First estimates of growth , recruitment pattern and length-at-first-capture of Nematopalaemon hastatus ( Aurivillius , 1898 ) in Okoro River estuary , southeast Nigeria

The Nematopalaemon hastatus prawn fishery in Okoro river estuary, Nigeria, is of great ecological value and forms the bulk of economic rent and livelihood of the artisanal fishers and rural households. The fishery lacks vital scientific information needed for its management and sustainability. This study provides information on its growth parameters, recruitment pattern and length-at-first-capture using FAO–ICLARM Stock Assessment Tools (FiSAT II) software to analyse its consecutive 12-month length-frequency data (April 2011 to March 2012). The von Bertalanffy length (Lt) growth function was established as: ; optimum length, Lopt = 52.47 mm, potential longevity, tmax ≈ 2.73 years and overall growth performance index, φ' = 3.8046. The shrimp exhibited the continuous bimodal recruitment pattern (the major being in the rainy season and minor early dry season). The recruitment pattern closely corresponds to its spawning season, implying need for reduced exploitation during this reproductive period. The length-at-first-capture, Lc = 22.29 mm suggests exploitation of the juvenile population; which was confirmed by the critical size ratio (Lc/L∞) of 0.292; indicating need for increase in mesh size to reduce fishing pressure on the stock and to improve the health status of the fisheries resource.