between adults and smolts is A = 0.22 S (R2 adjusted: 49%, SE: 448), giving a mean return rate of 22% (ranging 18–26%).

316

Sea Trout Table 20.4

Smolt-to-adult return rates (%).

Downstream years

Smolts estimated N

1983 1984 1985 1986 1987 1992 1993 1994 1996 1997 1998 1999 Mean

Adult numbers

Smolt return rate (%)

0SW

1SW

2SW+ maiden

All adults

1SW only

8083 2212 7318 7295 3790 3960 4574 5815 6836 8091 9402 5655

n.d. 161 88 71 88 55 54 58 79 79 114 177

1370 765 938 1004 1335 883 510 885 1487 1571 2114 1938

53 51 77 95 111 42 95 40 89 106 164 n.d.

44.2 15.1 16.0 40.5 24.7 14.4 16.9 24.2 21.7 25.4

16.9 34.6 12.8 13.8 35.2 22.3 11.1 15.2 21.8 19.4 22.5 34.3

6086

93

1233

84

21.7

24.3

30

40 %

Smolt-to-adult

Egg-to-smolt

n.d.: no data

0.20 0.30

%

0.4

22.3 22.0

0

0

10

20

Fig. 20.5 River and marine survival rates: Grey = annual and mean values; black = values given by Ricker model.

Discussion Simultaneous data on the biological characteristics of sea trout, adult and smolt run sizes and return rates are available for very few rivers. In this respect, the Bresle data set is very valuable, despite some gaps in the time series. The estimates of both smolts and spawners abundance are considered to be reliable, because the trapping was very intensive, trap efficiency was evaluated annually from mark-recapture results versus counts and the

Population Dynamics and Stock–Recruitment

8

4 adults (× 1000)

(b) 5

smolts (× 1000)

(a) 10

6 4

317

3 2 1

2

0

0 0

1

2

3

4

5

0

2

Spawners (× 1000)

(c)

4

6

8

10

smolts (× 1000)

10

smolts (× 1000)

8

6

4

2

0 0

(d)

1

2

3

4

5

Spawners (× 1000) 10

8 RM 6

4

2

0 0

SG SM 1

SR

2 3 Spawners (× 1000)

4

5

Fig. 20.6 Stock and recruitment relationships for Bresle sea trout. (a) Smolts versus spawners data; (b) adults versus smolts data; (c) Ricker (solid line) and Beverton and Holt (dashed line) fitted curves and (d) BRPs; SM = 995, SG = 605, SR = 1550, RM = 7000.

318

Sea Trout Table 20.5 Parameters of Ricker and Beverton & Holt models. R = smolts, Se = eggs (estimated from run size times ‘average spawner’ fecundity, i.e. 2530 eggs per adult fish). Models

Ricker

smolts versus spawners

R = Se

a(1−S/b)

Beverton & Holt R = aSe /(1 + (a/b)Se )

a b R2 adjusted Standard error (SE) Survival s # slope at origin Recruitment (Rmax ) Spawning stock (Smax ) Egg deposition max

2.970 (2.090–3.850) 2 837 (1 873–3 801) 39.63% 2 245 0.79% (0.33–1.89%) 6 900 (2 665–17 050) 955 (897–987) 2 364 000

0.0084 (−0.035–0.052) 7 205 (–597–15 000) 40.65% 1 904 0.84% (…−5.17%) 7 200 ( …−15 000) ∞

correlation between April flow and size run enabled estimates of the numbers of fish when the above methods failed. Smolt identification and therefore the confidence in the estimates of smolt numbers, requires further investigation. There are uncertainties in the association between morphological features and physiological smolt status, as shown for example by gill ATPase activity monitoring before and during the smolt run (Tanguy, 1993), though the large size of Bresle smolts does make selection easier. ‘Resident’ brown trout can contribute up to 12% to the ‘smolt’ run in the Bresle, similar to the 15% rate given by Ombredane et al. (1996) for a tributary of the River Touques (Lower-Normandy). It will be important to determine the true contribution of these fish to the downstream run, because they could affect the estimates of river survival and return rates, though only within the order of the distance of confidence limits on numbers. All the same, the S–R relationship described here do not seem to have to be basically questioned. Although both Ricker and Beverton and Holt S/R models give parameter values that are consistent with those for other river systems and stocks (Prévost et al., 1996; Walters, 1996), the variability of recruitment (by factor of 3 for two sets of similar stock sizes) suggests that recruitment is independent of stock. However, there is a moderately strong inverse relationship between stock and river survival. Because of the small numbers of pairs for modelling, their median place in the possible range and the lack of contrast (limited range in egg deposition (Hilborn & Walters, 1992), the S/R relationship cannot be considered robust. Very low spawning sea trout stocks seem improbable in the Bresle, given the present stock size level. In this context, the case of salmon has not to be neglected. Census data show that the smolt and adult salmon are, on average, ×3 and ×13 lower than the sea trout runs (Euzenat & Fournel, unpublished data) and sea trout thus has the advantage of numbers over salmon. Any joint stock–recruitment relationship has yet to be investigated on the Bresle, but in such small chalk streams, it may be that interspecific interactions are more important than in larger rivers (see Milner et al., 2006) and are underestimated.

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Considering that there are few observations on the dynamics of sea trout and the great similarity of Bresle sea trout with grilse salmon, on the basis of their age structure, and long distance marine migration, it seems reasonable to compare their life-history straits and demographic characteristics. At 1285 eggs per 100 m2 of accessible habitat, the average sea trout egg deposition is near to that for grilse salmon, for example, 1100 eggs in the Nivelle (Dumas & Prouzet, 2003), 1400 eggs in the Oir (Prévost et al., 1996). Furthermore the estimated egg density that maximises sea trout smolt production in the Bresle fits the range values for salmon: between 700 and 1000 eggs per 100 m2 unit (Gardiner & Shackley, 1991; Kennedy & Crozier, 1993). The smolt output of the Bresle is low, at 2.3 smolts per 100 m2 , similar to that of salmon observed on other monitored French rivers such as the Oir, Scorff and Nivelle (Baglinière & Champigneulle, 1986; Prévost et al., 1996; Dumas & Prouzet, 2003), but much lower than values in northern salmon rivers (Kennedy & Crozier, 1993; Chadwick, 1996). Adding the estimates of salmon yield (Euzenat & Fournel, unpublished data) the whole river capacity for migratory salmonids is nearer to three smolts per 100 m2 (range: 1.6–4.5). Considering the very bad river survival, and in comparison with the model results (SG and SM being 55% and 30% lower respectively), the sea trout egg deposition seems high and wastefully high. Egg-to-smolt survival of sea trout was indeed very low at 0.2% and below the mean rate observed for grilse salmon in the Bresle itself (around 0.6% on average, Euzenat & Fournel, unpublished data) and in other French and foreign rivers: 0.45% for the Nivelle (Dumas & Prouzet, 2003), 0.36% for the Oir (Prévost et al., 1996) and 0.36–0.62% for the Burrishoole in Ireland (Anon., 1998). It is less than the usual values of 1–5% for salmon populations in the world (Bley & Moring, 1998; Hutchings & Jones, 1998). It is not known why survival in freshwater was so low. The relatively high egg depositions, the always low survival rate, the inverse relation between some stocks–recruits pair data, and the inverse relation between stocks and survival rate suggest that compensatory densitydependence may be high on the Bresle. But random environmental factors, such as flow regimes, as indicated by the inverse relation between survival and the rainfall during fry emergence, may also be important. However, Elliott (1985a, b, c) did not find this adverse effect, and the impact of environmental factors on hatching success and fry to parr stage populations need to be investigated. The cause is evidently a mix of biological and physical regulation mechanisms, which are probably difficult to distinguish. The low survival rate of juvenile sea trout appears to be compensated by high growth rate in the Bresle, as shown by the large 1+ smolt and the low MSA. Fahy (1978) recorded 6 year classes of smolts from the British Isles, with mean lengths ranging from 14 to 25 cm and MSA greater than 2. This good growth in the Bresle probably leads to better sea survival, as shown by the high return rate and the highest returns given by runs of a high component of 2+ smolts. Similar observations have been reported for Atlantic salmon (Peterson, 1971; Larsson, 1977; Chadwick, 1986), steelhead (Ward & Slaney, 1988) and coho salmon (Bilton et al., 1982). The low freshwater production is partly offset by the high return rates to the river (see also Fournel et al., 1990). The return rate of 1+ fish, is high at 24.3%, similar to the rate recorded for 1+ sea trout in the Irish River Burrishoole (21.2%) before the collapse in the

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late 1980s (Poole et al., 1996; Anon., 1998), or in the Vardnes river in Norway, 25% (Berg & Jonsson, 1990), and far higher than the common value for grilse in Bresle itself: 6.5% (Euzenat & Fournel, unpublished data) and other salmon rivers of the north-east Atlantic area: 6.2%, 7.2%, 8.4%, 9.6% and 12.6% in the Imsa (Norway), Ellidaar (Iceland), Corrib (Ireland), North Esk (Scotland) and Nivelle (France), respectively (Dumas & Prouzet, 2003; Anon., 2004). Although less drastic than the regulation within the river, regulation at sea is noticeable. A factor ×3 in the range of return rate leads to a spawning stock size variation equal to 60–150% of SM , which has a delayed effect on the regulation in the river and therefore on population dynamics. On the whole, it seems that the Bresle environment, through the limited spawning habitat and the probable adverse effect of flow and water quality during the early life, acts against the development of the high reproductive potential of sea trout and buffers its variation. This leads to an apparent inter-annual balance as seen in the adult data series and in the proximity between the average adult run and the replacement stock SR , around 1550 fish. The balance is achieved at the expense of eggs, because half of the annual egg depositions seems to be ‘in excess’. The biological reference points (BRPs) of the Bresle model, SM and SG indicate that 600–950 fish would be harvestable, that being in agreement with the current catch situation. Mean annual catch of sea trout in the Bresle is 835 fish, in a ratio 5 : 1 between net and rod fisheries. This catch is 38% of the home waters returns and is equivalent to 60% of the escapement (Fournel et al., 1999). Considering the apparent high level of the current stock in relation to the observed S/R relationship, some additional fish could be caught without reducing the stock’s sustainability: for example, by doubling the current rod catch which exploits only 10% of the run. The model must be used with caution, but it does suggest how to use the sea trout stock’s productivity better. Though a lot has been learnt about Bresle sea trout in this 20-year study, it must be continued in order to understand better and to explain the past as much as the future. Monitoring the runs has to be continued to make up for the interruptions in the time series and to strengthen the models. In particular, it will be instructive to follow the population’s response to the increase in juvenile habitat availability expected to result from the current programme of fish passage restoration. The high mortality in fresh water also needs to be investigated and comparisons with other studies made, as new data become available. In both cases, the question of anadromy versus residency is important, because the possible shifts in resident/anadromous habits in the population may throw light on the balance between environment and genetic factors in controlling migration. It will be informative to study the possible interactions between the healthy sea trout population and the low stock of salmon, the Bresle offering a rare opportunity to do that. Finally, the migrations, behaviour and survival of smolts and post-smolts in the sea are poorly understood, but are an essential part of understanding stock dynamics. This will aid management decisions on exploitation control and help to predict the consequence of environmental change in sea and in fresh water, given the links between freshwater growth/maturation balance and subsequent marine performance. International collaborative effort through marking experiments will be needed for this.

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Clearly, the long-term study on Bresle sea-trout population belongs to the very rare ‘club’ of index rivers where such studies are carried out, with the Burrishoole, North Esk, Black Brows Beck and Dee in Ireland, Scotland, England and Wales respectively (Piggins, 1976; Pratten & Shearer, 1983; Elliott, 1994; Poole et al., 1996; Davidson et al., 2000). Effort has to be made to protect and prolong these studies so that essential background data for the interpretation of short-term fluctuations and trends are thus provided and made available.

Acknowledgements We thank the Head of CSP, at national and regional levels, for their administrative and financial support during this long-term study, the Anglers Federation of the Department of Somme, owner of the secondary trap to let us to use this facility, the CSP agents and other local people for their assistance in the field. Thanks also to Alain Bellido (senior lecturer, University of Rennes), Sébastien Delmotte (PhD student, University of Toulouse), Michel Larinier (hydraulic engineer R&D, CSP Toulouse) who provided advice in data processing.

References Anon. (1998). Annual report of the Salmon Research Agency of Ireland/Marine Institute, Furnace, Newport, No. 44, p. 66. Anon. (2004). Annual report of the Working Group on North Atlantic salmon. ICES, 2003, p. 99. Bagliniere, J.L. & Champigneulle, A. (1986). Population estimates of juvenile Atlantic salmon, Salmo salar, as indices of smolt production in R. Scorff, Brittany. Journal of Fish Biology, 29, 467–82. Bagliniere, J.-L. & Maisse, G. (1991). La Truite, Biologie et Écologie. INRA Edition, Paris, Serie Hydrobiologie et Aquaculture, 303 pp. Berg, O.K. & Jonsson, B. (1990). Growth and survival rates of the anadromous trout, Salmo trutta, from the Vardnes River, northern Norway. Environmental Biology of Fishes, 29(2), 145–54. Beverton, R.J.H. & Holt, S.J. (1957). On the dynamics of exploited fish populations. Fishery Investigations, London, Series 2, Vol. 19, pp. 1–553. Bilton, H.T., Alderdice, D.F. & Schnute, J.T. (1982). Influence of time and size at release of juvenile coho salmon (Onchorynchus kisutch) on returns at maturity. Canadian Journal of Fisheries and Aquatic Science, 39, 426–47. Bley, P. & Moring, J.R. (1988). Freshwater and ocean survival of Atlantic salmon and steelhead: a synopsis. US Fish and Wildlife Service, Biological report, Vol. 88(9), 22 p. Chadwick, E.M.P. (1986). Relation between Atlantic salmon smolts and adults in Canadian rivers. In: Atlantic Salmon: Planning for the Future (Mills, D. & Piggins, D., Eds). Proceedings of the Third International Atlantic salmon Symposium, 21–23 October 1986, Biarritz, France, pp. 301–324. Chadwick, E.M.P. (1996). Transportability of stock and recruitment relationships: theoretical constraints and practical recommendations. (Prévost, E. & Chaput, G., Eds). International Workshop on Spawning Targets for the Assessment and Management of Atlantic Salmon Stocks, Pont-Scorff. Crozier, W.W., Potter, E.C.E., Prevost, E., Schon, P.-J. & O’Maoileidigh, N. (Eds) (2003). A coordinated approach towards the development of a scientific basis for management of wild Atlantic salmon in the North East Atlantic (SALMODEL). Queen’s University of Belfast, Belfast, p. 431. Davidson, I.C., Wyatt, R.T. & Milner, N.J. (2000). Assessment of the effectiveness of byelaws in controlling salmon exploitation on the river Dee. In: Management and Ecology of River Fisheries (Cowx, I.G., Ed.). Fishing News Books, Blackwell Scientific Publications, Oxford, pp. 373–87. Dumas, J. & Proujet, P. (2003). Variability of demographic parameters and population dynamics of Atlantic salmon (Salmo salar L.) in a southwest French river. Journal of Marine Science, 60, 356–70. Elliott, J.M. (1985a). The choice of a stock–recruitment model for migratory trout, Salmo trutta, in an English Lake District stream. Archiv für Hydrobiologie, 104(1), 145–68.

