Microsatellite polymorphism and the population structure of Atlantic cod (Gadus morhua) in the northwest Atlantic

Allelic variation in six highly polymorphic microsatellite loci (mean heterozygosity, 86%) provided evidence that cod (Gadus morhua) in the northwest Atlantic belong to multiple genetically distinguishable populations, and further that genetic differences may also exist between northwestern and southeastern cod aggregations within the northern cod stock complex off Newfoundland. Cod were sampled from winter aggregations ranging from Hamilton Bank to the northern Grand Bank in the northern cod complex, and from the Flemish Cap, the Scotian Shelf, and the Barents Sea. Tests of allele frequency homogeneity (χ 2 ), FST , and (δμ) 2 , allele sharing, and Rogersi distance measures revealed significant differences among northern cod, Flemish Cap, Scotian Shelf, and Barents Sea samples. Within the northern cod complex, two pooled samples, NORTH (Hamilton, Funk, and Belle Isle banks) and SOUTH (northern Grand Bank area), were distinguishable using χ 2 , (δμ) 2 , and allele sharing measures. Both (δμ) 2 and Rogersi distances clustered western Atlantic samples in two groups distinct from the divergent Barents Sea sample; one comprised NORTH, SOUTH, and Scotian Shelf, and the other, Flemish Cap. Resume : La variation allOlique de six loci de microsatellites fortement polymorphes (hOtOrozygotie moyenne de 86%) a mis en Ovidence le fait que les morues (Gadus morhua) du nord-ouest de liAtlantique appartiennent ‡ de multiples populations gOnOtiquement distinctes, et quiil peut en outre exister des diffOrences gOnOtiques entre les concentrations de morues du nord-ouest et du sud-est dans le complexe de stocks de morue du nord situO prs de Terre-Neuve. Des morues ont OtO OchantillonnOes dans le complexe de stocks de morue du nord, du banc Hamilton au nord du Grand Banc; sur le Bonnet