Assessing fish assemblages in reed habitats of a large shallow lake—A comparison between gillnetting and electric fishing

To know the possible bias of different fishing methods is essential in fisheries management, ecology and conservation. In this study species number, abundance, biomass, length class distributions and predefined ecological features of fishes were compared across two data sets collected simultaneously using gillnet sampling and electric fishing in the reed habitats of the shallow and eutrophic Lake Balaton, Hungary. With increasing sample size, electric fishing proved to be more effective in detecting new species, and samples collected with this method were more species rich when standardized to the number of individuals collected. Ordinations based on relative abundance and biomass data indicated highly contrasting differences between the two methods. Bleak were caught by multi-mesh gillnets in much higher relative numbers. However, the shape and size selectivity of the gillnets also reinforced differences between the two methods. Size distribution data showed that gillnets caught relatively more middle-sized fish compared with electric fishing. Estimates of the abundance and biomass of non-native species by gillnetting and electric fishing differed, and differences were found in the proportions of various guilds (feeding, spawning and habitat). However, it was not possible to conclude which gear’s estimate is closer to reality. The study illustrates that reliance on single-gear surveys can be misleading in assessing fish assemblages in reed habitats of a large and shallow, eutrophic lake.