Growth, Mortality and Exploitation Rate of Pagellus bellottii Harvested from the Marine Territorial Waters of Sierra Leone

Abstract

The study investigated growth, mortality and exploitation rate of Pagellus bellottii collected off Sierra Leone, aimed to support efficient management of its stock.  A total of 8, 216 specimens of Pagellus bellottii were collected at random from January-November, 2016 on-board a demersal trawler. Data analysis employed methods implemented in the computerized FiSAT II software using pooled length-frequencies in constant class size. Growth parameters gave asymptotic length (L_∞ = 33.63cm), growth rate (K = 0.63yr^-1), growth performance index (ɸ = 2.85), theoretical age (t_o = -0.6years) and life-span (t_max = 5.50years) whereas the length (L_m50) and age (t_m50) at first maturity were estimated as 22.40 cm and 2.30years respectively. Besides, the current fishing mortality rate (F = 6.58yr^-1) exceeded the optimum (F_opt = 0.50yr^-1), limiting (F_limit = 0.81yr-¹) and natural (M = 1.22yr^-1) mortality rates, and the current exploitation rate (E_current) was 0.84yr^-1. Results depicted low life expectancy, fast growth and late first maturity (L_m50 = 33.4%, but < L_∞) in Pagellus bellottii. Also, the stock of P. bellottii was overexploited (E_current > 0.5), buttressed by the alarming current fishing mortality beyond optimal and permissible limits. This was very worrisome and the current exploitation rate should be reduced to 0.5yr^-1 (40.5%) and fishing mortality rate to 0.5yr^-1 (92.4%) in order to achieve at least optimal level of exploitation (E_current = 0.5) and fishing mortality rate (F_current = F_opt) respectively, through institution of closed fishing seasons and reduction in fleets targeting the species.

Keywords: Exploitation; growth;  life-span; mortality; stock