Comparison of catch composition of demersal trawl fishery performed in open and closed fishing areas in Southern Blacksea

In this study, species diversity, dominance status of species, some bio-ecological characteristics of species and biomass in seasonal at different depths in the two regions that open trawl area (Samsun) and closed trawl area (Ordu) was compared in 2010 and 2011. A total of 87 trawl operations were performed. It was found 65 species at the total belonging to 51 families (3 chondrichthyes belonging 3 families, 35 osteichtyes belonging 26 families, 12 crustacea belonging 9 families, 12 mollusca belonging 10 families, 2 echinoderm belonging 2 families and 1 tunicata belong 1 family). Diversity index value was 2.40 for all study. Osteichtyes was the most intense group and composed the 92%, chondrichthyes 6% and 2% other (crustacea, mollusca, echinoderm, tunicata) of total catch. Species diversity was the highest in 0-30≤ m, winter season and closed trawl area; the lowest in 60≥ m, summer season and open trawl area. Merlangius merlangus euxinus and Mullus barbatus were the most intense species and consisted of 71% of total catch (51% and 20%, respectively). Total biomass value was calculated as 8273.51 kg/km². The highest biomass value was calculated in summer (11309.29 kg/km²) and the lowest in spring (5320.201 kg/km²). biomass value was higher in summer at open trawl area, in spring, autumn, winter at closed trawl area. According to depth, biomass values were calculated the lowest 0-30≤m and the highest 30-60 m in spring and summer seasons, 30-60≤ m in winter and autumn seasons. Biomass values were calculated as 7687.992 kg/km² for osteichtyes, 594.46 kg/km² for chondrichthyes and 154.79 kg/km² for other groups. Diversity index, the size distribution of the dominant species in the catch composition and biomass values were higher in the closed trawl area. As a result, aquatic populations in open trawl area have been faced more fishing pressure and influence than closed trawl area.