A new grid-net design to eliminate by-catch for the veined rapa whelk beam trawl fisheries in the south-eastern Black Sea

Abstract

The beam trawl fisheries in the Black Sea only target the veined rapa whelk (Rapana venosa) individuals, and other species like fishes and crabs are thrown back into the sea dead or alive. Furthermore, small bivalves and crabs are packed with the target species without any elimination. In this study, a grid-net design (GND) with two different bar spacing was tested to reduce the by-catch. In total 30 hauls (15 hauls for each bar spacing) were carried out in the south-eastern Black Sea between 17 and 26 August 2017. A commercial diamond mesh and one of the grid-net beam trawls were towed simultaneously onboard a commercial vessel to compare the by-catch compositions. Results showed that there were statistically significant (p<0.01) 78% and 83% decreases in the mean weight of the by-catch for 20 and 30 mm grid-nets, respectively. When compared to the conventional gear, a commercial loss of 14% in the 20 mm GND, and 39% in the 30 mm GND in landing values were estimated. In conclusion, use of grid-nets in south-eastern Black Sea beam trawl fisheries can significantly reduce the by-catch of most benthic species. However, it also causes some commercial loss which might be compensated by providing some compensation to fishers such as extension of the fishing season.