Standardisation of hydroacoustic techniques for fish in fresh waters

The European Union Water Framework Directive requires monitoring of biological quality elements to assess the ecological status of aquatic ecosystems and assure their good quality. Hydroacoustics could provide an effective tool for monitoring certain aspects of fish populations in fresh waters, but to ensure the comparability of datasets between lakes and reservoirs across Europe standardisation is required for equipment, survey design, data acquisition, data analysis, and data reporting. In the present paper we investigate the repeatability and precision of hydroacoustic fish surveys in a deep lake comprising two basins (mesotrophic and eutrophic) conducted in accordance with a provisional CEN standard. Results are presented from an international hydroacoustic intercalibration that included six systems comprising hardware from three manufacturers using four sound frequencies (70, 120, 200 and 400 kHz), together with analysis software from three manufacturers. The findings are very encouraging and demonstrate a considerable degree of similarity in the measures of fish biomass and fish abundance produced by these six diverse hydroacoustic systems operated under the mesotrophic and eutrophic conditions of this deep lake.