Update on the distribution of freshwater crayfish in Croatia
Four indigenous European and two non-indigenous American freshwater crayfish species inhabit Croatian freshwater habitats. Generally, the noble crayfish (Astacus astacus), the narrow-clawed crayfish (Astacus leptodactylus) and the stone crayfish (Austropotamobius torrentium) are distributed in the water bodies of the Black Sea drainage while the white-clawed crayfish (Austropotamobius pallipes) inhabits rivers of the Adriatic Sea drainage. However, a few records of the noble and the stone crayfish populations in the Adriatic Sea drainage exist. Non-indigenous species the signal crayfish (Pacifastacus leniusculus) and the spiny-cheek crayfish (Orconectes limosus) are distributed in northern Croatia, in the water bodies of the Black Sea drainage. Recently, the distribution of Croatian crayfish populations has been studied more intensely within the frame of Natura 2000. In this paper we present results of field work conducted from 2005 till 2010, and compare them with previous data. Approximately 520 sites were investigated. Results indicate that non-indigenous crayfish are spreading and displacing the noble and the narrow-clawed crayfish. No mass mortalities in the contact zone have been reported. This survey also revealed the spread of the narrow-clawed crayfish westwards and southwards displacing the noble and the stone crayfish from their habitats. The stone and the white-clawed crayfish populations have undergone the biggest decline in numbers. The main reasons for this are disturbance of their habitats and intensive droughts which have been pronounced of late. Collected data are helpful as a starting point for development of management strategies by state institutions dealing with protection of endangered crayfish species.