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Elliott, J.M. (1985b). Population regulation for different life-stages of migratory trout, Salmo trutta, in a Lake District stream, 1966–83. Journal of Animal Ecology, 54(1), 617–38. Elliott, J.M. (1985c). Population dynamics of migratory trout, Salmo trutta, in a Lake District stream, 1966–83, and their implications for fisheries management. Journal of Fish Biology, 27 (Suppl. A), 35–43. Elliott, J.M. (1994). Quantitative Ecology and the Brown Trout. Oxford Series in Ecology and Evolution, Oxford University Press, Oxford, 286 pp. Elliott, J.M. (2001). The relative role of density in the stock–recruitment relationship of salmonids. In: Stock, Recruitment and Reference Points, Assessment and Management of Atlantic salmon (Prévost, E. & Chaput, G., Eds). INRA edn., Paris, pp. 25–66. Elliott, J.M. & Elliot, J.A. (2006). A 35-year study of stock-recruitment relationships in a small population of sea trout: assumptions, implications and limitations for predicting targets. In: Sea Trout: Biology, Conservation and Management (Harris, G.S. & Milner, N.J., Eds). Proceedings of the Ist International Sea Trout Symposium, July 2004, Cardiff, Wales, UK. Blackwell Publishing, Oxford, pp. 257–78. Elliott, J.M., Crisp, D.T., Mann, R.H.K. et al. (1992). Sea trout literature review and bibliography. Fisheries Technical Report, 3. NRA, 141 p. Euzenat, G., Fournel, F. & Fagard, J.L. (1991). La truite de mer en Normandie/Picardie. In: La Truite, Biologie et Écologie (Bagliniere, J.L. & Maisse, G., Eds). Vol. 303, Serie Hydrobiologie et Aquaculture, INRA, Paris, pp. 183–213. Fahy, E. (1978). Variation in some biological characteristics of British sea trout, Salmo trutta L. Journal of Fish Biology, 13, 123–38. Fournel, F., Euzenat, G. & Fagard, J.L. (1987). Rivières à truites de mer et à saumons de Haute-Normandie. Réalités et perspectives. Le cas de la Bresle. In: Restauration des Rivières à Saumons (Thibault, M. & Billard, R., Eds). Hydrobiologie et aquaculture, INRA, Paris, pp. 315–25. Fournel, F., Euzenat, G. & Fagard, J.L. (1990). Evaluation des taux de recapture et de retour de la truite de mer sur le bassin de la Bresle (Haute-Normandie/Picardie). Bulletin Français de la Pêche et de la Pisciculture, 318, 102–14. Fournel, F., Euzenat, G. & Fagard, J.L. (1999). La truite de mer et le saumon dans le Nord-Ouest. Stock, captures et échappement. Le point sur les programmes de restauration. Réunion du GRISAM, St Valéry-s/Somme, 10 p. Gardiner, R. & Shackley, P. (1991). Stock and recruitment and inversely density-dependent growth of salmon, Salmo salar L., in a Scottish stream. Journal of Fish Biology, 38, 691–6. Hilborn, R. & Walters, C.J. (1992). Quantitative Fisheries Stock Assessment: Choice, Dynamics and Uncertainty. Chapman & Hall, New York, 570 pp. Hutchings, J.A. & Jones, M.E.B. (1998). Life history, variation in growth rate thresholds for maturity in Atlantic salmon, Salmo salar. Canadian Journal of Fisheries and Aquatic Sciences, 55 (Suppl. 1), 22–47. Kennedy, G.J.A. & Crozier, W.W. (1993). Juvenile Atlantic salmon, Salmo salar, production and prediction. In: Production of Juvenile Atlantic Salmon, Salmo salar, in Natural Waters (Gibson, R.J. & Cutting, R.E., Eds). Canadian Special Publication on Fisheries and Aquatic Sciences, 118, pp. 178–87. Larsson, P.O. (1977). Size dependent mortality in salmon smolts plantings. ICES CM 1977/M, 43, p. 8. Milner, N.J., Karlsson, L., Degerman, E., Jholander, A., MacLean, J.C. & Hansen, L.-P. (2006). Sea trout (Salmo trutta L.) in Atlantic salmon (Salmo salar L.) rivers in Scandinavia and Europe. In: Sea Trout: Biology, Conservation and Management (Harris, G.S. & Milner, N.J., Eds). Proceedings of Ist International Sea Trout Symposium, July 2004, Cardiff, Wales, UK. Blackwell Publishing, Oxford, pp. 139–53. Ombredane, D., Siegler, L., Bagliniere, J.L. & Prunet, P. (1996). Migration et smoltification des juvéniles de truite (Salmo trutta) dans deux cours d’eau de Basse-Normandie. Cybium, 20 (Suppl. 3), 27–42. Peterson, H. (1971). Smolt rearing methods, equipment and techniques used successfully in Sweden. In: Atlantic Salmon Workshop (Carter, W.M., Ed.). Manchester, New Hampshire. 25–26 March 1971, pp. 32–62. International Atlantic Salmon Foundation, p. 88. Piggins, D.J. (1976). Stock production, survival rates and life-history of sea trout of the Burrishoole river system. Salm. Res. Trust Irel. Inc., Ann. Report XX, pp. 45–57. Poole, W.R., Whelan, K.F., Dillane, M.G., Cooke, D.J. & Matthews, M. (1996). The performance of sea trout, Salmo trutta L., stocks from the Burrishoole system western Ireland, 1970–1994. Fisheries Management and Ecology, 3, 73–92. Poole, W.R., Dillane, M., DeEyto, E., Rogan, G., McGinnity, P. & Whelan, K. (2006). Characteristics of the Burrishoole sea trout population: census, marine survival, enhancement and stock recruitment, 1971–2003. In: Sea Trout: Biology, Conservation and Management (Harris, G.S. & Milner, N.J., Eds). Proceedings of

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the Ist International Sea Trout Symposium, July 2004, Cardiff, Wales, UK. Blackwell Publishing, Oxford, pp. 279–306. Pratten, D.J. & Shearer, W.M. (1983). Sea trout of the North Esk. Fisheries and Management, 14, 49–65. Prévost, E. & Chaput, G. (1996). Spawning Targets for the Assessment and Management of Atlantic Salmon Smolts. Determination, Precision, Transportability and Risks. International workshop, Pont-Scorff, France, 24–28 June, 1996. Prévost, E. & Chaput, G. (2001). Stock, Recruitment and Reference Points, Assessment and Management of Atlantic Salmon. INRA, Paris, 223 pp. Prévost, E., Bagliniere, J.-L., Maisse, G. & Nihouarn, A. (1996). Premiers éléments d’une relation stock– recrutement chez le saumon Atlantique ( Salmo salar) en France. Cybium, 20 (Suppl. 3), 7–26. Ricker, W.E. (1954). Stock and recruitment. Journal of the Fisheries Research Board of Canada, 11, 559–623. Ricker, W.E. (1975). Computation and interpretation of biological statistics of fish populations. Bulletin of the Fisheries Research Board of Canada, 2196. Solomon, D.J. (1995). Sea trout stocks in England and Wales. National Rivers Authority, R&D Report 25, 102 pp. Tanguy, J.M. (1993). La smoltification de la truite de mer (Salmo trutta): caractérisation éco-physiologique des juvéniles en milieu contrôlé et en milieu naturel. Thèse de 3è cycle, ENSA Rennes, 107 pp. Walters, C. (1996). Analysis of stock and recruitment data for deriving spawning targets: models, fitting, precision, diagnostics, pitfalls. In: International Workshop on Spawning Targets for the Assessment and Management of Atlantic Salmon Stocks. Determination, Precision, Transportability and Risks. (Prévost, E. & Chaput, G., Eds). Report of the Atlantic Salmon Spawning Target Workshop, Pont-Scorff, France, 24–28 June, 1996. Ward, B.R. & Slaney, P.A. (1988). Life history and smolt-to-adult survival of Keogh steelhead trout (Salmo gairdneri) and the relationship to smolt size. Canandian Journal of Fisheries and Aquatic Sciences, 45, 1110–22.

Section 4

MANAGING STOCKS AND FISHERIES

Chapter 21

The Spawning Habitat Requirements of Sea Trout: A Multi-Scale Approach A.M. Walker1 and B.D. Bayliss2 1 Centre

for Environment, Fisheries and Aquaculture Science, Lowestoft Laboratory, Pakefield Road, Lowestoft, Suffolk, NR33 0HT, UK 2 Environment Agency, Ghyll Mount, Gillan Way, Penrith 40 Business Park, Penrith, Cumbria, CA11 1BP, UK Abstract: The aim of this chapter is to further our understanding of the spawning habitat requirements of sea trout, Salmo trutta L., in order to facilitate the assessment of spawning habitat availability throughout catchments. Habitat data collected in the immediate vicinity of sea trout redds are presented from surveys in rivers of the southern, south-western and north-western regions of England and of central Wales, conducted over the period 1999–2003. In addition, the distribution of sea trout spawning throughout a catchment is assessed in relation to physical habitat characteristics, with data extracted from a GIS database and from paper maps. Keywords: GIS, redd, Salmo trutta L., sea trout, spawning habitat.

Introduction An understanding of the spawning habitat requirements of fish is vital for the effective and sustainable conservation of stocks and the management of associated fisheries. This allows us to evaluate the potential impacts of habitat change/destruction, establish management priorities and provide baseline data for the calculation of biological reference points (BRPs) (e.g. conservation limits [CLs]). A large number of physical habitat characteristics associated with spawning sites (redds) chosen by various salmonid species have been examined, and the most common variables are grouped into three classes as: (1) hydraulic (depth, velocity); (2) spatial (redd dimensions, stream width, distance from the bank) and (3) substratum (particle size distribution, percentage of fine materials and various related indices) (see Bardonnet & Bagliniere, 2000). In comparison with other species, however, there have been very few studies on sea trout spawning habitats. Crisp & Carling (1989) collected microhabitat data from redds constructed by Atlantic salmon (Salmo salar L.) and by sea and brown trout (Salmo trutta L.) from spate rivers and chalk-streams in England and Wales, but reported analyses using the combined data set. Elsewhere, the spawning habitat characteristics of sea trout have been reported from Norway (Heggberget et al., 1988) and France (Ingendahl et al., 1995). At present, therefore, our knowledge of the spawning habitat requirements of sea trout is insufficient to include information on the availability and extent of suitable spawning 327

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habitat in models used to develop and set BRPs as management tools. Such knowledge is of particular importance to terrestrial and aquatic habitat management plans for the conservation of sea trout spawning habitats. The aim of this research was to investigate methods by which we can further both our knowledge of sea trout spawning habitat and develop tools to facilitate the assessment of spawning habitat availability and utilisation in relation to conservation and management. Here, we first report the physical microhabitat characteristics, that is, in the immediate vicinity, of sea trout redds surveyed from rivers in England and Wales. The description of microhabitats associated with redds underpins the assessment of available spawning habitat, that it facilitates the identification of suitable habitats. However, it is difficult to apply microhabitat-based knowledge across a catchment, except where the catchment has been comprehensively mapped, and analytical methods are required which allow the availability of spawning habitat to be quantified using survey techniques applied at a much greater geographical scale. Such models have been developed to study the distributions of fish species and the abundances of salmonid juvenile populations at catchment (e.g. Beechie et al., 1994; Porter et al., 2000) and even regional scales (e.g. Kruse & Hubert, 1997; Argent et al., 2003) in the USA, but few studies have focused on the habitats used by spawning salmonids (Montgomery et al., 1999; Dauble & Geist, 2000). Therefore, second, we assessed the distribution of spawning sea trout throughout a catchment with respect to Geographic Information System (GIS) and other map-derived habitat features in order to explore the suitability of this method for the prediction of catchment-wide spawning habitat availability, and thus provide a method by which to prioritise areas for protection or restoration.

Methodology Microhabitat

Study sites Sea trout spawning habitats were investigated in five spate river catchments in England and Wales (Fig. 21.1, Table 21.1). The Rivers Blackwater and Beaulieu drain areas of the New Forest; although the Blackwater is a tributary of the chalk-stream River Test. The River Fowey drains central and southern Bodmin Moor and enters the sea from the south Cornish coast. The River Melindwr is an upper tributary of the Welsh River Rheidol. The Cumbrian River Kent is described in greater detail in the Catchment Scale Section.

Survey methods Reaches where sea trout were known to spawn were identified with the assistance of local Environment Agency staff and surveyed during the spawning seasons (typically October–January) between November 1999 and December 2003. Redds were surveyed within 24 h of the fish having completed spawning and then departed the redd site, and care was taken not to disturb spawning fish. Most sea trout spawned during the hours of darkness

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R.Kent

R.Melindwr (Rheidol)

R.Test R.Blackwater R.Beaulieu R.Fowey

Fig. 21.1 England and Wales with the locations of the five rivers in which sea trout spawning habitats were investigated.

Table 21.1 Location and physical catchment characteristics of rivers surveyed for spawning sea trout, the study period and numbers of redds sampled and water chemistry measured at the time redds were sampled.

Region Catchment area (km2 ) Mean daily flow (m3 /s) Sampling period No. redds sampled Water temperature (◦ C) pH Conductivity (μS)

Blackwater

Beaulieu

Fowey

Melindwr

Kent

New Forest 105 0.85 Dec 1999 5 na na 282–380

New Forest na na Dec 2000 7 10–11 5.1–6.1 146–153

Cornwall 171 5.18 Nov 2000–Jan 2001 11 7–8 5.7–6.1 42–82

Mid-Wales 182 9.35 Nov 2001 11 9–11 6.1–6.6 63–67

Cumbria 209 8.94 Dec 2003 15 7 5.2–6.9 62–155

Note that catchment area and mean daily flow statistics (1965–2001) are for the entire catchment, and for the River Rheidol of which the Melindwr is a tributary (EA data).

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or during spates when water clarity was poor. However, the lengths of 11 females observed spawning in the Rivers Fowey and Melindwr were visually estimated with reference to objects in or near the redd (total length range = 35–60 cm). The length and width of both the ‘pot’ and the ‘tail’ of redds were measured (cm) and total area (m2 ) calculated as if pot and tail were two ellipses (Ottaway et al., 1981). Depth (cm) and water velocity were measured over undisturbed substrate immediately upstream of the pot. Water velocity (m/s, averaged over 60 s) was measured at 0.6 of depth using a Valeport ‘Braystoke’ BFM002 current flow meter. For the Rivers Melindwr and Kent, channel width and distance from mid-pot to the nearer-bank were measured to the nearest centimetre (cm), and cover was assessed in terms of (1) the depth of undercut bank (if any); (2) for the River Kent only, height above water surface of the bank nearer the redd (both to nearest cm) and (3) the proportion of sky directly above the redd that was occluded by vegetation (visual estimate). Redd substrate size was measured using two methods during the study. For the Rivers Blackwater, Beaulieu, Fowey and Melindwr, a substrate sample was collected from the side of the tail using a square fronted scoop with side 15 cm and depth 25 cm. This sample was then sorted through a stack of sieves with mesh diameters of 0.045, 0.063, 0.125, 0.25, 0.5, 1.0, 2.0, 4.0, 8.0, 16.0, 31.5 and 63.0 mm. The particles retained by each sieve were weighed and the cumulative percentage weight was plotted against particle size. A number of statistics can be used to characterise substrate composition (see Kondolf & Wolman, 1993), but here we report the median particle size. Based on the requirements for a comparative study of microhabitat selection between sea trout and Atlantic salmon (A.M. Walker, in preparation), the survey protocol was modified for the River Kent in order to facilitate sampling from a greater number of redds within the time restraints imposed by river conditions. A graduated (1 cm) quadrat, of side 10 cm, was placed on the surface of the redd tail and a digital video image recorded (after Geist et al., 2000). Still frames were subsequently captured from the video footage and substrate particles were measured within a 100 cm2 area (long-axis diameter and surface area) using image analysis software (Optimus). The particle size distribution for each sample was binned into six levels (longest axis 150 mm; after Geist et al., 2000) and a dominant size class derived according to percentage surface area per size bin. Particles that lay partially within the frame were measured and the area within the frame assigned to the appropriate bin.

Catchment scale Study site The River Kent catchment (∼209 km2 ) comprises the main River Kent (35 km in length and sourced at an elevation of 750 m) and two major tributaries, the River Sprint (19 km) and the River Mint (20 km), with numerous other smaller tributaries. Average annual rainfall (1968–2001) over the catchment was 1914 mm. The mean daily discharge measured near the estuary during the same period was 8.94 m3 /s, with Q10 and Q95 flows

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of 21.08 and 1.123 m3 /s, respectively (Environment Agency data). The River Sprint flows through the glacial valley of Long Sleddale, running south-east and largely parallel to the River Kent. Unlike the Kent valley, which widens and narrows several times over its length, the Sprint valley is relatively uniform in width and has an even gradient. The River Mint’s headwaters initially flow in a south-easterly direction before turning south-west towards Kendal and its confluence with the main River Kent. Land use in the upper reaches of the main stem and throughout the major tributaries is primarily agricultural with livestock grazing rough pasture. Land use further down the River Kent around Burneside becomes more mixed with increased urban characteristics affecting the nature of the river corridor. Much of the River Kent through Kendal has been modified as part of the River Kent Flood Prevention Scheme that was undertaken by North West Water between 1972 and 1977. The works involved channel widening and re-grading approximately 7 km of river, including lowering the level of the riverbed, bridge modifications and river wall construction. Downstream from Kendal, the river travels south through mainly agricultural land (improved pasture) with some steeply banked wooded areas and also passes through numerous deep limestone troughs before flowing into Morecambe Bay. Sea trout and salmon populations Densities of juvenile trout and salmon are probably close to carrying capacity across the majority of the Kent catchment (based on regular juvenile monitoring surveys by the Environment Agency). The average annual run of sea trout past the resistivity counter at Sedgwick Weir, towards the mouth of the river, is 3957 fish for the period 1995–2004 (Anon., 2005). The average reported sea trout rod catch during the same period was 394 fish. The corresponding values for salmon are 2478 and 436 fish, respectively. Spawning distribution and physical habitat data The Environment Agency (north-west region) has historical records of the numbers and distribution of sea trout redds constructed throughout the River Kent catchment for a number of years. For the purposes of data recording, the entire catchment was split into reaches, typically bounded by landmarks (e.g. bridges, fences, weirs and overhead cables). Reach lengths varied between 0.24 and 4.46 km. Surveys were conducted by the same experienced EA fisheries staff member who walked the riverbank during the hours of daylight over a representative period principally towards the end of the spawning season. The numbers of sea trout redds observed within each reach were recorded on Ordnance Survey (OS) 1 : 50 000 maps. At the commencement of the study, complete records were available for 5 years (seasons 1992–93, 1993–94, 1994–95, 1996–97 and 1998–99). Although the reach boundaries were consistent between years, data were not recorded for each reach every year, and adjoining reaches were combined in some years. Therefore, data were first extracted from the 1993–94 dataset that included the maximum number of reaches (48), and data from other years were added to this spreadsheet, with reaches combined where necessary.

