Improving escape efficiency in selective devices with the use of a dark tunnel

Abstract

Despite management efforts, like the implementation of escape panels and openings, unwanted catch remains a challenge in demersal trawl fisheries. Studies report that selectivity in escape panels and openings can be low. We explore the selective potential of a large escape opening placed at the aft of the trawl. We then examine if adding a dark tunnel behind the escape opening can increase the escape efficiency of fish by triggering a station-holding behaviour. Our results showed limited escapement through the large escape opening; however, significant for narrow length ranges of some species. Adding the dark tunnel significantly increased the escapement for all analysed species, with escapement up to 70% (40%–83%) and 63% (8%–93%) for roundfish and flatfish, respectively. As target species, a loss of crustaceans up to 85% (60%–96%) highlighted the importance of optimising the integration of the dark tunnel in demersal trawls. Providing the dark tunnel is integrated correctly, our results suggest that currently implemented escape panels and openings with low selective efficiency could be substantially improved by simple means like the dark tunnel.