Flatfishes: Biology and Exploitation

By Robin N. Gibson

Fascinating and instantly recognizable, flatfishes are unique in their asymmetric postlarval body form. With over 800 extant species recognized and a distribution stretching around the globe, these fishes are of considerable research interest and provide a major contribution to commercial and recreational fisheries worldwide. This second edition of Flatfishes: Biology and Exploitation has been completely revised, updated and enlarged to respond to the ever-growing body of research. It provides:

• Overviews of systematics, distribution, life history strategies, reproduction, recruitment, ecology and behaviour
• Descriptions of the major fisheries and their management
• An assessment of the synergies between ecological and aquaculture research of flatfishes.

Carefully compiled and edited by four internationally-known scientists and with chapters written by many world leaders in the field, this excellent new edition of a very popular and successful book is essential reading for fish biologists, fisheries scientists, marine biologists, aquaculture personnel, ecologists, environmental scientists, and government workers in fisheries and fish and wildlife departments. Flatfishes: Biology and Exploitation, Second Edition, should be found in all libraries of research establishments and universities where life sciences, fish biology, fisheries, aquaculture, marine sciences, oceanography, ecology and environmental sciences are studied and taught.

Reviews of the First Edition

• A solid, up-to-date book that advanced students and research scientists with interests in fish biology will find interesting and useful. Aquaculture International
• A data-rich book that outlines much of what you might ever want to know about flatfishes. Fish & Fisheries
• Well presented with clear illustrations and a valuable source of information for those with a general interest in fish ecology or for the more specialist reader. You should make sure that your library has a copy. J Fish Biology
• An excellent and very practical overview of the whole, global flatfish scene. Anyone interested in flatfish at whichever stage of the economic food chain should invest in a copy immediately. Ausmarine
• Because of the high quality of each chapter, written by international experts, it is a valuable reference. Reviews in Fish Biology and Fisheries

• Language: English
• Publisher: Wiley
• Release date: Nov 18, 2014
• ISBN: 9781118501177

Book preview

Table of Contents

Title Page

Copyright

List of contributors

Series editor's foreword

Preface to the second edition

Reference

Preface to the first edition

1.1 Notes

Acknowledgements

Chapter 1: Introduction

1.1 The fascination of flatfishes

1.2 A brief history of flatfish research and its contribution to fish biology and fisheries science

1.3 Scope and contents of the book

1.4 Nomenclature

Acknowledgements

References

Chapter 2: Systematic diversity of the Pleuronectiformes

2.1 Introduction

2.2 Systematic profile of the Pleuronectiformes

2.3 Intrarelationships of the Pleuronectiformes

2.4 Brief synopses of the suborders and families

2.5 Diversity of the Pleuronectiformes

2.6 Patterns of species discovery among pleuronectiform families

2.7 Conclusions

Acknowledgements

References

Chapter 3: Distributions and biogeography

3.1 Introduction

3.2 Geographic distribution of pleuronectiform lineages

3.3 Global patterns of species richness for the Pleuronectiformes

3.5 Historical biogeography

Acknowledgements

References

Chapter 4: Life-history traits in flatfishes

4.1 Introduction

4.2 Diversity in life-history traits of flatfishes

4.3 Variation according to geographical area, habitat use patterns and functional guilds

4.4 Intraspecies variability

4.5 Anthropogenic impacts on life-history traits

4.6 Future directions

References

Chapter 5: Ecology of reproduction

5.1 Introduction

5.2 Spawning

5.3 Gonad development

5.4 Age and size at first maturation

5.5 Energetics

5.6 Fisheries-induced evolution in reproduction and growth

5.7 Reproductive potential

References

Chapter 6: The planktonic stages of flatfishes: physical and biological interactions in transport processes

6.1 Introduction

6.2 Variations in time and space in the plankton

6.3 Physical mechanisms of transport and retention

6.4 Adaptations to transport conditions: geographical and species comparisons

6.5 Transitioning from the plankton

6.6 Implications

Acknowledgements

References

Chapter 7: Development and regulation of external asymmetry during flatfish metamorphosis

7.1 Introduction

7.2 Development and evolution of flatfish external asymmetry

7.3 Regulation of flatfish eye-sidedness

7.4 Pigmentation

7.5 Hormonal regulation

7.6 Summary and future work

Acknowledgements

References

Chapter 8: Recruitment level and variability

8.1 Introduction

8.2 Range of distribution

8.3 Average recruitment levels

8.4 Recruitment variability

8.5 Future perspectives

References

Chapter 9: Age and growth

9.1 Introduction

9.2 Age estimation

9.3 Growth of larvae

9.4 Growth during metamorphosis

9.5 Growth on the nursery grounds

9.6 Growth of adults

9.7 Longevity

References

Chapter 10: Distribution and dynamics of habitat use by juvenile and adult flatfishes

10.1 Introduction

10.2 Distribution of habitat associations

10.3 Nursery role of juvenile habitats

10.4 Dynamics of habitat associations

10.5 Future emphasis

Acknowledgements

References

Chapter 11: The trophic ecology of flatfishes

11.1 Introduction

11.2 Major flatfish feeding groups

11.3 Flatfish predators

11.4 Flatfish competitors

11.5 Flatfish trophic dynamics: a case study of Georges Bank

11.6 Summary and conclusions

Acknowledgements

References

Chapter 12: The behaviour of flatfishes

12.1 Introduction

12.2 Locomotion and related behaviour

12.3 Reproduction

12.4 Feeding

12.5 Predation and reactions to predators

12.6 Movements, migrations and rhythms

12.7 Behaviour in relation to fishing

12.8 Behaviour in relation to aquaculture and stock enhancement

12.9 Conclusions

References

Chapter 13: Atlantic flatfish fisheries

13.1 Introduction

13.2 Main species and nature of the fisheries

13.3 History of exploitation

13.4 Economic importance

13.5 Management

13.6 Notes

Acknowledgements

References

Chapter 14: Pacific flatfish fisheries

14.1 Introduction

14.2 Main species and nature of fisheries

14.3 History of exploitation

14.4 Economic importance

14.5 Management

References

Chapter 15: Tropical flatfish fisheries

15.1 Introduction

15.2 Main species and nature of the fisheries

15.3 History of exploitation

15.4 Importance

15.5 Management and conservation

Acknowledgements

References

Chapter 16: Assessment and management of flatfish stocks

16.1 Concepts and terms

16.2 Population dynamics, assessment, and management

16.3 Assessment and management summary

16.4 Conclusions

Acknowledgements

References

Chapter 17: Synergies between aquaculture and fisheries

17.1 Introduction

17.2 Species

17.3 Population structure and genomics

17.4 Life history stages

17.5 Future directions for common goals and synergies between fisheries and aquaculture

References

Appendix A: List of scientific and common names of living flatfishes used in the book

