Gillnet selectivity estimates for five commercially important fish species in Tono Reservoir, Northern Ghana

Gillnet selectivity is crucial for the effective and sustainable management of fisheries. However, there is inadequate information on gillnet selectivity for commercially important species in Tono Reservoir. To facilitate the sustainable exploitation of fish species, this study was conducted to estimate the selectivity parameters of commonly used monofilament gillnets for commercially important fish species in Tono Reservoir from January 2015 to June 2016. Two common nylon monofilament gillnets used by fishermen in Tono Reservoir with stretched mesh sizes 5 and 7 cm and equal dimensions were placed in the same fishing area and retrieved within 12 h. The fish catches were assessed, and selectivity parameters for Sarotherodon galilaeus, Oreochromis niloticus, Coptodon zillii, Clarias gariepinus and Auchenoglanis occidentalis were estimated using the Holt model. The catch per unit effort of the two gillnets exhibited no significant difference. The optimum total lengths of capture of four fish species excluding C. zillii ranged from 13.53 to 25.43 cm for the 5 cm gillnet, and 18.95 to 35.60 cm for the 7 cm gillnet. Common selection factors varied from 2.71 to 5.09. The mean total length at first sexual maturity for all five fish species ranged from 8.60 to 28.86 cm. Both the 5 and 7 cm gillnets were found to be inappropriate for use in the reservoir. Accordingly, their use should be discouraged to protect juvenile fish so that the sustainable exploitation and conservation of fish species in this multispecies fishery can be achieved.