Theorie et pratique de l'analyse de cohortes

Foreword: Sequential analysis of the demographic structures revealed by catches is currently the method most used, in particular by work groups working together within the framework of the C.I.E.M., to assess the characteristic parameters of exploited marine populations. The reasons for its success are due to a simple analytical definition, the absence of restrictive hypotheses, and especially a singular property thanks to which the results converge towards the parameters' true values. Due to its quasi-systematic use at the outset of the process leading to exploitation regulations, it is particularly important to take in the method's advantages, limits and rules of usage. This study is, in part, a review of the principal work performed on and around cohort analysis, all of them, as it were, published in the English language, complemented by a few personal observations. In one of the first parts, we apply ourselves to describing the method and its characteristic properties, in particular the convergence property that is the source of its originality, with the help of basic examples. Each time that it seemed to us that it would aid the reader's comprehension or satisfy his curiosity, we have detailed the demonstration of the fundamental analytical expressions; in spite of appearances, it contributes to our sense of proving the simplicity of the technique and the rigour of its development. The second part is devoted to the method's uses as it is practiced within the context of the work groups, and we succinctly show its importance in the development of steps for managing stocks while mentioning methods based on the results that it supplies. Because this document was conceived as a manual for work group participants and benefits from the experience of a few of them, we fervently hope that it will give rise to discussions and that readers will contribute to its completion by sharing their personal remarks or questions for which they do not find a satisfying answer here.