Study of the population parameters of the bigeye grunt, Brachydeuterus auritus (Valenciennes, 1831) in Ghanaian coastal waters and its implications for management

Abstract

Some vital population parameters of the bigeye grunt, Brachydeuterus auritus (Valenciennes, 1831), within Ghana’s coastal waters were evaluated based on monthly pooled length-frequency data from June 2014 to January 2015 using the FiSAT Tool II. The estimated growth parameters from 1675 samples were: asymptotic length (L∞) = 16.28 cm standard length, growth rate (K) = 0.78 per year, growth performance index (ɸ) = 2.315, longevity (tmax) = 4 years, theoretical age (to) = -0.24 years and the ratio of Z/K = 1.26. The length at first capture (Lc50), length at first maturity (Lm50) and length at first recruitment (Lr) were estimated at 3.95 cm, 10.9 cm, and 3.5 cm respectively. The observed recruitment pattern portrayed an absence of recruitment overfishing while the ratio of Lc50/L∞ (0.24) showed the presence of growth overfishing. Total mortality rate (Z), natural mortality rate (M) and fishing mortality rate (F) were estimated at 3.21 per year, 1.73 per year and 1.48 per year, respectively. The current exploitation rate (Ecurrent) was 0.46 whereas the maximum exploitation level (Emax) was 0.48. The yield isopleth indicated that small sized Brachydeuterus auritus are harvested at low fishing effort level – characteristic feature of a fishery at the developing stage. Results from the study indicated that Brachydeuterus auritus stock is vulnerable to collapse in the absence of urgent management interventions such as mesh size regulations and monitoring of fishing efforts