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Table 21.2 GIS-derived catchment scale habitat variables analysed and their definitions (after Dawson et al., 2002). Variable code

Definition

Altitude

Altitude of site (m) from the mean of altitude at the nearest points 500 m upstream and 500 m downstream of the sample point Gradient at site (m/km) from the difference in altitude between sites approximately 500 m upstream and downstream along the course of the river, divided by their actual distance apart Total length of watercourses upstream of the site (km) Catchment area above the site (km2 ) Distance from the site by the shortest route to the furthest point upstream (km) Distance from the site (km) by the shortest route to the defined tidal limit Stream order according to Strahler (1957)

Gradient Upstream Catchment Source Tide Order

The 500 m interval is a feature of the CEH database and was chosen as the database was intended to underpin the River Habitat Survey method (Raven et al., 1997) for which 500 m is the survey unit.

The physical habitat characteristics associated with the lowermost boundary of each reach were derived either from GIS or map-based sources (Table 21.2). GIS data were extracted from the CEH River Network database (Dawson et al., 2002). Reach channel length (RL) and straight-line length (SL) were estimated from 1 : 10 000 scale OS maps and the sinuosity index was calculated as the quotient of SL and RL (Fukushima, 2001). Statistical analyses Analyses were conducted separately for two subsets of the data: either redds present/absent or, where redds were present, the density of redds per reach (log transformed). Habitat parameters were classed as continuous variables except for Order, which was treated as a category with six levels (1–6). The importance of each habitat variable in explaining the observed distribution of redds was assessed by a logistic (redds present/absent) or least squares (density of redds) regression model, but controlling for (1) the effects of sample year to account for differences in the numbers of redds observed at particular reaches between years and (2) for reach length in the presence/absence analysis alone. Multiple regression models were developed using a forward selection method and parameters retained if they improved the model fit. Statistical significance was assessed at α = 0.05 and all tests were conducted with JMP 5.1.1.

Results Redd microhabitat A total of 49 redds were sampled during the study (Table 21.1). The range and central tendencies of redd area, depth, water velocity and substrate size for each river, and for all redds combined, are presented in Table 21.3. Analysis of variances (ANOVA) indicated significant differences between rivers for redd area (d.f. = 43, F = 2.86, P = 0.04), depth (d.f. = 42, F = 31.06, P < 0.0001), water velocity (d.f. = 42, F = 3.77, P = 0.02) and

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Table 21.3 Summary of spatial and physical habitat characteristics for sea trout redds from five rivers in England and Wales, and the data from all rivers combined. Blackwater Total redd area n 3 1.63–3.35 Range (m2 ) Mean ± 2.43 ± 0.87a,b SD Depth n 0 Range (cm) Mean ± SD Velocity n 0 Range (m · s−1 ) Mean ± SD Substrate n 5 Range 13.8–27.5 (mm) Mean ± 22.1 ± 5.7a,b SD Dominant class Range na (mm) Median na (mm)

Beaulieu

Fowey

Melindwr

Kent

Pooled

4 2.01–3.58

11 0.41–3.40

11 0.91–3.01

15 0.5–2.95

44 0.41–3.58

2.88 ± 0.65a

1.96 ± 0.95a,b

1.5 ± 0.58b

1.64 ± 0.84a,b

1.85 ± 0.87

6 22–41

11 26–51

11 8–31

15 12–23

43 8–51

32.5 ± 7.6a

37.9 ± 8.9a

17.0 ± 6.3b

16.0 ± 3.7b

24.2 ± 11.6

6 0.18–0.53

11 0.40–0.77

11 0.28–0.77

15 0.32–0.83

43 0.18–0.83

0.39 ± 0.12b

0.60 ± 0.11a,b

0.51 ± 0.17a,b

0.46 ± 0.14a,b

0.50 ± 0.15

7 11.6–27.5

11 3.7–39.6

9 18.4–42.7

15 na

32 3.7–42.7

18.6 ± 6.4b

20.6 ± 9.4a,b

30.0 ± 8.7a,b

na

23.0 ± 9.0

na

na

na

6–25 to 75–150

na

na

na

na

25–50

na

Means sharing the same letter code are not significantly different at α = 0.05 (Tukey’s HSD test).

substrate (d.f. = 31, F = 3.22, P = 0.04). Post hoc tests split the rivers into two groups for depth, but the distribution was less clear for the other parameters (Table 21.3). As female spawner size was unknown for most redds and microhabitats were not fully surveyed at each spawning reach, it is not possible to determine whether differences in redd microhabitat parameters between rivers were a result of differential habitat selection by spawning fish, or whether the differences were in the habitats available to the fish. Redd tail length was not significantly associated with water velocity (ANOVA: d.f. = 40, F = 0.46, P = 0.50), but was associated with median substrate size, though not significantly so (ANOVA: d.f. = 29, F = 3.78, P = 0.06). Redds were located across the width of the channel (26 redds), distance of mid-pot from the bank as a proportion of channel width ranged from 6% to 50% (mid-point), but tended to be constructed towards the edges of the channel (channel position: mean ± SD = 28 ± 12%); even for those two sea trout that spawned in a relatively wide channel of 16–18 m (Fig. 21.2). An undercut bank was associated with three of 26 surveyed redds

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Mid-pot to bank (m)

8

6

4

2

0

0

2

4

6

8

10

12

14

16

18

20

Channel width (m) Fig. 21.2 Channel position of sea trout redds from the Rivers Melindwr (open diamonds) and Kent (filled diamonds) in relation to channel width. Mid-channel is represented by the dashed line.

(range 22–32 cm deep). The median nearer-bank height was 90 cm (range 60–170 cm). Overhead cover was present above 8 of 15 redds surveyed on the River Kent, with a mean estimated sky occlusion of 53% (range 10–75%). Catchment scale

Spawning distribution A total of 3156 sea trout redds were recorded during the five spawning seasons from the 80.32 km of watercourse, partitioned into 42–48 reaches dependent on survey year. Sea trout redds were never found in two reaches: Kentmere Reservoir (0.46 km) and Sadgill (1.46 km), being the uppermost reaches of the Rivers Kent and Sprint, respectively. Overall, sea trout utilised 97.4% of the surveyed catchment for spawning. However, redds were not found in a number of other reaches in one or more years (range 23–75% of reaches).

Relationship between spawning distribution and habitat features When tested individually, all habitat variables except Gradient and Sinuosity had a significant influence on the probability of predicting redd presence or absence (Table 21.4). When habitat variables were combined, the most statistically significant fit (d.f. = 7, χ 2 = 85.270, P < 0.001, r 2 = 0.278) was yielded by the model including distance from Source and Gradient (Table 21.5). The probability of sea trout spawning in a reach was associated with (1) increasing altitude and distance from tide; (2) decreasing channel length upstream; (3) catchment area and distance from source and (4) third-order

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Table 21.4 Stepwise model selection results from logistic regression of physical habitat data explaining the distribution of sea trout and salmon redds throughout the River Kent catchment, Cumbria: response variable is redds ‘present’ or ‘absent’. Term

Estimate

SE

χ2

P

Altitude Slope Upstream Catchment Source Order (1) Order (2) Order (3) Order (4) Order (5) Tide Sinuosity

0.013 −0.006 −0.007 −0.0002 −0.103 0.576 0.559 0.847 0.117 0.383 0.097 −0.351

0.003 0.019 0.001 10

10

>10

Lune

60 Percentage

5 6 7 Size category (lb)

40 20 0 10% for 10 rivers, >20% for 5 rivers, >30% for 3 rivers and >40% for 1 river. For all 16 rivers, the entire whitling component (as a proportion of all seaage groups and categories of previously spawned fish encountered) represented: 20% for 14 rivers, >40% for 11 rivers, >60% for 6 rivers and >80% for 5 rivers. Information on the mean length of whitling also showed a wide range in the sizes of the fish returning to different rivers of between 271 and 355 mm for the 31 rivers reviewed by Solomon (1995) and typically from 309 to 356 mm for those studied by Harris (2000). There are no minimum size limits currently in force to protect the whitling component of sea trout stocks other than those fixed to protect juvenile parr and smolts (Table 31.3). At best, these provide token protection for only the very smallest fish within the annual whitling run. This is not seen as a problem in relation to the net fishery as the statutory regulations on the size of mesh that may be used in the construction of nets are such that maiden whitling sea trout and the smaller sizes of repeat spawning whitling on their second return to fresh water (as 1SM fish) are not generally vulnerable to capture because they are theoretically able to pass through the mesh (Evans et al., 1995). However, the lack of any minimum size limit is very relevant to the extent of exploitation of whitling in the rod fishery because they can be caught in very large numbers. It is apparent that the whitling component makes a significant contribution to the numerical abundance and structure of most sea trout stocks in England and Wales and it may be of crucial importance to spawning success in terms of its contribution to total egg deposition in many rivers: although this has yet to be modelled. In addition, whitling may also be very important in maximising the use of the available wetted area within a catchment for spawning and juvenile trout production as they are better able to penetrate the smaller tributaries and they spawn in gravel of a smaller size than that utilised by larger fish.

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Multi-sea winter fish Those sea trout that return to fresh water to spawn for the first time as maiden fish after spending at least two winters feeding and growing in the sea (i.e. as MSW fish) are normally larger than fish in the younger maiden sea-age groups. Most sea trout return to fresh water to spawn for the first time either as 0SW or 1SW maiden fish, but the occurrence of variable proportions of older, MSW maiden fish has been observed. Solomon (1995) recorded that while the incidence of 3SW fish was rare and generally restricted to only the occasional fish in eight rivers in England and Wales, 2SW fish were more common and occurred in 23 rivers. The greatest proportion was in the Tweed (47%), but was less than 16% for all the remaining rivers. Harris (2000) reviewed the historical data on differences in the temporal stock composition of MSW fish for seven rivers where scale-reading studies had been undertaken over different periods of time. Only the Dyfi and Tywi had been studied previously on three separate occasions. In the Dyfi the proportion of 2SW sea trout had declined progressively from 11.1% in 1933 to 3.3% in 1970 and then to 1.2% in 2000. In the Tywi the decline was from 7.2% in 1970 to 5.6% in 1994 and then to 1.8% in 2000. While these results may not be strictly comparable because of selective sampling bias (Harris, 1995), they nevertheless indicate a significant general decline in the incidence of MSW sea trout in these rivers. Robust regulations have recently been applied throughout England and Wales to the conservation of the MSW component of salmon stocks to maintain genetic diversity and to reinstate the early runs of salmon derived from this stock component that are important in increasing the duration of the salmon fishing season. However, no similar measures are currently in force to conserve the MSW component of sea trout stocks; even though their importance in terms of genetic diversity and their greater contribution to spawning success as a consequence of their larger size and fecundity is precisely the same as that of MSW salmon. Previous spawners Unlike Atlantic salmon, which rarely survive to spawn more than once in the British Isles (Mills, 1989), adult sea trout exhibit the potential ability to live longer and to make multiple spawning visits to fresh water – if allowed to do so. The maximum number of spawning marks reliably recorded on the scales of any sea trout in the British Isles to date is x11 (Nall, 1930). Harris (2000) compared the relative proportions of maiden and previously spawned sea trout for 16 rivers and showed that fish which had spawned at least once represented a variable but often very significant proportion of the annual stock. Values for all previous spawners as a proportion of all fish sampled (maidens and previous spawners) ranged from 6.5% to 51.5% and exceeded 20% for nine rivers. A further breakdown of the frequency of spawning within this stock component showed that the maximum number of spawning marks detected on the scales of any fish was: x2 in 16 rivers, x3 in 15 rivers, x4 in 14 rivers, x5 in 8 rivers and x6 in 3 rivers. The proportions of fish that were returning to spawn for at least the third time when captured ranged from 10.0% to 26.1% for all 16 rivers and for those returning to spawn for the fourth time it ranged from 2.5% to 12.7% in 15 rivers.

450

Sea Trout

There are two principal reasons for providing some appropriate measure of protection for the repeat spawning component of any stock of sea trout: 1. On returning to fresh water to spawn again after a period of further feeding and growth in the sea, each female fish will be larger and more fecund than on its previous spawning visit. Consequently, the cumulative contribution to spawning success derived from repeat spawning fish will be disproportionately greater than their numerical abundance within the total spawning population in any year. The largest sea trout recorded from the Dyfi in recent years weighed 10.9 kg (24 lb). It was a female fish that had spawned consecutively on x7 previous occasions (scale formula = 2.2+7SM+). By extrapolation from known data on possible size and fecundity for each year of return for Dyfi sea trout (Harris, 1970), it can be calculated that the cumulative contribution to spawning success over the lifetime of this one fish was roughly 100 000 eggs. This represents the egg deposition equivalent of roughly 130 whitling. 2. Multiple spawning sea trout, by definition, have proven their ability to survive in both the freshwater and marine environments and can be viewed as the ‘fittest’ members within any stock. As such, they may have important genes as the expression of repeat spawning may be a heritable trait that represents an important part of the genetic diversity contained within each stock (Saunders & Bailey, 1980). There are currently no regulations to protect and conserve previously spawned sea trout after their migration to sea as kelts and during the fishing season on their subsequent return to fresh water. Large ‘specimen’ sea trout Most rivers in England and Wales have produced sea trout that are ‘unusual’ or ‘exceptional’ for a particular river system because of their very large size at some time in the past. ‘Large’ is a relative term that may vary widely in different regions of the British Isles. Any sea trout in excess of 2.7 kg (6 lb) weight would be considered ‘large’ by Irish standards, whereas fish in excess of 4.6 kg (10 lb) or even 6.8 kg (15 lb) are not unusual in several rivers throughout much of Wales and in some English regions. Indeed a few rivers, such as the Dyfi and Tywi in Wales, regularly produce very large sea trout. Apart from any other consideration, these specimen sea trout have a very important ‘cachet’ value within the angling community that adds greatly to the attraction and economic value of a fishery. A sea trout may become large by some combination of its longevity and the quality of its feeding in the sea (Harris, 2000). In north-east England sea trout are relatively short-lived and very few survive to spawn more than once or twice. However, they can attain a very large size because of rich feeding and very rapid growth in the sea. In contrast, sea trout in Wales and north-west England appear to experience poorer feeding conditions in the sea but can attain a very large size because they live longer and survive to make more spawning visits to fresh water. All maiden sea-age groups appear to have the potential ability to spawn repeatedly and eventually attain a larger size. Harris (1972) examined scales from 105 ‘specimen’ sea trout in excess of 10 lb from various regions of the British Isles. The proportions that had

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first-returned to fresh water as maiden fish after each year of sea-absence were: 6.6% as 0SW whitling, 60.0% after 1SW, 28.6% after. 2SW and 3.8% after. 3SW. Of these, the largest fish weighed 11.2 kg (24.5 lb), the oldest fish was 11+ years of age and the maximum number of spawning marks was x8. There are currently no statutory regulations to protect very large ‘specimen’ sea trout.

