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Theory and management of tropical fishery
has totally interfered with the netting yam construction. The sub-chapter, properties of netting yarns, includes a comprehensive description of equipment for testing of the breaking strength of netting twines and the parameters influencing it, such as twine construction, dimensions, twist hardness, knots, etc. The user can here, in several tables and d&rams, find useful information on the specific breaking strength as a function of twine thickness (no., tex, diameter) for different materials and twine constructions. Other important twine properties for fishing gear, such as fiextural stiffness, change of length in water, extensibility and elasticity, and abrasion and weathering resistance are also thoroughly dealt with in this chapter. Chapter 3: Choice of Materials for Fishing Gear, deals with netting materials for bottom and midwater trawls, purse seines and gill nets. Wisely enough, the author in this part of the manual does not pretend to be too conclusive in his statements, obviously being aware of the sometimes contradictory views on the subject among fishermen, netmakers and even fishing experts of different countries or fishing areas. However, some useful information is given on the applicability of the different materials for specific fishing purposes, and a lot of examples are given of materials actually used for specific gear which are valuable as guidance for any user of the manual. Netting Materials for Fishing Gear, by G. Klust is, to the knowledge of the reviewer, the most comprehensive work (available in .English) at present on this special subject. In addition to the extensive and detailed contents, the book is also well-edited which, together with a wealth of tables and wellprepared illustrations and diagrams, also makes it easy to use as a book of reference. LIJDVIG KARLSEN Institute of Fisheries. University of Tromso. Postboks 3033. Guleng, 9001 Tromso, Norway
TROPICAL
FISHERY
Theory and Management of Tropical Fishery, D. Pauly and G. Murphy (Editors). Proceedings of the ICLARMCSIRO Workshop on the Theory and Management of Tropica! Multispecies Stocks, 12-21 January 1981, Cronulla, Australia, published by ICLARM, Manila, Philippines, 1982, 360 pp., paperback price US$28.50, ISBN 971-04-0022-3. This book constitutes the proceedings of the ICLARM%SIRO workshop on theory and management of tropical multispecies stocks held in Cronulla, Australia, 12-21 January 1981, the objectives of which were to define the
data requirements for assessment and management, to review the models presently available for assessment of tropical resources, to identify major constraints in stock assessment and management and to formulate a feasible plan of action to overcome them. Stated briefly, the contents of the book include a review and bibliography of the (incomplete) data base available for Southeast Asia (Simpson), a catalogue of techniques usable for single-species stock assessment in the tropics (Pauly, Munro), a review of simple multi-species models (Kirkwood), a description of a complex model of an inshore marine ecosystem (James and Starck), a critical review of the present complex multi-species models questioning ‘heir utility for management (Larkin and Gasey), an interpretation of some tropical stock/recruitment data sets (Murphy) and a plea for more sensitive analysis of models (Majkowski). The ecological basis for demersal tropical fisheries and the structure and dynamics of coral reefs are reviewed by Sain>,bury and Sale, respectively. Jones gives broad conclusions on ecosystems food chains and fish yields, with some implications for management, while Marten and Polovina compare fish yields from a variety of tropical ecosystems and show interesting relationships (whose variance is unfnrnrmtely too high to allow for prediction). Gulland describes the preecnt state of tropical resource management, and Marr draws attention to the t.eed to include socioeconomic considerations in any management process. 4 thoughtful concluding paper is provided by Larkin. With iuch contents, the book is strongly oriented towards parameter esthnaticn, stock assessment and understanding of tropical resources. Despite irs indisputable usefulness, it does not entirely live up to the promise of its tit e; principally, perhaps, because it tends to confuse the provision of advice or: some biological aspects of management with management itself, a common klistake of fisheries biologists. As recognized by Professor Larkin in his intrcduction, the individual contributors do not deal with the broader social and economic context of fisheries and this matter is only superficially touched or by Gulland and Marr in their respective papers. Gulland briefly reviews tht~ present state of management in tropical areas, underlining the lack of eif&,ive control, the difficulty of controlling artisanal fisheries, the minim:4 role played by stock assessment in the past, the overriding impact of “development” policies, and the widespread conflict between the artisanal and industrial sectors. He stresses that biological advice (and probably economic advice too) will still, in the near future, have to be based on production models. A number of the presented papers fortree tropical fisheries management as necessarily pragmatic, adaptive (Marten and Polovira), realistic, locally based and strongly linked with rural developmeat (Marr), but ,;hey do not give any further practical guidance. However, the general agreement is that, above ail it should be empirical. This last important statement, which implies ma.?ogement by careful trial and error and monitoring (a strategy used by mar.kind since its origin) stems from an explicit recognition that the present
