Characterizing the pelagic fish assemblage in Lake Paanajärvi: scarce stocks and large individuals

Abstract

The structure of fish stocks in the pelagic areas of Paanajärvi, a deep northern lake in a natural state, was characterized by means of echo surveys and test fishing in 1992-1994. More than 90% of the pelagic fish identified in echo surveying were at depths between 4 and 34 m. The highest pelagic fish density was in the western part of the lake and the lowest in the eastern part. The pelagic fish were in general relatively large, their size distribution resembling more that of pelagic areas in practically unfished natural lakes than that of exploited lakes. The structure of the pelagic fish assemblage in Paanajärvi stresses the importance of nature conservation as means of evaluating gradual changes in the environment caused by human activities. Monitoring fish stocks in lakes located in nature conservation areas could be used as a control method, e.g. for detecting and assessing the effects of land-use activities in a drainage area or fishing in a lake.