Abstract

A seasonal migration of introduced Orconectes limosus (Rafinesque) between a brook and reservoir was observed in a small tributary of a large reservoir in southwest Czech Republic that was identified as suitable habitat for indigenous crayfish. Sixteen capture events (between April 2007 and October 2008) and one radio-telemetry study (from October to November 2007) were conducted. A significant trend of downstream migration to the reservoir was found in autumn. Orconectes limosus showed the ability to move downstream rapidly (max. 139 m per day). Seasonal fluctuations in crayfish density were observed and suggested that the occurrence of crayfish in the brook goes through periodic changes. A lower water temperature in the brook throughout the year, and possible fish predation pressure in the reservoir, could contribute to this phenomenon. The occurrence of O. limosus in reservoirs of big rivers, its periodic migrations, as well as the threat of potential crayfish plague transmission, accentuate their serious threat to indigenous crayfish.

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