The selectivity of hook sizes in bottom longline used for whiting (Merlangius merlangus Euxinus Nordmann, 1840) in the Eastern Black Sea (Artvin)

In this study, the selectivity parameters of the hooks in bottom longline consisting of 11, 12, 13 and 14 mm mouth openings, which were used for fishing of whiting in the coastal areas of Artvin, were estimated. As a result of fishing with bottom longline, a total of 552 fishes of 4 different fish species were caught. At the end of the fishing operations, 502 (90.94%) whiting (Merlangius merlangus euxinus), 28 (5.07%) stingray (Raja clavata), 13 (2.36%) rockfish (Gobius spp.) and 9 (1.63%) horse mackarel (Trachurus mediterraneus) were caught. The length of whiting individuals caught varied between 10.6-20.0 cm and their weight between 10.0-50.00 g. Selectivity curves were drawn and the selectivity parameters were estimated by using 5 different models (Bi-Modal, Gamma, Log-Normal, Normal-Location and Normal-Scale) in the SELECT method of 4 different-sized hooks constituting the longline for whiting. According to the results of the SELECT method, which was applied using the length-frequency distributions of whiting that were caught by different hook mouth openings, the Bi-modal model with the lowest deviation value of 65.62 and 28 degrees of freedom was determined as the most suitable model. According to the Bi-modal model, the optimum selectivity lengths of hooks for 11, 12, 13 and 14 mm mouth openings were estimated as 12.40, 13.53, 14.66 and 15.78 cm, respectively. It was determined that all individuals caught by 14 mm mouth opening hook used in the study were above the minimum landing size (13 cm) which was specified for this species. However, the proportion of individuals below the minimum landing size caught by hooks with mouth openings of 11, 12, 13 mm were determined as 32.09%, 6.98% and 0.68%, respectively.