Discussion The development of a long-term strategy for the conservation and sustainable management of our sea trout fisheries will need to address the many unknowns and uncertainties that currently limit our ability to manage our sea trout stocks effectively and efficiently (Harris & Milner, 2006; Milner et al., 2006). This should be viewed as a stepwise process in its evolution and some of the more obvious requirements for better management information relating to the ways in which the fisheries may need to be regulated can be briefly listed as: (1) (2)

(3)

(4)

(5)

(6)

The determination of robust ‘biological reference points’ (BRPs) that define the status and well-being of individual trout stocks (Walker et al., 2006). The patterns of migration and feeding behaviour of adult fish in the sea (as both maiden fish and kelts) and the extent to which the apparent near-coastal feeding behaviour of most sea trout results in the occurrence of mixed-stock fisheries. Reviews of the few studies undertaken in the British Isles (Elliott et al., 1992; Solomon, 1995) suggest a seemingly contradictory array of different behaviours that warrant further investigation. The nature and extent to which sea trout are subject to illegal or inadvertent capture in other fisheries for marine fish species. We have no information other than a passing reference to the illegal landing of sea trout at seven locations by Pawson & Benson (1983). The extent of non-catch fishing mortality on sea trout stocks from damage caused by the mesh size and materials used by commercial fishing gears in estuarial and coastal waters. The only published information for sea trout in England and Wales (Evans et al., 1995; Solomon, 1995) relates to the Seine nets licensed for salmon and sea trout fishing. Solomon (1995) suggests that large numbers of the smaller sea trout that can pass through the mesh may be damaged and we need much more information for other types of net, mesh sizes and materials used in fishing for other species of fish in coastal and estuarine waters. The accuracy, reliability and interpretation of catch records from the rod and net fisheries as true measures of the total catch and rate of exploitation in quantitative and, of equal importance, in qualitative terms. This core topic has recently been reviewed for salmon (Shelton, 2002), and there is a pressing need for an authoritative appraisal of the entire subject with respect to sea trout. The rates of exploitation by rod and net fisheries on adult stocks and the selective nature of such exploitation on different stock components. Solomon (1995) and Shields et al. (2006) provide the only information available on exploitation rates in England and

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Sea Trout Wales. This relates to just eight rivers for the rods and only one river for the nets. It shows such a wide variability (range 0.5–30%) for the rods between different rivers that further studies, covering different fisheries and a longer time series of observations on single fisheries, are clearly indicated.

The history of fisheries management has clearly established the practical merits of taking proactive steps to maintain a healthy fishery before the symptoms of a stock collapse trigger reactive regulatory measures to address those symptoms – as has been necessary over the past decade for many salmon fisheries throughout England and Wales. Although Evans & Greest (2006) have examined the long-term record of rod catches for 67 rivers in England and Wales over the 30-year period between 1974 and 2003 and concluded that the total national rod catch has generally remained stable over the period, they also noted that catches have declined on 31 of these rivers (significantly so on 14 rivers) and it is evident that this decline has been largely offset by an increase in the catch from 19 other rivers (many of which are continuing to recover from the effects of historical pollution). Irrespective of any concerns about the accuracy of the catch data for the rod and net fisheries and attempts to interpret that data into an estimate of stock abundance for any year (Shelton, 2002), it is a matter of fact that we are not yet in any position to judge if our sea trout stocks are healthy and performing at their fullest natural potential. More importantly still, in the absence of any BRPs (Walker et al., 2006), we do not know if the present rate of exploitation by the rod and net fisheries is sustainable in the longer term. Nevertheless, within these unknowns and uncertainties, there are certain basic precautionary measures to conserve and improve existing stocks that can be implemented by the fishing community as a matter of prudence and common sense. These are the introduction of: (1) a lower ‘minimum’ size limit to protect whitling; (2) an upper ‘maximum’ size limit to protect the larger, MSW and repeat spawning sea trout and (3) a catch limit defining the maximum number of sea trout that may be retained in any period of fishing by any one angler. Lower minimum size limit The present minimum size limit introduced to protect juvenile fish and smolts (Table 31.3) does nothing whatsoever to protect the whitling component that returns to fresh water during the same year that it migrated to sea as smolts. For many stocks in England and Wales, the runs of immature whitling should be viewed as the ‘seed-corn’ from which future stocks will be derived to a lesser or greater extent and which should be carefully protected and nurtured during their first return as maiden fish. Thus, the minimum size limit should be increased to a length that affords whitling a significant measure of protection. This would be approximately 36 cm (14 in.) for most rivers in England and Wales (Solomon, 1995; Harris, 2000). On returning to fresh water, sea trout lose their characteristic silver sheen. They become darker and their spotting becomes more obvious as they begin to become sexually mature and adapt their camouflage to their new freshwater environment. In some situations their external appearance can become virtually indistinguishable to that of certain types of brown

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trout found in the same river system. This can lead to enforcement difficulties with size limits and bag limits when sea trout are mistakenly (or intentionally) misidentified by their captors as ‘brown trout’ and killed. This problem would be avoided by the adoption for each river of the same minimum size limit for both the migratory and non-migratory forms of Salmo trutta in those rivers where whitling represent a major part of the total run of adult sea trout.This simple approach has ‘added-value’ as it would also provide important long-term benefits in improving the future quality of the brown trout fishery. Upper maximum size limit Specific measures to conserve MSW and multiple repeat spawning sea trout as discrete and separate components of the stock are impracticable because of the extensive overlap in the range of sizes encountered and the lack of any reliable diagnostic features based on their external appearance. However, the introduction of a maximum size limit above which all fish must be returned alive to the water immediately after capture could provide an important measure of protection for both stock components. There can be no generally acceptable ‘one-size-fits-all’ criterion in this respect and so the actual maximum size limit selected for each river, which could also serve to protect large ‘specimen’ sea trout by default, would need to be carefully defined in relation to the characteristics and structure of each stock. Thus, while the condition factor (K) expressing the length–weight relationship of sea trout can vary within and across stocks and is usually greater for maiden fish than for previous spawners (Nall, 1930), a length of 61 cm (24 in) equates very roughly to 2.7 kg (6 lb) for most Welsh stocks (Solomon, 1995; Harris, 2000). If, for example, this were to be adopted as the maximum size limit on the Dyfi and applied to known data on stock structure for that river (Harris, 1970), it would serve to protect: (1) all MSW maiden fish and all previous spawners within that group; (2) all 1SW group fish on their third return visit to fresh water and (3) all 0SW group fish on their fourth return visit to fresh water. This would then result in the release of roughly 15% of the rod catch to further supplement the spawning population. A similar size limit on the Coquet, where the major stock component consists of 1SW and 2SW maidens that rarely survive to spawn more than once, would protect 16% of the stock and embrace all 2SW fish and all 1SW fish on their second return visit. In contrast however, a maximum size limit of 61 cm would protect only 2.3% and 1.8% of the stock respectively for those rivers with slow growing fish and relatively few 1SW and no MSW fish such as the Tamar and Camel. Here, a lower maximum size limit would be required to protect a greater proportion of 1SW maidens and previous spawners. Catch limits With the notable exception of the nine rivers where a catch limit has already been applied, there are no statutory measures to restrict the total number of fish that may be retained by an individual angler at any time during the fishing season. Every fish caught by lawful means may be retained by its captor regardless of the status and well-being of the fishery. In the absence of any statutory power to restrict the total number of anglers and their total

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combined fishing effort on any river system, this situation is potentially untenable in the absence of any reliable information on the status and well-being of individual stocks of sea trout. It is therefore appropriate that careful consideration should now be given to the introduction of a precautionary catch limit that fixes the maximum number of sea trout that may be retained by any angler in order to restrict the rate of overall exploitation to within biologically ‘safe’ limits. This should be linked to the existing categories of ‘daily’, ‘weekly’ and ‘season’ rod licences issued by the Environment Agency and separate catch limit attached to each period. The actual limits applied on different rivers may vary in practice depending on an initial judgement of the intensity of the angling pressure and the status and well-being of each stock. However, for most fisheries in England and Wales at this time, catch limits fixing the maximum number of fish that may be retained by an individual angler at: (1) 4 fish any 1 day; (2) 10 fish in any 1 week and (3) 30 fish in any 1 fishing season appear to represent a preliminary basis for further discussion at a local level on each river system until the range of catches by individual anglers has been modelled to determine more precisely the actual bag limits necessary to conserve existing stocks and to improve future stocks. Apart from any other practical consideration, it is to be noted that the very existence of a ‘catch limit’ serves as a constant reminder to each angler of the need to conserve stocks for future generations. The adoption of the proposals for upper and lower size limits would create a ‘slot’ defining the range of sizes within which the catch limit would apply. While any one of the three elements outlined here could make a worthwhile contribution to future stock conservation on most rivers, due consideration should be given to their introduction as a basic package of measures that can be adopted and adapted to suit local circumstances. For most rivers in England and Wales where maiden and previously spawned whitling constitute a significant or major part of the annual run of sea trout, priority should be given to the introduction of effective measures to protect whitling in the first instance. It is not possible under the present fisheries legislation in England and Wales to prohibit anglers from selling their catch: and it is inevitable that any proposals to introduce new catch limits and size limits will encounter opposition from certain sections within the angling community. However, the strength of that opposition will be weakened considerably when the respective Governments in England and in Wales act on their declared intention to accept the recommendation in the recent Review of Salmon and Freshwater Fisheries (Anon., 2000) to prohibit the sale of rod-caught fish as this will remove any incentive for anglers to catch and kill the greatest possible number of salmon or sea trout in order to profit financially from their fishing. The existing statutory procedures for making new by-laws are complicated, onerous and protracted. They can also be very costly if, as may be necessary, a ‘Local Public Inquiry’ is required to resolve formal written objections to any new by-law proposals or if, as is also possible, compensation has to be paid to the owner of a fishery for financial loss occasioned by the introduction of any new regulations. Consequently, it is perhaps understandable that the Environment Agency gives careful consideration before promoting new statutory regulations including assessing that there is appropriate scientific evidence of the need to do

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so for reasons of stock conservation. There is therefore cause to see the private owners within each single river catchment become much more proactive in taking direct responsibility for protecting their fisheries by the introduction of effective systems of voluntary rules that avoid the need to impose statutory regulations. It remains to be seen if this can be achieved within the framework of the often fragmented private ownership of freshwater fisheries in England and Wales.

References Anon. (2000). Salmon and Freshwater Fisheries Review. Ministry of Agriculture Fisheries & Food, London, 199 pp. Anon. (2004). Fisheries Statistics 2003. Environment Agency, 28 pp. Anon. (2005a). Statistical Bulletin. Scottish Salmon and Sea Trout Catches, 2004. Fisheries Series No. Fish/2005/1. Anon. (2005b). An annual assessment of salmon stocks in England & Wales 2004. A preliminary assessment prepared for ICES, March 2005. Centre for Environment, Fisheries & Aquaculture Sciences and Environment Agency, 74 pp. Elliott, J.M., Crisp, D.T., Mann, R.H.K. et al. (1992). Sea trout literature review and bibliography. National Rivers Authority. Technical Report No. 3, 141 pp. Environment Agency (2003). National trout & grayling fisheries strategy. Environment Agency, Bristol, 21 pp. Evans, R. & Greest, V. (2006). The rod and net sea trout fisheries of England & Wales. In: Sea Trout: Biology, Conservation & Management (Harris, G.S. & Milner, N.J., Eds). Proceedings of the First International Sea Trout Symposium, July 2004, Cardiff Wales, UK. Blackwell Publishing, Oxford, pp.107–14. Evans, D.M., Mee, D.M. & Clarke, D.R.K. (1995). Mesh selection in a sea trout, Salmo trutta L., commercial Seine net fishery. Fisheries Management & Ecology, 2, 103–11. Gargan, P.G., Tully, O. & Poole, W.R. (2003). The relationship between sea lice infestation, sea lice production and sea trout survival in Ireland, 1992–2001. In: Salmon at the Edge (Mills, D., Ed.). Proceedings of the 6th International Atlantic Salmon Symposium, Edinburgh, UK. July 2002, pp 119–35. Harris, G.S. (1970). Some aspects of the biology of Welsh sea trout. PhD Thesis, University of Liverpool, 263 pp. Harris, G.S. (1972). Some specimen sea trout from Welsh, English & Scottish Waters. Salmon & Trout Magazine, 196, 223–34. Harris, G.S. (1995). The design of a sea trout stock description sampling programme. National Rivers Authority, R&D Note 418, 87 pp. Harris, G.S. (2000). Sea trout stock descriptions: the structure & composition of adult sea trout stocks from 16 rivers in England & Wales. Environment Agency R&D Technical Report W224, 93 pp. Harris, G.S. & Milner, N.J. (2006). Setting the scene: sea trout in England & Wales – a personal perspective. In: Sea Trout: Biology, Conservation & Management (Harris, G.S. & Milner, N.J., Eds). Proceedings of the First International Sea Trout Symposium, Cardiff Wales, July 2004, pp. 1–10. Mills, D.M. (1989). The Ecology & Management of Atlantic Salmon. Chapman & Hall, London, 351 pp. Milner, N.J., Harris, G.S., Gargan, P. et al. (2006). Perspectives on sea trout science and management. In: Sea Trout: Biology, Conservation & Management (Harris, G.S. & Milner, N.J., Eds). Proceedings of the First International Sea Trout Symposium, July 2004, Cardiff Wales, UK. Blackwell Publishing, Oxford, pp. 480–90. Nall, G.H. (1930). The Life of the Sea Trout. London, Seeley Service & Co., 335 pp. Nall, G.H. (1932). Sea Trout on the Solway Rivers. Fisheries Scotland, Salmon Fisheries, No. III, HMSO Edinburgh, 72 pp. National Rivers Authority. (1996). A strategy for the management of salmon in England & Wales. National Rivers Authority, Bristol, 36 pp. Pawson, M.G. & Benford, T.E. (1983). The Coastal Fisheries of England & Wales, Part 1: A review of their status in 1981. MAFF Directorate of Fisheries Research, Internal report No. 9, 54 pp. Saunders, R.L. & Bailey, J.K. (1980). The role of genetics in Atlantic salmon management. In: Atlantic Salmon: Its Future (Went, A.E.J., Ed.). Proceedings of the 2nd International Atlantic Symposium, Edinburgh. Fishing News Books Ltd. Farnham, pp. 182–200.

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Shelton, R. (Ed.) (2002). The Interpretation of Rod and Net Catch Statistics. Proceedings of a Workshop held at the Centre for Environment, Fisheries & Aquaculture Science, Lowestoft, England, 6–7 November 2001. Atlantic Salmon Trust ‘Blue Book’, 107 pp. Shields, B.A., Aprahamian, M.W., Bayliss, B.D., Davidson, I.C., Elsmere, P. & Evans, R. (2006). Sea trout (Salmo trutta L.) exploitation from five rivers in England & Wales. In: Sea Trout: Biology, Conservation & Management (Harris, G.S. & Milner, N.M., Eds). Proceedings of the First International Sea Trout Symposium, July 2004, Cardiff, Wales, UK. Blackwell Publishing, Oxford, pp. 417–33. Solomon, D.J. (1995). Sea trout stocks in England & Wales. National Rivers Authority. R&D Report No. 25, 102 pp. Walker, A.M., Pawson, M.G. & Potter, E.C.E. (2006). Sea trout fisheries management: should we follow the salmon? In: Sea Trout: Biology, Conservation & Management (Harris, G.S. & Milner, N.J., Eds). Proceedings of the First International Sea Trout Symposium, July 2004, Cardiff, Wales, UK. Blackwell Publishing, Oxford, pp. 466–79.

Chapter 32

An Appreciation of the Social and Economic Values of Sea Trout in England and Wales P. O’Reilly1 and G.W. Mawle2 1

Swyn Esgair, Drefach Felindre, Llandysul SA44 5XG, UK Environment Agency, Waterside Drive, Aztec West, Almondsbury, Bristol BS12 4UD, UK 2

Abstract: Most of the economic and social values associated with sea trout are poorly documented and difficult to dissociate from those of salmon. The existence value of sea trout may be significant and the presence of sea trout, especially leaping fish, enhances property values in urban areas. Most of the remaining net fisheries for sea trout have little commercial value and, although there are probably exceptions, most netsmen probably fish for enjoyment as much as for profit. Nationally, the sea trout net catch generates only about £160 000 gross income annually to netsmen. Some traditional net fisheries may have a significant heritage value; for example, the public in Wales is willing to pay £1.5 million to retain a minimum coracle fishery. Rod fisheries for migratory salmonids are worth over £100 million to fishery owners across England and Wales, with sea trout probably now contributing as much to that value as salmon. Expenditure by salmon and sea trout anglers can contribute significantly to local rural economies and constitutes an estimated £8 million annually to the Welsh economy; the greater part of this is probably now attributable to sea trout. All aspects of value can be changed and enhanced through effective management and marketing. A case study on the Teifi suggests that sea trout rod fisheries in Wales could generate around another 100 full-time equivalent jobs in the Principality compared with 1997 levels. Keywords: Sea trout, socio-economic value, angling, net fishing, marketing, community benefits.

