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Genetic isolation by distance and localized fjord population structure in Pacific cod (Gadus macrocephalus): limited effective dispersal in the northeastern Pacific Ocean

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Genetic population structure of Pacific cod, Gadus macrocephalus, was examined across much of its northeastern Pacific range by screening variation at 11 microsatellite DNA loci. Estimates of FST (0.005± 0.002) and RST (0.010± 0.003) over all samples suggested that effective dispersal is limited among populations. Genetic divergence was highly correlated with geographic distance in an isolation-by-distance (IBD) pattern along the entire coastal continuum in the northeastern Pacific Ocean (~4000km; r2 = 0.83), extending from Washington State to the Aleutian Islands, and over smaller geographic distances for three locations in Alaska (~1700km; r2 = 0.56). Slopes of IBD regressions suggested average dispersal distance between birth and reproduction of less than 30km. Exceptions to this pattern were found in samples taken from fjord environments in the Georgia Basin (the Strait of Georgia (Canada) and Puget Sound (USA)), where populations were differentiated from coastal cod. Our results showed population structure at spatial scales relevant to fisheries management, both caused by limited dispersal along the coast and by sharp barriers to migration isolating smaller stocks in coastal fjord environments.

Nous avons examiné la structure génétique de la population des morues du Pacifique, Gadus macrocephalus, dans presque toute son aire de répartition dans le nord-est du Pacifique, par la détermination de la variation à 11 locus microsatellites d’ADN. Les valeurs estimées de FST (0,005 ± 0,002) et RST (0,010 ± 0,003) pour l’ensemble des échantillons laissent penser que la dispersion entre les populations est limitée. Il y a une forte corrélation entre la divergence génétique et la distance géographique selon un patron d’isolement par la distance (IBD) sur l’ensemble du continuum côtier dans le nord-est du Pacifique (~4000 km; r2 = 0,83), depuis l’état de Washington aux îles Aléoutiennes, ainsi que sur des distances plus courtes dans trois sites d’Alaska (~ 700 km; r2 = 0,56). Les pentes des régressions d’IBD indiquent que la distance moyenne de dispersion de la naissance à la reproduction est inférieure à 30 km. Des exceptions à ces patrons se retrouvent dans les échantillons provenant des environnements de fjords dans le bassin de Géorgie, soit le détroit de Géorgie (Canada) et Puget Sound (É.-U.), où les populations se différencient des morues de la côte. Nos résultats présentent une structure de population à des échelles qui sont d’intérêt pour la gestion des pêches, causée à la fois par une dispersion restreinte le long de la côte et par d’importantes barrières à la migration qui isolent les stocks plus petits dans les environnements des fjords côtiers.

Document Type: Research Article

Publication date: 2009-01-01

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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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