FAO FISHERIES TECHNICAL PAPER 283 An ecological framework for marine fishery investigations CONTENTS

by
J.F. Caddy
Senior Fishery Resources Officer
Marine Resources Service
FAO Fishery Resources and Environment Division
and
G.D. Sharp
Center for Climate-Ocean Resources Studies
PO Box 12294
Gainesville, Florida, USA

The designations employed and the presentation of material in this publication do not imply the expression of any opinion whatsoever on the part of the Food and Agriculture Organization of the United Nations concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries.

M-43
ISBN 92-5-102510-X

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 or otherwise, without the prior permission of the copyright owner. Applications for such permission, with a statement of the purpose and extent of the reproduction, should be addressed to the Director. Publications Division, Food and Agriculture Organization of the United Nations, Via delle Terme di Caracalla, 00100 Rome, Italy.

FOOD AND AGRICULTURE ORGANIZATION OF THE UNITED NATIONS Rome, 1986
©FAO

PREPARATION OF THIS DOCUMENT

First presented as background document of the ACMRR Working Party on the Assessment of Living Resources in near-shore Tropical Waters, Rome 28 February – 4 March 1983, some of the sections in this first document were extracted in a paper presented at the “Simposio Internacional sobre las Areas de Afloramiento mas importantes del Oeste Africano (Cabo Blanco y Benguela)” sponsored by Instituto de Investigaciones Pesqueras, Barcelona, 21–25 November 1983. Permission to extract sections from the conference paper is gratefully acknowledged. The original ACMRR paper, since revised and extended, is intended to provide access to the extensive literature on marine eco-systems, and in particular to some of the theoretical and practical implications of the concept of trophic interractions, which is becoming recognized as a vital prerequisite for understanding the dynamics of multi-species fisheries systems. As such, the present paper can be considered supplementary reading for those beginning work in various fields related to renewable marine resources, particularly stock assessment, whose calculations can hopefully be placed in a more realistic eco-logical context following study of some of the literature referred to in this document.

We have felt very conscious as authors of the difficulties of avoiding a subjective approach because of the “agglomerative” nature of much ecological research nowadays: separate schools of thought and practice with different ecosystems seems to be independently discovering and converging on similar principles - it is often just the time and space scales and objectives of the research that are different: it would therefore seem unwise to judge between them prematurely at this stage. As a result, the structure of the paper provides first (Part I) a very broad brush description of some of the main elements of fisheries ecology, which can be regarded as a self-contained account of the topic. The rest of the text (Part II) deals in rather more detail with individual topics touched on in the text, in a series of sections which can be read essentially independently of those preceeding and following.

ACKNOWLEDGEMENTS

The authors wish to express their gratitude to those many colleagues who have contributed to the work through discussions and exchange of ideas. Jim Kapetsky, Robin Welcome, Jorge Csirke and Serge Garcia come particularly to mind; Ken Mann and Al Tyler also provided comments and encouragement, but cannot be held responsible for any facts or opinions expressed herein. Kathy Dorsey made an important contribution by reorganizing the first draft of this manuscript into a more coherent form. We would also express a debt of gratitude to the patient FAO typists who have suffered the many revisions to this document, especially Anna Rita Colagrossi, Emanuela Cheli, and Jackie Ellis, and to Gloria A. Soave who checked the bibliography. Sandro Cassola prepared most of the figures. The views expressed here are those of the authors, and do not necessarily reflect a formal policy on the part of FAO.

FAO gratefully acknowledges copyright permission to reprint the quotations on page v from:

THE LOG FROM THE SEA OF CORTEZ by John Steinbeck
Copyright John Steinbeck and Edward F. Ricketts, 1941
Copyright John Steinbeck, 1951
By permission of McIntosh and Otis, Inc.

THE LOG FROM THE SEA OF CORTEZ by John Steinbeck and Edward F. Ricketts
Copyright 1941 by John Steinbeck and Edward F. Ricketts
Copyright renewed (C) 1969 by John Steinbeck and Edward F. Ricketts, Jr
Copyright 1951 by John Steinbeck,
renewed (C) 1979 by Elaine Steinbeck, Thom Steinbeck and John Steinbeck IV
Reprinted by permission of Viking Penguin Inc.

“…Our own interest lay in relationships of animal to animal. If one observes in this relational sense, it seems apparent that species are only commas in a sentence, that each species is at once the point and the base of a pyramid, that all life is relational to the point where an Einsteinian relativity seems to emerge. And then not only the meaning but the feeling about species grows misty. One merges into another, groups melt into ecological groups until the time when what we know as life meets and enters what we think of as non-life: barnacle and rock, rock and earth, earth and tree, tree and rain and air. And the units nestle into the whole and are inseparable from it.”

