Estimation of population parameters and length-based stock assessment of Pontastacus leptodactylus in Hirfanlı Dam (central Anatolia), Türkiye

Abstract

Abstract This study focused on assessing the stock of crayfish, Pontastacus leptodactylus, which is a commercially valuable species in Türkiye's inland fisheries, within Hirfanlı Dam Lake, a key production site in the region. The research was conducted between June 2017 and May 2018 through monthly research surveys carried out at six different stations across the dam lake. The stock assessment process was conducted using the TropFishR package (v.1.6.3). A total of 5,920 crayfish were captured during the fishing trials, including 2,595 females and 3,325 males, with carapace lengths ranging from 19.65 mm to 81.14 mm. The “von Bertalanffy growth function” (VBGF) parameters K, L∞, and to were computed as 0.38 yr⁻¹, 84.72 mm (carapace length), and -0.24, respectively. The coefficients for total mortality (Z), natural mortality (M), and fishing mortality (F) were calculated as 1.86 yr⁻¹, 0.47 yr⁻¹, and 1.39 yr⁻¹, respectively. The values of E, Emax, E05, Fmax, and F05 were determined as 0.75, 0.64, 0.20, 1.16, and 0.36 respectively. Considering the biological reference points obtained, the stock can be considered overfished (F > Fmax). To ensure the sustainability of the crayfish stock in Hirfanlı Dam Lake at a target level of 0.40 “Spawning Potential Ratio” (SPR), the fishing mortality rate must be reduced to 0.54, which requires a 61.2% reduction in the current fishing pressure.