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Cadima, E.L. The manual follows the same order of the lectures in the last course held in IPIMAR (November/December 1997). It starts with an introduction to the mathematical models applied in Fish Stock Assessment and some considerations on the importance of fisheries. The need for a rational management of the fishing resources is then stressed, this being indispensable for an adequate exploitation, aiming at conservation, to occur. The basic assumptions about a model and the concepts of different variation rates of a characteristic in relation to time (or to other characteristics) are presented, highlighting the most important aspects of the simple and exponential linear models which are used in the chapters that follow. After some considerations on the concept of cohort, models for the evolution in time of the number and weight of the individuals that constitute the cohort are developed, including models for the individual growth of the cohort. In the chapter concerning the study of the stock, the fishing pattern and its components are defined, the most used models for the stock-recruitment relation are presented, as well as the short and long term projections of a stock. With regard to fishing resources management, the discussion is focused on the biological reference points (target points, limit points and precautionary points) and fisheries regulation measures. The last chapter, which presents and discusses theoretical models of fish stock assessment, deals with production models (also designated as general production models) and with the long and short-term projections of the catches and biomasses. Finally, the general methods of estimating parameters are described and some of the most important methods are presented, with special relevance to the cohort analysis by age and length. Then a solution of the exercises from the last course held in IPIMAR, is presented by the author and the scientist Manuela Azevedo. |
TO MY FIRST MASTERS AND OLD-TIME FRIENDS
Ray Beverton
John Gulland
Gunnar Sætersdal
