Development and Testing a New Flatfish By-Catch Reduction Device in Baltic Cod-Directed Trawl Fishery

Flatfish discard rates are high in the Baltic Sea trawl fishery targeting cod. We present a study on a new selection device (freswind) originally proposed by the industry to reduce flatfish catches without loss of commercial cod catches. Experimental fishing was conducted on a commercial vessel using a twin-rig to assess the effect of freswind on the catch composition. The reference gear followed a commercial specification with the mandatory bacoma codend, while the test gear was the same but mounted with freswind ahead of the codend. Catch comparison analysis was carried out using a new approach based on structural modelling. It was used to estimate the mean catch comparison curve (CC) for Cod, Plaice and Flounder. The catch ratio curve (CR) and three usability indicators were estimated to predict the effect of adopting the freswind in commercial fisheries. The experimental data analysis revealed a significant flatfish catch reduction by up to 68% due to the freswind effect. A 32% undersized cod catch reduction was also found in the test gear, while losses of marketable cod were minor (7%). Further the study revealed a flatfish catch reduction above 50% under a potential adoption of freswind in commercial fishery.