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Comment on “Differences in predicted catch composition between two widely used catch equation formulations”

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Branch (2009. Can. J. Fish. Aquat. Sci. 66: 126–132) described the two most common catch equation formulations in stock assessment models: the continuous (Baranov) one, which represents fishing mortality as an instantaneous rate, F, and the discrete one, in which it is represented as an exploitation rate, u. He claimed that the continuous formulation is preferable at high fishing mortality where a fish could encounter multiple sets of gear within a year. This claim is wrong for two reasons. First, it is based on the false supposition that the discrete catch equations require the assumption that fish encounter at most only one set of fishing gear in a year. Second, it is not possible to determine, for a specific stock assessment, whether one formulation is preferable to another solely on the basis of information about the fishery. The appropriate way to make this decision is to see which fits the data better.

Branch (2009. J. can. sci. halieut. aquat. 66 : 126–132) a décrit les deux formulations de l’équation des captures les plus usitées dans les modèles d’évaluation des stocks, soit la continue (de Baranov) qui représente la mortalité due à la pêche comme un taux instantané, F, et la discontinue qui la représente comme un taux d’exploitation, u. Il soutient que la formulation continue est préférable aux forts taux de mortalité lorsque le poisson peut faire face à plusieurs ensembles d’engins de pêche pendant une année. Cette assertion est fausse pour deux raisons. D’abord, elle est basée sur la présomption erronée que les équations discontinues des captures présupposent que les poissons rencontrent au plus un ensemble d’engins de pêche au cours d’une année. Deuxièmement, il est impossible de déterminer, pour une évaluation de stock donnée, si l’une des formulations est préférable à l’autre seulement d’après les renseignements sur la pêche. La façon appropriée d’arriver à cette décision est de voir laquelle s’ajuste le mieux aux données.

Document Type: Discussion

Publication date: 2010-04-01

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  • Published continuously since 1901 (under various titles), this monthly journal is the primary publishing vehicle for the multidisciplinary field of aquatic sciences. It publishes perspectives (syntheses, critiques, and re-evaluations), discussions (comments and replies), articles, and rapid communications, relating to current research on cells, organisms, populations, ecosystems, or processes that affect aquatic systems. The journal seeks to amplify, modify, question, or redirect accumulated knowledge in the field of fisheries and aquatic science. Occasional supplements are dedicated to single topics or to proceedings of international symposia.
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