Genetic population structure of vendace (Coregonus albula) in the Gulf of Finland and in adjacent watercourses

Vendace (Coregonus albula) is a freshwater species found in brackish water in the northern Baltic Sea. It has been most abundant in the northernmost part of the Gulf of Bothnia and in the easternmost parts of the Gulf of Finland (GoF), where the stocks have been declining. We assessed the level of genetic diversity and differentiation among the vendace populations in the GoF and adjacent areas. We analysed a total of 385 vendace samples from eight sampling sites. All the samples were genotyped at 17 microsatellite loci. Levels of genetic diversity were generally high within the sampled vendace populations, but the genetic differentiation between the populations was relatively low. The vendace population in the easternmost GoF is genetically close to the freshwater vendace of Lake Ladoga, flowing into the GoF via the Neva River. A previously known local vendace population in Virolahti Bay, on the Finnish coast 150 km west of the mouth of the Neva River, appears to have become extinct during the last 30–40 years. In the Pyhtää archipelago, close to the mouth of the Kymijoki River, there is still a small local vendace population, which is genetically close to the sea-spawning vendace population in the Bothnian Bay. This still genetically viable Pyhtää population evidently carries the genes of a sea- or estuarine-spawning vendace that, based on observations from the previous century, sporadically occurred along the entire Finnish coast. This population is an important part of the local fish biodiversity.