Empirical Analysis of Stock-Recruitment Relationships for Ethmalosa fimbriata in the Bight of Benin, Ondo State

Stock-recruitment relationship modelling is a cornerstone of fisheries stock assessment, yet empirically parameterised models for bonga shad (Ethmalosa fimbriata) populations exploited by artisanal fishers along the Ondo State coastline have not been published. This study empirically analyses the stock-recruitment relationship for Ethmalosa fimbriata in the Bight of Benin using time-series catch and effort data spanning seven years collected from landing sites in Igbokoda and Ilaje. Spawning stock biomass was estimated from catch composition data using age-structured virtual population analysis. Ricker and Beverton-Holt stock-recruitment models were fitted to annual spawning biomass and subsequent recruitment estimates using non-linear least squares regression. Population growth parameters including asymptotic length, growth coefficient, and natural mortality were estimated from length-frequency data using the FISAT II software package. The Beverton-Holt model provided a significantly better fit to the observed data than the Ricker model, suggesting that density-dependent compensation rather than overcompensation governs recruitment dynamics in this stock. Estimated maximum sustainable yield was 5,840 tonnes, compared to the estimated current yield of 7,120 tonnes, indicating significant overexploitation. The study provides the first quantitative stock assessment for E. fimbriata in Ondo State coastal waters and recommends the implementation of a maximum sustainable yield-based catch quota, minimum mesh size enforcement, and seasonal closed areas for spawning aggregations as urgent management measures for this ecologically and economically important species.

Keywords: Ethmalosa fimbriata, stock-recruitment, virtual population analysis, Bight of Benin, Ondo State