231
state of understanding of tropical resources (not even considering tropical societies) is best conceptualized by some islands of knowledge located in a dark deep ocean of ignorance. In that respect, this volume is a valuable attempt to measure how much we know about the tropics, and is certainly very successful in showing how much we do not. Temperate fishery science is not yet mature, as proved by the anomalously high proportion of methodological papers in the literature, and it can safely be said that this is even more true as far as tropical fishery science is concerned, where northern concepts, approaches and methodologies have often been applied to sometimes drastically different environments. Most authors acknowledge tbie fact, in one way or another, throughout the whole book when underlining possible similarities with, or differences from, temperate systems. Analysing stock-recruitment relationships, Murphy concludes that tropical fish behave like temperate ones, and more specifics&r that “most seem to have density-dependent reproductive curves”. In face of the evidence, given the poor fit of some models and the overriding impact of environmental variations in the very short series of data analysed, we would have concluded instead tiiat for tropical as for temperate wetem, there is as yet very little statistically significant evidence of density-dependence in recruitment of marine fish stocks. The recognized lack of proper information and properly oriented research leads logically to the rather pessimistic views of Kirkwood, as well as Larkin and Gazey, about the usefulness of presently available multi-s:>ecies models of all sorts (production, ecological, trophirdynamic, etc. . .) for management; at present there are simply not enough data to test them. In an attempt to compensate for the obvious limitation!; of the data base some useful “simple” tools are proposed. Pauly presents a set of methods essentially based on his own developments of length-frequency analysis, including a generalized version of the Von Bertalanffy growth function and his achievements in automatic analysis of length data (the Elephan program) for estimating growth, mortality and recruitment. He gives an empirical relationship between natural mortality M, growth parameters X and L, and temperature. He advocates the use of “simple” estimators of stock size, catch potential, and recruitment. Munro also gives a set of “simple” methods or concepts applicable to coral-reef communities, based on his own work in Jamaica. Considering the present need for biological advice on management of tropical stocks, and the shortage of data, the “quick and dirty” spproaches advocated have an unquestionable value. However, despite the fact that some quick methods are probably less dirty in the end than some more sophisticated ones, their use requires some caution. For instance, an often recommended simple estimator like Beverton’s equation Z = K (L,-T)/(i--I,)
232
is very sensitive to small changes in 7 and I, (Majkowski) and the average annual size (T) of a stock of fast-growing sho&lived animals with sex-d5 ferences in growth is certainly not always an “easily derived statistic”, as stated by Munro. In the same way, estimating the recruitment R, in year n by Y,J( Y/R),, and then plotting R, against, Y,, (i.e. without any lag time) to produce a stock-recruitment relationship, as proposed by Pauly, can be valid only under very strict adherence to assumptions on equilibrium and lie-span. It might only be used for species where generation time is much shorter than one year, and tends anyway to confuse somewhat the S + R relationship with its trivial converse R + S. The need for caution when using short-cut methods is rightly stressed by Lsrkin, Murphy and Majkowski. We can agree that attention should be paid to not relaxing the “rules” of application too much, and to continuously checking the effect of such relaxation, as well as the sensitivity of these “fast” estimators to input errors. The real danger could in fad be that a myth will creep into the literature; namely that stock assessment in the tropics will be based for ever on short-cut single species methods originating long ago in the very first days of temperate fisheries science, just because they are the only ones usable now in a situation of acute shortage of data and manpower. It is necessary to stress that they are only a temporary solution, giving very approximate, sometimes questionable, results which have to be used with a lot of caution when providing biological advice on management. The main obstacle to progress to be removed is the general