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Update on signal crayfish, Pacifastacus leniusculus (Dana, 1852) range expansion in Croatia: A 10-year report

The signal crayfish (Pacifastacus leniusculus) is the most successful crayfish invader in Europe. In Croatia it was firstly recorded in the Mura-Drava river basin in 2008, as a result of natural dispersal by Slovenian populations. In 2012 it was recorded in the Korana River in the continental part of Croatia, where it was illegally introduced. In both rivers, a high dispersal rate was observed. The aim of this study was to explore the range expansion of the signal crayfish 10 years after its first record in Croatia. We collected literature data and conducted field studies in summer 2018 along the Korana and Drava rivers. In the Korana River, we observed an increase in the range of P. leniusculus by 5 km in 2 years. The invasion range now stretches along a total of 30 km. Dispersal rates were higher in the upstream direction, potentially due to differences in competitive pressure from native crayfish. Abundance of the native narrow clawed crayfish (Astacus leptodactylus) was six times lower at the upstream invasion front than downstream. In the centre of the P. leniusculus invasion range in the Korana river no native crayfish were captured, suggesting a displacement of the narrow clawed crayfish by the invasive signal crayfish. In the Drava River, the extent of the newly recorded invasion front corresponds to projections from an earlier study that estimated signal crayfish dispersal over 10 years. Our new records suggest that signal crayfish dispersal rates in this river have remained among the highest in Europe.

invasive species, signal crayfish, range expansion, dispersal rate

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