Influence of season, depth and mesh size on the trammel nets catch composition and discard in the Southern Black Sea, Turkey

The present study was conducted with trammel nets, which are intensively used in the Black Sea region, in order to investigate the influences of season, depth and mesh size on species composition and discard rates. In total, 27 species, belonging to 4 taxonomic groups (24 fish, 1 gastropod, 1 bivalve and 1 crustacean) were obtained. The percentage distribution of the total catch was 8.32% target species, 14.59% non-target landing and 77.09% discard. The discard rate of Mullus barbatus in the total catch was 0.61%. Among the total catch, Brachyura (22.74%) was the main group discarded, while the other important discard species were Rapana venosa (16.90%), Scorpaena porcus (13.71%) and Uranoscopus scaber (9.65%). The lowest and highest discard rates were found in spring and autumn, respectively. According to depth, the lowest discard rate was from depths > 30 m (37.5%) and the highest at depths < 16 m (91.8%). Regarding the mesh size, minimum and maximum discard rates were obtained from 16 and 22 mm mesh sizes, respectively. According to one-way analysis of similarity (ANOSIM), there was a significant difference in discard species composition between spring and summer and between the < 16 m and > 30 m depth groups (P < 0.05). However, no significant difference was found between mesh size and discard composition (P > 0.05).