Contents
Preface
Acknowledgements
1 Marine fisheries ecology: an introduction
1.1 Introduction
1.2 Fisheries of the world
1.3 Patterns of exploitation
1.4 Why manage fisheries?
1.5 Objectives of management
1.6 Meeting management objectives
1.7 Structure of this book
2 Marine ecology and production processes
2.1 Introduction
2.2 Primary production: sources and magnitude
2.3 Phytoplanktonic production
2.4 Non-phytoplanktonic production
2.5 Heterotrophic production
3 Fished species, life histories and distribution
3.1 Introduction
3.2 Fishes
3.3 Invertebrates
3.4 Life histories
3.5 Distribution in space and time
4 Population structure in space and time
4.1 Introduction
4.2 Recruitment
4.3 Density-dependent habitat use
5 Fishing gears and techniques
5.1 Introduction
5.2 From shoreline gathering to satellites
5.3 Modern commercial fishing gears
5.4 Other fishing techniques
5.5 Conservation methods
6 Fishers: socioeconomics and human ecology
6.1 Introduction
6.2 Motivations for fishing
6.3 Modifications to fishing behaviour
6.4 Conflicts and conflict resolution
7 Single-species stock assessment
7.1 Introduction
7.2 Balancing birth and death
7.3 Surplus production models
7.4 Delay–difference models
7.5 Virtual population analysis
7.6 Statistical catch-at-age methods
7.7 Yield-per-recruit models
7.8 Incorporating recruitment
7.9 Confronting risk and uncertainty
7.10 Biological reference points
8 Multispecies assessment and ecosystem modelling
8.1 Introduction
8.2 Multispecies surplus production
8.3 Multispecies yield per recruit
8.4 Multispecies virtual population analysis
8.5 Predators, prey and competitors
8.6 Size spectra
8.7 Ecosystem models
9 Getting the data: stock identity and dynamics
9.1 Introduction
9.2 Stock identification
9.3 Stock dynamics
9.4 The impact of errors
10 Getting the data: abundance, catch and effort
10.1 Introduction
10.2 Abundance
10.3 The fishery
11 Bioeconomics
11.1 Introduction
11.2 The value of fisheries
11.3 Bioeconomic models
11.4 Economic vs. social management objectives
12 Fishing effects on populations and communities
12.1 Introduction
12.2 Vulnerability to fishing
12.3 Intraspecific effects
12.4 Community effects
13 Bycatches and discards
13.1 Introduction
13.2 Catches, bycatches and discards
13.3 Alternatives to discarding
13.4 Fisheries and bycatches
13.5 Incidental captures
13.6 Methods to reduce bycatches
13.7 Ghost fishing
13.8 Sociocultural differences
14 Impacts on benthic communities, habitats and coral reefs
14.1 Introduction
14.2 Fishing disturbance
14.3 Direct effects of fishing gear on the seabed
14.4 Effects of static fishing gears
14.5 Long-term effects
14.6 Fishing as a source of energy subsidies
14.7 Indirect effects on habitats
15 Fishery interactions with birds and mammals
15.1 Introduction
15.2 Birds
15.3 Mammals
16 A role for aquaculture?
16.1 Introduction
16.2 Aquaculture past and present
16.3 What is cultivated?
16.4 Production systems
16.5 Feeding constraints
16.6 Prospects for expansion
16.7 Case studies
17 Management and conservation options
17.1 Introduction
17.2 Management objectives, strategies and actions
17.3 Improving management
17.4 Multispecies and ecosystem-based management
17.5 Managing fisheries for conservation
17.6 Future trends
Appendix 1: List of symbols
Appendix 2: Fisheries websites
Appendix 3: Geographic index
References
Index
© 2001 by Blackwell Science Ltd,
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First published 2001
Reprinted 2003
Library of Congress Cataloging-in-Publication Data
Jennings, Simon.
Marine fisheries ecology / Simon Jennings, Michel J. Kaiser,
John D. Reynolds.
p. cm.
Includes bibliographical references (p. ).
ISBN 0-632-05098-5
1. Fishery management. 2. Marine fishes—Ecology.
3. Fisheries—Environmental aspects. I. Kaiser, Michel J.
II. Reynolds, John D. III. Title.
SH328. J46 2000
333.95’6—dc21
00-021514
A catalogue record for this title is available from the British Library.
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Preface
Fisheries play a key role in providing food, income and employment in many parts of the world. We might expect fishing to be a profitable and effective way of getting food, since fishers take harvests that they need not sow. Sadly, this is rarely true. Fisheries are often subsidized, wasteful, cause excessive environmental damage and ignite conflicts between otherwise friendly nations. Relatively few fisheries realise their potential benefits to fishers and society.
For many years, the main objective of fishery management was to maximize the yield taken from a fishery without compromising future catches. Intuitively, this seemed a simple and sensible objective, but in practice, there were good biological, sociological and economic reasons why it was rarely achieved. Not only were some fisheries so heavily fished that they collapsed, but they became economically inefficient and threatened species and habitats of conservation concern that were not their intended targets. Clearly, there is much scope to improve management of fisheries and the way we utilize the marine environment.
