Trawl performance during the barents sea cod and haddock survey: potential sources of gear-related sampling bias

Abstract Hydroacoustic instruments were used to determine the operating dimensions of the bottom trawls used by Norwegian research vessels to assess the cod and haddock resources in the Barents Sea, with the goal of identifying gear performance characteristics that might have influenced the sampling efficiency of the gear. The observations revealed several aspects of the geometry and performance of the gear that could have reduced its efficiency at sampling demersal and semidemersal o organisms, particularly small fish. These included excessively high door spreads and wing spreads, and low vertical openings. The influence of the trawl's geometry on its sampling efficiency and selectivity is discussed, referring to other studies on gear performance and fish behaviour.