TRAWL SELECTIVITY OF FISHING GEARS TARGETING RED MULLET (Mullus barbatus L.) IN BULGARIAN MARINE ZONE

摘要

Red mullet (Mullus barbatus) is one of the most important commercial species for the multi-species Mediterranean demersal trawl fisheries, and gain commercial interest in last year's in Black Sea trawl fishery, as the species is under overexploitation and the scientific advice is to reduce fishing mortality. The experimental trials have been conducted in 2019 (July and September) on board of F/V Sveti Nikola in the Nessebar Bay at depths of 36 to 52 m, using benthic trawl. We quantify the codend size selectivity for red mullet by two parameters: L-50, the length of red mullet with a 50% probability of being retained given that they enter the codend; and selection range (SR), the difference in length of fish having respectively 75 and 25% probability of being retained. Results showed that commercially used 14 to 16 mm trawl codend, with L-50 =11.1 and 11.6 cm is not selective enough to release the immature red mullet. Mesh size of alpha =18 mm, would result in 50% retention of red mullet with a total body length of 12.4 cm. The single technical measure in place concerning red mullet exploitation in the Bulgarian Black Sea is the minimum landing size. The present research shed light on the need for new technical measures introduction - determination of mesh sizes for nets, the requirement of selective gears to reduce unwanted catches, specifications for design and use of gears, and measures to minimise the impact of fishing on the marine ecosystem and environment.