Fisheries science is now a more exciting and varied field of study than ever before. This is because contemporary management objectives are increasingly diverse, and our attempts to manage and conserve fisheries are based on a much broader scientific understanding of fishers and the fished ecosystem. Indeed, many fishery scientists are now asked to address biological, economic and social concerns. These range from dealing with uncertainty and reducing incidental catches of dolphins to ensuring that fished coral reefs remain attractive to tourists, that fisheries are profitable, and that conflicts between fishers are minimized.
Effective fisheries management requires clear objectives and a decision-making process supported by the best scientific advice. The aim of this book is to give the reader a broad understanding of biological, economic and social aspects of fisheries science and the interplay between them. The overall emphasis, however, is deliberately ecological. By the time you have read this book we hope that you will appreciate:
Previous fisheries textbooks have concentrated almost exclusively on the mechanisms of stock assessment and management with little reference to the ecosystem in which the management practices are applied. However, students have often told us that they wanted to learn more about various fisheries-related issues that traditionally receive scant coverage in fisheries textbooks. These include trawling impacts, coral reef fisheries, discarding, seabirds, marine mammals, and poverty and conflict in fishing communities. They found it difficult to relate ‘fisheries’ courses that focused purely on quantitative assessment of population dynamics to many of the issues that confronted them in their own lives, the media and even in future employment. Thus, we wanted to write a book that reflected the global diversity of fished species, fisheries and fishing behaviour and showed how useful generalities could be drawn by working across conventional boundaries and treating fisheries as part of an ecosystem that includes the fishers. We also hope to convey our enthusiasm for fisheries ecology through our personal experiences and convince you that it is an exciting subject area that is helping to drive our understanding of marine ecosystems.
We begin this book by introducing the world’s fisheries, their diversity and history, suggesting why we need to conserve fisheries and the marine environment and discussing the main objectives of management. The remaining chapters can be divided into related groups that treat various aspects of fisheries ecology and their relevance to the assessment and management of fisheries. Chapters 2, 3 and 4 cover production processes, the species that are fished, the food chains that support them, and the factors that control the rates and variability of production. Chapters 5 and 6 consider the fishers: how and why people go fishing, the social importance of fisheries and the factors that affect the ways in which people fish. Chapters 7–11 deal with fishery assessment: how to assess the effects of fishing on target species, multispecies communities and ecosystems, bioeconomics, and how to get the data needed for assessments. Chapters 12–15 look at the wider effects of fishing, on community structure, diversity, population genetics, habitats, seabirds, marine mammals and species of conservation concern. In Chapter 16 we ask whether aquaculture can replace fishing as a source of protein, and in 17 we show how knowledge of production processes, fishers, assessment and fishing effects can be used to reach a range of management and conservation objectives.
We introduce most of the quantitative methods used for fisheries assessment but this is not a recipe book, and our emphasis is on why such models are needed, their assumptions and potential pitfalls. Many ideas are illustrated conceptually rather than mathematically, since several excellent texts already deal with quantitative stock assessment. For those who want to develop expertise in quantitative assessment we strongly recommend the excellent texts by Clark (1985), Hilborn and Walters (1992) and Quinn and Deriso (1999). These are packed with useful ideas and examples of their application. The history of fishery science and its contribution to wider ecological thinking are well described by Smith (1994).
Before you start reading we would like to draw your attention to the structure of this book. The chapters were written with the intention that they would be read in sequence, although each chapter has its own introduction and summary and can be read in isolation by the casual browser. We have referenced the text rather more extensively than many student textbooks. Our aim was to cite classic references from people who developed an idea coupled with contemporary sources that reveal the state of understanding that has now been achieved. These allow an easy lead-in to the research literature on a particular topic. For the reader who would like to know more, each chapter ends with a ‘further reading’ section. This lists 3–4 key books or reviews that develop ideas introduced in the chapter. Lecturers can download the figures that appear in this book from the Blackwell Science website (www.blackwell-science.com/jennings).
All places mentioned in the text are indexed on page 389 and their locations are shown on the accompanying map. Key terms are shown in bold at their first significant use and accompanied by a brief description. In the subject index, the pages on which these terms appear are shown in bold italic so the description can be found. The meanings of all symbols used in equations are given at their first usage and in the table on page 380. Note that biologists and economists often use the same symbols to denote different parameters. Common and species names are given in full at first usage and the taxonomic family to which they belong is shown in parentheses. This can be used to trace the taxonomic affiliation of the species in Tables 3.2 and 3.4. Common and scientific names of all species mentioned are indexed on page 393. The appendices also include a list of fisheries websites that provide a wealth of fisheries information and from which software, data and publications may be downloaded.
We hope you enjoy reading this book and find it useful.
