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A fishery-independent assessment of an overfished rockfish stock, cowcod (Sebastes levis), using direct observations from an occupied submersible

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Abstract:

A meaningful assessment of cowcod (Sebastes levis) has been conducted using visual, nonextractive, habitat-specific methods. Following the precipitous decline of rockfish (Sebastes spp.) stocks along the Pacific coast, it was evident that more effective methods were needed to assess several species in untrawlable habitats. Cowcod were surveyed within large Cowcod Conservation Areas (CCAs) off southern California using direct observations from the research submersible Delta over eight major offshore rocky banks in depths of 74 to 322 m. Maps of seafloor substratum and bathymetry were used to identify and quantify these areas. A line-transect analysis of fish counts, perpendicular distances of fish from the track line, lengths of survey tracks, and area of each rocky bank was used to estimate abundance. Biomass, calculated from abundance, fish length, and a weight–length relationship, varied with mean size of cowcod on these banks. These fishery-independent results have contributed to the recent assessment of cowcod by the Pacific Fishery Management Council. A time series of results from visual surveys is now necessary to evaluate a trend in cowcod biomass with respect to increased time of protection within the CCAs.

Nous avons fait une évaluation significative du sébaste Sebastes levis (« cowcod ») en utilisant des méthodes visuelles qui ne nécessitent pas de retraits et qui sont spécifiques à l’habitat. Après le déclin rapide des stocks de sébastes (Sebastes spp.) le long de la côte du Pacifique, il est devenu évident qu’il fallait des méthodes plus efficaces pour évaluer plusieurs des espèces dans les habitats dans lesquels on ne peut utiliser de chalut. Nous avons inventorié les S. levis dans de grandes aires de conservation de S. levis (« Cowcod Conservation Areas », CCA) au large du sud de la Californie au moyen d’observations directes faites du submersible de recherche Delta sur huit bancs rocheux du large à des profondeurs de 74–322 m. Des cartes du substrat du fond de la mer et la bathymétrie ont servi à identifier et à quantifier ces zones. Nous avons estimé l’abondance à partir de l’analyse des dénombrements de poissons sur des transects linéaires, des distances perpendiculaires des poissons à partir d’un tracé linéaire, des longueurs des tracés d’échantillonnage et de la surface de chaque banc rocheux. La biomasse, calculée à partir de l’abondance, de la longueur des poissons et d’une relation masse–longueur, varie en fonction de la taille moyenne des S. levis sur ces bancs. Ces résultats obtenus indépendamment de la pêche ont contribué à l’évaluation faite récemment de S. levis par le Pacific Fishery Management Council. Il faudra maintenant établir une série chronologique de résultats provenant des inventaires visuels afin d’évaluer la tendance de la biomasse des S. levis en fonction de la durée croissante de la protection dans les CCA.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: December 1, 2007

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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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