“… But all the fish actually were eaten; if any small parts were missed by the birds they were taken by the detritus-eaters, the worms and cucumbers. And what they missed was reduced by the bacteria. What was the fisherman's loss was a gain to another group. We tried to say that in the macrocosm nothing is wasted, the equation always balances. The elements which the fish elaborated into an individuated physical organism, a microcosm, go back again the undifferentiated macrocosm which is the great reservoir. There is not, nor can there be, any actual waste, but simply varying forms of energy. To each group, of course, there must be waste - the dead fish to man, the broken pieces to gulls, the bones to some and the scales to others - but to the whole, there is no waste. The great organism, Life, takes it all and uses it all. The large picture is always clear and the smaller can be clear - the picture of eater and eaten. And the large equilibrium of the life of a given animal is postulated on the presence of abundant larvae of just such forms as itself for food. Nothing is wasted; 'no star is lost'.

“And in a sense there is no over-production, since every living thing has its niche, a posteriori, and God, in a real, non-mystical sense, sees every sparrow fall and every cell utilized…”

John Steinbeck:
“The Log from the Sea of Cortez”

FOREWORD

It is important to recognize at the start of any discussion of the relevance of marine ecology to fisheries, that a degree of understanding of the ecological context within which a harvesting activity is taking place is essential if adverse impacts of these activities are to be minimized, and the systems ability to support productive human activity is not to be endangered. We should also be aware that exploited components of complex biotic systems are linked to other components, not all of which are harvested, but may be essential to the economic productivity of the system. These linkages need to be understood where at all possible since one fundamental ecological principle is that “you can't change just one thing”: all ecosystem components are interlinked.

It is relevant also to note that although a “Maximum Sustainable Production” may be postulated for the system as a whole, this will itself vary in time, depending on the stability of the system, although this whole system variability will be less than that for each of its major components considered individually.

System stability itself is a function of a range of extrinsic factors acting through meteorological and hydrographic influences; each modulated in turn, by the geographic, especially bathymetric, configuration of the area of interest, and expressed through a set of characteristic species, which through evolution, have come to evolve their own mutual checks and balances.

In an ideal world, the first step towards gaining a “degree of understanding” of a fishery, would be to proceed from the general to the particular; starting with an overall description or “mapping” of the natural system, its geography and hydrography, and from a listing and distribution of the main taxa, their biology, migrations and interrelationships; and from a knowledge of the fisheries as well as the importance of the fishing ground for the whole spectrum of human activities, before focussing attention on individual components of key interest at this point in time. This is basically the approach we are advocating in this document: recognizing that although there are a variety of approaches to ecosystem analysis and management, starting with as wide a view as possible of the system will avoid, to the extent possible, major ommissions and a “tunnel vision” in developing hypotheses and approaches.

To a large extent, this is the way that fisheries science developed in “pioneering” areas such as the North Sea, where a long tradition of descriptive work preceded attempts to manage individual stocks; an activity that only got fully underway well after the 2nd world war. The large body of information on North Sea ecosystems accumulated during and since the last century was necessary to the pioneering syntheses of scientists such as Alistair Hardy in the 1920s–40s, whose description of the interractions between plankton and commercial fish stocks provided much of the early impetus for the development of the (then) new discipline of biological oceanography. In the last years of his life (he died in May 1985), there has been a revival of attempts to arrive at a quantitative synthesis of interractions between components of North Sea food web components that has dominated meetings of the International Council for the Exploration of the Seas (ICES) in recent years. To a significant extent, this document recognizes the correctness of Sir Allister Hardy's earlier conclusions on the importance of food webs.

For several important areas of the world's oceans this detailed early descriptive work involving mapping and data gathering on the resource and environment has never been carried out, and although the FAO Species Identification Sheets are now published for many tropical areas (Table 1), a knowledge of the biology of key components and their interactions is not yet available. Thus, the important industrial fisheries that sprang into existence, often as late as the 1960s and 1970s as a result of technology transfer from high latitude fisheries, usually lacked a proper basis of biological information for their control and management, often with serious consequences. The unit stock and single species assessment rationales first used in attempting to manage these fisheries, notably the generalized production model, and more recently, short-cut methodologies based on broad generalizations on growth and mortality, have mostly considered the exploited species in isolation. This has obvious drawbacks in complex tropical systems, and has accentuated an interest in multispecies fisheries theory. The latter is still, however, in an early stage of development, although recently attempts have been made to address this question (e.g., Pauly and Murphy, 1982; May, 1984). Good work is now being done, but the search for a suitable theoretical framework is largely inconclusive to date, and in many tropical areas at least, seems to have pushed ahead of the necessary basic field studies and experimentation that preceeded similar work in the simpler high latitude ecosystems.

The need for a basic understanding of fisheries ecosystems and their interactions, especially in the tropics, is an urgent one, and recent conferences have been useful especially in examining the physical systems themselves within which important tropical fisheries take place.

It is hoped that even though our priorities and interpretation of the field may not meet with universal agreement, that the present compilation of concepts and references in this field will be useful in providing workers unfamiliar with the literature on marine ecosystems, with some access to this extensive body of information, that may help to place their fisheries problems in a proper ecological context.

