Stock assessment of the fish stocks exploited by midwater trawl in Middle Black Sea region

This study was carried out in middle part of the Black Sea coast of Turkey, in 2009-2010 fishing season. In the study, stock size of some pelagic fish species, European Anchovy (Engraulis encrasicolus L., 1758), European Sprat (Sprattus sprattus L., 1758) and Mediterranean Horse Mackerel (Trachurus mediterraneus S., 1868), caught by mid-water trawls were estimated. For this purpose, stock size of the mentioned species estimated by Swept Area Method (SA) and Length based Virtual Population Analysis (LVPA) Methods. Furthermore, the optimum fishing pressure should be applied to stock in order to obtain Maximum Sustainable Yield (MSY) was determined by Length based Thomson and Bell Method (LTB).The fishable stock sizes of European Anchovy (EA), European Sprat (ES) and Mediterranean Horse Mackerel (MHM) in the study area estimated by SA were 260.289±109.111 tons, 145.979±28.684 tons and 16.027±4.474 tons, respectively. Furthermore, the stock sizes of the species in the Turkish coasts of the Black Sea were estimated as 1.573.583±659.631 tons, 882.523±173.410 tons and 96.893±27.047 tons for each species, respectively.The estimated stock sizes of the species calculated by LVPA were 961.399 tons for EA, 196.255 tons for ES and 77.104 tons for MHM. Optimum fishing pressure level estimations calculated by LTB method to obtain MSY showed that the fishing pressure on the stocks should be reduced to 63% and to 71% of the present fishing pressure level for EA and ES, but increased to 116% of the present fishing pressure level for MHM. If the new levels of fishing pressure applied to stocks, MSY will be 190.320 tons for EA, 53.912 tons for ES and 13.823 tons for MHM. Furthermore, the steady-state biomass will be increased to 681.250 tons for EA, 102.209 tons for ES and will be decreased to 41.780 tons for MHM.