Distribution of crayfish species in Hungarian waters

Three native crayfish species, i.e. Astacus astacus, Astacus leptodactylus and Austropotamobius torrentium, occur in Hungary. Lately, however, non-indigenous crustaceans have also invaded the country Their most recent distribution and impact on the occurrences of the native species is not clear. Consequently, the first object of the present study was to investigate the present-day distribution and habitat preference of the native and invasive crayfish and crab species in Hungary according to water types and surface water velocity values. The second aim was to investigate the changes in the distribution patterns of all species over the last 20 years and to identify potential risks for native species in Hungary. Although A. astacus was discovered on several new locations the overall distribution of the species is decreasing. The rarest crayfish is A. torrentium which was found only at three locations, making this the most endangered crayfish in Hungary. Although A leptodactylus used to occur especially in the main branches of the Danube and Tisza Rivers it shifted towards its tributaries after O. limosus appeared here. Despite their overlapping habitat preference and the fact that O. limosus is a carrier of the lethal crayfish plague, both species still co-occur at a few locations in Hungary Pacifastacus leniusculus is invading the country from the West and although it is not present in large numbers yet, it has replaced the local A. astacus populations and may further impact its distribution when it further increases its range in the future. Although occurrences of the Chinese mitten crab (Eriocheir sinensis) the marbled crayfish (Procambarus fallax f. virginalis) and the red swamp crayfish (Procambarus clarkii) have been reported in the literature, these species were not encountered during the survey Thus indicating that their occurrence in Hungary is not widespread yet. The increasing distribution of the invaders forms a constant threat to native crayfish populations in Hungary To ensure the survival of the native species it is important to keep track of the ongoing changes in crayfish distributions. Nevertheless, additional protection measures will be required to safe-guard the survival of the native crayfish populations in Hungary.