Abstract

A study was carried out over seven years to monitor the effects of different trapping strategies and intensive exploitation on the dynamics of a noble crayfish (Astacus astacus) population in the small (42 ha) Lake Linnajärvi in southern Finland. Three different exploitation strategies were used in isolated parts of the lake: a minimum capture size of 9 cm TL, a minimum capture size of 10 cm TL, and a total ban on trapping (control area). The effects of different exploitation strategies were monitored by test trappings and mark-recapture. The variables tested included population size structure, proportion of reproductive females, reproduction potential, growth, sex distribution, size at maturity, and catch per unit effort (CPUE). The different experimental management strategies led to the following outcomes: reproduction declined slightly due to exploitation; changes were observed in the mean size of the catch; a decline in the market size proportion of the catch; and an increase in the proportion of small sized crayfish. Growth was not affected. The conclusions were that both trapping strategies resulted in a similar population response, but it is possible that some of the responses could have been masked by climatic and other factors.

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