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

The genetic consequences and gene flow of pikeperch (Sander lucioperca) stocking were assessed in three boreal lakes based on admixture model analysis and comparison of the pre- and 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 fish from foreign populations caused significant changes in the genetic structure of the recipient population. The largest changes were observed in Lake Oulujärvi, where the post-release sample was almost identical to the released Lake Vanajanselkä population, and about 90% of the catch was composed of the released population. The genetic composition of Lake Lohjanjärvi pikeperch also shifted markedly towards that of the released Lake Vanajanselkä population, and about half of the later catch was of released Vanajanselkä origin. In Lake Vanajanselkä, 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 artificial gene flow 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 benefits of the release programmes.

Coastal and freshwater pikeperch (Sander lucioperca) populations differ genetically in the Baltic Sea basin.

Microsatellite DNA based analysis of the pattern of genetic diversity among three coastal and five freshwater populations of pikeperch Sander lucioperca in the northern part of the Baltic Sea drainage basin indicated marked genetic differentiation between the coastal and lake populations. The F(st) between these population groups was as high as 0.25 and R(st) =0.32. In general, the lake populations showed higher genetic diversity than the coastal ones. In terms of genetic distance, the three coastal populations (Vanhankaupunginlahti, Västanfjärd and Taivassalo) grouped tightly together. The freshwater samples formed a looser group, in which the northern Lake Kemijärvi showed greater distance from the southern lakes than these did from each other. The two lake populations originally established through stockings (Lakes Painio and Averia) grouped near to their source population of Lake Lohjanjärvi and their diversity level was nearly the same. Safeguarding the unique Baltic coastal populations of S. lucioperca against gene flow from increasing hatchery releases using freshwater S. lucioperca should be a high management priority.

Genetic differentiation among European whitefish ecotypes based on microsatellite data.

The amount of genetic differentiation at DNA microsatellite loci in European whitefish (Coregonus lavaretus) was assessed among ecotypes, populations and run-timing types. The magnitude of genetic changes potentially caused by hatchery broodstock rearing were also compared with those observed in corresponding natural populations. A total of 35 populations were studied, including 33 Coregonus lavaretus populations and two samples of Coregonus peled. Five of the six whitefish ecotypes in Finland were represented within C. lavaretus populations. Genetic diversity among C. lavaretus populations proved to be high compared to two C. peled populations. The genetic D(A) distance between these two species was as high as 0.86. The genetic differentiation among ecotypes was generally low and thus gives support for the hypothesis of one native European whitefish species in Scandinavia. Among the ecotypes the northern, large sparsely-rakered, bottom-dwelling whitefish was most unique. Thus, observed genetic differences in quantitative traits have either developed independently of phylogenetic lineages, or have mixed and later changed according to environments and selection pressures. Overall genetic distances between the anadromous whitefish populations along the Finnish coast, especially in the Bothnian Bay area, were small. Populations of this area have been heavily influenced by human activities, and they also have the highest probability of mixing by natural means. In two cases, the Rivers Iijoki and Tornionjoki, statistically significant genetic differences could be observed between summer- and autumn-run spawning-time types. Wild populations had slightly higher allelic diversity than hatchery-reared populations of corresponding rivers. Although some reduction in genetic diversity during hatchery rearing is possible, it is an important aid in maintaining endangered populations.