ignorance of the basic functioning of harvestable tropical ecosystems. This is sufficiently underlined in this book, whose content, in fact, goes largely beyond tropical areas and gives a refreshingly critical review of the validity and limitations of traditional temperate fishery science also. If carefully used, and entirely read, including the very enlightening discussion which follows each paper, and above all starting i. ith the closing paper of Larkin, “Directions for future research ln tropical multispecies fisheries”, which puts it in its full perspective, the book is certainly a very useful contribution to tropical fishery science for which ICLARM and CSIRO must be given credit. As a closing remark, I will add that I hope that the concepts developed in the book will last longer than my personal “short-lived” paper-back version which fell apart after a single read-through. S. OARCTA Fishery Resources Division Dent, of Fisheries F. A. 0. Via delle Terme di Carocollc
00100 Rome, Italy
TROPICAL
FISHERY
Theory and Management of Tropical Fishery, D. Pauly and G. Murphy (Editors). Proceedings of the ICLARMCSIRO Workshop on the Theory and Management of Tropica! Multispecies Stocks, 12-21 January 1981, Cronulla, Australia, published by ICLARM, Manila, Philippines, 1982, 360 pp., paperback price US$28.50, ISBN 971-04-0022-3. This book constitutes the proceedings of the ICLARM%SIRO workshop on theory and management of tropical multispecies stocks held in Cronulla, Australia, 12-21 January 1981, the objectives of which were to define the
data requirements for assessment and management, to review the models presently available for assessment of tropical resources, to identify major constraints in stock assessment and management and to formulate a feasible plan of action to overcome them. Stated briefly, the contents of the book include a review and bibliography of the (incomplete) data base available for Southeast Asia (Simpson), a catalogue of techniques usable for single-species stock assessment in the tropics (Pauly, Munro), a review of simple multi-species models (Kirkwood), a description of a complex model of an inshore marine ecosystem (James and Starck), a critical review of the present complex multi-species models questioning ‘heir utility for management (Larkin and Gasey), an interpretation of some tropical stock/recruitment data sets (Murphy) and a plea for more sensitive analysis of models (Majkowski). The ecological basis for demersal tropical fisheries and the structure and dynamics of coral reefs are reviewed by Sain>,bury and Sale, respectively. Jones gives broad conclusions on ecosystems food chains and fish yields, with some implications for management, while Marten and Polovina compare fish yields from a variety of tropical ecosystems and show interesting relationships (whose variance is unfnrnrmtely too high to allow for prediction). Gulland describes the preecnt state of tropical resource management, and Marr draws attention to the t.eed to include socioeconomic considerations in any management process. 4 thoughtful concluding paper is provided by Larkin. With iuch contents, the book is strongly oriented towards parameter esthnaticn, stock assessment and understanding of tropical resources. Despite irs indisputable usefulness, it does not entirely live up to the promise of its tit e; principally, perhaps, because it tends to confuse the provision of advice or: some biological aspects of management with management itself, a common klistake of fisheries biologists. As recognized by Professor Larkin in his intrcduction, the individual contributors do not deal with the broader social and economic context of fisheries and this matter is only superficially touched or by Gulland and Marr in their respective papers. Gulland briefly reviews tht~ present state of management in tropical areas, underlining the lack of eif&,ive control, the difficulty of controlling artisanal fisheries, the minim:4 role played by stock assessment in the past, the overriding impact of “development” policies, and the widespread conflict between the artisanal and industrial sectors. He stresses that biological advice (and probably economic advice too) will still, in the near future, have to be based on production models. A number of the presented papers fortree tropical fisheries management as necessarily pragmatic, adaptive (Marten and Polovira), realistic, locally based and strongly linked with rural developmeat (Marr), but ,;hey do not give any further practical guidance. However, the general agreement is that, above ail it should be empirical. This last important statement, which implies ma.?ogement by careful trial and error and monitoring (a strategy used by mar.kind since its origin) stems from an explicit recognition that the present
231
