Data-poor stock assessment of Narrow-Clawed Crayfish (Pontastacus leptodactylus) in Keban Dam Lake (Türkiye) Using CMSY Method

Abstract

In this study, as a data-poor fish stock assessment method CMSY was used to assess the current stock status of the Keban reservoir crayfish stock due to not having further data set for using the data-rich models. A total of 27 years catch data (from 1995 to 2021) was used in the analysing process of study. Estimated CMSY model parameters with confidence intervals are as follows: r=0.426 (0.357 - 0.509) year-1, k=146 (118 - 180) ton, MSY=15.7 (13.0 - 18.0) ton, B2021=77.9 (59.5 - 86.7) ton, BMSY=72.8 (58.9 - 89.9) ton, F2021 = 0.295 (0.265 - 0.386) year-1, FMSY = 0.213 (0.179 - 0.254) year-1, B2021/ BMSY = 1.07 (0.818 - 1.190) and F2021/FMSY = 1.38 (1.240 - 1.81). Our study has found that the crayfish population in the Keban reservoir has been in decline due to overfishing since the late 1990s. However, the population has shown signs of recovery since 2013 due to reduced fishing activity. After all overexploitation occurred again in 2021. Our analysis also showed that the current quota of 30.5 tons is significantly higher than the MSY of 15.7 tons. Therefore, it is recommended to reduce the crayfish quota to 15.7 tons in order to sustain the population and prevent further decline.