Improving crayfish (Astacus leptodactylus eschscholtz, 1823) fyke net selectivity

Crayfish is one of the most valuable fresh water species in Turkey. In this study, determining of selectivity properties and improving selectivity, based on some modification on standard crayfish fyke nets were aimed. Field works were carried out in January, April, June and October of 2017 by seasonally in Eğirdir Lake (Isparta-Turkey). In determining of the selectivity covered codend method was used. A new covered codend with 14 mm stretched mesh size and 210d/12 rope thickness was designed all of trial groups. Selectivity of different 7 trial groups each consisting of 20 fyke net were researched in study. Trial fyke nets were composing of closed codend "control"; mesh with 34, 42 and 54 mm mesh size rigged on last codend "Ağ34", "Ağ42", "Ağ54" and grid with 20, 25 and 30 mm bar spaced implement on last codend "Izg20", "Izg25", "IZg30" groups. Caught crayfish were firstly classified by trial groups and codend type and then measured biometrical characteristic. L50 and SR values were estimated as 8.88 (2.21), 10.56 (1.41), 11.33 (1.61), 12.19 (1.78), 10.29 (2.28), 10.50 (1.40) and 11.13 (0.82) cm for control, Izg20, Izg25, Izg30, Ağ34, Ağ42 and Ağ54, trial groups respectively. As a result, length selectivity of commonly used current crayfish fyke-nets was determined as below the minimum landing size (10 cm) of A. leptodactylus. To improving the selectivity of this gears, grid with 20 mm bar length implementation is advised on fyke net codend by us. Keywords: Crayfish, fyke net selectivity, grid, Eğirdir Lake