state of understanding of tropical resources (not even considering tropical societies) is best conceptualized by some islands of knowledge located in a dark deep ocean of ignorance. In that respect, this volume is a valuable attempt to measure how much we know about the tropics, and is certainly very successful in showing how much we do not. Temperate fishery science is not yet mature, as proved by the anomalously high proportion of methodological papers in the literature, and it can safely be said that this is even more true as far as tropical fishery science is concerned, where northern concepts, approaches and methodologies have often been applied to sometimes drastically different environments. Most authors acknowledge tbie fact, in one way or another, throughout the whole book when underlining possible similarities with, or differences from, temperate systems. Analysing stock-recruitment relationships, Murphy concludes that tropical fish behave like temperate ones, and more specifics&r that “most seem to have density-dependent reproductive curves”. In face of the evidence, given the poor fit of some models and the overriding impact of environmental variations in the very short series of data analysed, we would have concluded instead tiiat for tropical as for temperate wetem, there is as yet very little statistically significant evidence of density-dependence in recruitment of marine fish stocks. The recognized lack of proper information and properly oriented research leads logically to the rather pessimistic views of Kirkwood, as well as Larkin and Gazey, about the usefulness of presently available multi-s:>ecies models of all sorts (production, ecological, trophirdynamic, etc. . .) for management; at present there are simply not enough data to test them. In an attempt to compensate for the obvious limitation!; of the data base some useful “simple” tools are proposed. Pauly presents a set of methods essentially based on his own developments of length-frequency analysis, including a generalized version of the Von Bertalanffy growth function and his achievements in automatic analysis of length data (the Elephan program) for estimating growth, mortality and recruitment. He gives an empirical relationship between natural mortality M, growth parameters X and L, and temperature. He advocates the use of “simple” estimators of stock size, catch potential, and recruitment. Munro also gives a set of “simple” methods or concepts applicable to coral-reef communities, based on his own work in Jamaica. Considering the present need for biological advice on management of tropical stocks, and the shortage of data, the “quick and dirty” spproaches advocated have an unquestionable value. However, despite the fact that some quick methods are probably less dirty in the end than some more sophisticated ones, their use requires some caution. For instance, an often recommended simple estimator like Beverton’s equation Z = K (L,-T)/(i--I,)
232
is very sensitive to small changes in 7 and I, (Majkowski) and the average annual size (T) of a stock of fast-growing sho&lived animals with sex-d5 ferences in growth is certainly not always an “easily derived statistic”, as stated by Munro. In the same way, estimating the recruitment R, in year n by Y,J( Y/R),, and then plotting R, against, Y,, (i.e. without any lag time) to produce a stock-recruitment relationship, as proposed by Pauly, can be valid only under very strict adherence to assumptions on equilibrium and lie-span. It might only be used for species where generation time is much shorter than one year, and tends anyway to confuse somewhat the S + R relationship with its trivial converse R + S. The need for caution when using short-cut methods is rightly stressed by Lsrkin, Murphy and Majkowski. We can agree that attention should be paid to not relaxing the “rules” of application too much, and to continuously checking the effect of such relaxation, as well as the sensitivity of these “fast” estimators to input errors. The real danger could in fad be that a myth will creep into the literature; namely that stock assessment in the tropics will be based for ever on short-cut single species methods originating long ago in the very first days of temperate fisheries science, just because they are the only ones usable now in a situation of acute shortage of data and manpower. It is necessary to stress that they are only a temporary solution, giving very approximate, sometimes questionable, results which have to be used with a lot of caution when providing biological advice on management. The main obstacle to progress to be removed is the general ignorance of the basic functioning of harvestable tropical ecosystems. This is sufficiently underlined in this book, whose content, in fact, goes largely beyond tropical areas and gives a refreshingly critical review of the validity and limitations of traditional temperate fishery science also. If carefully used, and entirely read, including the very enlightening discussion which follows each paper, and above all starting i. ith the closing paper of Larkin, “Directions for future research ln tropical multispecies fisheries”, which puts it in its full perspective, the book is certainly a very useful contribution to tropical fishery science for which ICLARM and CSIRO must be given credit. As a closing remark, I will add that I hope that the concepts developed in the book will last longer than my personal “short-lived” paper-back version which fell apart after a single read-through. S. OARCTA Fishery Resources Division Dent, of Fisheries F. A. 0. Via delle Terme di Carocollc
00100 Rome, Italy