Population dynamics of Bigeye grunt, Brachydeuterus auritus (Valenciennes, 1831) in Ghana and management implications

Abstract

Population dynamics of Brachydeuterus auritus harvested from Ghana’s coastal waters was assessed following previous indications that this important species is collapsing. In view of this, a total of 849 samples of B. auritus were collected from February 2016 to January 2017, measured for total lengths and examined using FiSAT II. The mean length was 13.7 cm with a growth pattern of 2.8. The asymptotic length (L∞) and growth rate (K) were 21.53 cm and 0.67 yr-1 respectively portraying that this species is a fast-growing species. The lengths at first maturity and capture were calculated as 14.4 cm and 6.02 cm respectively which indicated the presence of growth overfishing. The critical length at capture (Lc=0.28) was lower than 0.5, supporting the earlier assertion that the investigated fish species is plagued with growth overfishing. Natural mortality rate (M=1.44/yr) was higher than fishing mortality rate (F=1.22/yr) an indication that small sized fished fishes were largely harvested. The recruitment layout was unremitting throughout the year with two major peaks showing the presence of strong recruitment into the stock - a strategy to avert extinction of its species. However, the exploitation rate (E=0.46) was slightly lower than the Emax (0.52) showing that the biomass of the investigated stock could surpass the maximum sustainable yield (Emax) if necessary fishery management options are not put in place. Furthermore, using the Quadrant rule, the investigated stock was categorized as developing, hence any unsustainable increase in fishing efforts could facilitate growth overfishing leading to its collapse. Therefore, to ensure sustainable exploitation and contribution to protein requirement for coastal community households, relevant fisheries measures are advocated