Detecting and correcting underreported catches in fish stock assessment: trial of a new method

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Abstract:

Landings from fisheries are often underreported, that is, the true landings are greater than those reported. Despite this bias, reported landings are widely used in fish stock assessments, and this might lead to overoptimistic exploitation strategies. We construct a statistical stock assessment model that accounts for underreported landings using the theory of censoring with sequential population analysis (SPA). The new model is developed and implemented specifically for the cod stock (Gadus morhua) from the southern Gulf of St. Lawrence (Canada). This stock is known to have unreported overfishing during 1985–1992. We show in simulations that for this stock, the new censored model can correctly detect the problematic landings. These corrections are nearly insensitive to subjective boundaries placed on real catches and robust to modifications imposed in the simulation of landings. However, when surveys are too noisy, the new SPA for censored catches can result in increased uncertainty in parameters used for management such as spawning stock biomass and age-structured stock size.

Les relevés de pêche effectués lors des débarquements sous-estiment souvent la pêche réelle. Malgré ce biais, ces relevés sont largement employés pour l’évaluation des points de repère biologiques, ce qui peut mener à une exploitation trop optimiste des ressources. Nous construisons un modèle statistique pour l’estimation des stocks de poissons qui permet l’utilisation de relevés de pêches sous-estimés, en incorporant de la censure au modèle d’analyse de population séquentielle. Ce nouveau modèle est ensuite développé et mis en oeuvre pour le stock de morue (Gadus morhua) dans le sud du Golfe du Saint-Laurent (Canada) qui a subi une forte surexploitation non relevée pendant les années 1985–1992. Nous montrons à l’aide de simulations que le modèle avec censure détecte correctement les relevés de pêche problématiques. Les corrections sont peu sensibles à des bornes arbitraires imposées aux vraies prises et robustes à des modifications du modèle pour la simulation des relevés. Cependant, lorsque les enquêtes sont bruitées, le nouveau modèle avec prises censurées peut donner des résultats peu précis pour des paramètres utilisés pour la gestion, tels que le niveau du stock ou des mesures de stock par âge.

Document Type: Research Article

Publication date: August 1, 2010

More about this publication?
  • 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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