New sites of the invasive signal crayfish, <i>Pacifastacus leniusculus</i> (Dana, 1852), from the Lutynia and Prosna rivers in Poland

Abstract This article presents new observations of the invasive signal crayfish, Pacifastacus leniusculus , in Poland. The species was detected for the first time in the Lutynia and Prosna rivers in southwest Poland. In total 59 and 50 individuals were captured. The population examined probably came from illegal releases, while the presence of juvenile specimens may suggest that the population is capable of reproduction. This species could continue to spread and expand its range to include additional aquatic ecosystems. Therefore, it is recommended to monitor the environment regularly and take appropriate remedial actions against this population.