Abstract

During 1979–1981, a simple and non-expensive monitoring programme for crayfish was developed in Lake Steinsfjorden. From the programme, which includes data on total trapping effort, catch statistics and population composition from test fishing before and after the fishing season, we have estimated yield and monitored population development since 1979. Based on data from the monitoring programme, an adaptive management scheme was introduced for the crayfish population. The results from the monitoring programme have been the basis for authorities when adopting changes in the management scheme and revealing the effects. High exploitation, catching non-legal sized crayfish, low fraction of mature females and the spread of Canadian pondweed have all challenged crayfish management regulations in Lake Steinsfjorden. Management regulations have changed several times during the study period. The major changes included reducing the trapping season from 147 to 7 days, a measure that is easy to enforce, and increasing the mesh size of traps from 17.5 mm to 23 mm. In spite of these measures, the harvest declined by 75%, mainly due to the Canadian pondweed invasion, as this plant now occupies a large part of the shallow areas in the littoral zone.

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