Figure 1 Hardy's herring feeding diagram. An early diagrammatic representation of the feeding relationship in the North Sea plankton. As used by Hardy (1924), the arrows point from the predator to the prey, implying a controlling influence of predators on prey biomass. This may not always be true, and recently the trend has been toward showing the flow of materials from the planktonic organisms to the herring biomass, and vice versa for some pelagic predators on larval herring: (thickness of arrows being roughly related to the degree of influence on the prey, or (in the opposite sense), to the proportion formed by each prey in the diet of the predator, herring)

Hyperlinks to non-FAO Internet sites do not imply any official endorsement of or responsibility for the opinions, ideas, data or products presented at these locations, or guarantee the validity of the information provided. The sole purpose of links to non-FAO sites is to indicate further information available on related topics.

CONTENTS

INTRODUCTION
PART I: INTRODUCTION TO THE MAIN CONCEPTS DISCUSSED, AND TO SOME KEY IDEAS IN FISHERY ECOLOGY
1. THE DIVERSE ORIGINS OF ECOSYSTEMS CONCEPTS
2. BIOTIC AND ABIOTIC FACTORS IN MARINE ECOLOGY
3. MOVEMENTS OF ENERGY IN SPACE AND TIME: TROPHIC LEVELS, OR FOOD WEDS AND PYRAMIDS OF NUMBERS?
4. CHANGES IN TROPHIC LEVEL IN THE LIFE HISTORY
5. “BOTTOM UP” OR “TOP DOWN” APPROACHES TO ECOSYSTEM ANALYSIS?
6. QUESTIONS OF BIOMASS AND SIZE OF ORGANISM
7. SOME PROPERTIES OF FOOD WEBS
8. ZOOGEOGRAPHY AND LIFE HISTORY STRATEGIES
9. LIMITATIONS ON FOOD WEBS IMPOSED BY AVAILABLE SURFACES
10. FISHERIES ECOLOGY AND ASSESSMENT OF RESOURCES
PART II: ELABORATION AND DEVELOPMENT OF SOME KEY CONCEPTS RELEVANT TO ECOSYSTEM MANAGEMENT
1. TEMPORAL CHANGES AND STABILITY OF FISHERIES SYSTEMS
2. SYSTEM STABILITY AND MANAGEMENT
3. SPATIAL CONSIDERATIONS: MAPPING FISHERIES RESOURCES
4. FISH PRODUCTION PER UNIT AREA ESTIMATES
5. COLLECTING AND ANALYSING DATA ON FEEDING PREFERENCES OF COMMERCIAL FISH SPECIES
6. EQUILIBRIUM CONCEPTS AND THE FLOW OF ENERGY THROUGH A SYSTEM AND ITS OPTIMAL UTILIZATION
7. QUALITATIVE CONSIDERATIONS IN ECOLOGY-THE MANGROVE ECOSYSTEM AND CORAL REEFS
8. DIAGRAMMATIC REPRESENTATION OF LINKAGES WITH SPECIAL REFERENCE TO FOOD WEBS
9. QUANTIFYING PRODUCTION WITHIN THE FOOD WEB: SOME PRELIMINARY APPROACHES
10. SIMPLE CATEGORIZATION OF LIFE HISTORY STRATEGIES: r- AND k-SELECTION AND THE ECOLOGICAL NICHE
11. FOOD WEB ANALYSIS IN PRODUCTIVE COASTAL ENVIRONMENTS: THE COASTAL KELP, SEA URCHIN AND LOBSTER SYSTEM IN HIGH LATITUDES, AND SEAGRASS NURSERY AREAS IN THE TROPICS
12. FOOD WEBS IN LOW AND HIGH ENERGY SYSTEM: A MEDITERRANEAN DEMERSAL FISH COMMUNITY VERSUS FISHERIES OF UPWELLING SYSTEMS
13. INTERACTIONS IN A PELAGIC ECOSYSTEM: INFERENCES FROM FISH PHYSIOLOGY AND BEHAVIOUR STUDIES
14. CONSIDERATIONS OF ECOLOGICAL EFFICIENCY AND LIFE HISTORY STRATEGIES
15. DIVERSITY AND STABILITY OF FISHERY ECOSYSTEMS: ARTEFACTS OF SCALE?
16. SAMPLING THE MARINE ECOSYSTEM: THE CONCEPTS OF CONTAGION, COMMUNITY AND ASSEMBLAGE
17. THE EFFECTS OF TEMPERATURE AND BODY SIZE ON FEEDING AND ON THE NATURAL MORTALITY OF PREY
18. ESTIMATES OF NATURAL MORTALITY RATES FROM WHOLE SYSTEM VARIABLES
19. SOME IDEAS FOR REPRESENTING FOOD WEBS IN THE FISHERIES CONTEXT
20. SINGLE SPECIES MANAGEMENT IN AN ECOSYSTEM CONTEXT
21. IMPACTS AT THE ECOSYSTEM LEVEL
22. REFERENCES