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

Abstract

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.

Population differentiation of zander (Sander lucioperca) across native and newly colonized ranges suggests increasing admixture in the course of an invasion

“…Strong evidence, that this also holds true for zander, is provided in a recent work of Salminen et al. (). Studying three lakes, they found low replacement of native gene pools, when natural recruitment of zander was high, but they observed extended replacement and high levels of admixture, when self‐recruitment was low.…”

“…However, more and more evidence is accumulating that stocking in the presence of self-sustaining fish stocks is rarely successful in a range of freshwater fish species (vendace Coregonus albula in Mehner et al 2010;pike in Larsen et al 2005; charr Salvelinus alpinus in Englbrecht et al 2002;trout in Hansen 2002). Strong evidence, that this also holds true for zander, is provided in a recent work of Salminen et al (2012). Studying three lakes, they found low replacement of native gene pools, when natural recruitment of zander was high, but they observed extended replacement and high levels of admixture, when self-recruitment was low.…”

Comparing RADseq and microsatellites for estimating genetic diversity and relatedness — Implications for brown trout conservation

“…Small‐scale introductions may have been made also in Tuhkajoki, which could explain the presence of hatchery genotypes in this population. Several studies have shown that introgression from hatchery stocks to wild fish populations occurs especially when the number of stocked fish is high compared to the number of wild individuals (Hansen, ; Hindar, Ryman, & Utter, ; Ozerov et al, ; Salminen, Koljonen, Säisä, & Ruuhijarvi, ), as is the case in Lake Oulujärvi area. Further, introgression from hatchery‐reared fish can occur at sites distantly located to the stocking location (Vasemägi, Gross, Paaver, Koljonen, & Nilsson, ; Finnegan & Stevens ).…”

“…Each of the studied wild populations appeared to be an isolated unit with very limited gene flow from the other rivers or from the hatchery-reared fish, which is in line with their historical and present-day connectivity. Although (Hansen, 2002;Hindar, Ryman, & Utter, 1991;Ozerov et al, 2016;Salminen, Koljonen, Säisä, & Ruuhijarvi, 2012), as is the case in Lake Oulujärvi area. Further, introgression from hatchery-reared fish can occur at sites distantly located to the stocking location (Vasemägi, Gross, Paaver, Koljonen, & Nilsson, 2005;Finnegan & Stevens 2008).…”

Recent genetic changes in enhanced populations of sea trout (Salmo truttam.trutta) in the southern Baltic rivers revealed with SNP analysis

“…These enhancements have included releases of artificially reared stocks or escapes of large numbers of individuals characterized by lower fitness (Satake and Araki 2011;Baskett et al 2013;Milot et al 2013;Naish et al 2013) and lower genetic diversity have been reported for some species, including Adriatic sturgeon (Boscari and Congiu 2014), Korean starry flounder ) and black sea bream in Japan (Blanco Gonzalez and Umino 2009). Other effects have been introductions of nonindigenous populations, such as salmon in Poland (Poćwierz-Kotus et al 2015a;Bernaś et al 2016); or alien populations of the same species and their subsequent hybridization a Corresponding author: rwenne@iopan.gda.pl with local native populations, as with salmon and brown trout in Bulgaria (Chelenkova et al 2012), Norway (Thaulow et al 2012), Hungary (Horváth et al 2013) and in Spain (Madeira et al 2005), pikeperch in Finland (Salminen et al 2012); unintentional escapes from hatcheries as red sea bream in Japan (Blanco Gonzalez et al 2015), salmon in Norway (Liu et al 2013) and Canada (Fraser et al 2008). Accidental or deliberate introductions of exotic and invasive species to new environments, often beneficial economically, causes distortions in the functioning of local ecosystems and can threaten native populations of fish and shellfish, as in the case of brown trout in Japan (Hasegawa and Maekawa 2008), Patagonia (Vigilano et al 2007;Young et al 2010) and in North America (Turek et al 2016), mussel Mytilus in Europe and South Africa (Kijewski et al 2009;McQuaid et al 2015 and oyster Crassostrea gigas (Carlton 1979;Meehan et al 1989;Miller et al 2012;Lallias et al 2015).…”