Appendix B: Common synonyms of Pleuronectidae used in the text

Index of scientific and common names

Subject index

End User License Agreement

List of Illustrations

Figure 2.1

Figure 2.2

Figure 2.3

Figure 2.4

Figure 2.5

Figure 2.6

Figure 2.7

Figure 2.8

Figure 2.9

Figure 2.10

Figure 2.11

Figure 2.12

Figure 2.13

Figure 2.14

Figure 2.15

Figure 3.1

Figure 3.2

Figure 4.1

Figure 4.2

Figure 4.3

Figure 4.4

Figure 5.1

Figure 5.2

Figure 5.3

Figure 5.4

Figure 5.5

Figure 5.6

Figure 5.7

Figure 5.8

Figure 5.9

Figure 5.10

Figure 5.11

Figure 5.12

Figure 5.13

Figure 6.1

Figure 6.2

Figure 6.3

Figure 6.4

Figure 6.5

Figure 6.6

Figure 6.7

Figure 7.1

Figure 7.2

Figure 7.3

Figure 7.4

Figure 7.5

Figure 7.6

Figure 7.7

Figure 8.1

Figure 8.2

Figure 8.3

Figure 8.4

Figure 9.1

Figure 11.1

Figure 11.2

Figure 11.3

Figure 11.4

Figure 11.5

Figure 12.1

Figure 12.2

Figure 12.3

Figure 12.4

Figure 12.5

Figure 12.6

Figure 12.7

Figure 13.1

Figure 13.2

Figure 13.3

Figure 13.4

Figure 13.5

Figure 13.6

Figure 13.7

Figure 13.8

Figure 13.9

Figure 13.10

Figure 13.11

Figure 13.12

Figure 13.13

Figure 13.14

Figure 13.15

Figure 13.16

Figure 13.17

Figure 13.18

Figure 13.19

Figure 14.1

Figure 14.2

Figure 14.3

Figure 14.4

Figure 15.1

Figure 15.2

Figure 15.3

Figure 15.4

Figure 15.5

Figure 15.6

Figure 15.7

Figure 15.8

Figure 15.9

Figure 15.10

Figure 15.11

Figure 16.1

Figure 16.2

Figure 16.3

Figure 16.4

Figure 16.5

Figure 16.6

Figure 17.1

List of Tables

Table 2.1

Table 2.2

Table 3.1

Table 3.2

Table 5.1

Table 5.2

Table 5.3

Table 6.1

Table 9.1

Table 9.2

Table 11.1

Table 13.1

Table 13.2

Table 13.3

Table 13.4

Table 13.5

Table 13.6

Table 13.7

Table 13.8

Table 13.9

Table 13.10

Table 14.1

Table 14.2

Table 14.3

Table 14.4

Table 14.5

Table 15.1

Table 15.2

Table 15.3

Table 15.4

Table 16.1

Table 16.2

Table 16.3

Table 16.4

Table 17.1

Flatfishes

Biology and Exploitation

Second Edition

Edited by

Robin N. Gibson

Mark Corner, Twynholm, Dumfries & Galloway, Scotland

Richard D.M. Nash

Institute of Marine Research, Norway

Audrey J. Geffen

Department of Biology, University of Bergen, Norway

Henk W. van der Veer

Royal Netherlands Institute for Sea Research, The Netherlands

Title Page

This edition first published 2015 © [2015] by John Wiley & Sons Ltd

First edition © 2005 Blackwell Science Ltd.

Registered office: John Wiley & Sons, Ltd, The Atrium, Southern Gate, Chichester, West Sussex, PO19 8SQ, UK

Editorial offices: 9600 Garsington Road, Oxford, OX4 2DQ, UK

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For details of our global editorial offices, for customer services and for information about how to apply for permission to reuse the copyright material in this book please see our website at www.wiley.com/wiley-blackwell.

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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.

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Limit of Liability/Disclaimer of Warranty: While the publisher and author(s) have used their best efforts in preparing this book, they make no representations or warranties with respect to the accuracy or completeness of the contents of this book and specifically disclaim any implied warranties of merchantability or fitness for a particular purpose. It is sold on the understanding that the publisher is not engaged in rendering professional services and neither the publisher nor the author shall be liable for damages arising herefrom. If professional advice or other expert assistance is required, the services of a competent professional should be sought.

Library of Congress Cataloging-in-Publication Data

Flatfishes : biology and exploitation. - Second edition / edited by Robin N. Gibson, Richard D.M. Nash, Audrey J. Geffen and Henk W. Van der Veer.

pages cm

Includes bibliographical references and index.

ISBN 978-1-118-50119-1 (cloth)

1. Flatfishes. 2. Flatfish fisheries. I. Gibson, Robin N., editor.

QL637.9.P5F58 2015

597′.69–dc23

2014026809

A catalogue record for this book is available from the British Library.

Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not be available in electronic books.

Cover image: 9th International Flatfish Symposium Artwork. Illustrations courtesy of Fishwatch.gov/National Marine Fisheries Service (NMFS)/NOAA, FOCI/RACE/Alaska Fisheries Science Center (AFSC)/NMFS/NOAA.

Cover design by Rebecca White AFSC/NMFS/NOAA

List of contributors

Kenneth W. Able

Rutgers University Marine Field Station, 80/132 Great Bay Boulevard, Tuckerton, NJ 08087, USA

[e-mail]

Kevin M. Bailey

Man & Sea Institute, LLC, 10335 46th Avenue NE, Seattle, WA 98125, USA

[e-mail]

Henrique N. Cabral

Departamento de Biologia Animal/Centro de Oceanografia, Faculdade de Ciências da Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal

[e-mail]

Steven X. Cadrin

University of Massachusetts Dartmouth, Department of Fisheries Oceanography, School for Marine Science & Technology, 200 Mill Road, Suite 325, Fairhaven, MA 02719, USA

[e-mail]

William G. Clark

6834 19th Ave. NE, Seattle, WA 98115, USA

[e-mail]

Juan M. Díaz de Astarloa

Instituto de Investagaciones Marinas y Costeras(IIMyC)-CONICET, Fac. de Ciencias Exactas y Naturales, Universidad Nacional de Mar del Plata, Funes 3350, B7602AYL, Mar del Plata Argentina

[e-mail]

Janet T. Duffy-Anderson

National Oceanic and Atmospheric Administration, Alaska Fisheries Science Center, 7600 Sand Point Way NE, Seattle, WA 98115, USA

[e-mail]

F. Joel Fodrie

Institute of Marine Sciences, University of North Carolina at Chapel Hill, 3431 Arendell St, Morehead City, NC 28557, USA

[e-mail]

Michael J. Fogarty

National Marine Fisheries Service, Northeast Fisheries Science Center, 166 Water Street, Woods Hole, MA 02543, USA

[e-mail]

Vania Freitas

Royal Netherlands Institute for Sea Research, PO Box 59; 1790 AB Den Burg Texel, The Netherlands

[e-mail]

Audrey J. Geffen

Department of Biology, University of Bergen, N-5020 Bergen, Norway

[e-mail]

