Genetic diversity among Atlantic salmon (Salmo salar L.) populations

The effect of deliberate or inadvertent transfers of cultured Atlantic salmon (Salmo salar L.) on wild conspecifics depends on the nature and extent of biologically important genetic diversity among wild and transferred fish. Tagging and genetic studies show that salmon are divided into local, reproductively discrete populations associated with individual river systems or tributaries within systems. These are likely to be linked by historical patterns of gene flow into larger aggregations, which can be conceptualized as metapopulations, within which an evolutionary dynamic of local population formation, genetic exchange and extinction probably occurs. Diversity among populations has been documented within and between rivers, between North American and European population groups, and between Baltic and Atlantic sub-groups within Europe. Diversity is in most cases associated with differences in biological performance relevant to survival and recruitment. As such, transfers have the potential to genetically alter native populations, reduce local adaptation, and negatively affect population viability and character.