Abstract

Stocks of noble crayfish have significantly decreased in Estonia because of several destructive factors - crayfish plague, habitat modification, mink and eel predation and overfishing. Results of standardized test fishing with trap nets, which was carried out in 127 lakes and 162 streams in the period 1994-2003, were analyzed to reveal recent trends in the status of the Estonian crayfish populations and define the factors causing their decline or recovery. With the exception of the island of Saaremaa, which has never been affected by crayfish plague and has retained a relatively rich stock (CPUE over 4 in 41% of sites), sparse or moderate populations were predominant (over 90%). The number of both studied crayfish populations and temporally relatively stable stocks is distributed unevenly over the country. Monitored populations could be classified as: moderate, but stable; moderate, but fluctuating; declining. Single examples of successful population restoration by means of restocking or spontaneous recovery were detected. Weather fluctuations (summer drought, oxygen deficiency in winter) had caused losses in several cases.

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