Robin N. Gibson

Mark Corner, Twynholm, Dumfries & Galloway, Scotland, UK DG6 4PR

[e-mail]

Albert K. Imsland

Akvaplan-niva, Iceland Office, Akralind 4, 201 Kópavogi, Iceland

Department of Biology, University of Bergen, N-5020 Bergen, Norway

[e-mail]

Richard W. Langton

National Marine Fisheries Service, Northeast Fisheries Science Center, Maine Field Station 17 Godfrey Drive, Suite 1, Orono, ME 04473, USA

[e-mail]

Bruce Leaman

International Pacific Halibut Commission, 2320 W. Commodore Way, Suite 300, Seattle, WA 98199-1287, USA

[e-mail]

William C. Leggett

Queen's University at Kingston, 74 University Avenue, Kingston ON, Canada K7L3N6

[e-mail]

Jason S. Link

National Marine Fisheries Service, Northeast Fisheries Science Center, 166 Water Street, Woods Hole, MA 02543, USA

[e-mail]

Thomas A. Munroe

National Systematics Laboratory, NMFS/NOAA, Post Office Box 37012 Smithsonian Institution, NHB, WC 60 MRC-153, Washington DC 20113-7012, USA

[e-mail]

Hideaki Nakata

Faculty of Fisheries, Nagasaki University, 1-14 Bunkyo-machi, Nagasaki 852-8521, Japan

[e-mail]

Richard D.M. Nash

Institute of Marine Research, PB 1870 Nordnes, N-5817 Bergen, Norway

[e-mail]

David B. Packer

National Oceanic and Atmospheric Administration, National Marine Fisheries Service, Northeast Fisheries Science Center, 74 Magruder Road, Highlands, NJ 07732, USA

[e-mail]

Karin Pittman

Department of Biology, University of Bergen, N-5020 Bergen, Norway

[e-mail]

Jan-Jaap Poos

Institute for Marine Resources and Ecosystem Studies, Haringkade 1, 1976 CP IJmuiden, The Netherlands

[e-mail]

Daniel Ricard

Biology Centre AS CR v.v.i., Institute of Hydrobiology, Na Sádkách 7, České Budějovice 370 05, Czech Republic

[e-mail]

Adriaan D. Rijnsdorp

Institute for Marine Resources and Ecosystem Studies, Haringkade 1, 1976 CP IJmuiden, The Netherlands

[e-mail]

Clifford H. Ryer

Alaska Fisheries Science Center, NOAA National Marine Fisheries Service, 2030 S. Marine Science Drive, Newport, OR 97365, USA

[e-mail]

Brian E. Smith

National Marine Fisheries Service, Northeast Fisheries Science Center, 166 Water Street, Woods Hole, MA 02543, USA

[e-mail]

Allan W. Stoner

Fisheries Behavioral Ecology Program, Alaska Fisheries Science Center, NOAA National Marine Fisheries Service, 2030 S. Marine Science Drive, Newport, OR 97365, USA

[e-mail]

Tohru Suzuki

Laboratory of Marine Life Science and Genomics, Graduate School of Agricutural Science, Tohoku University, Aoba-ku, Sendai, Miyagi 981-855, Japan

[e-mail]

Masaru Tanaka

Hirano 5-2-530, Gokasyo, Uji, Kyoto 611-0011, Japan

[e-mail]

Cindy J.G. van Damme

Institute for Marine Resources and Ecosystem Studies, Haringkade 1, 1976 CP IJmuiden, The Netherlands

[e-mail]

Henk W. van der Veer

Royal Netherlands Institute for Sea Research, PO Box 59; 1790 AB Den Burg Texel, The Netherlands

[e-mail]

Catarina Vinagre

Centro de Oceanografia, FCUL, Campo Grande, 1749-016 Lisboa, Portugal

[e-mail]

Stephen J. Walsh

Northwest Atlantic Fisheries Centre, Fisheries and Oceans Canada, 80 East White Hills Rd., PO Box 5667, St John's, NL, Canada, A1C5X1

[e-mail]

Thomas Wilderbuer

US National Marine Fisheries Service, Alaska Fisheries Science Center, 7600 Sand Point Way NE, Seattle, WA 98115, USA

[e-mail]

Peter R. Witthames

40 Plumtrees, Lowestoft, Suffolk, UK, NR32 3JH

[e-mail]

Chang Ik Zhang

Pukyong National University 559-1, Daeyeon 3-dong, Nam-gu Busan 608-737, Korea

[e-mail]

Series editor's foreword

…flatfish, thirsting, trawled by grief

‘Falling on Grass’, by Elizabeth Biller Chapman

Fish researchers (a.k.a. fish freaks) like to explain, to the bemused bystander, how fish have evolved an astonishing array of adaptations; so much so that it can be difficult for such researchers to comprehend why anyone would study anything else. Yet fish are among the last wild creatures on our planet that are hunted by humans for sport or food. As a consequence, today we recognize that the reconciliation of exploitation with the conservation of biodiversity provides a major challenge to our current scientific knowledge and expertise. Even evaluating the tradeoffs that are needed is a difficult task. Moreover, solving this pivotal issue calls for a multidisciplinary consilience of fish physiology, biology and ecology with social sciences such as economics and anthropology in order to probe the frontiers of applied science. In addition to food, recreation (and inspiration for us fish freaks), it has, moreover, recently been realized that fish are essential components of aquatic ecosystems that provide vital services to human communities. Sadly, virtually all sectors of the stunning biodiversity of fishes are at risk from human activities. In freshwater, for example, the largest mass extinction event since the end of the dinosaurs occurred as the introduced Nile perch in Lake Victoria eliminated over 100 species of endemic haplochromine fish. But, at the same time, precious food and income from the Nile perch fishery was created in a miserably poor region. In the oceans, we have barely begun to understand the profound changes that have accompanied a vast expansion of human fishing over the past 100 years. The Wiley-Blackwell Series on Fish and Aquatic Resources is an initiative aimed at providing key, peer-reviewed texts in this fast-moving field.

Flatfishes, ubiquitous from the poles to the tropics, are instantly recognizable; yet some biologists regard them as just another advanced teleost, so why, we may ask, do they deserve a monograph and conferences all to themselves? In fact, flatfishes, defined as members of the monophyletic order of Pleuronectiformes, are endowed with a number of special and unique features (they underlie that instant recognition), and so your series editor is pleased to host this second edition of Flatfishes: Biology and Exploitation in the Fish and Aquatic Resources series. The first and second editions of this book grew out of a series of triennial international symposia on flatfishes held since 1990: there is now need for a second edition on account of significant advances in the science of flatfishes since the first edition was published in 2005. The second edition is a brainchild of a small team of eminent editors: Robin Gibson, Richard Nash, Audrey Geffen and Henk Van der Veer. The 17 chapters are authored by 37 experts in the field of flatfish biology from 11 countries.