Acknowledgements
We could not have produced this book without the help of many people. Sections of the draft text were read by John Coppock, Isabelle Côté, Chris Darby, Dan Duplisea, Chris Francis, Tim Hammond, Joe Horwood, Rognvaldur Hannesson, Alex Lincoln, Iago Mosquera, Mike Pawson, André Punt, Terry Quinn, Jo Ridley and Bill Sutherland, while Jeremy Collie read everything! Their comments substantially improved the final text. We apologise to the undergraduate students who served as guinea pigs for some of the material in this book and thank them for their feedback! Ian Sherman, Dave Frost and the staff of Blackwell Science were helpful, patient and a pleasure to work with.
Unpublished manuscripts, reprints, materials, data and advice were provided by David Agnew, Geoff Arnold, Mike Beardsell, Andrew Brierley, Martin Collins, John Cotter, Mark Chittenden, Tas Crowe, Chris Darby, Nick Dulvy, Jim Ellis, Karen Field, Nick Goodwin, Ewan Hunter, Diane Kaiser, John Lancaster, Ray Leakey, Chris Mees, Julian Metcalfe, Richard Millner, Jack Musick, John Nichols, Carl O’Brien, Hazel Oxenford, Daniel Pauly, Mike Pawson, Nélida Pérez, Nick Polunin, John Pope, André Punt, Callum Roberts, Rob Robinson, Stuart Rogers, Garry Russ, Ian Russell, Melita Samoilys, John Stevens, Rob Tinch, Geoff Tingley and David Walton.
Photographs were kindly provided by Frank Almeida, Gian Domenico Ardizzone, David Barnes, Quentin Bates, David Berinson, Steve Blaber, Dan Blackwood, Lesley Bradford, Nigel Brothers, Blaise Bullimore, Channel 7 News (Perth, Australia), the Countryside Council for Wales, Derek Eaton, Fishing News International, Fisheries Research Services (Aberdeen), the Food and Agriculture Organization of the United Nations, Bob Furness, Brett Glencross, Thomas Heeger, Cecil Jones, Adam Jory, John LeCras, Berend Mensink, Steve Milligan, North-west Marine Technology, Alfonso Angel Ramos-Esplá, Rudy Reyes, Will Reynolds, Paul Rozario, Joseph Smith, David Solomon, Ian Strutt, the United States National Marine Fisheries Service, Page Valentine, Clem Wardle and Ted Wassenberg. We apologise to those whose photographs could not be included. Martin Collins, Dennis Glasscock, Julian Metcalfe, Graham Pickett and Monty Priede helped us to track down photographic material. Sheila Davies reproduced many photographs, Jim Jennings drew the fish, invertebrates and fishing gears in Figs 3.1, 3.2 and 5.4, and John Nichols provided the larval fish drawings for Fig. 4.9. The staff of the excellent CEFAS library were a great help throughout. Thank you everyone.
Simon would like to say a special thank you to Jess, friends and family for their support and sense of fun and to John Cotter, Mike Pawson, Nick Polunin, John Ryland the late Ray Beverton who, as supervisors and managers, gave him the time, space and encouragement to develop a wide-ranging interest in fisheries and ecological issues. He is also grateful to the University of East Anglia and CEFAS for providing support and facilities and to all at the Marine Studies Programme, University of the South Pacific who did so much to stimulate his interest in tropical fisheries. Michel would like to thank Diane and Holly for their love and inspiration. He would also like to thank his friends and former colleagues at CEFAS whose help and encouragement gave him a privileged insight into the world of fisheries science. He’d also like to thank his PhD supervisor Roger Hughes who gave him the enthusiasm to convey his science to a wider audience and has made writing a pleasure. John would like to thank Isabelle and Geneviève for their support and patience. Many friends and colleagues at the University of East Anglia and at CEFAS provided insights that helped him to bridge his interests in ecology, evolution and conservation. He also thanks five key supervisors from successive stages of his career: Richard Knapton, Jim Rising, Fred Cooke, Mart Gross and Paul Harvey.
We hope to update and improve the book. Please send any comments, suggestions, gifts or abuse to us at ‘Marine Fisheries Ecology’ c/o Simon Jennings, CEFAS, Lowestoft Laboratory, NR33 0HT, United Kingdom, or e-mail mfe@cefas.co.uk.
Simon Jennings
Michel Kaiser
John Reynolds
July, 2000
Humans have fished since prehistoric times, but in the last 50 years fisheries have expanded faster than ever before. Marine fisheries now yield around 90 million tonnes per year, more than 80% of global fish production. Catches have increased because a growing human population demands more food and because improved technology has simplified capture, processing, distribution and sale. Greater fishing power and increased competition between fishers, vessels or nations has led to the economic collapse of some fisheries that had flourished for centuries. The resultant reductions in fish production, income and employment are usually seen as undesirable by society. This is why governments intervene to regulate fisheries.
Effective fisheries management requires that managers work towards clearly specified objectives. These may be biological, economic and social. Thus, the fisheries scientist has to understand links between different disciplines and the ways in which science can usefully inform the manager. This chapter introduces the history and diversity of the world’s fisheries, their current status and the main problems they face. This provides a basis for suggesting why we need to conserve fisheries and the marine environment and identifies the main objectives of fishery management.
