Discards from Deep-water Bottom Trawling in the Eastern-Central Mediterranean Sea and Effects of Mesh Size Changes

摘要

Data on discards were collected during deep-water bottom seasonal trawling surveys targetting red shrimps (Aristeus antennatus and Aristaeomorpha foliacea) in the Ionian Sea (Eastern-Central Mediterranean). The performance of 3 codends, with stretched mesh sizes of 40, 50 and 60 mm, was tested. A cover with a stretched mesh of 20 mm was employed on each codend. The discarded catch constituted an important fraction of the total catch (20-50%). This was almost exclusively due to unwanted fish species, while discards of the target species and other commercial species were negligible. Discard rates increased with total catch and depth. No substantial differences were seen in the overall performance of the codends used. Differences were only detected in the biomass of the escaped fraction of the catch (both marketable and discards) and in the size selectivity. The 40 mm mesh size was not selective in Aristeus antennatus. Larger mesh size codend (50 and 60 mm) allowed a higher number of small specimens to escape. The 50% retention sizes increased according to the mesh size in all examined species.