Determination and improving of the selectivity of bottom trawl nets used in the Black Sea

Bottom trawl is the most commonly used fishing gear for catch benthic fish in the Black Sea. For this reason, reducing the unnecessary catch rates of juveniles is very important in order to accurately sustainability of both stocks and fisheries. Determination of the selectivity of 40 mm diamond cod end which is compulsory to used legally for fisherman in the Black sea, 40 mm square (40S) and 50 mm diamond (50D) cod ends which are obliged used in the seas of the European Union is aimed in this study. In addition, the effect of two radial square-mesh escape panels (RSEP) which were added to the front and back sections of 40D on selectivity was determined. A total of 61 trawling operations were carried out on the Sakarya coast of the South West Black Sea from August 23 to October 24, 2016, by participating in 22 - day fishery activities of a commercial trawler (LOA: 14.95 m, 380 HP). The selectivity data were recorded for 44 valid hauls with a total time of 52 hours using covered cod end method. The L50 values obtained from the all cod ends were estimated (40D: 12.9 cm, 40S: 15.6 cm, 50D: 15.2 cm, RSEPf: 14.6 cm, RSEPr: 13.8 cm) in all operations where red mullet was the target species. It was determined that radial square escape panels positively effect on the selectivity.