Population Parameters and Exploitation Rate of Porogobius schlegelii (Perciformes: Gobiidae) in Lake Ahémé (Benin, West Africa)

Abstract

Lake Ahémé is one of the main fishing areas in the Couffo basin. Porogobius schlegelii (Gunther, 1861) is one of the fish most exploited by artisanal fishing after the cichlid species. Sustainable management of the species requires reliable data on the current pressure of traditional fishing in order to find measures to adjust fishing activities to the recruitment capacity of the species. Therefore, from January to December 2020, data on total length, total weight and sex were collected monthly on a total of 3447 specimens of P. schlegelii caught by local fishermen. The size at first maturity (L₅₀) determined with the statistical package sizeMat was estimated at 6.5 and 6.2 cm for males and females, respectively. The asymptotic length obtained with the TropFishR statistical package was 14.8 cm for both sexes. The growth coefficient and growth performance index were 0.87 year⁻¹ and 2.28, respectively, with a normalised adjustment value of 0.21. Estimates of total, natural and fishing mortality were 3.55, 1.53 and 2.02 year⁻¹, respectively. The current exploitation rate was 0.57 and as such remained above the exploitation rate at 50% of its unexploited biomass (E_0,5 = 0.37). Therefore, a reduction in the current exploitation rate is required by at least 35.1% to maintain sufficient biomass. The estimated size at first capture of 5.9 cm is smaller than L₅₀ for both sexes. These parameters clearly reflect a current trend of overexploitation. Monitoring of fishing efforts and sensitisation of fishermen to catch fish measuring at least 9.3 cm (optimal length) are among the management measures recommended to sustain the P. schlegelii fishing in Benin.