Introduction Sea trout benefit society in a range of different ways, their value to the individual depending on personal circumstances and preferences. In managing sea trout stocks and fisheries for the benefit of society, it is important to appreciate how these values are generated and to whom. This chapter summarises what is known about the current status of a range of social and economic values associated with sea trout in England and Wales, but values are not static. Their magnitude can change or be changed, not only with the status of sea trout stocks, and of similar resources such as salmon, but also with the preferences of society (such as anglers’ preference to fish for wild rather than stocked trout, Simpson & Mawle, 2001), the costs of fishing (including travel) and the management and marketing of the associated fisheries. 457

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Existence and associated values Fish are not only valued for themselves, similar to other fauna, but also because they are perceived as indicators of environmental quality (Department of the Environment et al., 1996). Their existence is valued. Salmonids, in particular, are widely recognised as requiring a good quality environment. As sea trout, similar to salmon, are frequently seen leaping at weirs when migrating upstream they are significant indicators of the improving quality of urban rivers (Mawle & Milner, 2003). The better the environment, the more willing people are to live and work in a particular area, thereby generating local economic benefits. In Cardiff, salmon and sea trout have been returning to the River Taff since the 1980s (Mawle et al., 1985). Apart from being a visible demonstration of improved river quality, they have also appeared as cultural symbols. Salmonids form part of a recent municipal sculpture in Cardiff and, more significantly, the emblem of a fish is etched on the windows of the headquarters of the Cardiff Bay Development Corporation, the body responsible for the economic regeneration of the dockland area of the city. Increasing fish populations, including Salmo trutta L., in the Thames have also been used by London Docklands (1996) to indicate improved living conditions and thereby promote property. No estimates have been made for the existence value of sea trout but existence values for salmon can be substantial. In a study commissioned by the Environment Agency, Spurgeon et al. (2001) estimated that people resident in the Thames catchment would be willing to pay £12 million per year to have a breeding population of salmon in the river. However, it would be a mistake to assume that the existence value of salmon and sea trout is only an indicator of environmental quality. For example, it is evident that people derive pleasure, and presumably value, from watching salmon and sea trout. Well-known falls where these fish may be seen leaping are an attraction and visitors’ expenditure can be significant for the local economy. O’Reilly (unpublished) has estimated that during the holiday season, expenditure by coach parties in the vicinity of Cenarth Falls on the River Teifi is around £50 000 per year.

Fishery values Perhaps more obviously, sea trout have value because they can be fished for, usually in conjunction with salmon, providing income from the sale of the catch or recreation or both. The net fisheries Net fisheries for migratory salmonids have been in long-term decline. The number of licences issued to net for salmon and sea trout in England and Wales has decreased by about 60% since the 1980s to 372 in 2003. In part, this decline reflects the reduced value of the catch. The price paid for wild salmon has reduced since the 1980s with the increased availability and reduced price of farmed salmon. Prices recorded by the Fishmongers Company at Billingsgate, adjusted by the Retail Price Index, show that from 1979–2002, the price of wild salmon in August decreased from about £14/kg to £7/kg, while the price of farmed salmon decreased from £12/kg to £3/kg. Given the similarity of the two species

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the price paid for sea trout, usually less than that for salmon (e.g. Radford et al., 1991), has been similarly affected. In 2003, the declared catch of sea trout in England and Wales was just over 50 tonnes of which three-quarters were taken in the north-east coastal fishery, mostly in T and J nets. Other significant sea trout net fisheries are: the coracle nets of the Tywi, Taf and Teifi (2.3t; 17 licences); the Seine nets at the mouths of the Hampshire Avon and Stour (1t; 6 licences), Teign (0.6t; 6 licences) and Dart (1t; 12 licences); and the coastal fisheries off East Anglia (3.6t; 45 licences).

Value to the netsmen So what is the catch worth to the netsmen? If the netting were being done on a purely commercial basis, the economic value would be the profit generated from selling the catch. The sale price paid to netsmen is quite variable. For example, in 2003, the price paid to Haaf netsmen on the Solway estuary reduced as low as £1.50/kg though when fish are scarcer, as in June 2004, the price has been £4.50. Taking £3/kg as an average sales price, the income to netsmen from sea trout would have been about £160 000 in 2003. When combined with an estimated £280 000 from sales of salmon (69 t at £4/kg), the income to netsmen in 2003 from migratory salmonids would be about £440 000. In 1996, netsmen’s costs were estimated to be about 75% (MAFF, 1998) which suggests a profit to netsmen, nationally, from both species of about £110 000 of which £40 000 is derived from sea trout. While this is a crude assessment, it does indicate that the level of profit for most of the 372 licensed netsmen is small, and for many there may be none. It seems likely that, whether they sell their catch, many netsmen similar to most anglers are fishing partly, if not largely, for enjoyment rather than for profit. Indeed, some netsmen, such as on the Solway and River Teifi, have indicated as much. However, for others, income from sea trout may be significant. For example, in 2003 the average gross income from sea trout for netsmen on the north-east coast was about £2000 per licence.

Heritage value Net fisheries may have other values than the profit and recreational value to the netsmen. Some of the salmon and sea trout fisheries use fishing techniques with a long tradition. A prime example is coracle fishing on the Tywi, Taf and Teifi in West Wales, while the Solway Haafnetters Association claim that the Vikings started their fishery. Are people aware of these traditional fisheries and do they value them? A study commissioned by the Environment Agency (Environment Agency, 2004) indicates that such traditional fisheries may indeed have what may be called a heritage value, though this value is not dependent on the catch or even the number of people fishing. For example, the study estimated that the people of Wales were willing to pay, as a one-off payment, £1.5 million to maintain a minimum coracle fishery in West Wales. The study also suggested that, through demonstrations and interpretative material, traditional fisheries might contribute to their local economies through tourism.

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The rod fisheries Nowadays, anglers catch more sea trout than netsmen do. In 2003, anglers took 60% of the declared catch, 45 101 sea trout, with only 29 248 reported by the netsmen. As with netting, angling for sea trout is often closely linked to salmon angling and evaluating sea trout alone is difficult. Anglers fishing for sea trout in England and Wales must hold an Environment Agency salmon rod licence. Each year, about 25 000 anglers currently buy such a salmon licence. The balance between these anglers’ interest in salmon and sea trout is unknown and will vary from river to river reflecting, in part, the local catches of salmon and sea trout and the timing of runs. Sea trout rod fisheries are valuable in at least three different ways: (1) to the fishery owner (all fisheries are privately owned); (2) to the angler and (3) to the local economy. This chapter focuses on the values to the fishery owner and to the local economy.

Value to fishery owners Sea trout add value to the market value of fishing rights, and so benefit the fishery owner, but how much they add is unclear. For salmon fisheries there is a generally accepted rule-ofthumb whereby the market value of a fishery is, on average, related to the size of the salmon catch, taking into account a number of other factors. One would expect the sea trout catch to be one such factor. Although Radford et al. (1991) did look for a relationship between fishery value and the sea trout catch, as yet no such rule has been demonstrated empirically. As part of a national evaluation of fisheries in England and Wales for the Environment Agency, Radford et al. (2001) used a per capita value of £8400 per salmon in the 5-year average annual catch to value fishing rights for migratory salmonids at £128 million. The contribution of sea trout to the value of fishing rights is subsumed within this and it should not be assumed that the sea trout catch is irrelevant. It is likely that the salmon catch works as a predictor of fishery value not only because of the value anglers place on salmon but also because, on average, the larger the catch the bigger the fishery. Given the similarity of the two species, one might expect that anglers might value catching salmon and sea trout of a given size equally. If they do, then a substantial component of the value of migratory salmonid fisheries is attributable to sea trout which now represent about half of the declared rod catch by weight in England and Wales, and 80% by number (see Fig. 32.1).

Value to the local economy Although expenditure by anglers fishing for salmon or sea trout may not be important for the economy of England and Wales as a whole, it may be significant for the local economies of some rural areas. The Environment Agency has a duty under the Environment Act 1995 to maintain, develop and improve salmon, trout, freshwater fish and eel fisheries in England and Wales. The latest statutory guidance from the Government (Defra, 2002; Welsh Assembly Government, 2002) on how to execute this duty emphasises that the Agency should ‘enhance

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100% 80% 60% 40%

salmon sea trout

20%

19 88 19 90 19 92 19 94 19 96 19 98 20 00 20 02

0%

Fig. 32.1 The relative proportions (%) of salmon and sea trout in the declared rod catch for England and Wales from 1988 to 2003.

the contribution salmon and freshwater fisheries make to the economy, particularly in remote rural areas and in areas with low levels of income’. To date, the main focus on the economic contribution of sea trout fisheries has been in Wales. An Environment Agency study (Spurgeon et al., 2001) estimated that salmon and sea trout angling contributed about £1 million in 1998 to the economy of the Teifi catchment in West Wales. This value was an estimate of expenditure within the catchment using a multiplier of 1.1 but no account was taken of costs so it is a gross rather than net value. Based on the Teifi study, Nautilus (2000), in a report for the Welsh Assembly Government, estimated that expenditure associated with salmon and sea trout angling contributed about £8 million to the Welsh economy. As with other values, it is difficult to separate the relative contribution of salmon and sea trout though the contribution of sea trout is likely to have been significant. At the time (1996–2000) anglers caught about five times as many sea trout, in Wales, as salmon. It is likely that the sea trout is more important than salmon to the Welsh economy.

A case study in supporting rural recovery via a sea trout fishery In 2001, a sample survey of club membership and visitor permit sales indicated that since 1981 the employment generated via all recreational fishing in Wales had decreased by at least 1000 full-time-equivalent (FTE) jobs – well over £30 million per year in angler expenditure. The Nautilus (2000) report estimated the employment based upon recreational fisheries at around 1500 FTE jobs. Clubs dependent on river fishing had suffered particularly; for example, over the 15-year period from 1985 to 2000, one South Wales club saw its membership decline from 250 to just 58. In West Wales, Llandysul Angling Association (AA) thrived in the days when brown trout were plentiful and salmon ran in the River Teifi throughout the year, but as salmon and trout stocks declined so did club membership and visitor permit sales (see Fig. 32.2). The decline in salmon and some brown trout stocks was not helped by almost a decade of zero budget for capital improvement works by the fisheries service in Wales. Throughout this period, investment in fisheries marketing by the Wales Tourist Board consisted of just one image-building brochure written and donated by enthusiastic amateurs (O’Reilly, 1998).

462

Sea Trout 1000 900 800 700 600 500 400 300 200 100 0

Waiting list Day/week permits Full members

1980

1990

2000

Fig. 32.2 The number of full members and the number of short-term permits sold by Llandysul Angling Association in 1980, 1990 and 2000, showing the number of anglers on the waiting list for a full permit in 1980.

When it came to the selling – providing the detailed information and turning their interest into actual angling tourism holiday bookings – the fisheries of Wales, for the most part angling clubs run by part-time amateurs, were unsupported by any state investment. The information on the website www.fishing-in-wales.com – developed by Llandysul AA and its partners – attracted two million separate visits annually but there was no professional monitoring of its effectiveness to indicate what proportion of these site visits were being converted into angling holidays in Wales. In 1997, Llandysul AA set about arresting and reversing the decline and saw its 30 miles of sea trout fishing as the key asset. The first step was customer research. The club received 60% written responses to a reply-paid questionnaire asking members and visiting anglers what they felt was needed. Some respondents felt that the club could do more to help restore salmon and trout stocks; but many other factors scored much more highly. These were, in order of priority: • • • • •

more detailed information about each fishing beat; better maps and signage for the club’s 22 fishing beats; a source of up-to-date river reports; support for newcomers to river fishing; improved access, especially for infirm and disabled people.

By far the most repeated call was for high-quality, detailed fishery information in a form that anglers can easily use. As well as the angling club, several community groups responded to these findings: the local canoe club, wildlife enthusiasts, accommodation providers and other tourism operators in the area were also actively involved. The recovery project was designed around the community’s aspirations and priorities. After struggling for many years to restore and protect fish stocks by improving river habitats – and making some modest gains, albeit on a small scale – the community’s efforts were given a major boost by the Welsh Assembly Government’s ‘Sustainable Fisheries’

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project and the Objective 1 programme. In 2002, community volunteers worked in partnership with the Environment Agency to open up several miles of a major tributary. That winter 68 salmonid spawning redds appeared there, and in 2003 the figure rose to 120 (Environment Agency, 2003). This pilot project also entailed major changes in marketing. On their own, the club’s image-building brochures and newsletters had not been enough to maintain visitor loyalty. A postal survey of 400 visitors to the club’s fisheries had underlined the need to provide detailed information to overcome their doubts and fears when choosing a new holiday venue. Information about how, when and where to fish, clear maps, details of fly hatches; tackle advice, where to stay in the valley, where to get food, fishing tackle, etc. and things for nonfishing members of the group to do – all this went into a 150-page guidebook (O’Reilly, 1999). The first 1000 copies of the book sold in 2 years, fully funding the rest of the publicity material and the club’s contribution to the habitat improvement programme. An interactive CD-ROM (O’Reilly, 2004) further cut the costs of publicity and raised the quality by including video and other multimedia material. The other vital ingredients for marketing success – the actual selling and making visitors welcome – were entirely dependent on the community. Anglers, canoeists, wildlife enthusiasts and accommodation providers worked together to put on Welcome Days throughout the tourist season. People were invited to the valley and given illustrated talks, casting lessons, fishing advice and guided tours of various fisheries; and they were introduced to accommodation providers. Each spring typically 50 people would attend, and of these about 40 became new members of the club, visiting the valley for 1 or 2 weeks per year. These newcomers to Wales made friends with local people. They had someone they could phone for advice on river conditions and fishing news. Four years on, most of these newcomers are still returning to the Teifi Valley for their fishing holidays and occasional short breaks. The results speak for themselves. Full membership rose each year since the launch of the recovery initiative. Figure 32.3 shows that 2004 brought a further substantial increase in full members and short-term visitor numbers. To put it in economic terms: in 6 years Llandysul Angling Association has arrested the decline and reversed it, in so doing creating the equivalent of three FTE jobs dependent 900 800 700 600 500 1998

1999

2000

2001

2002

2003

2004

Fig. 32.3 Full membership and visitor permit sales, including juniors, during the ‘Recovery’ project (2004 results estimated based on data to end of July).

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on angling tourism. Provided that improvements to the fishery can be maintained, the club has the potential to create another two FTE jobs, at which point it would be necessary to restart a waiting list for membership. Compared with the 1997 level, the potential increase in employment that could be generated is estimated to be five FTEs. It is instructive to view this from a national perspective. Llandysul AA generates about one-third of the sea trout rod catch from the Teifi which itself provides 15% of Wales’s rod catch of sea trout. If the rest of Wales’s sea trout fisheries could generate an increase in employment proportional to that at Llandysul, an additional 100 FTE jobs could be created across Wales, above the 1997 level. The potential, additional angler expenditure in Wales would be about £3 million a year, compared with the total contribution of salmon and sea trout angling of £8 million estimated by Nautilus (2000). Such an employment boost would be for the most part in rural areas where there are few other opportunities for economic development. To achieve this, Wales must invest effectively in its sea trout fisheries and get the marketing and selling right.

Acknowledgements We are grateful to the officials and members of Llandysul Angling Association for the use of their club records and to the Fishmongers Company for information on the prices of salmon at Billingsgate. We would also like to thank all the Environment Agency staff involved in the collation of the catch statistics and of course the fishermen who provided them.

