Data-Limited Stock Status Assessment of Bonga Shad, Ethmalosa fimbriata (Bowdich, 1825) and Lesser African Threadfin, Galeoides decadactylus (Bloch, 1795) in the Central Gulf of Guinea

This study presents a comprehensive data-limited stock assessment of bonga shad (Ethmalosa fimbriata) and lesser African threadfin (Galeoides decadactylus) in the Central Gulf of Guinea using complementary catch- and abundance-based approaches, including Abundance-based Maximum Sustainable Yield (AMSY), Catch-based Maximum Sustainable Yield ++ (CMSY++), and the Bayesian State-space Schaefer Model (BSM). These models were applied because they are suitable for evaluating stock status in data-limited fisheries using catch and abundance information. While AMSY primarily uses abundance information, CMSY++ integrates catch and productivity priors, whereas BSM incorporates state-space error structures to account for observation uncertainty. Catch time series (1990–2021) were extracted from Food and Agricultural Organization (FAO) FishstatJ accessed in 2023, with catch values for 2022–2023 cautiously extrapolated from recent trends due to the temporary absence of updated official statistics. Standardized and scaled relative abundance indices from Cameroonian and Nigerian EEZ were used to support model estimation and assess the stock status. For Ethmalosa fimbriata, the results from CMSY++ and BSM yielded an MSY estimate of 126 × 103 t and 95.5 × 103 t, respectively, while for G. decadactylus, MSY from CMSY++ and BSM were 9.1 × 103 and 13.4 × 103, respectively. Stock status indicators suggested the stock was fully exploited based on both AMSY (F/FMSY = 0.83) and CMSY++ (F/FMSY = 1.03) and overfished based on BSM (F/FMSY = 1.77). For G. decadactylus, the analysis based on AMSY suggested an overfished stock state (F/FMSY = 1.2), while under CMSY++ and BSM, the stock is fully exploited. The log scale CPUE was symmetrical within the expected bounds, and the posterior parameter distributions were constrained, indicating that the model passed the convergence test and had robust parameter estimates. The study recommends maintaining catches within MSY-based reference points as the total allowable catch (TAC) and emphasizes the need for improved data continuity, regional collaboration, and precautionary management for long-term sustainability of fisheries resources in the Central Gulf of Guinea.