When the oldest fossils appeared in the Eocene (53 million years BP), flatfishes already exhibited a diversity that suggests the order evolved in the Paleocene from perchlike marine ancestors. Today there are about 820 flatfish species in 123 genera, but relations within the group remain problematic. In this book systematics and biogeography are covered in two chapters (Munroe). Common and Linnaean names from the international fish database FishBase are used, except where recently revised.

During development each flatfish metamorphoses from a rounded, symmetrical fishlike larva to the characteristic flattened adult, with head skewed to remain horizontal as the fish lies on either its left or right side; one eye recapitulates early flatfish evolution and migrates to the upper side. Left- and right-handed eye position appears to be no guide to flatfish taxonomic relationships and the functional advantage of eye handedness remains a mystery. A chapter reviews the evolution and development of this dramatic asymmetry (Suzuki and Tanaka).

In a chapter on reproduction (Rijnsdorp, van Damme, and Witthames), we learn that, because flatfishes live in intimate contact with sediments, the effects of human pollutants on flatfish ecology are large. For example, oil spills reduce ovary development and fecundity, aromatic hydrocarbons and polychlorinated biphenyls in sediments produce smaller eggs, and some pesticides, polychlorinated biphenyls, phthalates and alkyl phenols mimic estrogen and disrupt female reproductive cycles or feminize males.

A chapter is devoted to the fascinating behaviour of flatfishes (Gibson, Stoner, and Ryer). Flatfishes employ a ‘swim-and-glide’ energy-saving locomotion by undulating the body. The 90° rotation in their body position means that flatfishes control vertical direction by changing the angle of the body, tail, and median fins; horizontal direction is altered, rather clumsily, by using the pectoral fin on the eyed side as a rudder. The characteristic flatfish camouflage serves both against detection by their prey and by their predators. Camouflage is achieved partly by very rapid second-by-second colour changes, images falling on the upper part of retina causing three types of chromatophore to expand and contact, and partly by slower changes over a number of weeks to the number and pigmentation of chromatophores, thereby altering the pattern of spots and flecks. All flatfishes can bury themselves rapidly in the substrate to aid camouflage. When this is done a muscular sac forces fluid into the orbit, causing the eyes to protrude above ground. Indeed this key feature of flatfish functional anatomy is diagnostic for the order. Flatfish eyes are independently mobile, providing 360° vision. Flatfishes are ambush predators; they may leave the bottom to capture prey in the water column and then become vulnerable to being eaten themselves. Some species avoid this problem by luring prey with a waggling pectoral fin, whereas a few species, like angler fish, have evolved specialized food-attracting lures. Prey are engulfed and sucked in by the back pressure from the highly protrusible advanced perch-pattern jaws.

A chapter covering the trophic ecology of flatfishes (Link, Smith, Packer, Fogarty and Langton) points out that flatfishes are largely piscivorous or eat benthic invertebrates like crustaceans and polychaete worms, so they generally have a trophic level of 3 or more. Some species specialize in eating the tips of bivalve siphons, especially when juvenile, whereas a few concentrate on echinoderms such as sand dollars and urchins. Flatfishes provide a tangible ‘ecosystem service’ for human benefit because they convert benthic production into a form suitable for consumption by higher predators and humans. Flatfishes are sought out as food by specialized predators such as sharks that can detect electrical impulses from their nervous systems.

Flatfishes have been eaten by humans for millennia; flatfish bones are found in ancient middens, flatfishes are portrayed in rock carvings and paintings from Europe to Australia, and clever, recurved hooks for catching large flatfishes are found among aboriginal peoples in the Pacific northwest and in northern Australia. Since the 1960s, almost 25% of all groundfish landings worldwide have consisted of flatfishes, and, in this book, the major Pacific, Atlantic and tropical flatfish fisheries each have their own chapters. Overall, the status of most fisheries is very poor and they are generally exploited way beyond levels of maximum sustainable production.

Atlantic flatfish fisheries (Walsh, Astarloa and Poos) paint a miserable story of overexploitation. The huge plaice fisheries of the early twentieth century have been severely depleted, Atlantic halibut is almost extinct and valuable sole, turbot and brill fisheries are reduced to shadows of their former glory. Species such the thin and watery-tasting Greenland ‘halibut’ (also misleading marketed as ‘turbot’) now dominate catches. The sad litany of stocks experiencing severe decline is accompanied by the realization that, over 80 years, these fisheries have been assessed and managed by some of the most advanced fisheries science in the world. As with other fish in the Atlantic, we have seen in the past an almost total failure of fisheries agencies to fulfil their mandate. However, in Europe, the jury is currently out on whether the corner has been turned. In the south Atlantic, flatfish stocks have been greatly overexploited, yet almost no good data exist with which to assess and manage the resources. An important exception to the generally dismal state of temperate flatfish resources is the Pacific halibut fishery, which has been managed conservatively by the International Pacific Halibut Commission for almost 100 years (see the chapter on Pacific flatfish fisheries by Wilderbuer, Leaman, and Zhang). Tropical flatfishes caught in fisheries (Munroe) tend to be small, taxonomically diverse and poorly known small individuals and species caught by commercial trawlers that generate huge and unreported amounts of discards.

Two new chapters for the second edition focus on flatfish life history strategies (Vinaigre and Cabral). The final chapter (Geffen, Pittman and Imsland) concentrates on the synergies between aquaculture and the biology of wild flatfishes.

This second edition continues to present timely and comprehensive ‘state-of-the-art’ reviews of flatfish biology, ecology, fisheries and aquaculture and readers will find all the components of synoptic synthesis concerning the role of flatfishes in today's depleted marine ecosystems. It therefore continues to provide a unique single source of reference on this group for all practitioners, students and policy makers concerned with marine biology, fish ecology, fishery science, marine conservation, and fisheries management.

Professor Tony J. Pitcher

Editor, Fish and Aquatic Resources Series

Fisheries Centre, University of British Columbia, Vancouver, Canada

Preface to the second edition

Instantly recognizable, flatfishes have long fascinated scientist and layman alike. The fascination stems principally from their unique asymmetric body form developed as an adaptation to a bottom-living lifestyle following metamorphosis from a bilaterally symmetrical larva. They are a relatively diverse group, over 800 extant species are currently recognized and are distributed from the Arctic to Australasia. This wide distribution, and the fact that they make important contributions to commercial and recreational fisheries in many parts of the world, means they have been the objects of research for more than a century. Over the past few decades there has been a surge of interest in all aspects of flatfish biology. This interest has found expression in, and been greatly stimulated by, the International Flatfish Ecology Symposia held triennially since 1990 and published initially (1991–95) in the Netherlands Journal of Sea Research and subsequently (1997 onwards) in the Journal of Sea Research. This large and growing body of information was synthesized into an authoritative account of the biology of this intriguing and economically important group of fishes in the first edition. That volume was well received but advances in knowledge and its application in all topics since then necessitated a second edition.

