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Catchability and the spatial distribution of fishing vessels

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Abstract:

A central problem when using commercial catch per unit effort (CPUE) as an index of fish stock abundance is that fishing vessels search for concentrations of fish. For a given stock abundance, CPUE may become high if the vessels succeed in finding patches of fish and low if the vessels distribute their catching operations more randomly. In this work, the relationship between catchability and two measures of the degree of spatial concentration of a trawl fleet (the fleet's spatial extent and the fleet's degree of spatial patchiness) is investigated for four different fish stocks. The catchability of northeast Arctic cod (Gadus morhua) is strongly related to the fleet's degree of spatial concentration, but the relationship is weaker for northeast Arctic haddock (Melanogrammus aeglefinus), and no relationships appear for two saithe (Pollachius virens) stocks. Our findings suggest that adjusting CPUE with a measure of the fleet's average degree of concentration relates CPUE more strongly with abundance for migratory stocks.

Les navires de pêche recherchent les concentrations de poissons, ce qui donne lieu à un problème sérieux lorsqu'on veut utiliser les données commerciales de prises par unité d'effort (CPUE) comme indice de l'abondance d'un stock de poissons. Pour une abondance donnée d'un stock, CPUE peut être élevé si les navires réussissent à trouver des regroupements de poissons et faible si les navires répartissent leurs opérations de pêche de façon plus aléatoire. Dans notre étude, nous examinons la relation entre la capturabilité et deux mesures du degré de concentration spatiale d'une flotte de chalutiers (la dispersion spatiale de la flotte et son degré de contagion) chez quatre stocks différents de poissons. La capturabilité des morues franches (Gadus morhua) du nord-est de l'Arctique est en forte corrélation avec le degré de concentration spatiale de la flotte, mais la relation est plus faible dans le cas des aiglefins (Melanogrammus aeglefinus) du nord-est de l'Arctique; pour deux stocks de goberges (Pollachius virens), il n'y a pas de relation. Nos résultats indiquent que l'ajustement de CPUE à l'aide d'une mesure du degré moyen de concentration de la flotte établit une meilleure relation entre CPUE et l'abondance des stocks de poissons migrateurs.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: March 1, 2003

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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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