Comparing hydroacoustic fish stock estimates in the pelagic zone of temperate deep lakes using three sound frequencies (70, 120, 200 kHz)

Abstract

Several decades of research have led to the acceptance of hydroacoustics as a reliable measurement method to monitor fish population in lakes, but full standardisation and intercalibration are still lacking. The aim of this study was to investigate the effect of sound frequency on acoustic parameters, such as volume backscattering strength, target strength, and the estimation of fish abundance. Data were recorded in situ using 3 frequencies (70, 120, 200 kHz) simultaneously in 2 different lakes. The results among the frequencies were compared and statistically tested. Data from the 70 and 120 kHz frequencies yielded similar results, but the 200 kHz echosounder estimates in temperate lakes seemed different, especially in cases of high fish abundance, which is typical of eutrophic ecosystems. This work indicates that the abundance estimates of fish populations in temperate lakes based on 200 kHz frequency may differ from results obtained using lower frequencies, and that further study is needed.