Gillnet selectivity for shabbout (Barbus grypus, Heckel, 1843) in Keban Dam Lake, Elazig, Turkey

Objective: This study was conducted to determine the selectivity of multifilament gillnets with 40, 50, 60, 70 and 80 mm nominal mesh size (bar length) for Shabbout (Barbus grypus Heckel, 1843), in Keban Dame Lake, Elazig. Research results will supply the valuable data for fisheries management of Dam Lake. Methods: In the 47 fishing operations performed by holding method, a total of 510 target species were caught between April 2012 and May 2013. Gillnets used present study have same properties except their mesh sizes. The nets were set at sunset and retrieved in the early hours, next day. The fish caught were segregated according to the mesh size of gillnet and grouped in to length groups at 1 cm interval. The SELECT method was used in determining selectivity parameters. Five different functional models (normal location, normal scale, gamma, log-normal and bi-modal) were used to fit the selectivity curve to the catch data. The bi-modal selectivity curve gave the best to fit the data. Results and Discussion: The model lengths obtained from bimodal function for gillnets with 40, 50, 60, 70 and 80 mm mesh sizes were estimated 39.36 cm, 49.20 cm, 59.04 cm, 68.88 cm and 78.72 cm, respectively. Spreads of selection curve were estimated 1.92 cm, 2.40 cm, 2.88 cm, 3.36 cm and 3.84 cm, respectively. One of the basic principles of sustainable fisheries is to ensure that the fish has reproduced at least once, before capture. Minimum catch size of this species is notified as 45 cm in the notification regulated commercial fisheries. According to results of this study, gillnets with 50 mm and above mesh size do not cause an over fishing on Shabbout stocks in Keban Dame Lake.