Mortality, recruitment pattern and exploitation rates of two Schilbe Oken, 1817 populations: Schilbe mandibularis and Schilbe intermedius from the Aghien Lagoon; estuarine system of West Africa

Abstract

In Cote d’Ivoire, the Aghien Lagoon is under heavy fishing pressure. Mortality, recruitment pattern and exploitation rate of Schilbe mandibularis and Schilbe intermedius were investigated in this lagoon. Fish samples of both sexes (N = 575) were collected monthly between June 2014 and May 2015 from artisanal and experimental captures. Natural mortality was higher in S. intermedius (M = 0.89 years-1) than in S. mandibularis (M = 0.58 years-1). The population of S. intermedius was more vulnerable to fishing (F = 2.90 years-1) than S. mandibularis (F = 0.51 years-1). The Z/K ratio (Z/K = 2.65 for S. mandibularis; Z/K = 4.85 for S. intermedius) indicated that mortality was predominant over growth for the two species. The recruitment pattern showed one Gauss curve translates was continuous for each species. For S. mandibularis, the exploitation rate (E = 0.47) was close to E 0.1 (E 0.1 = 0.46), indicating that S. mandibularis’s stock was in an optimum state of exploitation. However, for S. intermedius, Emax was lower (Emax = 0.57) than the exploitation rate (E = 0.77). This result reflected overexploitation of this species. Key words: Schilbe mandibularis, Schilbe intermedius, mortality, recruitment, exploitation, Aghien Lagoon.