Genetic structure of pike (Esox lucius Linnaeus, 1758) populations along the Polish coast of the southern Baltic Sea: Comparison to Danish brackish population

Abstract

The northern pike is a species of eco-evolutionary and socio-economic importance, originally freshwater but adapted to the conditions of brackish bays, lagoons and rivers flowing into seas. It was widespread along the entire coast of the Baltic Sea. A drastic decline in the stocks of Baltic pike in the 20th century caused large-scale stocking activities in the area, often based on non-native material from more abundant freshwater pike populations. Research into the genetic variation and structure of this species in the Baltic Sea is necessary as part of the key knowledge required for the management and conservation of the species. Applying eleven microsatellite markers, we analysed the genetic structure of 495 Baltic Sea pike sampled along the Polish coastal waters and including distant Danish population, collected in Præstø Fjord, in south-eastern Zealand Island. Using traditional F-statistics and a Bayesian approach we confirmed the presence of genetic structure within the analysed region. It was most likely the result of both evolutionary forces and anthropogenic factors. The analyses showed that genetic differentiation observed for the Danish and the others populations generally increased with the geographical distance, populations from the Puck Bay were distinct from the other, and the populations related to the Vistula delta and the Vistula itself form a strong common cluster. Our results contribute to current knowledge on the population genetics of Baltic Sea pike in a previously unstudied area and are in line with calls for on-going conservation, management and restoration activities for coastal Baltic pike to preserve existing genetic differences between different populations and avoid activities that potentially increase genetic homogenization.