Population parameters and stock assesment of freshwater crayfish (Pontastacus leptodactylus (Eschscholtz, 1823)) in Eğirdir lake (Turkey)

This study was carried out to determine the catch composition, length-weight relationship, reproductive characteristics, catch per unit effort, shell structure and rate of individuals with lesion, together with the stock assessment of crayfish (Pontastacus leptodactylus (Eschscholtz, 1823)) population in Lake Eğirdir. TropFishR R package was used for estimation of growth parameters and stock analysis and sizeMAT R package was used to determine the length of sexual maturity (L50) of female crayfish. In the monthly study conducted between June 2021 and July 2022, 14919 individuals were caught between 29.92 and 163.38 mm in total length. The female:male ratio of the population was found to be 0.82/1.00. It was determined that positive allometric growth occurred in all sex groups (female, male, female+male). In female individuals, pleopodal eggs were encountered between December and May. The sexual maturity length (L50) was 86.9 mm, the mean egg number was 277.90, and the mean egg diameter was 2.88 mm. The condition factor (KF) was 2.54, the rate of individuals with soft shells was 8.98%, and the rate of individuals with lesions was 10.19%. The catch per unit effort, CPUE and YPUE were found to be 0.46 units/pinter/day and 11.78 g/pinter/day, respectively. Growth parameters L∞, K and Ф were determined as 86.06 mm, 0.59 year-1 and 3.64, respectively. Annual mortality coefficients Z, F and M were calculated as 3.02, 2.38 and 0.64, respectively. The exploitation rate (E), Fcurr/Fmax ratio and SPR were estimated as 0.78, 1.79 and 0.13, respectively. It has been concluded that the crayfish stock is under overfishing pressure and it is necessary to reduce the fishing mortality rate in order to ensure its sustainability.