References Defra (2002). The Environment Agency’s objectives and contributions to sustainable development: statutory guidance. Department for Environment, Food and Rural Affairs. December 2002, 15 pp. Department of the Environment, Ministry of Agriculture, Fisheries & Food, and Welsh Office (1996). The Environment Agency and sustainable development, 29 pp. Environment Agency (2003). Fish pass and river improvements spawn success. News release TC312/03MW. 1 December 2003. Environment Agency (2004). Study to develop and test a method for assessing the heritage value of net fisheries. R&D Technical Report, 57 pp. London Docklands (1996). Advertisement. Daily Telegraph, 17 March, p. 35. MAFF (1998). Economic value of salmon net and rod fisheries in England and Wales in 1996. Unpublished paper. Ref. HX 1183. MAFF, Economics (Resource Use) Division, 9 pp. Mawle, G.W. & Milner, N. (2003). The return of salmon to cleaner rivers – England and Wales. In: Salmon at the Edge (Derek, M., Ed.). Blackwell Science, Oxford, pp. 186–99. Mawle, G.W., Winstone, A.S. & Brooker, M.P. (1985). Salmon and sea trout in the Taff – past, present and future. Nature in Wales, New Series, 4 (1&2), 36–45. Nautilus (2000). Study into inland and sea fisheries in Wales. Prepared for the National Assembly for Wales by Nautilus Consultants Limited, 120 pp. O’Reilly, P. (Ed.) (1998). Fishing in Wales. Wales Tourist Board, 58 pp. O’Reilly, P. (Ed.) (1999). Tribute to the Teifi. Llandysul Angling Association, Llandysul, Wales, UK, 145 pp. O’Reilly, P. (2004). Multimedia guide to salmon, trout and sea trout fishing and other outdoor activities in the Teifi Valley. First Nature, Llandysul, Wales, UK, 120 pp. Radford, A.F., Hatcher, A.C. & Whitmarsh, D.J. (1991). An economic evaluation of salmon fisheries in Great Britain. Volume I. Principles, Methodology and Results for England and Wales. A report prepared

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for the Ministry of Agriculture, Fisheries and Food. Centre for Marine Resource Economics, Portsmouth Polytechnic, 290 pp. Radford, A.F., Riddington, G. & Tingley, D. (2001). Economic evaluation of inland fisheries. Environment Agency R&D Project W2-039/TR/1 (Module A). Simpson, D. & Mawle, G. (2001). Surveys of Rod Licence Holders. R&D Technical Report. Project W2-057. Environment Agency, Bristol, 100 pp. Spurgeon, J., Colarullo, G., Radford, A.F. & Tingley, D. (2001). Economic evaluation of inland fisheries. Environment Agency R&D Project W2-039/PR/2 (Module B). Welsh Assembly Government (2002). The Environment Agency’s objectives and contributions to sustainable development in Wales: statutory guidance from the National Assembly for Wales, 15 pp.

Chapter 33

Sea Trout Fisheries Management: Should We Follow the Salmon? A.M. Walker, M.G. Pawson and E.C.E. Potter Centre for Environment, Fisheries and Aquaculture Science, Lowestoft Laboratory, Pakefield Road, Lowestoft, Suffolk, NR33 0HT, UK

Abstract: The aim of this chapter is to evaluate whether tools used for managing Atlantic salmon (Salmo salar L.) fisheries could be applied to sea trout (Salmo trutta L.). The scientific basis of management measures adopted for salmon fisheries is reviewed and discussed, focusing in particular on setting appropriate targets (e.g. biological reference points, BRPs) and on the practicability of such measures and targets for management of sea trout fisheries. We conclude that BRPs based on stock–recruitment relationships (as used for salmon) are not presently feasible for sea trout management, given the limited understanding of the complex array of life strategies demonstrated by S. trutta. We suggest, instead, that BRPs could be defined in terms of juvenile abundance in relation to carrying capacity, bearing in mind the management requirement for conserving stock diversity both within and between anadromous and freshwater-resident components. Keywords: sea trout, management, salmon, biological reference points.

Introduction The sea trout (Salmo trutta L.) has an important ecological role in the majority of freshwater systems in the UK and Ireland, and the associated fisheries have a considerable social, recreational and economic value (e.g. Mawle & O’Reilly, 2006). Despite this, efforts to conserve sea trout stocks and to manage their exploitation for recreational (anglers) or commercial purposes have often been reactive rather than proactive (Harris, 2006), and have been implemented principally as a by-product of salmon (Salmo salar L.) management. This weakness became particularly apparent during the late 1980s and early 1990s, when sea trout catches declined in many rivers throughout the UK and Ireland (Whelan, 1991; Anon., 1992; Walker, 1994a). Sea trout catches in rivers in England and Wales recovered quickly and stocks are now considered to be healthy: the declared rod catch in 2004 was 36 000 fish (Anon., 2005). In contrast, some sea trout stocks in rivers in the north and west of Scotland and Ireland that crashed during the same period have failed to recover (Gargan, 2000; Butler, 2002). While a number of possible causes have been investigated, it is generally agreed that the crashes were attributable primarily to reduced survival in the marine environment (Walker, 1994a; Poole et al., 1996). These events have highlighted the pressing need to address the specific management requirements of sea trout. 466

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Similar decline in the abundance of many salmon stocks throughout the species’ native range during the past two to three decades have forced scientists and managers to reconsider and improve their approach to management (e.g. Crozier et al., 2003). This has led to the adoption of a precautionary approach to salmon management and the use of biological reference points (BRPs) to provide the scientific basis for measures designed to bring about reductions in fisheries exploitation and in reclamation and conservation of freshwater habitats. Within England and Wales, the Salmon and Freshwater Fisheries Review (Anon., 2000) recommended that sea trout fisheries should be managed ‘to protect stocks from overexploitation’. The Review Group also suggested that the principles applied to the regulation and management of salmon fisheries might be applied to sea trout. Given the broad similarities between the anadromous life history and coastal and freshwater fisheries of salmon and sea trout, such an approach would appear to have merits, but sea trout have far more complex and varied life-history strategies than salmon. As a result, the pros and cons of adopting such an approach need to be explored in detail. In this chapter, we outline the management strategy and its scientific basis as presently applied to salmon stocks, focusing in particular on that applied in England and Wales. We then consider whether this approach might be suitable for the management of sea trout stocks, or whether alternative approaches might be more appropriate.

Salmon management The present approach to managing salmon stocks throughout the North Atlantic region follows the agreement by Parties to the North Atlantic Salmon Conservation Organization (NASCO) that salmon stocks should be conserved by ensuring that an adequate number of spawners enter each river to optimise annual production (NASCO, 1998). The derivation of an ‘adequate’ spawning stock size is based on the assumption that the number of fish produced in the next generation (recruitment) is related to the number of adult fish in the previous generation (stock). Salmonids are among the few fish species studied where this premise has been clearly demonstrated (Chaput & Prevost, 2001). Recruitment in anadromous salmonids is largely determined by density-dependent regulation in the early life stages because of limited resources (chiefly space and food) in fresh water (Gibson, 1993; Elliott, 1994). Though salmonid recruitment is strongly influenced both by intrinsic (genetic) and extrinsic (environmental) factors, long-term studies indicate that a density-dependent stock–recruitment (SR) model should generally apply (reviewed by Elliott, 2001). Several model types can be applied to explain the SR relationship (Elliott, 1994), each assuming that the proportional survival of offspring decreases as the stock size increases. The effect of this is that the number of recruits (or offspring that survive to adulthood) increases to a maximum as the spawning stock increases, and, in some modelling scenarios, may then decline again at high spawning stock levels (Fig. 33.1). Of course, the SR curve is simply a mathematical interpretation of the trend in recruitment at different stock levels, based on a scatter of observations from various years’ data. Not only should such curves be interpreted with care, but attention must be given to the variation in observations around the curve.

468

Sea Trout Replacement line

Adults produced (×1000)

6

SR curve

4

2

SMSY

0 0

2

4 Spawners (×1000)

Yield 6

Fig. 33.1 Ricker SR curve for hypothetical stock showing BRP, SMSY , adopted by NASCO as the CL for salmon stocks (Potter, 2001).

The prime objective of salmon fisheries management is the conservation of the stock and the diversity within it. If this is achieved, we can then begin to determine sustainable levels of exploitation and consider optimum allocation of the exploitable surplus among fisheries. The difference between the points on the SR curve and the replacement line (RL) (the number of fish that will give rise to an equal number of spawners in the next generation; RL in Fig. 33.1), at any given stock size, is the surplus that can be removed by the fishery (yield), whilst still allowing sufficient recruits to maintain that stock size. The exploitation rate associated with these variations in yield increases from zero, at the stock size where the RL crosses the SR curve, to a maximum where the stock size is reduced to almost zero. Thus, a wide range of exploitation rates may result in the stock and catches varying around what would appear from the SR curve to be stable, sustainable levels (Hilborn & Walters, 1992). However, the risk to sustainability varies considerably between different levels of spawning stock biomass, and there is a need to ensure reasonable protection against years in which recruitment is unexpectedly poor for other reasons. There is, therefore, a need to demarcate undesirable stock levels (and/or levels of fishing activity), and the ultimate objective when managing stocks and regulating fisheries will be to ensure that there is a high probability that these undesirable levels are avoided (Potter, 2001). This has been achieved by setting conservation limits (CLs) for stocks. A wide range of different BRPs have been proposed for managing fish stocks and fisheries, and there is no ideal. In determining which point should be established as the CL for salmon stocks, consideration was given to the need to be able to set comparable reference points for the large number of different river stocks. One strong candidate is the stock size at which yield should be maximised in the long term (SMSY ). This point can be mathematically defined for any density-dependent SR relationship, as the net gain curve (yield) is always

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dome-shaped (Fig. 33.1). ICES (1995) proposed that, by maintaining stocks at or close to SMSY , the maximum sustainable yield or catch should be generated in the long term (other factors being equal). However, the increasing slope of the SR curve below SMSY indicates that relative recruitment begins to fall rapidly as stock size diminishes and there is, consequently, an increasing risk that recruitment will be insufficient to insure against the risk of stock collapse. NASCO (1998), therefore, adopted SMSY on an adult-to-adult Atlantic salmon SR relationship as a threshold or limit reference point, the CL. Stock levels below this are considered undesirable and are to be avoided. Clearly, the choice of SMSY as a limit means that the objective is not to maximise the catch (Potter et al., 2003) but to ensure stock/fishery sustainability.

Salmon reference points for England and Wales In 1996, the National Rivers Authority (NRA, pre-Environment Agency, EA) in England and Wales launched their National Salmon Management Strategy (Anon., 1996), which included the requirement to develop river-specific CLs in terms of numbers of spawning salmon and egg deposition. Following examination of a number of approaches to BRPs, the use of SR curves and a CL approach was adopted (Milner et al., 2000). Estimates of stock and recruitment over a wide range of spawning escapements and a large number of years are required to derive a SR model (e.g. Buck & Hay, 1984; Elliott, 1993; Kennedy & Crozier, 1993), and such SR data are available for only about 30 of the 2000+ salmon stocks in the Atlantic region (Crozier et al., 2003, chapter 2). None was available from rivers of England and Wales in the mid-1990s. The NRA (Anon., 1998), therefore, chose to take as a base the salmon SR model for the River Bush in Northern Ireland (Kennedy & Crozier, 1993), a river similar in character to many in England and Wales and for which a long-term (1973 onwards) dataset of adult and smolt run size has been obtained using total-run trapping facilities. River-specific CLs for England and Wales are calculated based on the egg (adult escapement)-to-smolt (recruitment) SR curve for the River Bush, but adjusted for freshwater habitat availability in each river, and a replacement line (RL) derived from estimates of marine survival and other life-history parameters, also specific to each river (Wyatt & Barnard, 1997). River-specific habitat availability (wetted stream area) was quantified in terms of 22 categories of altitude and stream order (Strahler, 1952), assessed by GIS. The carrying capacities for 0+ and >0+ salmon parr for each category were derived from EA electro-fishing surveys of pristine (i.e. not affected by adverse water quality or habitat) sites throughout England and Wales. Maximum smolt production for each river was predicted using category-specific Ricker-type egg-to-smolt curves from the Bush data, raised by the accessible wetted area of each habitat category in the catchment. The estimated number of eggs produced per smolt leaving the river (replacement) was calculated using river-specific sex and sea-age ratios for spawners, national estimates of marine survival for grilse (11%) and multi-sea winter salmon (MSW) (5%), based on data from the N. Esk River, Scotland (ICES, 2003), and a length–fecundity relationship derived for salmon from six Scottish rivers (Pope et al., 1961).

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Stock status in relation to the CL is assessed annually in terms of estimated egg deposition (e.g. Anon., 2005, Table 19), derived either from estimates of post-fishery escapement based on the rod catch, raised to include an estimate of non-reported catch, and an estimate of exploitation rate or, in 13 rivers, from trap or counter data. The EA established management targets (MTs) for all 64 whole-river salmon stocks for which CLs had been set. The MT was defined as the target stock size that would meet or exceed the CL in 4 years out of 5, based on variation in egg deposition estimates during the previous 11 years (Anon., 2004). Clearly, there are a number of areas of uncertainty associated with this method (Milner et al., 2000), not least the use of rod catches to estimate run size, and efforts continue to further develop the method and incorporate these uncertainties (Wyatt, 2002, 2003). Two other components of the salmon’s life history that could be monitored to assess the status of stocks are juveniles (fry and parr) and smolts, both representing freshwater production resulting from egg deposition. Juvenile abundance is surveyed on most salmonproducing catchments throughout England and Wales, and the smolt run is monitored on six rivers (Anon., 2004), but only estimated on two. At present, these data are not used as a formal BRP in the assessment of salmon stock status, but they are used as diagnostics to support interpretation of the CL compliance results.

Sea trout management Stock–recruitment model The extrapolation, or transport (Wyatt & Barnard, 1997), of a salmon SR relationship from one river to another, as from the River Bush to rivers of England and Wales, is based on the assumption that the population dynamics (eggs-to-smolts-to-eggs) of each stock are similar and that differences in river-specific production are primarily attributable to differences in habitat quantity and quality, that is carrying capacity. Establishing similar egg depositionbased BRPs to evaluate the status of sea trout stocks of England and Wales would, therefore, require SR data for at least one ‘typical’ sea trout river, and a method by which to ‘transport’ the relationship from this reference river to others, including knowledge of the numbers and sex composition of spawners, and a size–fecundity model. At present, published data for sea trout SR relationships are available for three rivers in north-western Europe: Black Brows Beck in England (Elliott, 1993); the Burrishoole system in Ireland (Poole et al., 1996) and the Bresle in France (Euzenat et al., 1999); data for all three are reported in this symposium (Elliott & Elliott, 2006; Euzenat et al., 2006; Poole et al., 2006). Black Brows Beck is a small, shallow tributary (length ∼500 m, mean width 0.8 m) of a spate river, the Cumbrian Leven, with a trout population supported entirely by sea-run fish. Almost all trout migrate to sea at age 2 and then return to spawn either the same year (males only) or the following year (both sexes); very few survive to spawn a second year (see Elliott, 1994). The Burrishoole system is a spate river catchment in western Ireland drained by approximately 45 km of shallow streams (16.7 km accessible to migratory salmonids), but

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characterised by two freshwater lakes (410 and 46 ha), where the majority of freshwater trout production occurs (Matthews et al., 1997). Before the stock collapse in the late 1980s, sea trout smolts were typically 2 (70%) or 3 (30%) years old and, based on catch returns for 1985 and 1986, the majority of sea trout returned as whitling (0 sea age: ∼56%) with the remainder being predominantly of sea ages 1 or 2 years (Poole et al., 1996). This system was stocked with almost 50 000 reared trout from 1993 to 1998 as part of a sea trout enhancement programme (Byrne et al., 2002). The Bresle is a chalk stream in the Upper Normandy-Picardy region of France, with a main channel of approximately 72 km in length, 40 km of which is accessible to sea trout and salmon. The majority (78%) of sea trout smolts go to sea at age 1, after which adults return annually to spawn, with the oldest fish having a sea age of 4 years (Euzenat et al., 1999). Thus, the three systems are very different in physical characteristics, as are the life histories of the sea trout they produce. Furthermore, the dynamics of sea trout stocks are, in many cases, far more complex and diverse than those of salmon, both between and even within river systems. Of key importance to diversity is the fact that, while some sea trout populations exhibit complete anadromy (Milner et al., 1993; Elliott, 1994), many are considered to be freely interbreeding fractions of a single trout population that includes both anadromous and freshwater-resident components. Progeny of anadromous and freshwater-resident trout have been shown to become both forms (Frost & Brown, 1967; Jonsson, 1985; Walker, 1990) and, while genetic differences have been reported between trout populations both within and between catchments, no study of neutral markers has provided conclusive evidence of genetic divergence between sympatric freshwater-resident and anadromous trout (Ferguson et al., 1995). Furthermore, the tendency to become anadromous often differs between the sexes, as evidenced by the female-biased sex ratios of sea trout during their spawning migrations (Le Cren, 1985), although the ratios may approach unity when maturing freshwater-resident brown trout are included in the calculations (Sambrook, cited in Solomon, 1995). As yet, the reproductive contribution of freshwater-resident trout to sea trout runs remains poorly understood, in part because of the technical difficulties in distinguishing between parr of resident, migrant or ‘mixed’ origins (but see Charles et al., 2004). Without this information, which is not accounted for in any measure of sea trout stock size based on monitoring spawning runs, it is impossible to transport a sea trout SR relationship between rivers. Even within the anadromous component, sea trout stocks demonstrate a considerable variety in life-history patterns. Within England and Wales, such variations include smolt age (1–4 years), sea age at first spawning (0–2 years), spawning frequency (once to several), growth rate at sea, and pattern and timing of return to fresh water, as reviewed for 80 rivers (Solomon, 1995) and in greater detail for 16 rivers (Harris, 2002). These differences would each affect how representative a sea trout SR model from one river would be of any other. For example, as parr survival decreases with time, smolt production rates might tend to be negatively correlated with mean smolt age (MSA), as reported for both sea trout and salmon (Saltveit, 1990). Furthermore, Harris (2002) reported that the proportion of maturing whitling varied between 0% and >98% amongst the 16 stocks studied. This information is

