Size Spectra of Pelagic Fish Populations in a Deep Lake—Methodological Comparison between Hydroacoustics and Midwater Trawling

Net sampling by trawling and hydroacoustics was used to methodologically compare size spectra (SS) of the pelagic fish community in a deep lake across 12 years sampling. Hydroacoustic SS were generated based on either single-echo detections (SEDs) or tracked-echo groups (TEGs) from 20 cross-lake transects. Trawl obtained midwater trawl four depth layers. All derived maximum likelihood estimations exponent b continuous body mass distribution. The arithmetic mean similar for all methods, there no significant differences among three methods years. However, visual inspection indicated that differed considerably between some years, primarily when high densities 0+ coregonid fishes strongly spatially aggregated hence caught trawl. Accordingly, correlation hydroacoustics. In contrast, SEDs TEGs significantly correlated, indicating reliability reproducibility obtaining estimated revealed positive trend over since 2005, potentially reflecting recent eutrophication Lake Stechlin, which may lead higher growth rates. We conclude help generate more precise our study than trawling. truthfulness estimates cannot be evaluated because inherent difficulty determining true sizes lakes.