Abstract
Abstract The distribution and overall biomass of an underfished vendace, Coregonus albula L., population in the mesotrophic Henne Reservoir (Germany) was studied using hydroacoustics and gill nets. Additionally, midwater trawling was carried out. Overall fish biomass, based on five hydroacoustic surveys (June to September 2002), ranged from 188 kg ha−1 in early August to 302 kg ha−1 in September 2002. The overall mean fish biomass was 256 kg ha−1 (±48 kg ha−1 SD). Biomass of fish smaller than 25 cm total length (mostly vendace) varied from 56 kg ha−1 in August to 99 kg ha−1 in September, with an overall mean fish biomass of 74 kg ha−1 (±17 kg ha−1 SD). The echograms showed temporal variation in fish distribution in Henne Reservoir. In June, fish were fairly evenly distributed over the whole reservoir but in September a dense aggregation of fish (mostly vendace) was found in the deeper water layers near the dam. The distribution of vendace stock, its impact on water quality and fisheries management, biomanipulation and effort for mass removal are discussed.
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