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Fish population dynamics: the implications for management
93 the repeated failure to strike a balance within it. The importance of understanding the biological characteristics of the resource before attempting population modelling is emphasized in the case studies. Modelling and yield per recruit assessments are discussed, and means of combining t h e m both in assessments are suggested. Short-term and long-term effects of climate on stocks such as shrimp, abalone and crabs are described. Of particular interest are the technological factors considered within the fisheries which have a direct impact on the stock, such as sorting and handling of discards and overexploitation of sedentary shellfish stocks with increasing mechanization. Forecasting of catch is illustrated not only in well-established oyster fisheries, but also in cases such as the Australian rock lobster fishery. In most fisheries management action is now more important than the sophistication of the population model. Management problems of sharing resources and of overcapitalized and overexploited fisheries are covered. Some comments are made on conflicts between fisheries and aquaculture. The unique uses of invertebrate species aside from food are also mentioned. The book is not intended to be a fisheries manual, and does not overwhelm the reader with numerical theory. On the contrary, a nice balance is struck between descriptions of the fisheries and methods of assessment and management. Invertebrate stock assessment owes much to the standard methods developed for traditional finfisheries. This book describes how some of these methods are adapted for invertebrate stocks without dwelling too long on their origins. For this reason the editor recommends fishery manuals as references. While the book provides a useful update for those involved in fisheries monitoring and development, it will undoubtedly have a wider appeal, especially for aquaculturalists, biologists and managers working in extensive cultivation. It abounds with details on marine matters presented in an intelligent and readable format. This book is not essential reading for those interested in aquaculture; nevertheless I believe many will find it a rewarding read. JOHN H. WILSON Curtis Krogh Hatchery P.O. Box 14 South WestRocks N.S. W. 2431, Australia FISH POPULATIONDYNAMICS REVISITED Fish Population Dynamics: The Implications for Management, J.A. Gulland (Editor). Wiley Interscience, Chichester, 2nd edn., 1988, 432 pp., hardcover, US$ 52.15, ISBN: 0-471-91151-8.
The first edition of this book, published in 1977, has been for the last dec-
94 ade a valuable basic reference for almost all aspects of fisheries population dynamics. The new edition bids fair to fill the same position for the next decade. While the scope and organization is essentially similar to the first edition, the present volume could fittingly be described as a new book rather than a new edition, as although many of the chapters can be aligned with those in the first edition, they have all, with one conspicuous exception, been entirely re-written, often by new authors. In his preface Gulland identifies the adoption of the Law of the Sea Convention in 1982 as being the factor which has had the greatest effect on the development of fisheries science during the period. It has brought scientists much closer to management decisions, and they are "no longer concerned with theoretical studies of how much better fisheries might be managed if only someone would listen to them". This has had both advantages and disadvantages: "the advances in the practical use of stock assessment ... have not been matched by advances in theory". The opening chapter, this time by T.D. Smith, is again historical; it is however entirely new. It describes the development of the essential concepts of fisheries management science from the earliest beginnings in about 1880 until about 1960, by which time much of the basis of modern fisheries science had been established. Developments since then have been essentially in the direction of increasing the sophistication and accuracy of modelling and estimation techniques, and it is these which are dealt with in the rest of the book. The next two chapters deal in general terms with the basic methods of stock assessment and its data requirements. The first, by J.G. Shepherd, considers both the kinds of data required for the principal sorts of assessments and, conversely, what assessments can be made given particular kinds of data. It classifies assessments into two main types: short-term and long-term. The following chapter, by J.G. Pope, deals with "how assessment data should be collected and how good they need to be to be useful". It discusses catch and effort data, commercial catch sampling by length and age as well as research vessel data including surveys by trawling, acoustic and photographic means as well as egg and larval surveys. Rather strangely, tagging as a major source of assessment is not considered in this general discussion, and only in passing in later chapters on cod and shrimps. Chapter 4, by A.A. Rosenberg and J.R. Beddington, deals with assessment methods based on length-distribution data, which constitute one of the most important developments in stock assessment techniques of the last decade. These methods include both those which involve an internal conversion to age data and those which draw valuable management information directly from the length data. The next two chapters discuss recruitment problems. Chapter 5, concerned with the nature of the stock recruitment relationship, is again by D.H. Cushing. It has been entirely rewritten, and, although still considering some of the