Humans living in coastal areas have always eaten marine organisms. Initially, animals and plants were simply collected by hand from the shore, but more effective fishing methods were soon developed. Fish hooks fashioned from wood and bone have been found at sites dated 8000 BC, and there are references to fisheries in Greek, Egyptian and Roman texts. In Egypt, nets and spears were in use by 2000 BC. As the Pacific Islands were colonized, fish provided protein on islands with few other animal resources, and the successful migration of Melanesian and Polynesian people often depended on their ability to catch reef fish. Fishers were aware of cycles in the abundance of species they caught, and the Greeks used storage ponds and fish farms to ensure a continuity of supply. Latterly, fish could be preserved by salting and drying, allowing fishers to work further from their home ports and fish products to be traded and exported.
As nations developed their seafaring skills and began to explore the oceans, they discovered abundant fish resources. Explorers reported that huge numbers of cod Gadus morhua (Gadidae) could be found off Newfoundand, and by the early 1500s, French and Portuguese fishers were already crossing the north Atlantic Ocean to fish for them. The cod were caught with baited hooks, dried and shipped to the Mediterranean countries and the Antilles where they were known as bacalao and fetched high prices. Subsequently, English vessels joined the fishery. The countries that fished for cod were the major sea powers of the time and fought to control trade routes. They were often at war and many fishing vessels were lost. In the Anglo-Spanish war of 1656–1659, 1000 English vessels were sunk. Cod were such a valuable commodity that the vessels were also targeted by pirates. Moroccan pirates would rob vessels returning to Mediterranean ports, and the Sallee rovers, French, Spanish and English pirates under the Turkish flag, attacked fishing boats in so many areas that the fishers eventually sailed in convoy for protection. In later years, the cod fishery on Georges Bank and Grand Bank was increasingly fished by boats from New England ports. By the midnineteenth century, cod were caught with hook and line from fleets of eight or more small dories that transferred their daily catches to a larger schooner for storage in ice and salt. In 1880, some 200 American schooners with eight or more dories were operating (Cushing, 1988a; Kurlansky, 1997).
In Europe, pre-industrial fisheries flourished in France and in countries bordering the North Sea. Sardines Sardina pilchardus (Clupeidae) were caught with fine nets off the French Breton coast from the seventeenth century. Initially they were sold fresh but with the development of the oil press, sardine oil was distributed all over Europe. Canneries were opened from 1822. There were around 3000 boats in the fishery at the end of the nineteenth century. A tunny Thunnus thunnus (Scombridae) fishery developed in the same area. Five hundred boats would spend up to 2 weeks at sea and catch tunny with trolled lures. The tunny could also be canned successfully. Swedish (Scanian) fishers started to catch Atlantic herring Clupea harengus (Clupeidae) from the North Sea in the eleventh century, and by the late sixteenth century, large fleets from Sweden, Holland, England and Scotland all fished for herring. The fish were caught in drift nets and preserved in barrels with salt. The fishing industry would move from port to port as they followed the shoals of herring on their seasonal migrations (Cushing, 1988a).
The power and range of fishing vessels increased rapidly at the time of the Industrial Revolution, as did the demand for fish and fish products. In the 1860s paddle tugs powered by steam were first used instead of sailing boats to drag fishing nets in the North Sea. Calm weather no longer limited fishing activities, and catch rates were four times those of sailing vessels. At much the same time, steamers started to fish for Atlantic menhaden Brevoortia tyrannus (Clupeidae) off the east coast of the United States. From the 1840s, there was rapid development of industry and growth of the US economy. A modern farming industry was needed to feed the growing urban population, and fishmeal was a potentially cheap and accessible source of high-protein animal feed. The first industrial fisheries began to catch small and abundant shoaling fish that were ground and dried to make fishmeal. In 1840, Charles Mitchell of Halifax Nova Scotia started to preserve fish in hermetically sealed tins. Such canned products could be distributed and sold throughout the world. The markets for fish became more accessible as rail and road transport improved and consumers were increasingly concentrated in cities where they sought work in factories and service industries.
Similar patterns of development followed elsewhere as farmers demanded fishmeal, and urban populations demanded food. Fishery landings rose rapidly and continued to do so until the present time. Although we have seen that European vessels fished across the Atlantic for several centuries, steel fishing vessels with diesel engines and cold storage facilities made all the oceans accessible to fishers who could remain at sea for months at a time. These were the so-called ‘distant water’ or ‘high seas’ fleets. Japanese vessels fished the tropical and subtropical oceans for tuna, the former Union of Soviet Socialist Republics (USSR) fished for krill Euphausia superba (Euphausiidae) in the Antarctic, and Alaskan pollock Theragra chalcogramma (Gadidae) in the North Pacific. The greatest expansion in high-seas fisheries took place after World War II and the fleets, mostly from the former USSR, Japan, Spain, Korea and Poland, were catching between 7 and 8 million tonnes by the 1970s, over 10% of global landings at that time.
