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, 85%) 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 (χ²), F_ST, and (δμ)², allele sharing, and Rogers' 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 χ², (δμ)², and allele sharing measures. Both (δμ)² and Rogers' 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.