Recent changes in distribution pattern of freshwater crayfish in Croatia − threats and perspectives

Abstract

Analysis of Croatian freshwater crayfish populations, aiming to gather new distributional data and complement previous surveys (2005–2011), was performed during 2014–2016, within the frame of Natura 2000 Integration Project. The research included different waterbodies across the whole of Croatia, harbouring both indigenous and non-indigenous crayfish species (ICS and NICS, respectively). Field work was conducted in 117 grid squares with dimensions 10 × 10 km, and up to four waterbodies were surveyed per grid square, making a total of 450 studied sites. Out of those, crayfish were not recorded in 368 sites. In the sites with crayfish presence (i.e., 82), the most frequently observed ICS was Astacus astacus (registered in 33 sites) followed by Austropotamobius pallipes (16 sites), Austropotamobius torrentium (12 sites), and Astacus leptodactylus (5 sites). Concerning NICS, the majority of records were for Orconectes limosus (13 sites), followed by Pacifastacus leniusculus (2 sites), whereas Procambarus fallax f. virginalis was registered in only one locality. Comparisons of obtained data with those from previous surveys showed that NICS are progressively spreading and displacing ICS, as recorded for A. leptodactylus that was almost completely displaced by O. limosus in waterbodies of the east Croatia. Existing ICS populations are under growing anthropogenic preassure, frequently fragmented and isolated. Moreover, this survey showed that in the last decade 55% of A. astacus and 67% of A. pallipes populations disappeared mainly as a consequence of anthropogenic influence onto their habitats. Further monitoring and conservation actions for ICS should be urgently applied to mitigate negative impacts of both NICS and anthropogenic influence.