An individual-based modeling approach to spawning-potential per-recruit models: an application to blue crab (Callinectes sapidus) in Chesapeake Bay

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Abstract:

An individual-based modeling approach to estimate biological reference points for blue crabs (Callinectes sapidus) in Chesapeake Bay offered several advantages over conventional models: (i) known individual variation in size and growth rate could be incorporated, (ii) the underlying discontinuous growth pattern could be simulated, and (iii) the complexity of the fishery, where vulnerability is based on size, shell status (e.g., soft, hard), maturity, and sex could be accommodated. Across a range of natural mortality (M) scenarios (0.375–1.2·year–1), we determined the exploitation fraction (µ) and fishing mortality (F) that protected 20% of the spawning potential of an unfished population, the current target. As M increased, µ20% and F20% decreased. Assuming that M = 0.9·year–1, our models estimated µ20% = 0.45, which is greater than field-based estimates of µ in 64% of the years since 1990. Hence, the commercial fishery has likely contributed to the recent population decline in Chesapeake Bay. Comparisons of our results with conventional per-recruit approaches indicated that incorporating the complexity of the fishery was the most important advantage in our individual-based modeling approach.

Une méthodologie de modélisation basée sur l'individu pour estimer les points de référence biologique du crabe bleu (Callinectes sapidus) dans la baie de Chesapeake présente plusieurs avantages par rapport aux méthodes conventionnelles : (i) on peut incorporer les variations individuelles connues de taille et de taux de croissance, (ii) on peut simuler le patron sous-jacent de croissance discontinue et (iii) on peut tenir compte de la complexité de la pêche dans laquelle la vulnérabilité dépend de la taille, de l'état de la coquille (par exemple, molle, dure), de la maturité et du sexe. Sur une gamme de scénarios de mortalité naturelle (M = 0,375–1,2 an–1), nous avons déterminé la fraction de l'exploitation (µ) et la mortalité due à la pêche (F) qui protègent 20 % du potentiel de ponte de la population non affectée par la pêche, ce qui est l'objectif actuel. Lorsque M augmente, µ20 % et F20 % diminuent. En assumant que M = 0,9 an-1, nos modèles estiment µ20 % à 0,45, ce qui est plus que les estimations de terrain de µ dans 64 % des années depuis 1990. La pêche commerciale a donc vraisemblablement contribué au déclin récent de la population dans la baie de Chesapeake. La comparaison de nos résultats à ceux des approches conventionnelles, qui font les calculs par recrue, indique que l'incorporation de la complexité de la pêche est l'avantage le plus significatif de notre méthodologie de modélisation basée sur l'individu.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: November 1, 2005

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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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