95 standard mathematical formulations of this relation, it places more emphasis than before on environmental effects and on the nature of larval mortality and the factors affecting it. Chapter 6, by M.P. Sissenwine, M.J. Fogarty and W.J. Overholtz, discusses recently developed methods for achieving management advice from stock assessment data in the face of variability in recruitment. It considers both the uncertainties in estimates of stock recruitment parameters under these conditions, and the variability which would occur in future recruitments even if the S-R functions were to be accurately known. Chapters 7-11 are concerned with the population dynamics of particular groups of species. The first two chapters deal with groups which were covered in the first edition. P.A. Larkin covers the Pacific salmon in a chapter which has been minimally altered from the original version. Only passing reference is made to two developments which have major implications for the management of these species: these are the application of decision-making theory in working out management recommendations, and the increase in national powers to regulate fisheries as a consequence of the adoption of the Law of the Sea Convention. By contrast, the chapter on North Atlantic cod, again by D.J. Garrod, is entirely new. It reviews, on classical lines, the status of all the principal stocks of this much-studied species, and the consequences, so far, of the changes in national jurisdictions. It culminates in the provocative suggestion that for a wide variety of species the critical fishing intensity for stock survival may be a value of 2.5 for the cumulative F summed over all ages up to that of 50% maturity. The previous chapter on whales has been replaced by a new one on marine mammals by K.R. Allen and G.P. Kirkwood. This covers seals as well as whales. It outlines the principal characteristics of the population dynamics of these animals and reviews much of the evidence on the ability of depleted populations to rebuild when no longer exploited. The previous specific chapters on elasmobranchs, North Sea plaice, clupeoids and tuna have been dropped, and new ones appear on tropical penaeid prawns and on small shoaling pelagic fish. Both these chapters, by S. Garcia and J. Csirke respectively, deal with fisheries which have expanded greatly in recent years. They review the ways in which the traditional techniques of population dynamics can be applied to animals with relatively short life spans and for which available yields are greatly affected by variability in recruitment. The next three chapters deal with another set of problems that has attracted much more attention in recent years, which relate to the management of multispecies fisheries. K. Brander examines these problems for the demersal fisheries of the Irish Sea, making special reference to the interactions between the fisheries for Norway lobsters and for cod, which preys on them. He also examines management systems involving two-layer TACs, overall and specific. The more typical multi-species fisheries are those of the tropics: for these, D. Pauly, in classical terms, describes the long-established fisheries of the Gulf of Thailand, while K.J. Sainsbury deals with the relatively new demersal fish-
96
eries of tropical Australia. The former are characterised by the typical features of competition between artisanal and trawl fisheries and the progressive replacement of large predatory fish by smaller forms. For the latter, analysis in terms of community theory leads to proposals, which are being adopted, for large-scale experimental management of the fishery. In a final chapter J.A. Gulland reviews the present status of population dynamics as a source of advice for fishery managers, noting that the main problems fall into the categories of maintaining the stocks, resolving conflicts and improving economic performance. For single species assessments the main uncertainties are still generally in the estimation of M and in means of forecasting future recruitments. Species interactions however remain an area in which much more needs to be understood, both in the complex tropical fish communities and between key species in temperate fisheries. Finally the recent beginning of a theoretical basis for management under uncertainty is briefly discussed. Compared with the first edition, the book, except for a few chapters, contains strikingly little mathematics. The aim, a laudable one, has clearly been to devote the text to the description of ideas and principal events and to refer the reader to the relevant literature for the mathematical detail. That the book has achieved a successful update in this way is shown by the fact that, excluding the introductory historical chapter, almost two-thirds of the 1000-odd references are dated 1980 or later. The book is well produced and pleasant to read and handle. The only printing error noticed was the appearance of Deriso as Devisi in the author index. K. RADWAY ALLEN
20/8 Waratah Street Cronula, NSW 2230 Australia
The first edition of this book, published in 1977, has been for the last dec-
94 ade a valuable basic reference for almost all aspects of fisheries population dynamics. The new edition bids fair to fill the same position for the next decade. While the scope and organization is essentially similar to the first edition, the present volume could fittingly be described as a new book rather than a new edition, as although many of the chapters can be aligned with those in the first edition, they have all, with one conspicuous exception, been entirely re-written, often by new authors. In his preface Gulland identifies the adoption of the Law of the Sea Convention in 1982 as being the factor which has had the greatest effect on the development of fisheries science during the period. It has brought scientists much closer to management decisions, and they are "no longer concerned with theoretical studies of how much better fisheries might be managed if only someone would listen to them". This has had both advantages and disadvantages: "the advances in the practical use of stock assessment ... have not been matched by advances in theory". The opening chapter, this time by T.D. Smith, is again historical; it is however entirely new. It describes the development of the essential concepts of fisheries management science from the earliest beginnings in about 1880 until about 1960, by which time much of the basis of modern fisheries science had been established. Developments since then have been essentially in the direction of increasing the sophistication and accuracy of modelling and estimation techniques, and it is these which are dealt with in the rest of the book. The next two chapters deal in general terms with the basic methods of stock assessment and its data requirements. The first, by J.G. Shepherd, considers both the kinds of data required for the principal