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required for both the stock with a known SR relationship and those stocks to which this is transported in order to correctly derive effective spawning stock size from estimates of adult returns. Similarly, pattern and timing of return to fresh water will influence pre-spawning survival through natural and fisheries-associated mortality rates, and hence will affect the relationship between returning stock and spawning stock. While fecundity is correlated with fish length, data from UK and Irish sea trout stocks (O’Farrell et al., 1989; Walker, 1994b; Elliott, 1995) suggest that length–fecundity relationships may differ between stocks, dependent on growth rates in fresh water (O’Farrell et al., 1989) or marine environments (Elliott, 1995), and that the use of a mean formula derived from these data to estimate egg deposition could lead to errors of up to 30% (Solomon, 1997). Given the variety and complexity of the population dynamics of S. trutta (resident and anadromous) stocks, it is highly unlikely that a SR model based on a single donor stock, especially one with such a limited dynamic as that of the Black Brows Beck population, or three stocks with such disparate population dynamics and habitats as those noted above, could be sufficiently representative of sea trout rivers throughout England and Wales. While some of these differences might be accounted for during the SR transport process, they would require a detailed knowledge of the population dynamics that is not available for most stocks. The resource (data and time) requirements to acquire this knowledge would be substantial and, though such an aspiration is laudable, there is a need for an alternative approach, at least in the short term.

Alternative BRPs for sea trout Catch-based indices The majority of salmon fisheries now collate some form of catch data and, although hampered by the influence of variations in effort and catchability, catch-based indices can provide a guide to stock status. One alternative to a SR-based approach, therefore, might be to derive sea trout abundance indices from catch records and compare them against reference catch levels. This is part of the approach being developed for salmon stocks in Scotland (Potter et al., 2003), in response to concerns that whole-river CLs do not take sufficient account of possible complex population structures within the rivers, and that the appropriate biological scale for setting CLs may be tributaries or smaller sections of the river (ICES, 1999). Rod catch records in Scotland have been collected in a systematic manner for many years, with catches of 1SW and MSW salmon recorded separately for each month of the fishing season and on a sub-catchment scale. It is intended that management actions will be targeted at those sub-catchments where adult abundance indices and juvenile densities decrease below reference levels. In contrast, rod catches of sea trout in many rivers in Scotland, England and Wales may be poorly recorded, and there are additional problems with catch-based indices (for both sea trout and salmon) including the influence of non-stock related factors (e.g. national Spring Salmon by-laws since 1999; foot and mouth disease in 2001) on catch and effort. Furthermore, stock size may appear stable in the short term but be insufficient to provide stable recruitment in the long term. It is difficult, therefore,

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to envisage how such a catch-based approach could be applied across the variety of sea trout stocks in England and Wales. Moreover, sea trout catch records could miss a potentially significant part of the spawning stock, the freshwater-resident trout. Therefore, sea trout catch data alone do not provide a sound basis for making decisions on management of sea trout fisheries. Juvenile-based assessments Given the significant difficulties of using adult-based assessments as a source of BRPs for sea trout (at least in the short–medium term), we should consider the other lifehistory components suggested earlier: juveniles and smolts. Salmon fry and parr abundance measures have been used to estimate spawner numbers in the previous winter (Kennedy & Crozier, 1993) or predict smolt output (Bagliniere et al., 1993). The EA routinely monitor the abundance of juvenile salmon and trout, particularly fry, throughout England and Wales. However, the parentage of juvenile trout can only be determined using destructive sampling methods, such as comparison of stable isotope ratios in recently emerged fry (Charles et al., 2004) or analysis of carotenoid pigment profiles (Youngson et al., 1997), neither of which could realistically be applied across large catchments. Whilst the adult salmon spawning stock of one small tributary has been genetically typed, allowing the parentage of juveniles to be assigned (Taggart et al., 2001), it is highly unlikely that resources would be available to apply this method to sea trout in large catchments. Similarly, the future form of juvenile trout cannot, at present, be predicted until a few days or weeks before their migration as smolts (Nielsen et al., 2004, but see Giger et al., 2006), because of the variable effects of environmental factors on life-history strategies. The present understanding is that anadromy within S. trutta is a threshold quantitative trait, that is, it is influenced by multiple genes and by the environment, but only expressed when the appropriate threshold combination, which presumably varies across and even within stocks, is reached (Ferguson, 2006). Thus, since the majority of sea trout stocks in rivers of England and Wales include both freshwater-resident and anadromous components, juvenile trout abundance data cannot, at present, be used to estimate sea trout spawning stock or to predict smolt output. Though smolt output clearly represents freshwater production and indicates the potential production of adults, our lack of understanding of the sea trout production dynamics means that we cannot transport a smolt output relationship from river to river. The monitoring programmes for salmon smolt runs on six rivers in England and Wales should certainly be adapted to provide sea trout data where possible. However, as there are at least 100 rivers producing sea trout in England and Wales (Solomon, 1995), this is not going to provide an index suitable for national sea trout management purposes.

Management of the Salmo trutta complex It is clear from the above that efforts to manage sea trout alone, and without considering the contribution of freshwater-resident trout, are severely hindered by their complex life history, diversity between stocks and our very limited knowledge of trout population dynamics.

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An alternative approach would be to consider the trout stock as a whole and to focus conservation efforts at that part of the stock that incorporates both freshwater-resident and anadromous components – the juveniles. A healthy juvenile trout population must provide the resource necessary for a sea trout population, though the environment and genes will determine what proportion adopt anadromy as a life strategy. For stock conservation purposes, the state of the juvenile population would have to be assessed in relation to potential freshwater production. This approach would be catchment-specific, and would explicitly focus management on both the fisheries and on the environmental quality of juvenile rearing habitats in fresh water. There has been an extensive study of the freshwater habitat utilisation and requirements of juvenile salmonids (most recently reviewed by Armstrong et al., 2003; Klemetsen et al., 2003), and several attempts to model the abundance, density or biomass of juvenile S. trutta based on habitat characteristics within its natural (e.g. Belaud et al., 1989; Milner et al., 1993; Baran et al., 1996; Lek et al., 1996; Jutila et al., 1999; Maeki Petaeys et al., 1999) and introduced ranges (e.g. Lanka et al., 1987; Scarnecchia & Bergersen, 1987; Lambert & Hanson, 1989; Newman & Waters, 1989; Jowett, 1995; Van Winkle et al., 1998). These empirical models, for example, HABSCORE (Barnard et al., 1995; Milner et al., 1995), can only account for the spatial component of stream-dwelling trout abundance variance, but for trout in English and Welsh streams this can be up to 73% of the overall variance (including temporal, error and interaction), of which the (HABSCORE) models explained up to 63%. Moreover, the proportions of spatial and temporal variation vary substantially with the scale of analysis, from tributary to catchment level (Milner et al., 1995). However, they do offer a mechanism by which to predict the potential average maximum abundance, the carrying capacity, of juvenile trout for riverine parts of a catchment, against which to compare measured densities and set BRPs. Recently, the entire freshwater salmon habitat of Ireland has been quantified in terms of wetted surface area, channel gradient and water quality using GIS (McGinnity et al., 2003) and efforts continue to improve the river-reach classification method for England and Wales (Wyatt & Barnard, 1997). However, it is not possible to predict the effects on adult sea trout numbers of either reducing or increasing juvenile abundance. Therefore, the a priori assumption of any juvenile-based BRP would have to be that, providing the juvenile abundance exceeded some predetermined level in relation to carrying capacity, the numbers of adult trout (anadromous and/or freshwater-resident) would be sufficient to meet the needs of stock conservation and associated fisheries. It is notable that recruitment at SMSY is generally between about 80% and 90% of maximum recruitment for typical salmonid SR curves (Healey, 1982; Potter et al., 2003). Thus a CL for juvenile trout production might be set at a similar proportion of the theoretical carrying capacity for S. trutta: this is analogous to the habitat utilisation index (HUI) of the HABSCORE models proposed by Barnard et al. (1995) as a benchmark for stream fisheries potential. There would also be a need to take account of the variability of juvenile recruitment and uncertainty in assessment methods. This approach is based on the conservation of the whole stock in a catchment, and could be regarded as a reasonable first step towards management for sustainable fisheries. However, other stock characteristics, such as the size (length at age) and age structure of the stocks,

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relative and absolute abundance of repeat spawners and the run timing of different stock components, should also be considered. For many sea trout stocks, the longevity and multiple spawning of individuals, the contributions of resident and migratory fish, and the different run-timing patterns may buffer recruitment against the impacts of short-term environmental change to habitats. Clearly, such diversity should be conserved for the continued robustness of the stock and form the basis of diversity targets, as recommended for salmon (ICES, 2003). While population structure must be taken into account at all stages, it will only be practical to apply CLs on the same scale that they will be used in management. As with salmon (Potter, 2001), however, we need to know the extent to which a catchment-based reference level will ensure conservation at a finer scale, and to what degree trout production and stock structure vary throughout a single catchment.

Conclusions Given the considerable problems with transport of any sea trout SR relationship to other rivers and the data requirements involved in the development of other, more representative, SR relationships, it appears that sea trout management cannot, in the immediate future, follow that of salmon. This is not to say that SR-based BRPs are unsuitable for sea trout stocks, but that this approach should only be considered as and when suitable data become available. Given the limited understanding of the dynamics of stocks that include freshwaterresident and anadromous components, we suggest focusing on trout as a whole, including both anadromous and non-anadromous individuals. BRPs should be defined in terms of juvenile abundance in relation to carrying capacity, whilst considering the management requirement for conserving stock diversity both within and between anadromous and freshwater-resident components. Whatever methods are adopted, there is no doubt that considerable investment is required in order to improve our understanding of the population dynamics of trout stocks. Nevertheless, the social and economic value of sea trout fisheries demands that stocks are conserved and associated fisheries are run in a sustainable manner.

Acknowledgements The authors’ attendance at the 1st International Sea Trout Symposium and the preparation of this chapter were supported by the UK Department of Environment, Food and Rural Affairs.

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Matthews, M.A., Poole, W.R., Dillane, M.G. & Whelan, K.R. (1997). Juvenile recruitment and smolt output of brown trout (Salmo trutta L.) and Atlantic salmon (Salmo salar L.) from a lacustrine system in western Ireland. Fisheries Research, 31, 19–37. Mawle, G. & O’Reilly, P. (2006). An appreciation of the social and economic values of sea trout in England and Wales. In: Sea Trout: Biology, Conservation and Management (Harris, G.S. & Milner, N.J., Eds). Proceedings of the Ist International Sea Trout Symposium, July 2004, Cardiff, Wales, UK. Blackwell Publishing, Oxford, pp. 457–65. McGinnity, P., Gargan, P., Roche, W., Mills, P. & McGarrigle, M. (2003). Quantification of the freshwater salmon habitat asset in Ireland using data interpreted in a GIS platform, Dublin, Ireland. Central Fisheries Board Irish Freshwater Fisheries Ecology and Management Series No. 3, 132 pp. Milner, N.J., Wyatt, R.J. & Scott, M.D. (1993). Variability in the distribution and abundance of stream salmonids, and the associated use of habitat models. Journal of Fish Biology, 43A, 103–119. Milner, N.J., Wyatt, R.J., Barnard, S. & Scott, M.D. (1995). Variance structuring in stream salmonid populations, effects of geographical scale and the implications for habitat models. Bulletin Français de la Peche et de la Pisciculture, 337/338/339, 387–98. Milner, N.J., Davidson, I.C., Wyatt, R.J. & Aprahamian, M.A. (2000). The use of spawning targets for salmon fishery management in England and Wales. In: Management and Ecology of River Fisheries (Cowx, I.G., Ed.). Fishing News Books, Oxford, pp. 361–72. NASCO (1998). Agreement on the adoption of a precautionary approach. Report of the fifteenth annual meeting of the Council, Edinburgh. NASCO, pp. 167–72. Newman, R.M. & Waters, T.F. (1989). Differences in brown trout (Salmo trutta) production among contiguous sections of an entire stream. Canadian Journal of Fisheries and Aquatic Sciences, 46, 203–13. Nielsen, C., Aarestrup, K., Norum, U. & Madsen, S.S. (2004). Future migratory behaviour predicted from premigratory levels of gill Na+ /K+ -ATPase activity in individual wild brown trout (Salmo trutta). Journal of Experimental Biology, 207, 527–33. O’Farrell, M.M., Whelan, K.F. & Whelan, B.J. (1989). A preliminary appraisal of the fecundity of migratory trout (Salmo trutta) in the Erriff catchment, western Ireland. Polskie Archive Hydrobiologie, 36, 273–81. Pirhonen, J. & Forsman, L. (1998). Effect of prolonged feed restriction on size variation, feed consumption, body composition, growth and smelting of brown trout, Salmo trutta. Aquaculture, 162, 203–17. Poole, W.R., Whelan, K.W., Dillane, M.G., Cooke, D.J. & Matthews, M. (1996). The performance of sea trout (Salmo trutta L.) stocks from the Burrishoole system, 1970–1994. Fisheries Management and Ecology, 3, 73–92. Poole, W.R., Dillane, M., deEyto, E., Rogan, G. & Whelan, K. (2005). Characteristics of the Burrishoole sea trout population: census, marine survival and stock recruitment. In: Sea Trout: Biology, Conservation and Management (Harris, G.S. & Milner, N.J., Eds). Proceedings of the Ist International Sea Trout Symposium, July 2004, Cardiff, Wales, UK. Blackwell Publishing, Oxford, pp. 279–306. Pope, J.A., Mills, D.H. & Shearer, W.M. (1961). The Fecundity of Atlantic Salmon (Salmo salar L.). Department of Agriculture and Fisheries for Scotland Freshwater Salmon Fisheries Research No. 26, 12 pp. Potter, E.C.E. (2001). Past and present use of reference points for Atlantic salmon. In: Stock, Recruitment and Reference Points: Assessment and Management of Atlantic Salmon (Prevost, E. & Chaput, G., Eds). INRA, Paris, pp. 195–223. Potter, E.C.E., MacLean, J., Wyatt, R.J. & Campbell, R.N.B. (2003). Managing the exploitation of migratory salmonids. Fisheries Research, 62, 127–142. Ricker, W.E. (1954). Stock and recruitment. Journal of the Fisheries Research Board of Canada, 11, 559–623. Saltveit, S.J. (1990). Effect of decreased temperature on growth and smoltification of juvenile Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) in a Norwegian regulated river. Regulated Rivers: Research & Management, 5, 295–303. Scarnecchia, D.L. & Bergersen, E.P. (1987). Trout production and standing crop in Colorado’s small streams, as related to environmental features. North American Journal of Fisheries Management, 7, 315–30. Solomon, D.J. (1995). Sea trout stocks in England and Wales. National Rivers Authority, R & D Report No. 25, Bristol, 102 pp. Solomon, D.J. (1997). Review of sea trout fecundity. Environment Agency, R&D Technical Report No. W60, Bristol, 22 pp. Strahler, A.N. (1952). Dynamic basis of geomorphology. Geological Society of America Bulletin, 63, 923–38.

