Investigation of the selectivity of the gill nets used in whiting (Gadus merlangus euxinus Nordmann, 1840) fishery in Eastern Black Sea

This study was conducted on the selectivity of whiting using 16, 17, 18, 20 and 22 mm mesh size gill nets which are used in fishing whiting between June 2010 and June 2011 in Rize region. At the end of the study, totally 1816 number of whiting individuals were caught by gillnets. The lengths range of whiting specimens varied from 7.6 to 23.6 cm and the mean length was found as 14.79±0.05 cm. The mean lengths corresponding to 16, 17, 18, 20 and 22 mm mesh sizes were found to be 14.18±1.552, 14.95±1.743, 14.98±1.914, 15.48±2.563 and 16.67±3.321 cm, respectively.Five different models (Bi-Modal, Gamma, Log-Normal, Normal-Location and Normal-Scale) in SELECT method that based on comparing number of fish caught by different mesh sizes were used to draw the selectivity curves and selectivity parameters were calculated. Bi-Modal model was found to be the best fit model corresponding to smallest deviance value for gill nets used in catching whiting. Optimum (modal) lengths and spreads, corresponding to 16, 17, 18, 20 and 22 mm mesh sizes for the Bi-Modal model were found as 14.81, 15.74, 16.66, 18.51 and 20.37 cm, and 1.35, 1.44, 1.52, 1.69 and 1.86, respectively. When the minimum allowable catch size is taken into account as 15 cm to ensure the conservation and sustainability of whiting stocks, the ratio under 15 cm caught by 16, 17, 18, 20 and 22 mm mesh sizes were calculated to be 71.8%, 45.6%, 46.6%, 43.9% and 35%, respectively. According to these findings, the majority of fish caught by 16 mm mesh size was under the first maturity size and it was observed that the caught ratio of large size length classes increased with increasing mesh sizes