Population dynamics of the estuarine prawn ( Nematopalaemon hastatus Aurivillius 1898) off the southeast coast of Nigeria

The population dynamics of Nematopalaemon hastatus off the inshore waters southeast of Nigeria was investigated using monthly length-frequency data (November 1986 to December 1988). Von Bertalanffy growth parameters were estimated as L ∞ = 16.7 mm carapace length, K = 0.62 per year, C(amplitude of seasonal growth oscillation) = 1.0 and WP(winterpoint) = 0.1. Total mortality ( Z) was estimated at 5.61 per year, and natural mortality ( M) at 2.92 per year. A fishing mortality ( F) of 2.68 per year and an exploitation rate ( E) of 0.48 were therefore obtained, suggesting that the stock of N. hastatus off the southeast coast of Nigeria was exploited almost at the level of optimum yield. This was supported by results from a yield-per-recruit analysis. Despite the preliminary nature of these results, it was concluded that caution should be exercised in development of the fishery in terms of fishing effort. Further unrestrained increases in effort in the fishery might lead to decreases in the shrimp stock to levels at which recruitment may be adversely affected, with adverse economic and social consequences to the fishing communities. Hence, the need to exercise control on effort increases in the fishery was highlighted.