Traditionally, the oceans were regarded as common property and fishers were free to go where they liked. Although marine tenure systems were in place around many tropical islands, and fishers in temperate waters protected their local fisheries from outsiders, the ‘ownership’ of marine resources rarely extended more than a few miles from land. From the fifteenth century until the 1970s there was little restriction on where fishing took place in the world’s oceans and what was done. It may seem strange that countries fished so freely in oceans many miles from their home ports when hunters could not take terrestrial mammals from countries without invading them and evading or repressing the local people, but the perception that land is owned and that the sea is open to all has persisted in many societies and for many centuries.
The existence of ‘freedom of the seas’ had a powerful influence on the development of the world’s fisheries. It was formalized in the sixteenth and seventeenth centuries when world powers decided to resolve ongoing and expensive conflicts over trade routes by allowing multinational access. In 1608, Hugo Grotius defended Holland’s trading in the Indian Ocean in Mare Liberum, and used fisheries to support his arguments for free access. He suggested that fish resources were so abundant that there would be no benefits from ownership and that large areas of national jurisdiction could never be defended. His argument prevailed and freedom of fishing became synonymous with freedom of the seas (FAO, 1993a; OECD, 1997).
However, as human populations grew and fisheries became more intensive, there was increasing conflict over fisheries. Scotland claimed exclusive national rights to inshore waters in the fifteenth century, and other countries followed. However, there was no international agreement on the size of territorial waters. The 1930 Hague Conference on the Codification of International Law decided that the claims to territorial seas were acceptable but did not suggest how large these claims could be. In practice, most countries claimed no more than a few kilometres of inshore waters while the high seas could still be fished by any nation with a suitable vessel.
Following World War II and two United Nations (UN) Conferences on the Law of the Sea, coastal states had greater expectations about the limits of their authority over fisheries. Many states increased their fishery limits to 12 miles (19.3 km) and by 1972, 66 countries had 12-mile limits. Even this did not satisfy countries with important fishing interests who were concerned about the status of ‘their’ stocks, and countries such as Iceland, where cod were fished by British and German distant water fleets, went to international court in an attempt to impose extended unilateral limits. This claim for jurisdiction was opposed by foreign fleets and led to the ‘cod wars’ of the 1970s (Burke, 1983).
Most 12-mile claims had little impact on the activities of high-seas fleets, but nations were increasingly concerned that they were not in control of their most accessible fish resources. Further territorial claims were inevitable. As early as 1947, Chile and Peru had claimed 200-mile jurisdiction, and by 1972 another eight countries had joined them. At the 1973 UN Conference on the Law of the Sea, the right to 200-mile limits was formalized. By 1974, 33 countries claimed this extended jurisdiction and another 18 joined them in the next 3 years. Since 90% of global fisheries yield was taken within 200 miles of the coast, these changes brought 90% of fisheries under national control. The catches of the high-seas fleets fell and many small island states were suddenly in control of vast fishery resources (Burke, 1994). The tiny Seychelles Islands in the Indian Ocean, for example, with a land area of 455 km2 and population of 75 000, were now responsible for fisheries in an Exclusive Economic Zone (EEZ) of 1 374 000 km2. Kiribati in the South Pacific, with a land area of 690 km2 and population of 72 000, took control of an EEZ of 3 550 000 km2, which included rich tuna fishing grounds. In subsequent years, small island nations would receive license payments from larger and wealthier nations who wanted to keep fishing in their EEZs. However, extended jurisdiction did not bring an end to battles over fisheries, and they continue to ignite conflicts between otherwise friendly fishers and nations (Fig. 1.1).
Fig. 1.1 Fisheries continue to ignite conflict between individuals and nations.
Marine capture fisheries now yield 86 million tonnes per year, more than four times that from freshwater fish production and aquaculture (FAO, 1999). The first sale value of fished marine species is around $US50 billion. Fished species include vertebrates, invertebrates and plants. Fish dominate landings and account for 80% by weight of the total (Box 1.1). Although there are around 17 000 species of marine fish, 50% of fish landings are composed of just 20 species. The other groups that dominate landings are molluscs and crustaceans that are commonly referred to as shellfish.
Few areas of the ocean remain unexploited and economic costs rather than technology now limit fishing power. Around 3.5 million fishing vessels are in use and most shelf seas to depths of 200 m or so are heavily fished. The main fish-producing nations are Peru, Japan, Chile, China and the United States. Target species are generally decreasing in abundance, but the high efficiency of modern fishing vessels makes catching them worthwhile. In the developed world, even the smallest inshore fishing vessels carry acoustic devices to provide images of the seabed and locate shoals of fish, accurate navigation systems to pinpoint fishing grounds and powered drums and blocks to haul fishing gear.
Box 1.1
Catches and landings.
The fish and invertebrates that fishers bring ashore are often called ‘catches’ or ‘landings’. Strictly speaking, these terms are not synonymous, since much of the catch is discarded at sea and never landed (Chapter 13). Landings statistics compiled by the FAO and other organizations reflect the quantities of fished species brought ashore, and not necessarily the quantities caught.
