Does the narrow-clawed crayfish, <i>Pontastacus leptodactylus</i> (Eschscholtz, 1823) (Decapoda: Astacidea: Astacidae), contribute to the decline of the noble crayfish, <i>Astacus astacus</i> Linnaeus, 1758 in the Belarusian Lakeland?

Abstract The noble crayfish, Astacus astacus Linnaeus, 1758, is the rarest crayfish species in Belarus, distributed mainly within the Belarusian Lakeland, a region of numerous lakes of glacial origin in northern Belarus. The territory has been surveyed for the species to recognize its conservation status. From a total of 44 previously known A. astacus habitats, the species now occurs in 23 of them, five of which cohabit with the narrow-clawed crayfish, Pontastacus leptodactylus (Eschscholtz, 1823) which occupies the majority of habitats where A. astacus populations have been lost. Based on the long-term capture data, we tracked the displacement of A. astacus by P. leptodactylus in Karavaino Lake. To our knowledge, this observation represents the first published field evidence showing the progressive and successful outcompeting of A. astacus by P. leptodactylus. Based on our results, as well as by comparing it with previously published information on the crayfish distribution in Belarus, we highlight the unrealised scale of P. leptodactylus expansion in its non-native area of occurrence in Belarus. Due to the invasive potential of P. leptodactylus, we stress the need for research on the influence of P. leptodactylus on overall biodiversity within its introduced range.