Mortality, exploitation rate and recruitment pattern of African lungfish, Protopterns annectens (Owen, 1839) from Orashi and Sombreiro Rivers, Niger Delta, Nigeria

Abstract

The study determined mortality, recruitment and exploitation rate of a commercially important fish, Protopterus annectens from Orashi River and River Sombriero between October 2013 and September 2014. A total of 347 individuals of P. annectens were collected fortnightly by commissioned fishers using multiple gear. The total mortality was 3.225 yr^-1, natural mortality was 1.465 yr^-1, fishing mortality was 3.107 yr^-1 and exploration rate was estimated as 0.355. The exploration rate (Emax) that gave maximum relative yield per recruit was 0.355. The exploitation rate at which marginal increase was E= 10% was 0.263. The exploitation rate E=50% which corresponded to 50% of the margin or unexploited stock was 0.229. The mean ratio of length at first capture (LC) and asymptotic length (L∞) was 0.050 while that of natural mortality (M) and growth rate (Kyr^-1) was 2.5. The recruitment pattern showed all year round recruitment with peak and latent periods. The parameters obtained were L∞ = 82.95, K = 0.18yr^-1, T = 29.1⁰C, L mean = 29.5cm, Lmax = 74.97cm. The fish was available all year round. There is need to ensure sustainability of the species in rivers by checking activities of indigenous inhabitants whose commercial activities may destroy the favourable environment of the fish.

Keywords: Mortality, exploitation rate, recruitment, Protopterus annectens