Growth, Mortality and Exploitation of Sardinella maderensis (Lowe, 1838) in the Liberian coastal waters

Abstract

This study examined some aspects of population dynamics of 1776 specimen of S. maderensis (Lowe, 1988) from Liberian coastal waters, from April 2013 to September 2013 (total of six months) using the FiSAT II for analysis. From the results, the growth was assumed to follow the von Bertalanffy growth function with asymptotic length (L∞) and the growth coefficient (K) estimated at 44.63 cm total length and 0.38 year-1 respectively. The growth performance index, longevity and the theoretical age at birth (t0) were estimated as 2.88, 7.51 years and -0.387 year-1 respectively. The length at first capture (Lc50=13.99 cm) was lower than the length at first maturity (Lm50=29.75 cm), an indication that most of the harvested stock were juveniles. Instantaneous rate of total mortality, natural mortality and fishing mortality were estimated as 1.24 year-1, 0.81 year-1 and 0.43 year-1 respectively. The current exploitation rate (E) and maximum exploitation rate (Emax) were calculated as 0.34 and 0.36 respectively. Results from the study indicated that the exploitation of S. maderensis is at the maximum sustainable yield coupled with the presence of growth overfishing and intense fishing pressure. Therefore, urgent management actions including increasing fishing gears mesh size and regulating fishing effort is needed to protect the S. maderensis stock.