Between-year variation in community structure and biomass-size distributions of benthic lake fish communities

The benthic fish communities of 26 Swedish lakes were monitored annually wi th multi-mesh gillnets in a standardized way in the years 1994-1997. No maj or environmental changes (e.g. in nutrient level or acidity) occurred withi n the lakes during the 4 years of study. In most of the lakes, the between- year variation of biomass (per unit of effort) was close to the sampling pr ecision, and biomass was usually less variable than abundance. Median value s of lake-specific indices of variance compensation indicated no general co variance of biomass between species, but a tendency for positive covariance between size classes. This indicates that the benthic fish communities of small to intermediate-sized Swedish lakes most often show low between-year variation in total biomass of fish older than 0+, and that their biomass-si ze distributions are not, in general, shaped by periodic strong year-classe s of keystone species. In a few individual lakes, density compensation was indicated as complementary proportions of a pair of species or size classes that made major contributions to the total biomass. (C) 1999 The Fisheries Society of the British Isles.