As before, the book brings together accounts written by internationally recognized experts in the field of flatfish biology. All the original chapters have been fully revised and updated and two new chapters on life-history strategies and the evolution and development of asymmetry have been added. The recent publication of a major work on flatfish culture and stock enhancement (Daniels & Watanabe 2010) rendered the original final chapter on aquaculture and stock enhancement largely redundant. That chapter has been completely rewritten and now concentrates on the synergies between studies of aquaculture and of the biology of wild flatfishes.

The first part of the book deals with systematics, distribution and life history strategies; the second with biology in the widest sense and covers development, ecology, growth and behaviour. The final five chapters describe and discuss aspects of exploitation including the major fisheries, management and assessment, and aspects of aquaculture. The volume therefore continues to represent a comprehensive review of the current ‘state of the art’ in flatfish biology and an invaluable source of reference for fish biologists, fisheries scientists and managers, and students of marine biology alike.

Reference

Daniels, H.V. & Watanabe, W.O. (eds) (2010) Practical Flatfish Culture and Stock Enhancement, Wiley-Blackwell, Ames, IA.

Preface to the first edition

Instantly recognisable, flatfishes have long fascinated scientist and layman alike. The fascination stems principally from the group's unique asymmetric body form developed as an adaptation to a bottom-living lifestyle following metamorphosis from a bilaterally symmetrical larva. They are a relatively diverse group, over 700 extant species are currently recognised, and they are distributed from the Arctic to Australasia and beyond. This wide distribution, and because they make important contributions to commercial and recreational fisheries in many parts of the world, means that they are familiar to most people and have been the objects of research for more than a century. In recent years there has been a surge of interest in all aspects of the biology of this group. The interest has found expression in, and been greatly stimulated by, the International Symposia on Flatfish Ecology held triennially in the Netherlands (1990, 1993, 1996), the USA (1999) and the UK (2002). A symposium on North Pacific flatfishes was also held in Alaska in 1994. It now seems timely for this rapidly growing body of information to be synthesised into an authoritative account of the biology of this intriguing and economically important group of fishes.

The book brings together accounts written by internationally recognised experts in the field of flatfish biology. The chapters cover systematics and distribution; reproduction and recruitment; ecology and behaviour of the main life history stages; the major fisheries and their management; and the latest developments in flatfish aquaculture and stock enhancement. The volume therefore represents a comprehensive review of the current ‘state of the art’ in flatfish biology and will be an invaluable source of reference for fish biologists, fisheries scientists and managers, and students of marine biology alike.

1.1 Notes

Proceedings of the International Symposia were published as follows. First Symposium: Netherlands Journal of Sea Research 1991, 27 (3–4); 1992, 29 (1–3). Second Symposium: Netherlands Journal of Sea Research 1994, 32 (2–4); 1995, 34 (1–3). Third Symposium: Journal of Sea Research 1997, 37 (3–4); 1998, 40 (1–2). Fourth Symposium: Journal of Sea Research 2000, 44 (1–2); 2001, 45 (3–4). Fifth Symposium: Journal of Sea Research 2003, 50 (2–3); 2004, 51 (3–4). Proceedings of the International Symposium on North Pacific Flatfish: Alaska Sea Grant College Program Report No. 95–04, University of Alaska Fairbanks (1995).

Acknowledgements

The first edition of this book was well received and the editors are grateful to Nigel Balmforth of Wiley-Blackwell for his encouragement to produce a second edition. It is a pleasure to acknowledge the enthusiasm of the authors in agreeing to revise and update their chapters. Their willingness to comply with suggestions, requests and questions relating to their contributions made the editors' task an enjoyable one.

The editors gratefully acknowledge Rebecca White, Alaska Fisheries Science Center/National Marine Fisheries Service/NOAA for allowing her design to be used on the cover of the book. The artwork was created for the International Flatfish Symposium using illustrations from the following resources: Ichthyoplankton Information System. 04 June 2012. National Oceanic and Atmospheric Administration http://access.afsc.noaa.gov/ichthyo/index.php and http://www.fishwatch.gov.

Chapter 1

Introduction

Robin N. Gibson

Mark Corner, Twynholm, Dumfries and Galloway, Scotland, UK

Abstract

The unique asymmetric structure and appearance of flatfishes, their abilities to change colour to match the background and to burrow in the sediment all make them a fascinating subject of study. Following a brief history of flatfish research and its contribution to fish biology and fisheries science, the scope and contents of Flatfishes: Biology and Exploitation are outlined. The contents can be roughly divided into three parts with numerous links between them. The first part deals with systematics, distribution and life history stategies; the second with biology and covers development, recruitment, ecology, growth and behaviour. The final five chapters describe and discuss aspects of exploitation including the major fisheries, management and assessment and the contributions of aquacultural studies to flatfish biology. A final section on nomenclature discusses the difficulties inherent in using common and scientific names and describes the method used to ensure that there is no ambiguity in the text.

Keywords: Flatfishes; systematics; distribution; life history; ecology; growth; behaviour; fisheries; management; aquaculture

1.1 The fascination of flatfishes

Most people's first encounter with flatfishes is on a fishmonger's slab where their unusual shape makes them instantly recognizable. Flatfishes have certainly featured in the human diet for millennia. They appear in prehistoric rock carvings (Muus & Nielsen 1999), their remains are found in ancient middens (Nicholson 1998; Barrett et al. 1999) and they continue to make up a significant proportion of the world groundfish catch today. Gastronomy apart, the interested layman's curiosity is aroused not only by the presence of both eyes on the same side of the head and their flattened shape, but also by the remarkable ability of flatfishes to match the colour and pattern of their background and to bury in the sediment. The last three characters are present in some other bottom-living fishes (e.g. skates and rays, anglerfishes) but together with eye migration in the larva and the less obvious features of protrusible eyes and a dorsal fin that continues onto the head, they make the flatfishes unique.

An intriguing question is why some flatfishes have their eyes on their right side whereas in others the eyes are on the left side. Examination of the occurrence of left and right ‘sidedness’ within the Order Pleuronectiformes shows that although some families are predominantly left or right sided (see Chapter 2 this volume), the trait for a particular direction of asymmetry does not reflect relationships within the order. This conclusion holds true whether morphological or molecular evidence is used to deduce interrelationships (Berendzen & Dimmick 2002). Furthermore, in some species, for example the fossil Amphistium (Friedman 2008), the primitive Psettodes and the European flounder (Platichthys flesus) and starry flounder (P. stellatus), ‘reversed’ individuals are common. Also, in these two Platichthys species at least, sidedness varies geographically (Policansky 1982a, 1982b; Fornbacke et al. 2002). Breeding experiments with starry flounder have demonstrated that the direction of asymmetry is predominantly under genetic control but there may also be some environmental influence (Policansky 1982a; Boklage 1984). The exact mechanism involved is unclear and remains a subject of debate (McManus 1984; Morgan 1991), although the optic chiasma may be involved (see Chapter 7, this volume). To return to the original question, inheritance of eye position suggests that there should be some selective advantage of having eyes on one or other side of the head. It seems intuitively reasonable to assume that it would be advantageous for all members of the population to have the same eye position (Policansky 1982a), particularly during mating, and in most species this is indeed the case. However, Fornbacke et al. (2002) have suggested that left-sided individuals of young European flounder may be favoured by less competition with the right-sided European plaice (Pleuronectes platessa). In addition, the two morphs of starry flounder are not simple behavioural images of one another. Differences in behaviour together with slight anatomical differences between them suggest that the morphs are not ecologically identical and that the polymorphism may be driven by competitive interactions between left- and right-sided forms (Bergstrom 2007; Bergstrom & Palmer 2007).

