Genetic effects of supportive stockings on native pikeperch populations in boreal lakes three cases, three different outcomes

The genetic consequences and gene fl ow of pikeperch ( Sander lucioperca ) stocking were assessed in three boreal lakes based on admixture model analysis and comparison of the preand post-release patterns of genetic variability at 9 DNA microsatellite loci in the recipient populations. In two out of the three cases, the releases of fi sh from foreign populations caused signifi cant changes in the genetic structure of the recipient population. The largest changes were observed in Lake Ouluj ä rvi, where the post-release sample was almost identical to the released Lake Vanajanselk ä population, and about 90% of the catch was composed of the released population. The genetic composition of Lake Lohjanj ä rvi pikeperch also shifted markedly towards that of the released Lake Vanajanselk ä population, and about half of the later catch was of released Vanajanselk ä origin. In Lake Vanajanselk ä , in contrast, releases of pikeperch from lakes Painio and Averia had only a small impact on the genetic structure of the pikeperch population. These results indicate that the current stocking practices create an effective artifi cial gene fl ow that may strongly shape and reduce the genetic differentiation among the remaining native pikeperch populations. A common feature of all three cases was the lack of prior appraisal of the potential genetic and ecological risks in relation to the expected benefi ts of the release programmes.