Population genetics of Atlantic salmon and brown trout and its relevance for management of genetic resources

Atlantic salmon (Salmo salar L.) and brown trout (Salmo trutta L.) are genetically highly structured species. The structuring on a broad distributional scale is the result of the glacial and postglacial history, therefore in Europe several main population groups of Atlantic salmon and anadromous form of brown trout, sea trout, have been identified and divergent sources of origin of these groups have been proposed. The pattern of substantial microgeographical differentiation results from the joint action of gene flow, genetic drift, mutation, and natural selection. It is important to understand the effects that the last glaciations have had on the distribution and genetic diversity of these species as well as how selection, genetic drift and gene flow can affect genetic variation within populations and genetic differences between populations in order to fully comprehend the genetic structure of populations and to implement the knowledge for conservation. Genetic management is an important component of strategies that ensure the conservation and recovery of salmon and trout populations. The major issues of genetic management are related with monitoring and conserving gene-level biodiversity, resolving spatio-temporal population structure as well as with genetic consequences of stocking practices. Studies of the population genetic structure are essential for providing estimates of the different sources of variation that determine species’ genetic composition over the geographic area. Knowledge from studies describing spatial and temporal genetic structure is needed to identify and analyze changes of gene level diversity caused by human mediated harvest as well as enhancement practices. Ignoring or not knowing the genetic population structure may result in loss of genetic diversity, reduced productivity and ecological damage. In Lithuania, future management considerations should focus both on maintaining individual populations even at tributary level and ensuring natural levels of gene flow among populations.