Abstract

Depth distribution of the noble crayfish Astacus astacus has been studied in the oligotrophic Sance Dam-Reservoir, Beskydy Mountains, Czech Republic. The aim, initiated by limited information in the available literature, was to receive preliminary data on a vertical zonation of the crayfish population. The data obtained are based on 133 crayfish specimens caught during the year 1997 with baited traps placed in depths of 5-15 m, 16-25 m, 26-35 m, and 35-43 m, respectively. The average number of crayfish per trap, as well as of males seems to increase with depth, displaying the highest number in the maximal depth zone. In females the depth distribution is more irregular, with a maximum in the depth zone of 16-25 m. The average length of the crayfish also increases with the depth. As a result, the deepest zone is occupied mainly by large males while smaller crayfish, both males and females, prefer shallower water. Regarding the age, the three-year old crayfish are the most frequent in the Sance Dam Reservoir. Additional studies are needed to confirm the present preliminary results on the vertical zonation of crayfish in deeper waters. More detailed data are also necessary to exactly estimate the entire population in the water body studied.

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