Population parameters of Oreochromis niloticus (L) from a semi-open lagoon (Sakumo II), Ghana and its implications on management

Population parameters of Oreochromis niloticus in the Sakumo II Lagoon, Ghana were investigated using the FiSAT software. Data were collected quarterly from August 2017 to June 2018. The measured total length of 229 specimens ranged from 4.5 to 18.5 centimeters (cm). The growth parameter (K) was estimated as 0.54 year–1 with asymptotic length (L∞ = 19.4 cm). The recruitment pattern was continuous year-round with two peaks. The total (Z), natural (M) and fishing (F) mortalities were 1.83 year–1, 1.50 year–1 and 0.33 year–1 respectively. The exploitation rate (E) was 0.29 and the relative yield/biomass per recruit (Emax) was 0.48. The fishing effort was found to be low, with catches dominated by small size individuals. The study revealed the growth-overfishing, thus, an increase in the mesh diameter should complement reduced fishing effort to preserve the population of the species.