Inverse method applied to autonomous broadband hydroacoustic survey detects higher densities of zooplankton in near-surface aggregations than vessel-based net survey

Throughout all oceans, aggregations of zooplankton and ichthyoplankton appear as horizontal sound scattering layers (SSLs) when detected with active acoustic techniques. Quantifying the composition density these is prone to sampling biases. We conducted a net trawl survey epipelagic fauna in northern Norway (70° N) June 2018 while an autonomous surface vehicle equipped broadband echosounder (283–383 kHz) surveyed same region. Densities from hydroacoustic were calculated using forward estimates relative trawl, inversion statistical data-fitting. All four methods (net, inverse methods) identified that copepods dominated SSL, pteropods, amphipods fish larvae present low densities. The method higher for mobile zooplankton, such euphausiid larvae, than other methods. concluded applied surveys can improve organisms by diminishing avoidance biases increasing spatio-temporal resolution ship-based surveys.