Conservation of genetic variation in harvested salmon populations

Management of a group of Atlantic salmon (Salmo salar) populations that are harvested together in the ocean, but separately in freshwater, is looked at from a genetic perspective. A model that estimates total effective population size from local effective population sizes and migration patterns is applied to a system of ten salmon populations in the Sognefjorden district, western Norway. This population system is dominated numerically by the River Lærdalselva population, which may act as a source of migrants into nine smaller populations in a “source–sink” metapopulation. The total effective population size of this system is to a large extent dependent on the effective population size of the Lærdalselva population, but the contribution per spawner to the total effective population size is greater for a fish from the smaller populations than for a fish from Lærdalselva. The results are discussed in light of conservation genetic theory, and empirical results on the fitness consequences of loss of genetic variation in salmonids. The genetic consequences of harvesting need to be assessed both at the levels of local populations and the metapopulation.