sorts of assessments and, conversely, what assessments can be made given particular kinds of data. It classifies assessments into two main types: short-term and long-term. The following chapter, by J.G. Pope, deals with "how assessment data should be collected and how good they need to be to be useful". It discusses catch and effort data, commercial catch sampling by length and age as well as research vessel data including surveys by trawling, acoustic and photographic means as well as egg and larval surveys. Rather strangely, tagging as a major source of assessment is not considered in this general discussion, and only in passing in later chapters on cod and shrimps. Chapter 4, by A.A. Rosenberg and J.R. Beddington, deals with assessment methods based on length-distribution data, which constitute one of the most important developments in stock assessment techniques of the last decade. These methods include both those which involve an internal conversion to age data and those which draw valuable management information directly from the length data. The next two chapters discuss recruitment problems. Chapter 5, concerned with the nature of the stock recruitment relationship, is again by D.H. Cushing. It has been entirely rewritten, and, although still considering some of the
95 standard mathematical formulations of this relation, it places more emphasis than before on environmental effects and on the nature of larval mortality and the factors affecting it. Chapter 6, by M.P. Sissenwine, M.J. Fogarty and W.J. Overholtz, discusses recently developed methods for achieving management advice from stock assessment data in the face of variability in recruitment. It considers both the uncertainties in estimates of stock recruitment parameters under these conditions, and the variability which would occur in future recruitments even if the S-R functions were to be accurately known. Chapters 7-11 are concerned with the population dynamics of particular groups of species. The first two chapters deal with groups which were covered in the first edition. P.A. Larkin covers the Pacific salmon in a chapter which has been minimally altered from the original version. Only passing reference is made to two developments which have major implications for the management of these species: these are the application of decision-making theory in working out management recommendations, and the increase in national powers to regulate fisheries as a consequence of the adoption of the Law of the Sea Convention. By contrast, the chapter on North Atlantic cod, again by D.J. Garrod, is entirely new. It reviews, on classical lines, the status of all the principal stocks of this much-studied species, and the consequences, so far, of the changes in national jurisdictions. It culminates in the provocative suggestion that for a wide variety of species the critical fishing intensity for stock survival may be a value of 2.5 for the cumulative F summed over all ages up to that of 50% maturity. The previous chapter on whales has been replaced by a new one on marine mammals by K.R. Allen and G.P. Kirkwood. This covers seals as well as whales. It outlines the principal characteristics of the population dynamics of these animals and reviews much of the evidence on the ability of depleted populations to rebuild when no longer exploited. The previous specific chapters on elasmobranchs, North Sea plaice, clupeoids and tuna have been dropped, and new ones appear on tropical penaeid prawns and on small shoaling pelagic fish. Both these chapters, by S. Garcia and J. Csirke respectively, deal with fisheries which have expanded greatly in recent years. They review the ways in which the traditional techniques of population dynamics can be applied to animals with relatively short life spans and for which available yields are greatly affected by variability in recruitment. The next three chapters deal with another set of problems that has attracted much more attention in recent years, which relate to the management of multispecies fisheries. K. Brander examines these problems for the demersal fisheries of the Irish Sea, making special reference to the interactions between the fisheries for Norway lobsters and for cod, which preys on them. He also examines management systems involving two-layer TACs, overall and specific. The more typical multi-species fisheries are those of the tropics: for these, D. Pauly, in classical terms, describes the long-established fisheries of the Gulf of Thailand, while K.J. Sainsbury deals with the relatively new demersal fish-
96
eries of tropical Australia. The former are characterised by the typical features of competition between artisanal and trawl fisheries and the progressive replacement of large predatory fish by smaller forms. For the latter, analysis in terms of community theory leads to proposals, which are being adopted, for large-scale experimental management of the fishery. In a final chapter J.A. Gulland reviews the present status of population dynamics as a source of advice for fishery managers, noting that the main problems fall into the categories of maintaining the stocks, resolving conflicts and improving economic performance. For single species assessments the main uncertainties are still generally in the estimation of M and in means of forecasting future recruitments. Species interactions however remain an area in which much more needs to be understood, both in the complex tropical fish communities and between key species in temperate fisheries. Finally the recent beginning of a theoretical basis for management under uncertainty is briefly discussed. Compared with the first edition, the book, except for a few chapters, contains strikingly little mathematics. The aim, a laudable one, has clearly been to devote the text to the description of ideas and principal events and to refer the reader to the relevant literature for the mathematical detail. That the book has achieved a successful update in this way is shown by the fact that, excluding the introductory historical chapter, almost two-thirds of the 1000-odd references are dated 1980 or later. The book is well produced and pleasant to read and handle. The only printing error noticed was the appearance of Deriso as Devisi in the author index. K. RADWAY ALLEN
20/8 Waratah Street Cronula, NSW 2230 Australia