Small-scale and artisanal fishers working from the shore, canoes or small boats account for 25% of the global catch and more than 40% of the catch for human consumption. The highly mechanized fisheries of the developed world contrast dramatically with subsistence fisheries in poorer countries where fish are a vital source of dietary protein and fishing may provide the only source of income (Fig. 1.2). In highly populated coastal regions of South-East Asia, Africa and Central America, people turn to the sea as a last possible source of food and income when no alternatives are available. The fishers are usually very poor, have little equipment and are sufficiently desperate to support themselves and their families that they do anything to maintain daily catches. In practice this may mean fishing with dynamite or poisons that destroy the fished habitat.
Despite the collapse of individual fisheries and the demise of some high-seas fleets, new resources have been exploited and total landings have risen steadily since 1950 (Fig. 1.3). Landings have increased because fishing effort has increased in response to growing demands for fish. Global landings are dominated by low-value species, such as anchovies and pilchards, which are mostly converted to fishmeals and oils for farming and food manufacture (Fig. 1.4). Despite the steady rise in overall landings, landings of individual species fluctuate widely. Catches by high-seas fleets rose and then fell with the imposition of extended jurisdiction (Fig. 1.5). At present, landings in less developed nations are rising faster than those in developed ones. This is partly because most resources in developed countries have already been located and fished as heavily as they can with the available technology. In developing countries, conversely, the availability of new technology and external funding has allowed access to new and lightly exploited resources. Developing countries took 27% of global landings in 1950 but now take over 60% (OECD, 1997).
Fig. 1.2 Relationship between the proportion of fish protein in human diets and the relative wealth of nations where those people live. Wealth is measured as the total gross domestic product (GDP) divided by the population size. GDP is the total income of a country from all sources. After Kent (1998).
Fig. 1.3 Landings of marine fishes and invertebrates by economically developed countries (shaded) and developing countries (unshaded). Data from OECD (1997) and FAO (1999).
Since 1950, the effort (e.g. time at sea or fuel consumed) needed to catch a given weight of fish has increased. Technological development and increases in fleet size meant that total yield rose, but for many vessels fishing was no longer cost effective and government subsidies kept vessels at sea and fishers in jobs. Of course, their continued activities further depleted stocks and made fishing even less profitable. In 1989, the former USSR fleet was estimated to have operating costs of $US10–13 billion and yet their landings of around 10 million tonnes of low-value species were worth $US5 billion. This left a deficit of $US5–8 billion, to be met by subsidy (FAO, 1994).
Fig. 1.4 Landings of the five marine species that have dominated global landings since 1950. These species are: Peruvian anchovy, Engraulis ringens (Engraulidae); Alaskan pollock, Theragra chalcogramma (Gadidae); Atlantic herring, Clupea harengus (Clupeidae); Atlantic cod, Gadus morhua (Gadidae); and Japanese pilchard, Sardinops melanostictus (Clupeidae). Data from FAO (1995a, 1999).
Fig. 1.5 Landings by distant water fishing nations (high-seas fleets) since 1950 and their landings as a proportion of the global total. After FAO (1999).
Fishery science has been recognized as a scientific discipline since the late 1850s, when the Norwegian government hired scientists to find out why catches of Atlantic cod fluctuated from year to year (Smith, 1994). Cod had been caught off the Lofoten Islands in northern Norway for several centuries and the local people relied on them for food and income. As in the Newfoundland fishery, cod were caught with lines and preserved by drying. The money made from exporting dried cod was used to import other foods and to pay traders and bank loans in southern Norway. If the cod fishery failed, then the people of northern Norway would default on their bank loans. For the Norwegian government, fluctuations in the cod fishery caused economic and political strain.
Soon, fishery scientists were also working in Germany, Sweden and Russia, and within 20 years fisheries research was in progress in the United States, Denmark, the Netherlands and the United Kingdom. Scientists were increasingly concerned that fluctuations in abundance could be driven by fishing. At the Great International Fishery Exhibition, held in England during 1883, Thomas Huxley, then president of the Royal Society, declared that ‘the cod fishery, the herring fishery and probably all the great sea fisheries are inexhaustible; that is to say, that nothing we do seriously affects the numbers of fish’. Although his statement is often used to suggest that people were generally unaware of the finite limits to natural resources at that time, Huxley himself had qualified many of these remarks, and many fishers in Europe had reported declining catch rates. Moreover, tens of generations of people who depended on the reef fish resources of tropical islands were well aware they could not sustain intensive harvesting and were forced to move to new islands as they depleted fish stocks. There was a growing scientific consensus that research was needed to identify the effects of fishing, and new laboratories were established in Europe and North America (Cushing, 1988a; Smith, 1994).
