Stock Assessment of Hemichromis fasciatus (Peters, 1857) and Oreochromis niloticus (Linnaeus, 1758) of the Lôkpôhô Dam Lake (Ferkessédougou, Côte d'Ivoire)

Abstract

This study assessed the exploitation status of Hemichromis fasciatus and Oreochromis niloticus in Lôkpôhô Dam Lake, Ferkessédougou, northern Côte d’Ivoire, using fish collected monthly between September 2021 and August 2022. A total of 863 H. fasciatus and 1,098 O. niloticus specimens were examined. Length-frequency data were analysed with FISAT II to estimate mortality, exploitation rates, capture selectivity and population structure. For H. fasciatus, total mortality (Z), natural mortality (M) and fishing mortality (F) were 3.63, 1.94 and 1.69 year⁻¹, respectively. The corresponding estimates for O. niloticus were 1.37, 1.16 and 0.21 year⁻¹. Exploitation rates were 0.47 and 0.15, respectively, both below the conventional reference value of 0.5. The estimated exploitation rates producing maximum yield per recruit were 0.650 for H. fasciatus and 0.361 for O. niloticus. Optimal capture sizes were 10.54 cm and 14.10 cm, while lengths at 50% capture probability were 10.70 cm and 14.22 cm, respectively. Virtual population analysis indicated a higher abundance of smaller fish and a decline in abundance with increasing length. These findings suggest lower fishing mortality than natural mortality for both species during the sampling period. Nevertheless, the exploitation rate of H. fasciatus was comparatively close to the conventional threshold, supporting a cautious, species-specific interpretation of stock status and continued monitoring.