The ability of flatfishes to camouflage themselves against the seabed on which they lie is also a source of fascination for many. Background matching is the result of rapid nervous and slower hormonal responses to visual stimuli received by the eyes and is achieved by differential responses of the chromatophores in the skin. In this way flatfishes can match not only the general colour of their background but also its pattern, even to the extent that the sizes of the spots on a spotted background can be mimicked (Ramachandran et al. 1996; Healey 1999; Burton 2010).

The variety of flatfishes and their adaptations to a benthic existence also make them intriguing subjects for study by fish biologists. Flatfishes vary in adult size from a few centimetres up to 2 m or more. They are widely distributed in cold, temperate and tropical seas in depths from the intertidal zone to the continental slope, including hydrothermal vents, but seem to be absent from the deepest parts of the sea (see Chapter 3 this volume). This variation in size and habitat means that they display a considerable range of patterns in ecology and life history and in physiological and behavioural adaptations to life on and in the bottom. Their value as food has also resulted in numerous investigations of these patterns and adaptations in relation to growth, feeding, reproduction and population structure, and the application of the results to management. Yet the intraspecific and interspecific roles of flatfishes in benthic ecosystems as predators, competitors and prey are still largely unresolved, even though flatfishes may account for around a quarter of groundfish species richness and biomass in some areas such as the North Sea (Daan et al. 1990). In some coastal nurseries, juvenile flatfishes may numerically dominate the benthic fish fauna (e.g. Gibson et al. 1993).

1.2 A brief history of flatfish research and its contribution to fish biology and fisheries science

Although flatfishes feature in many early descriptive zoological treatises and several common species were given their scientific names by Linnaeus in 1758, the first detailed articles describing research on flatfishes appear in the scientific literature at the end of the nineteenth century. Much of this early research was stimulated by the need for information on the biology of the common foodfishes and was fuelled by a concern for the state of their fisheries and why catches fluctuated (e.g. Petersen 1894; Holt 1895). At that time, fluctuation in catches was considered to be due principally to changes in migration patterns but also to the possibility that stocks were being overfished, challenging the earlier assertion by T.H. Huxley that the sea was an inexhaustible resource. It was realized that basic information was lacking and this lack led to the development of numerous research programmes to collect data on age, growth and size at maturity and examine whether fishing did, in fact, have any effect on populations. It rapidly became evident that fishing could have significant effects and Holt (1895), for example, recommended the imposition of a size limit for European plaice and common sole (Solea solea) in the North Sea. He also considered the possibility of protected areas, close seasons, mesh restrictions and artificial propagation. He dismissed stock enhancement using reared young stages as impractical and uneconomic even though the development of rearing techniques for fishes on a large scale both in North America and Europe had been in progress for some time (Ewart 1885; Dannevig 1897; Blaxter 1975; Smith 1994). Subsequent trials indicated that Holt's opinion was correct and the emphasis in the North Sea moved to the transplantation of wild fish with some success (see Blaxter 2000 for review). Flatfishes played a significant part in the development of these conclusions following experiments in Scotland and the ‘Great Fishing Experiments’ resulting from cessation of fishing in the North Sea during the two World Wars (summarized by Smith 1994). In these ‘experiments’ it was clearly demonstrated that the population structure of North Sea plaice could be greatly altered by fishing but was also capable of recovery when fishing pressure was released.

The early studies in Europe and the United States represented the beginnings of fisheries research and contributed to the formation of bodies such as the International Council for the Exploration of the Sea (ICES) (Rozwadowski 2002) and the International Pacific Halibut Commission (Smith 1994). Much of this work is summarized in subsequent chapters in this book and it has made significant contributions to fish biology and fisheries science. Particular mention can be made of the classic early works on tagging (Petersen 1894) and colour change (e.g. Mast 1914). Beverton & Holt's (1957) seminal treatise on the dynamics of exploited populations incorporated the results of many flatfish studies and intensive investigations of flatfish movements in the North Sea (summarized by Harden Jones 1968) added greatly to our understanding of migration, a topic that continues to produce novel insights into fish behaviour (e.g. Metcalfe & Arnold 1997; Metcalfe et al. 2006). The development of ageing techniques for fishes owes much to studies of flatfish species (see Chapter 9 this volume) and the renewed interest in mass rearing to the juvenile stage pioneered in Europe (Rollefsen 1934; Shelbourne 1964) provided material for studies of larval behaviour and physiology that would not have been possible using wild-caught individuals (see, for example, Blaxter 1986). Studies of sex determination and the endocrine control of metamorphosis in flatfishes have also contributed significantly to our wider understanding of these topics (Borski et al. 2010). Mass rearing techniques, which for several species are now routine (Daniels & Watanabe 2010), also paved the way for further evaluation of the feasibility of flatfish stock enhancement, particularly in Japan, using juveniles rather than eggs and larvae. The International Flatfish Ecology Symposia (see Preface) provide a platform for the presentation and discussion of the most recent studies.

In a wider context, anatomical studies of flatfishes have contributed to discussions of evolutionary mechanisms. The origins of flatfishes were a contentious issue in early debates because intermediate stages between symmetric and asymmetric forms (i.e. those with incomplete eye migration) had not been found. Furthermore it was considered that such intermediate forms could not be adaptive. Consequently, arguments for saltatory change were invoked and even natural selection itself was attacked. However, the subsequent discovery and description of the fossils Amphistium and Heteronectes, the most primitive flatfishes currently known, showed that the attainment of asymmetry of the eyes and of cranial anatomy could indeed have been gradual (Friedman 2008).

1.3 Scope and contents of the book

The book is an overview of the biology and exploitation of flatfishes. Although necessary constraints on length mean that the coverage of each topic is not fully comprehensive, each chapter does represent a succinct summary of the ‘state of the art’ in its own field. Furthermore, as Hensley (1997) and several authors in this volume continue to point out, current detailed knowledge is based on only a few, mostly north temperate, species of economic interest.

The contents can be roughly divided into three parts with numerous links between them. The first part deals with systematics, distribution and life history stategies; the second with biology in the widest sense and covers development, ecology, growth and behaviour. The final five chapters describe and discuss aspects of exploitation including the major fisheries, management and assessment and the contributions of aquacultural studies to flatfish biology.

