Population dynamics of Engraulis encrasicolus (Linnaeus, 1758) within Ghana’s coastal waters

Abstract

The population dynamics of Engraulis encrasicolus (Linnaeus, 1758), from catches landed along the eastern coastline of Ghana, was evaluated based on monthly length-frequency data from July, 2014 to January, 2015. The growth parameters were estimated as; asymptotic length (L∞) = 11.03 cm standard length, growth rate (K) = 0.58 per year, growth performance index (ɸ) = 1.849, theoretical age at birth (to) = - 0.37 and maximum lifespan of 5 years. Using the Powell-Wetherall plot, the Z/K ratio was 3.90, implying that the stock is mortality dominated. Total mortality (Z) was estimated at 3.40 per year, while natural mortality (M) was 1.59 per year and fishing mortality (F) at 1.81 per year. The estimated fishing mortality (F = 1.81) was found to be greater than the optimum fishing mortality (Fopt = 0.64). Further, the current exploitation rate (E) was calculated as 0.53, portraying unhealthy Engraulis encrasicolus stock. The length at first maturity (Lm50), length at first recruitment (Lr) and length at first capture (Lc50) were obtained at 7.4 cm, 3.5 cm and 3.71 cm respectively. The yield-per-recruit analysis revealed that the current exploitation rate (E) of the Engraulis encrasicolus fishery is very close to the maximum exploitation level (Emax =0.58), an indication of unsustainable heavy exploitation. Based on the quadrant rule, the Engraulis encrasicolus fishery within the investigated area fell in the overfished category. From the study, it was confirmed that the Engraulis encrasicolus stock within Ghana’s coastal waters is currently overfished