Size composition, growth, mortality and yield of Alectis alexandrinus (Geoffory Saint -Hilaire) in Bonny River, Niger Delta, Nigeria

Abstract

A twelve month study on the size composition, growth, mortality and yield of Alectis alexandrinus revealed a
length range of 11.5 - 33.8 cm (standard length) . Employing the length frequency method in the FISAT II
package gave the following results for the Von Bertanlanffy growth parameters: L = 35.23, K = 0.680, to = 0.3214
and = 2.926. The total mortality (Z) was 2.47, natural mortality (M) 1.39 and fishing mortality (F) 1.08.The relative
biomass per recruit (knife edge selection) was Lc/ L = 0.05, E10 = 0.355 and E50 = 0.278. Although the exploitation
rate (E) was 0.44 the Emax was 0.421 indicating moderate exploitation of the fish in Bonny River. There is room
for increased effort in the fisheries.