Aspects of population dynamics of Pseudotolithus typus (Bleeker, 1863) with management implications within the coastal waters of Liberia

Abstract

This research article seeks to provide information about some aspects of population dynamics of P. typus in the Liberia coastal waters for strategic management and sustainability. A total of 1,822 specimens of P. typus were collected for six months from April to September 2013. The length frequency data was analyzed using FiSAT II and yield software. The asymptotic length, growth rate, growth performance index and the theoretical age at birth were estimated as: L∞ = 84 cm SL, K = 0.04 yr –1, o = 2.451 and to = -0.276 yr –1 respectively, with the maximum age (tmax) at 74.75 years. Total instantaneous mortality rate (Z), natural mortality rate (M) and fishing mortality rate (F) were 0.26 yr –1, 0.16 yr –1 and 0.10 yr –1. Exploitation rate (Ecurrent) and maximum exploitation rate (Emax) were estimated as 0.40 and 0.671 respectively. Growth overfishing existed in P. typus fishery, length at first maturity (Lm50= 56 cm) was higher than length at first capture (Lc50= 28.48 cm). The recruitment pattern was continuous with two major recruitment pulses. Visual Population Analysis results showed that mid- length 45 cm experienced the highest fishing mortality. The fishing regime of P. typus fell in the eumetric stage based on the quadrant rule. Maximum Sustainable Yield (MSY) was 6,621.54 tonnes. From the results growth overfishing was identified within P. typus fishery within Liberian waters dovetailed with absence of recruitment overfishing. P. typus was underexploited, requiring management interventions to increase exploitation sustainably.