Fine-scale genetic structure of Atlantic salmon (Salmo salar) using microsatellite markers: effects of restocking and natural recolonization

1. An important goal of conservation biology is to preserve the evolutionary potential of a species by maintaining natural levels of genetic diversity. Here, we assess the population differentiation in the Atlantic salmon, Salmo salar, listed in Annex II of the European Habitats Directive, to provide valuable information for its conservation in Normandy (France).
2. Samples collected from 10 natural sites revealed that 13 of 14 microsatellite loci were polymorphic. Significant differentiation among populations was detected ( F _ST = 0.054, P  <   0.001), and all F _ST pairwise comparisons except one were significant. A genetic split was observed between populations inhabiting streams with limestone geology compared to those inhabiting streams with siliceous geology, which could reflect adaptative differences.
3. Hatchery stocks used for the restocking of two rivers were genetically distinct from native stocks.
4. Analysis of three stream habitats restored in 1995 showed that all were recolonized naturally by wild salmon from geographically close populations and no founder effects were detected. Allelic richness was similar between recolonized and wild populations.
5. From a management perspective, our study revealed that restoration of habitat is very effective to recreate new populations in rivers from which salmon have disappeared and that natural recolonization can be fast and effective in terms of genetic diversity.