Longline hook selectivity for whiting (Merlangius merlangus euxinus) with a perspective on small-scale fisheries management in the Black Sea, Türkiye

This study investigated the selectivity parameters of bottom longlines for the Whiting (Merlangius merlangus euxinus) in the small-scale fisheries of the Southeastern Black Sea. Experimental fishing operations were conducted using longlines with hook of 11, 12, 13, and 14mm gaps. A total of 552 fish specimens from four species were captured, with Whiting, the target species, accounting for 90.94% (502 specimens) of the total catch by numbers. The sizes of the Whiting ranged from 10.6 to 20.0 cm Total Length (TL), with a mean size of 15.79 ± 0.087 cm TL. The longline selectivity parameters and curves were fitted using the SELECT method, with the bi-modal model offering the best-fit, based on the lowest deviance value. The modal sizes of specimens caught using the hook of 11, 12, 13, and 14-mm gaps were 12.40, 13.53, 14.66, and 15.78 cm TL, respectively. The modal sizes and spread values increased proportionally with hook size. All the individuals caught by the 14-mm gap hooks exceeded the minimum landing size (MLS) of 13 cm. However, the proportions of individuals below the MLS for the 11, 12, and 13-mm gap hooks were 32.09%, 6.98%, and 0.68%, respectively. Based on the MLS, hooks with gaps larger than 11 mm were found to be highly selective and are recommended for sustainability of the fisheries while ensuring the conservation of immature individuals in the Whiting stocks of the Black Sea. These findings contribute to the much-needed data and information for the design of sound management plans for the small-scale fisheries in the region.