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Isolation or metapopulation: whence and whither the Smith Sound cod?

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Abstract:

In April 1995, a spawning aggregation of “northern” Atlantic cod (Gadus morhua) (10000t) appeared in Smith Sound, Newfoundland, growing to 26000t by year 2000. The origin of the founder year classes (primarily the 1990 and 1992year classes) and potential for expansion remains controversial, with genetic isolation used to justify reopenings of coastal fisheries. We investigated the origin using historical, demographic, and genetic data. History provided no evidence of large aggregations before 1995. Demographics in the early 1990s suggested few spawners in Smith Sound, but many in the adjacent Bonavista Corridor. The strong 1990year class was not evident until 1995 and the strong 1992year class until 1997 (both age 5 and first maturity). Genetic study of six microsatellite loci from 791 cod from overwintering aggregations in Smith Sound and offshore regions indicated little to no differentiation (FST) among southern groups (Smith Sound, Bonavista Corridor, Halibut Channel). These results provide a perspective that these groups comprise a metapopulation and that the Smith Sound aggregation arose not from self-recruitment but immigration. By 2009, the aggregation had dispersed, with large concurrent increases in the Bonavista Corridor.

En avril 1995 est apparu dans le détroit de Smith, Terre-Neuve, un rassemblement reproducteur de morues franches (Gadus morhua) (10000t) «du nord» qui a atteint 26000t en l'an 2000. L'origine des classes d'âge fondatrices (principalement les classes annuelles de 1990 et 1992) et leur potentiel d'expansion sont toujours des sujets de controverse et leur isolement génétique a servi à justifier la réouverture des pêches côtières. Nous en avons recherché l'origine à l'aide de données historiques, démographiques et génétiques. Historiquement, on ne trouve aucune indication de grands rassemblements avant 1995. Les données démographiques du début des années 1990 indiquent la présence de peu de reproducteurs; mais il y avait de nombreux reproducteurs dans le corridor adjacent de Bonavista. La forte classe annuelle de 1990 n'est pas en évidence avant 1995 et la forte classe annuelle de 1992 pas avant 1997 (toutes les deux d'âge 5 et à leur première maturité). L'étude génétique de six locus microsatellites chez 791 morues provenant des rassemblements d'hiver du détroit de Smith et des régions du large montre peu ou pas de différentiation (FST) entre les groupes du sud (détroit de Smith, corridor de Bonavista, chenal Halibut). Ces résultats semblent démontrer que ces groupes forment une métapopulation et que le rassemblement du détroit de Smith provient non d'un recrutement local mais de l'immigration. En 2009, le rassemblement s'était dispersé et d'importants accroissements simultanés se sont produits dans le corridor de Bonavista.

Document Type: Research Article

Publication date: January 1, 2011

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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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