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 popu lations, and further that genetic differences may also exist between n orthwestern and southeastern cod aggregations within the northern cod stock complex off Newfoundland. Cod were sampled from winter aggregati ons ranging from Hamilton Bank to the northern Grand Bank in the north ern cod complex, and from the Flemish Cap, the Scotian Shelf, and the Barents Sea. Tests of allele frequency homogeneity (chi(2)), F-ST, and (delta mu)(2), allele sharing, and Rogers' distance measures revealed significant differences among northern cod, Flemish Cap, Scotian Shel f, and Barents Sea samples. Within the northern cod complex, two poole d samples, NORTH (Hamilton, Funk, and Belie Isle banks) and SOUTH (nor thern Grand Bank area), were distinguishable using chi(2), (delta mu)( 2), and allele sharing measures. Both (delta mu)(2) and Rogers' distan ces 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.