By the end of the nineteenth century, scientists had developed techniques for ageing fish and tagging them to follow their migrations, but had not shown why catches varied. Work focused on whether killing small fish, before they were able to spawn, would cause catches to fall, whether fishing affected the size and abundance of fish, and what could be learnt from the collection and analysis of catch and effort data from the fishery. The major breakthrough came early in the twentieth century, when a Norwegian scientist, Johan Hjort, showed that the abundance of a year class of fish was established within the first few months of life and that renewal of fish stocks did not take place by a constant annual production of young but by highly irregular annual production with a few fish surviving in most years and many fish surviving in a very few years. Changes in the rate of survival would cause fluctuations in catches. Soon, fisheries scientists would predict catch rates in some of the larger fisheries by measuring the abundance of young fish in the years before they grew large enough to be caught by fishers.
The number and efficiency of vessels fishing increased rapidly in the years before World War I and the fish caught were getting smaller and less abundant. During World War I, military activity led to a drop in fishing effort, and when the war ended in 1918 fishers caught larger fish and enjoyed higher catch rates. It was clear that the reduction in fishing effort during the war allowed fish populations to recover from the effects of fishing, and fishery science increasingly focused on understanding these effects. By the 1950s, 100 years after fisheries science had begun, models that described the dynamics of fish populations and their responses to fishing were developed by scientists working in the United States, England and Canada. These predicted the yields from fisheries when fish were killed at different rates and provide the background to much of the science we describe in this book. In subsequent years, fishery science would play a leading role in the field of ecology as a whole, describing why populations fluctuate and how population structure changes in space, time and in response to increased rates of death imposed by humans.
Many countries had interests in the same fisheries and there was strong international cooperation between fishery scientists. In 1902, the International Council for the Exploration of the Sea (ICES) was established in Europe and set up a number of international programmes to examine the effects of fishing. Despite the cooperation between scientists, only two fisheries were managed internationally before World War II, the Pacific halibut Hippoglossus stenolepis (Pleuronectidae) and Baltic plaice Pleuronectes platessa (Pleuronectidae). After the war, many new scientific and regulatory bodies were established. The International Commission for North-west Atlantic Fisheries (ICNAF) and the Inter-American Tropical Tuna Commission (IATTC) formed in 1949, to be followed by a series of Food and Agriculture Organization (UN) commissions.
In the late twentieth century, concerns about fish stock collapse, the uncertainty that underlies fisheries assessment and the recognition that management objectives do not relate solely to the fished stock, has led to a diversification of fisheries science. There is increasing input from sociologists and economists who consider how different management strategies will affect the lives and incomes of fishers and associated communities. There is also greater emphasis on the effects of fishing on the marine environment and the impacts on species or habitats of conservation concern. Fisheries laboratories are found in many countries around the world, many fisheries are assessed by more than one country and international fisheries statistics are collected by the Food and Agriculture Organization of the United Nations (FAO) (Box 1.2).
The sheer diversity of fisheries makes fisheries science a fascinating field. Fishers are found on almost any coastline and working in any ocean. At one end of the spectrum a woman will fish daily with hook and line from a coral reef flat in Kiribati to supply food for her family. She winds the line on a simple spool and holds the bait and catch in a bag of woven palm leaves. She collects small crabs from the shore to use as bait and may glean shellfish for food at the same time. Most of her fishing is done within a few hundred metres of her village and total investment in fishing equipment is probably less than $US1. At the other extreme, a purse seining vessel pursues schools of tuna over the entire Pacific Ocean using satellite navigation devices. The vessel carries a helicopter to search for fish, a crew of 35 and costs $US40 million. One catch may weigh 30 tonnes and can be frozen to −20°C in a few hours. After several weeks at sea the frozen fish are delivered to a processing plant where they are thawed, cooked and canned for distribution to all the continents of the world. Between these extremes, fishing ranges from trawling for prawns in the muddy waters off Louisiana in the United States to hand-netting fish for the aquarium trade in Sri Lanka.
Box 1.2
International assessment and management of fisheries.
For the purposes of collecting fisheries data, the FAO divides the world’s oceans into Statistical areas shown in Fig. B1.2.1 and listed in Table B1.2.1. International fishery management areas are not necessarily the same as the FAO statistical areas. There are many international fisheries organizations that try to develop rational management policies for fish that migrate across national boundaries. Some examples are given in Table B1.2.2.
References: FAO (1994, 1999) OECD (1997).
Fig. B1.2.1 Boundaries of FAO statistical areas.
Table B1.2.1 FAO statistical areas.
| Area code | Statistical area | Area (million km2) |
| Atlantic Ocean and adjacent seas | ||
| 18 | Arctic Sea | 7.3 |
| 21 | North-west Atlantic | 5.2 |
| 27 | North-east Atlantic | 16.9 |
| 31 | Western Central Atlantic | 14.7 |
| 34 | Eastern Central Atlantic | 14.0 |
| 37 | Mediterranean and Black Sea | 3.0 |
| 41 | South-west Atlantic | 17.6 |
| 47 | South-east Atlantic | 18.6 |
| 48 | Atlantic Ocean–Antarctic | 12.3 |
| Indian Ocean and adjacent seas | ||
| 51 | Western Indian Ocean | 30.2 |
| 57 | Eastern Indian Ocean | 29.8 |
| 58 | Indian Ocean–Antarctic | 12.6 |
| Pacific Ocean and adjacent seas | ||
| 61 | North-west Pacific | 20.5 |
| 67 | North-east Pacific | 7.5 |
| 71 | Western Central Pacific | 33.2 |
| 77 | Eastern Central Pacific | 48.9 |
| 81 | South-west Pacific | 28.4 |
| 87 | South-east Pacific | 30.0 |
| 88 | Pacific Ocean–Antarctic | 10.4 |
Table B1.2.2 Examples of International fisheries organizations.
