A test of sampling methods for fishes in the littoral zone of Lake Vänern, Sweden

Abstract

Shallow, vegetated habitats play an important role as spawning and nursery areas for several species of fish. Such habitats are often laborious to monitor with conventional sampling methods. We evaluated two quantitative methods for sampling of young fishes in shallow habitats; point abundance with electrofishing and low-impact pressure wave sampling using small underwater detonations. The study was conducted in the littoral zone of an archipelago area in Lake Vänern, Sweden. Both methods rendered quantitative estimates on the most common fish species. However, underwater detonations yielded more species and lower variation among samples. These differences are likely due to the larger sample area of detonations. Species distribution and juvenile fish density estimates and size-structure were compared with results from multi-mesh gill nets. The dominant fish species in the gill net program were recorded with both active methods although the relative composition differed, mainly as a consequence of differences in species and size selectivity. Detonations provided additional, small-bodied, species that were not recorded in the gill net program. Quantitative methods can provide relevant information for identifying essential fish habitats, understanding ecosystem dynamics and providing a baseline for assessing long-term changes (e.g. due to climate change or new water level regimes) in Lake Vänern.