The book starts with chapters on systematics and biogeography that review our current understanding of the evolution and taxonomic diversity of flatfishes. Flatfish fossils are rare but the oldest known date from at least 45 million years ago when many lineages had already diversified. The Order Pleuronectiformes is considered to be monophyletic and over 800 species in 15 family level taxa are presently recognized, but the total species diversity for the order is unknown. The flatfish fauna of north temperate regions is generally well known but those of the tropics and deeper water are not. Tropical flatfishes are small, difficult to identify and many tropical habitats have not been well sampled. These factors, together with the growing realization that taxa formerly considered to be widespread single species may actually be species complexes, indicate that many flatfish species still await discovery. The companion Chapter 3 provides an overview of flatfish distributions by describing the global occurrence of the flatfish families and their patterns of species richness in terms of geographical region and specific environments. Although flatfishes have a virtually worldwide distribution, this distribution is not uniform; the East China Sea, for example, is particularly speciose but freshwaters, the deeper parts of the sea and high latitudes in the Southern Ocean are comparatively species poor. Consideration of the historical biogeography of the group provides an explanation of some of these patterns but, here again, incomplete knowledge of systematics and distribution prevents as yet a full picture being obtained. Clearly, much remains to be done in this field of flatfish biology. After an introduction to life-history theory, the next chapter describes the diversity in life-history traits of flatfishes and how they vary according to geographical area, habitat use patterns and functional guilds. Intraspecies variability is also examined with particular reference to phenotypic plasticity, local adaptation, cogradient variation and parental effects. Finally, anthropogenic impacts such as fishing pressure and climate change on life-history traits are discussed. Chapter 5 describes the reproduction of flatfishes and focuses on those characteristics that affect the production of offspring and their survival namely, egg size, spawning, gonad development and fecundity, onset of sexual maturity, and the energetics of reproduction and growth. The authors explore the adaptive significance of patterns of reproduction from the viewpoint that reproductive characteristics have evolved, and continue to evolve, in response to environmental conditions. They discuss these characteristics in relation to the geographical distribution of species and their implications for population dynamics and the resilience to perturbations caused by exploitation and pollution.

Most flatfish eggs and all larvae that hatch from them are planktonic. Consequently their rate and direction of dispersal after spawning is largely dependent on the characteristics of local water movements. Chapter 6 describes the types of water movement to which eggs and larvae are exposed and the physical mechanisms by which they are transported to, or conversely retained in, their appropriate nursery grounds. Most transport is assumed to be passive, especially as flatfish larvae are relatively feeble swimmers, but the ability of larvae to migrate vertically enables them to exert some control over their net direction and speed of movement. A comparison of species and genera in the same and different locations reveals remarkable variety in transport patterns, all of which are adapted to local hydrographic conditions and which link spawning grounds to nursery areas. Coupled physical and biological models can contribute greatly to the understanding of this process. The extent of variation in the success of transport to suitable nursery grounds has considerable implications for population genetics and connectivity, management and recruitment.

At the end of their planktonic stage, larvae begin the process of metamorphosis and their transition to a benthic way of life. The metamorphosis of flatfishes is characterized by the migration of one eye to the opposite side of the head and by subsequent pigmentation of the ocular side only. Chapter 7 describes the systems involved in the development and regulation of these external asymmetries and how they may have evolved. An important finding related to eye-sidedness is that the Nodal pathway, which is known to control laterality of internal organs, fixes eye-sidedness through a series of novel mechanisms. Regarding pigmentation, latent precursors that give rise to the adult-type chromatophores that confer colour to the ocular side are localized along the base of the dorsal and anal fins until metamorphosis.

Chapter 8 reviews the data and hypotheses relating to the generation, regulation and variability of recruitment and analyses three factors relevant to these processes; namely a species' range, and its average level of, and annual variability in, recruitment. Temperature is considered to be the predominant factor determining range but it is also important in determining the duration of the egg and larval stages and hence the critical distance between spawning and nursery grounds. With respect to recruitment level, the authors conclude that level is governed by two distinct processes; the effect of food availability on adult condition at spawning time and density dependent mortality of juveniles on the nursery grounds. This density dependent mortality, which results from the concentration of juveniles in two dimensions after settlement, may also be an important contributing factor to the lower recruitment variability of flatfishes compared with other groups.

A knowledge of growth rates and patterns is essential for many areas of fish and fisheries biology and flatfish growth is summarized in Chapter 9. The range of longevity within the group is large (<2 to 60 years) and a complex range of factors affect growth throughout life. Some of the earliest studies seeking methods for ageing fish were carried out on flatfishes and led to the recognition of the value of otoliths as records of past growth. Otoliths are now routinely used for ageing all stages from larva to adult but our knowledge of flatfish growth patterns has arisen from a combination of both laboratory and field studies. These studies have demonstrated the vital importance of temperature in determining growth rate but numerous other factors come into play with differing importance throughout the life history. Food supply is particularly critical in the larval and juvenile stages and there has been much discussion of the question of density dependent growth. In some areas juvenile growth rates have been used to assess the quality of nursery grounds. In the adults, growth patterns and their interpretation are strongly affected by reproduction and the effects of exploitation. The next chapter describes the distribution and dynamics of habitat use by juvenile and adult flatfishes. In many species, but not all, there are considerable differences between the distribution of these two stages because the inshore areas where metamorphosing fishes settle are separated from the offshore feeding and spawning grounds of the adults. Particular attention is given to the ‘nursery’ role of these early juvenile habitats. Growth on these nursery grounds is subsequently followed by a gradual movement into deeper water. Superimposed on this gradual ontogenetic change in distribution, however, are shorter frequency variations in habitat occupation varying from tidal to annual timescales. The factors controlling these movements are for the most part unknown and although numerous studies have identified abiotic variables such as depth, salinity, temperature and substratum type, which correlate with distribution, there may not necessarily be any causal relationship between them. Instead, or in addition, gradients of abiotic factors may be used to locate areas that fulfil the requirements of the particular life history stage. Consideration of spatial scale is also relevant. Whereas large and small-scale differences in distribution may be defined by depth, salinity and temperature it is likely that biotic factors such as food availability and predator avoidance are important at smaller scales. Nevertheless, substratum type may be of greater importance in determining habitat occupation for flatfishes than for many other groups. It is certainly true that the substratum is the source of food for the great majority of flatfishes and whereas some species are piscivorous, most prey on invertebrates living in and/or in sediments.

Chapter 11 reviews the trophic ecology of flatfishes first by defining the main feeding types and the factors affecting their diet and then by examining the range and effects of flatfish predators and competitors. The evidence for intra- and interspecific competition is ambiguous but in some cases is strongly suspected. Predation on flatfishes, on the other hand is intense particularly in the youngest stages, and predators range from crustaceans through birds and mammals, not the least of which is man. These various aspects of trophic ecology are combined in a case study of Georges Bank in which the authors demonstrate shifts in abundance and species composition, potential competitive interactions and the extent of predation by and on flatfishes, which may be considerable. Nevertheless, better assessments of in situ competition and population-level impacts, together with a greater understanding of the impacts of changes to benthic communities, and their broader implications for flatfishes, are still required.

