Mark-recapture experiments with noble crayfish, Astacus astacus L., in a Norwegian lake

Abstract

. In July and August 1980–1987, mark-recapture experiments with noble crayfish, Astacus astacus L., were performed to estimate density in Lake Steinsfjorden, south-east Norway. Recapture rates were examined for variation according to sex, length, sampling method or length of recovery period, i.e. the time between release and recapture. Lake Steinsfjorden supports a dense, heavily exploited population of noble crayfish with few large individuals. Recapture rates did not vary with sex, but were significantly lower among crayfish smaller than 90mm total length than for larger crayfish. Different sampling methods (baited traps and scuba) prior to marking did not influence the rate of recapture (in baited traps). When the recovery period was increased from 2 to 4 days, the recapture rate increased two- to threefold, but a further increase in the recovery period to 4–6 days did not increase the recapture rate. The estimated density of noble crayfish varied between 013 and 036 individuals 5 70 mm total length per m2 (95% CL. varied from 84 to 280%).