We will introduce many fishing methods in subsequent chapters, but hope that Figs 1.6 and 1.7 capture some of their variety. It is vital to appreciate this variety because fisheries provide different things for different people and thus the objectives of management differ too. Thus, the provision of a constant food supply may be essential for the small fishing villages in Kiribati while maximum profitability may be essential for a multinational company that catches tuna for canning. Despite the diversity of fisheries, many common principles describe the way in which fished species respond to fishing and the effects of fishing on the environment. Fisheries scientists realize that research in tropical waters can usefully inform scientists working in temperate waters and vice versa. We have attempted as far as possible to use examples that reflect the global diversity of fisheries.
Fisheries are not static, as any study of the history of exploitation will show. Fisheries develop, some fish stocks collapse, some fishers get rich, other fishers go bankrupt and move elsewhere and into other jobs. An examination of numerous fisheries around the world shows that when a potentially fishable resource is discovered, new fishers start to explore its potential and begin exploitation as soon as possible. Indeed, on an individual basis, the faster they can exploit the new fishery the more income they will receive. Other fishers who find out about the new fishery and think it has more potential than their own will join the race to fish there. Eventually, there will be too many fishers chasing too few fish, the stock will be depleted and catch rates and profits will fall. Once fishing is no longer profitable, the fishers who can will redirect their energies, but those who cannot may continue to fish the depleted stock. To avoid the unemployment and social costs from fishers becoming bankrupt, governments may subsidize fishers to continue exploiting the depleted stock. By this stage, production of the stock is minimal and it will either recover because fishers shift their attentions elsewhere, or collapse, because fishers have no choice but to keep fishing.
Fig. 1.6 The diversity of fisheries. (a) Fish traps set in the Lupar Estuary in Sarawak to catch prawns and small fish (see Blaber, 1997), (b) cast-netting for prawns in a small estuary near Mukah, Sarawak, (c) a tuna purse seiner trans-shipping catches to a freezer vessel in the Seychelles, and (d) tuna fishing from a small boat off Cape Verde Islands (d). Photographs copyright S. Blaber (a, b), S. Jennings (c), M. Marzot (FAO photo, d).
Fishers can exploit fisheries at rates exceeding their capacity for replenishment. As this occurs, so the fishery passes through a series of phases (Fig. 1.8). These can be described as fishery development, full exploitation, over-exploitation, collapse and recovery (Hilborn & Walters, 1992). During each of these phases, there are clear trends in the abundance of fished species, fleet size (or fisher number), catch and profit. While the trends rarely follow the smooth and necessarily stylized curves shown in Fig. 1.8, the general patterns are consistent.
As a new fishery develops so more fishers or boats enter the fishery because it is profitable for them to do so. The fishers who start fishing first, or catch most with least effort, will make the greatest profit. During fishery development, the effects of fishing are seen as a slight reduction in catch rates and the size of individuals in the catch. Total catch will rise as fishing effort increases. Prior to industrialization and the human population boom on many tropical coasts, fisheries often stayed in the ‘development’ phase and replenishment was easily fast enough to counter the effects of fishing. As more fishers enter the fishery, it passes through the fully exploited phase. Here, abundance falls and total catch increases. During the fully exploited phase replenishment is sufficient to maintain fish production and hence catches. If yet more fishers enter the fishery, their catching capacity will exceed the rate of replenishment (over exploitation). This usually leads to a fall in profits because more fishers are competing for a dwindling resource. As profits tend to zero, so fishers stop entering the fishery. Total catch will peak close to the time when the number of fishers reaches a maximum, and subsequently fall as abundance and the capacity for replenishment is reduced. If fishing effort is not reduced then the fishery will ultimately collapse, with marked falls in abundance and catch. Following collapse, the fishery will no longer be profitable. If fishers can afford to leave the fishery they usually will, and recovery, the rebuiding of stock biomass, may begin. In other cases, the fishers’ only option will be to stay because they have to keep fishing to pay loans on boats and equipment.
Fig. 1.7 More diversity of fisheries. (a) Unloading sardines from a coastal purse-seiner in the Portuguese port of Aveiro, (b) a Japanese squid jigger sailing to fishing grounds off Hokkaido, (c) fishing with dynamite on a reef in the Philippines, and (d) a large catch of demersal (bottom dwelling) fish on a Russian stern trawler. Photographs copyright Fishing News International (a, b, d) and T. Heeger (c).
We will now look at four examples of the many fisheries that have followed this common pattern. They are for different species, in different countries and have been overexploited on different time scales.
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