Abundance and stock management of whiting (Merlangius merlangus) in Southeastern Black Sea fisheries

In this study, 1.579 Merlangius merlangus were sampled from commercial trawl fisheries in the Eastern Black Sea. The collected samples' growth, recruitment, and stock structure were evaluated using the ELEFAN-I, Y/R, B/R, VPA, and Thompson and Bell models in the FISAT-II software package. The von Bertalanffy growth parameters, including asymptotic length (L∞), growth constant (K), and t0, were calculated as 40.89 cm, 0.10 cm, and -1.1411 cm, respectively. The first catch length (Lc50) varied between 11.82 cm and 13.40 cm. Total, natural, and fishing mortality rates were estimated at 0.85, 0.29, and 0.56, respectively. Three distinct recruitment periods were identified, occurring in March, August, and November. Based on VPA data, the fixed biomass was estimated at approximately 569,620.7 tonnes. The analysis suggests that the maximum sustainable yield (MSY) for whiting could be reached with an exploitation rate of 0.66. At the current exploitation level, calculated at 449.70 tonnes using the Thompson and Bell method with an F-factor of 0.56, the biomass has decreased. An F-factor of 1.0, representing the MSY, corresponds to 498.180 tonnes. At the current fishing rate (F = 0.56), the biomass has been reduced by 25% (168,026 tonnes) from its unfished state of 666,206 metric tonnes.