Chapter 12 describes aspects of flatfish behaviour in some detail. It includes a summary of locomotion but concentrates on the key activities of spawning, feeding and reactions to predators that enable fishes to reproduce, grow and survive. These activities take place at a range of spatial scales from localized foraging to long distance migrations and the chapter also includes a brief account of movement patterns that have evolved to make the most effective use of the environment. Much remains to be learnt about flatfish behaviour and recent studies have demonstrated that they spend much more of their time off the bottom than was previously realized. Finally, the significant role of behaviour in the capture and culture of flatfishes is discussed and its importance attempts to design selective fishing gear and to augment and conserve wild flatfish populations through stock enhancement.

The last section of the book is concerned with the exploitation of flatfishes. Three chapters, written in a similar format to allow comparison, describe flatfish fisheries in the Atlantic and Pacific Oceans and the tropics. Each first describes the main species involved, their relative importance and the nature of the fisheries in the region. Following a short history of flatfish exploitation, an assessment is made of their economic importance and each chapter ends with a description and discussion of management strategies, results and problems for each region. The major fisheries are in the northern hemisphere where the larger species of righteye flounders (Pleuronectidae), soles (Soleidae) and lefteye flounders (Bothidae, Scophthalmidae) are the main targets and include the largest of all flatfishes, the halibuts. In the southern hemisphere catches are smaller and consist mostly of Soleidae, Bothidae, large-tooth flounders (Paralichthyidae) and some tonguefishes (Cynoglossidae). Tropical flatfishes, in contrast to those at higher latitudes, are mainly caught as bycatch rather than in targeted fisheries and the catches are much more diverse. Here, American soles (Achiridae), tonguefishes and psettodids (Psettodes spp.) also feature in the catches together with smaller numbers of species from other families. In terms of total fish catches, flatfishes form a small but significant proportion in the north Pacific and Atlantic (∼10 – 30%) but much less in the southern hemisphere (<2% in the south Pacific) and the tropics. Nevertheless, they can command a high price and their economic value is often relatively much higher than landings statistics would suggest.

The increasing exploitation of flatfishes led to the realization that management strategies would need to be put into place to protect stocks. Such strategies were first mooted in Europe at the beginning of the last century, somewhat later in the North Pacific and are still largely lacking in the southern fisheries and tropics. For the most part, such strategies are overseen by international bodies but in some areas (e.g. Japan) may be under more local control. Regrettably, and for a variety of reasons discussed in the three chapters, many of these management plans have not prevented stock declines. There are success stories, however, as in yellowtail flounder (Limanda ferruginea) and Pacific halibut (Hippoglossus stenolepis), where a long history of research and management by the International Pacific Halibut Commission has resulted in one of the most successful fishery management programmes in the world. Successful management requires data and that is often lacking, particularly in the southern hemisphere and the tropics. In tropical regions, landings are gross underestimates of the total catch because bycatch and the products of artisanal fisheries are not included. Landings are mostly not identified, so that catches of individual species are impossible to estimate. Locally, tropical flatfishes are becoming more important as a food source as catches of other ground fishes have declined. In these regions, solutions to overfishing and habitat destruction will not be prevented by traditional approaches to fisheries management that attempt to regulate only resources. Rather, management will have to focus on people, not fish, to find solutions.

The penultimate chapter takes an overview of assessment and management in general but necessarily concentrates on those areas (the northeastern Pacific and the North Atlantic) where most data are available. The authors first consider aspects of flatfish population dynamics that are important for assessment and management, particularly the relationship between stock size and reproductive success which they consider to be historic basis for evaluating stock dynamics and conservation targets and limits. They then illustrate how traditional approaches are changing as the exploration of the effects of environmental forcing on growth and recruitment proceeds. Finally, they present a summary of stock assessment results and harvesting policies currently in use in Europe and North America and note that many more advanced stock assessment methods have been developed in the last few years. They conclude that although many stocks continue to decline some are stable or increasing. It seems that future developments will require greater use of the precautionary approach and an emphasis on cooperation between scientists, managers and fishers, all of whom are ultimately seeking the same goal.

Apart from the need to regulate exploitation, the concern over the decline of wild stocks stimulated two other approaches to maintaining the supply of flatfishes for human consumption. First, the enhancement of wild stocks by supplementation with reared individuals and second, intensive farming. Both these approaches required the development of mass culture techniques. The final chapter in the book examines the relationships between research and developments in flatfish aquaculture and studies of the ecology and fisheries of wild populations. The benefits of knowledge exchange between studies of wild and captive populations are often overlooked, as are the synergies that have arisen from work on the same species under different conditions. Examples are presented of how additional knowledge has been acquired by drawing on work with wild and cultured populations, especially the early life-history stages, and in areas such as understanding metamorphosis, the mechanisms controlling maturation and reproduction, and the importance of population genetic structure. Significant synergies have grown out of the development of genomics tools in particular, contributing to advances in aquaculture, ecotoxicology, and a greater understanding of population structure and local adaptations.

1.4 Nomenclature

Finally, a note on nomenclature. Like most groups the scientific nomenclature of flatfishes is in continual flux and, as with many other commercial species, their common names are confusing. A few examples will make the problem clear. ‘Flounder’ is widely used as a general term for all flatfishes and is applied with epithets to a great variety of species. ‘Sole’ is similarly but more restrictively used. Common names in the English language vary notoriously from place to place as in ‘American plaice’ and ‘long rough dab’ for Hippoglossoides platessoides. Furthermore, species described as a ‘flounder’ or ‘sole’ may not necessarily reflect their systematic position. The ‘English sole’ (Parophrys vetula), for example, is neither English nor a sole. The question then arises of which system of nomenclature should be used in a book on flatfishes that is both unambiguous and reflects current systematic thinking. One approach would be to use the names used by the authors of individual chapters without any attempt to adopt a uniform system. On this basis, reference to the original publications cited would make the identity of species clear. However, this approach could lead to confusion particularly as there have been major changes in flatfish nomenclature in the past few years, some of which are reflected in recent publications whereas others are not. The approach adopted here will hopefully minimize ambiguity and maximize the readability of the text. In each chapter a species is defined at first mention by its scientific and English common name. Thereafter only the common name is used. The scientific names used are those given in FishBase (www.fishbase.org) at the time of going to press (2014), except for those members of the Pleuronectidae whose names have been recently changed following the extensive taxonomic revision by Cooper & Chapleau (1998). Common names are those given in FishBase although in some cases no common names are available. In such cases the common name used by the chapter author has been used. Two appendices are provided at the end of the book that list the scientific and common names used throughout the text and the pleuronectid scientific names used before and after Cooper & Chapleau's (1998) revision.

Acknowledgements

I am grateful to Kevin Bailey, Andrew Cooper, S.J. de Groot, Tom Munroe and Tom Wilderbuer for their help and advice in writing the original version of this chapter.

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