The demography of a haemoglobin polymorphism in the Atlantic cod, Gadus morhua L.

Genetic stability was investigated at a polymorphic haemoglobin gene‐locus in 13 124 Atlantic cod, Gadus morhua L. A total of 30 year‐classes, sampled over 18 years, were variously sampled in 33 named localities. Regional populations showed distinctive allele frequencies, and each major cod fishery showed some degree of genetic imbalance, which was expressed as excessive numbers of homozygotes. This imbalance occurred seasonally in a proportion of the population samples in each of the major cod fisheries. The findings are attributable to migrations of distinctive genetic populations.