Abstract

The state of noble crayfish stocks in the lakes of Southern Estonia was estimated by means of test fishing in the period 1993-1998. Crayfish were present in 67% of the 54 lakes investigated, but only in 7 lakes more than 2 crayfish were caught per trap night. Crayfish have disappeared from several former crayfish lakes and the CPUE has decreased during the research period in some lakes. Burn spot disease, porcelain disease and Psorospermium haeckeli occurred in a few lakes but cannot be considered the main reason for the decline. Frequency of losses of claws which may indicate a high abundance of crayfish enemies or high competition among the crayfish was not related to the CPUE. Oxygen deficiency in the eutrophic lakes caused by hard winters must be considered among the reasons for the decline in crayfish stocks.

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