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Symons, P.E.K. (1979). Estimated escapement of Atlantic salmon (Salmo salar) for maximum smolt production in rivers of different productivity. Journal of the Fisheries Research Board of Canada, 36, 132–40. Taggart, J.B., McLaren, I.S., Hay, D.W., Webb, J.S. & Youngson, A.F. (2001). Spawning success in Atlantic salmon (Salmo salar L.): a long-term DNA profiling-based study conducted in a natural stream. Molecular Ecology, 10, 1047–60. Van Winkle, W., Jager, H.I., Railsback, S.F., Holcomb, B.D., Studley, T.K. & Baldrige, J.E. (1998). Individual-based model of sympatric populations of brown and rainbow trout for instream flow assessment: model description and calibration. Ecological Modelling, 110, 175–207. Walker, A.F. (1990). The sea trout and brown trout of the River Tay. In: The Sea Trout in Scotland (Picken, M.J. & Shearer, W.M., Eds). The Dunstaffnage Marine Research Laboratory, NERC, Oban, Scotland, pp. 5–12. Walker, A.F. (1994a). Sea trout and salmon stocks in the western Highlands. In: Problems with Sea Trout and Salmon in the Western Highlands. 24th November 1993, Atlantic Salmon Trust, Inverness, pp. 6–18. Walker, A.F. (1994b). Fecundity in relation to variation in life history of Salmo trutta L. PhD Thesis, University of Aberdeen, Aberdeen. Whelan, K.F. (1991). Disappearing sea trout: decline or collapse? Salmon Net, 23, 24–31. Wyatt, R.J. (2002). Estimating riverine fish population size from single- and multiple-pass removal sampling using a hierarchical model. Canadian Journal of Fisheries and Aquatic Sciences, 59, 695–706. Wyatt, R.J. (2003). Mapping the abundance of riverine fish populations: integrating hierarchical Bayesian models with a geographic information system (GIS). Canadian Journal of Fisheries and Aquatic Sciences, 60, 997–1006. Wyatt, R.J. & Barnard, S. (1997). The transportation of the maximum gain salmon spawning target from the river Bush (NI) to England and Wales, Environment Agency, R&D Technical Report No. W65, Swindon, 38 pp. Wyatt, R.J., Barnard, S. & Lacey, R.F. (1995). Salmonid modelling literature review and subsequent development of HABSCORE models. National Rivers Authority, R&D Project Record No. 338/20/W, 189 pp. Youngson, A.F., Mitchell, A.I., Noack, P.T. & Laird, L.M. (1997). Carotenoid pigment profiles distinguish anadromous and nonanadromous brown trout (Salmo trutta). Canadian Journal of Fisheries and Aquatic Sciences, 54, 1064–6. Zalewski, M., Frankiewicz, P. & Brewinska, B. (1985). The factors limiting growth and survival of brown trout, Salmo trutta m. fario L. introduced to different types of streams. Journal of Fish Biology, 27A, 59–73.

Chapter 34

Perspectives on Sea Trout Science and Management N.J. Milner1 , G.S. Harris2 , P. Gargan3 , M. Beveridge4 , M.G. Pawson5 , A. Walker6 and K. Whelan7 1

Address for correspondence: Environment Agency, C/O School of Biological Sciences, University of Bangor, Bangor LL57 2UW, Wales, UK 2 Fishskill, Greenacre, Bwlch, Brecon, Powys LD3 7PZ, Wales 3 Central Fisheries Board, Balnagowan, Mobhi Road, Dublin 9, Ireland 4 FRS Freshwater Laboratory, Faskally, Pitlochry, Scotland 5 CEFAS, Pakefield Road, Lowestoft, Suffolk, NR33 0HT, England 6 FRS Freshwater Laboratory, Faskally, Pitlochry, Scotland 7 Marine Institute, Furnace, Newport, Co Mayo, Ireland Abstract: The sea trout presents unique opportunities and problems for scientists and fishery managers, because of its variety of life histories and occupancy of diverse marine, estuarine and freshwater habitats. This Symposium brought together much of the current knowledge and showed that sea trout stock assessment and fishery management and underpinning science have advanced since the last large conference on this topic held 20 years ago. Sea trout have assumed greater significance and economic value in recent years, but in parts of their natural range there are significant concerns about the status of stocks that in some cases have suffered catastrophic or more gradual decline. Reasons for the decline are varied and include notably the impact of sea lice infection associated with marine salmon farming. Other problems are common to many anadromous fish, such as over fishing, diffuse pollution, flow regimes, access and fish passage, but complicated in sea trout by the possibility of response to environmental perturbation thorough shifts in life history strategy. Sea trout are the anadromous form of Salmo trutta, and the phenotypic plasticity in life history of the species is their dominant feature. The balance of genetic and environmental factors in determining the incidence of anadromy remains a central research question, but progress in this area is now being made as a result of improvements in genetic techniques and understanding. The Symposium made several recommendations for future management and research, particularly with respect to ecology and fisheries in the sea (noting the opportunities for integration with freshwater studies), assessment methodologies and the basis of life history variation. Keywords: Sea trout, life-history variation, socio-economic importance, stock status, management developments, scientific advances, research needs.

Introduction Anadromous fish present particular challenges for scientists and managers. The sea trout exemplifies these perhaps more than any other fish species in the Northern Hemisphere

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because of the diversity in life-history strategy displayed across its extensive geographical range (see Ferguson, 2006; Jonsson & Jonsson, 2006). Fisheries protection, management and enhancement are difficult in a species with such a plastic migratory habit without an adequate understanding of the factors affecting its life history. The sea trout’s occupation of freshwater, estuarine and marine habitats exposes it to environmental impacts and fishing exploitation in all three. However, this characteristic of sea trout also brings opportunities. The successful completion of its life cycle requires good conditions in both freshwater and marine environments; thus the sea trout offers potential as a key sentinel fish species and as a link for integrating ecosystem studies across the freshwater–transitional–marine interfaces. This is in keeping with the trent of fisheries and wider catchment management towards the ecosystem approach (Garcia et al., 2003, Water Framework Directive). A similar argument has been advanced for integrated studies on the scaenid spotted sea trout (Cynoscion nebulosus) in the eastern USA (Bortone, 2003). This variety of life histories also adds significantly to the biodiversity of waters, including the many smaller coastal streams and tributaries which are home to juvenile sea trout, but which are often neglected by regulatory agencies. There are also fisheries opportunities. As a natural resource, sea trout have socio-economic value that exceeds that of salmon in some areas. Moreover, in contrast to salmon, its main production takes place in local inshore waters where fisheries and many environmental conditions have a reasonable prospect of being positively influenced by management actions. It is significant that the Symposium attracted sponsorship and participatory support from a wide range of influential non-governmental bodies and government departments. Many groups including fishermen, conservationists, fisheries managers and scientists share the recognition of sea trout as the basis of valuable, sustainable fisheries. It is essential to retain and develop this diversity of active interest. The determination of management goals and research priorities will be more effective if it is inclusive. All interested groups should be encouraged to participate and feel responsible for the results of managing stocks and fisheries. This chapter summarises the principal messages from the Symposium and extracts some priorities for sea trout science and management, under three broad headings: (1) recognition of stock and fishery status; (2) improved management of sea trout fisheries and (3) future research to support better fisheries.

Stock and fishery status The status of sea trout stocks and fisheries varies across its range according to the influence of local factors. In the western British Isles, where the coastal topography allows intensive marine salmon farming, sea trout stocks have collapsed or suffered dramatic declines because of the effect of sea lice infestations arising from their proximity to salmon farms (Butler & Walker 2006; McKibben et al., 2006; Poole et al., 2006). In the northern Baltic region over-exploitation in coastal fisheries appears to have jeopardised stocks (Jutila et al., 2006) and in the Black Sea a combination of uncontrolled illegal fishing in coastal waters and environmental problems in fresh water have brought stocks into the seriously ‘at risk’

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category (Okumus et al., 2006.). Elsewhere, sea trout stocks appear to be in a more healthy condition but, in common with Atlantic salmon, the potential for damaging effects of environmental factors is high. Many different types of sea trout fisheries were described at the Symposium, but speakers from all countries reported the need for better data on catches, fishing effort and exploitation rates determined at scales ranging from local to international. This was particularly so in the marine fisheries where there are major gaps in knowledge, including the extent of illegal fishing, whether targeted directly at sea trout or where they are taken as a by-catch in other types of fishing. As so often in fisheries, the regulation of sea trout catches and the underlying science are linked by the nature and quality of the monitoring programmes that service both routine stock assessment and the demand for data that is the raw material for much research. For sea trout in many countries, even the basic descriptions of population characteristics, stock structures and stability and fishery trends are not as comprehensive as for salmon. While sea trout catch statistics are approaching adequacy in some parts, those for the freshwater brown trout are poor almost everywhere and if the two forms are to be managed as one, then significant improvements in catch statistics for both are necessary. The Symposium showed that sea trout assessment is also constrained by limited availability of long time series of monitoring data, other than those provided by catches (e.g. electro-fishing surveys, counters). The trade-offs between data costs and information value will be difficult to negotiate, but if public stakeholders, policy makers and managers require robust scientific, risk-based decision-making they will have to make the appropriate investment.

Fisheries management for sea trout Considering fisheries management, an obvious question is what is special about sea trout? Why should they be regarded and managed any differently from S. trutta as a whole? The taxonomist might say that they should not be, but that is to ignore some obvious and important practical differences that make sea trout very different from the freshwater trout for managers and fishermen. From a biological perspective it is evident that anadromy is a threshold quantitative trait controlled by a combination of environment and genes (Ferguson, 2006). The sea-going habit confers large average size on returning spawners. Those trout populations dominated by the anadromous habit also have different freshwater age structures, within-catchment distributions and habitat linkages that differ from their freshwater relatives. Sympatry of the two forms is common, but most often it appears to be unbalanced through sex-selective migration favouring females. Genuine sympatry (as opposed to simply occurring in the same catchment) of abundant populations of both freshwater and anadromous form seems to be much less common, but we cannot be sure because systematic, extensive data are lacking. Fisheries for the migratory and resident forms often differ greatly in their locations and methods; consequently, legislation and regulatory controls are different. One could argue that such an approach is inconsistent with the taxonomy of S. trutta, and should be changed, but it does match many aspects of the biology, distribution and fisheries of the

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two forms and so, pragmatically, the division is sensible. However, for the scientist and for science-based management the continuum is important and cannot be ignored. For example, to set biological reference points (BRPs), it will be necessary to know the contributions of both forms to total trout production, irrespective of whether the BRPs are based on juveniles (Walker et al., 2006), on adults as in salmon (e.g. Crozier et al., 2003) or on some combination of assessments. In the freshwater stage, the inability to distinguish anadromous from freshwater trout on morphological grounds means that carrying capacity, habitat models and effective population sizes will probably be based upon total S. trutta populations, perhaps incorporating age structure data. This may change with the development of tools to recognise the identities and location of anadromous and non-anadromous trout. But all this is speculative at this stage and is the subject of current research. However they are derived, BRPs and all sea trout stock assessments will require better consistency and standards of monitoring data for adults and juveniles. Habitat protection, restoration and enhancement in rivers have normally been applied in the interests of Atlantic salmon or non-migratory trout. Coincidentally, this may also meet sea trout requirements, because of their similarities in ecology, but this has not been tested. However, sea trout make greater use of small coastal streams and smaller tributaries than salmon for rearing (Baglinière & Maisse, 1999; Milner et al., 2006; Walker & Bayliss, 2006). Their size makes these waters often fragile and vulnerable to environmental pressures such as pollution of low flows and they may require special designation and protection. Ferguson (2006) has outlined the implications of the genetic basis of anadromy noting that trout life-history strategy could shift with comparatively small environmental changes. The potential responsiveness of the migratory habit to freshwater environmental quality, operating through juvenile growth rate (Jonsson, 1985; Cucherousset et al., 2005; Jonsson & Jonsson, 2006) means that changes to productivity that may follow habitat alteration could affect sea trout in ways that are not yet understood or predictable. An undeveloped area of study that bears on this is the description and modelling of lifetime habitat usage by trout within catchments and how this might be influenced by the juxtaposition and connectivity of habitats at catchment scale. Similarly, the consequences of artificial stocking to restore or enhance sea trout stocks are not well understood. Stocking is an important fishery management tool in some countries, especially those Baltic countries where loss of freshwater rearing areas makes it essential to support fisheries artificially. However, its effectiveness in restoring natural populations has been questioned (e.g. Laikre, 1999; Jutila et al., 2006; Pedersen et al., 2006) and Lundqvist et al. (2006) have demonstrated some of the risks to wild stocks (see also Laikre, 1999; Ruzzante et al., 2004; Ferguson, 2006). In contrast, others have considered that the caution over stocking may have been over-played in some cases (e.g. Guyomard, 1999). Carefully planned and well-managed stocking has an essential role in stock restoration and conservation programmes, but in all cases it needs to be complemented by protection of resulting spawners through fishery regulations (e.g. Jutila et al., 2006). The prior removal of limiting factors is also essential to success, for example the failure of sea trout stocking to restore stocks in some western Irish (Ferguson, 2006; Gargan et al., 2006) and Scottish rivers (Hay & McKibben, 2006) may have been because of the continuing problems of

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marine survival. The sea trout stocking debate brings fisheries management hard up against the genetic/environment questions and, at the very least, a precautionary line needs to be adopted until the effectiveness and impacts of stocking are clearer. It is hoped that sound genetic principles will become incorporated into all future stocking programmes as has been the case in Denmark (Rasmussen, 2006). Significant detrimental environmental factors reported by speakers from most countries were physical barriers to migration, reduced river flows, siltation and nutrient enrichment through intensive agriculture, river habitat destruction and increased predation. Whilst the classical fish responses to environmental impacts (e.g. higher mortality, recruitment failure and contracted distribution) are to be expected in sea trout, the species is also capable of substantial changes in life-history patterns that could involve shifts between migratory and non-migratory behaviour, with enormous consequences for fisheries. Most salmonid fishery regulations in Europe have historically been implemented for the protection of salmon and non-migratory trout. But the case for a greater concern for sea trout has been recognised in some cases, and measures are in hand to refine catch controls through various options such as bag limits, size and catch and release (Environment Agency, 2004; Butler, 2005; Harris, 2006). The use of catch and release or slot size limits to protect the larger, older multiple spawners seems to be of particular value for sea trout (Harris, 2006; Solomon & Czerwinski, 2006). The priorities for future sea trout management are the following: • •

• • • • •

protection of the smaller rivers, sub-catchments and streams generally favoured as spawning and nursery grounds by sea trout; better monitoring of catch and effort in all fisheries in freshwater, estuarine and coastal zones; the inclusion of information on stock composition and fishing effort is considered to be essential to complement and interpret basic catch data; better definition and implementation of regulations to prevent illegal fishing or overfishing and to eliminate sea trout by-catch in coastal and estuarine fisheries; modification of catch regulations to afford better protection to the larger adult female sea trout; adoption of a precautionary approach for all trout stocking programmes; continuing effective control and management of sea lice on marine salmon farms to enable sea trout fishery recovery in affected areas and provision of integrated scientific advice that takes account of other species of fish and a wide range of ecosystem components.

Progress in sea trout science In spite of decades of research on S. trutta, there are still many unresolved questions about the ecology, life-history strategies and population dynamics of the migratory form. The central role of anadromy and causes of its variation remain dominant issues and the determining influence of genetics has been well reviewed and discussed at the Symposium (Bruford, 2006; Ferguson, 2006). New methods and technologies are enabling better description of life-history patterns (e.g. Cucherousset et al., 2005), direct exploration of the role of the

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genome in phenotypic variation (Bruford, 2006; Ferguson, 2006; Giger et al., 2006) and in developing theories about the basis of anadromy. The population dynamics of S. trutta have been extensively studied in many countries and there are many key papers, reviews and books (e.g. Allen, 1951; Frost & Brown, 1957; Mills, 1971; Le Cren, 1973; Elliott, 1994; Baglinière & Maisse, 1999; Crisp, 1999). Perhaps the classic study has been that of Elliott & Elliot (2006), who demonstrated the great value of long-term data sets. Elliott’s seminal research was conducted on a very small stream with adult sea trout of limited sea-age diversity and few other competing species. While that does not detract from the insights it reveals into processes, there is much more to be discovered about population dynamics in different stream types where habitats will be more complex, the range of life-history strategies may be greater, ecosystem complexity is higher and multi-species interactions operate. Rasmussen (2006), Milner et al. (2006) and others have noted that, while electro-fishing sampling (the commonest freshwater survey method) may be extensive, it is mostly confined to smaller streams (e.g.