Assessment of Artisanal Fishery Impacts on West African Croaker Pseudotolithus elongatus in the Cross River Estuary, Nigeria, Using Length-Based Models

Abstract

In Nigeria and other countries of the Gulf of Guinea, the genus Pseudotolithus is predominant in the catches of both artisanal (small-scale, commercial, or subsistence) and industrial fisheries. Data on this fishery are readily available, enabling resource managers to track stock dynamics. The study objective was to ascertain the status of an exploited stock of West African croaker (also known as the giant captainfish) P. elongatus using von Bertalanffy growth models. Length distribution data were collected monthly from landings of artisanal fisherfolk at the Cross River estuary, Nigeria, between March and August 2008. A fisheries stock assessment tool developed by the United Nations' Food and Agriculture Organization was used to calculate estimates of the von Bertalanffy growth function based on these data. The asymptotic length was 61.5 cm, the curvature parameter was 0.40/year, the oscillation constant was 0.3, the winter point was 0.40, and the goodness-of-fit index was 0.515. The instantaneous rates of total, natural, and fishing mortality were 3.71, 0.78, and 2.93 per year, respectively. The resultant exploitation ratio was 0.79, indicating that the fishery is overexploited. Management regulation, particularly seasonal closures coinciding with the period of peak spawning, should be implemented to avoid the eventual collapse of this fishery. Particular attention should be given to the conservation of the mangrove habitat that sustains the productivity of this system. Previous recommendations for the management or conservation of this stock have neglected the depletion of the mangrove ecosystem supporting this species. It is imperative to include habitat conservation as one of the regulatory measures for this stock.