Population Dynamics and Stock Structure of Bonga Shad (Ethmalosa fimbriata) in Nigerian Coastal Waters

Bonga shad (Ethmalosa fimbriata) is the single most important artisanal fisheries species in Nigeria by landed weight and value, supporting the livelihoods of hundreds of thousands of fishers and processors along the coast and in inland delta communities, yet its population dynamics, stock structure, and sustainable harvest level in Nigerian waters remain poorly characterised, generating fundamental uncertainty in its management. This dissertation provides a comprehensive investigation of the population dynamics and stock structure of Ethmalosa fimbriata in Nigerian coastal waters using integrated biological sampling, population genetics, and quantitative stock assessment modelling. Biological sampling of 8,400 individuals is conducted monthly from eight major landing sites distributed from Lagos (South West) to Calabar (South South) over 36 months from 2021 to 2024, measuring fork length, weight, sex, gonadal development stage, otolith increments, and age. Growth parameters are estimated from length-frequency data using ELEFAN and from otolith ring measurements, with von Bertalanffy growth function parameters computed separately by sex and region. Spawning seasonality and batch fecundity estimates inform a stage-structured reproductive output model. Population genetic structure among five geographic sampling locations is assessed using 5,000 SNP loci generated by restriction site-associated DNA sequencing, with discriminant analysis of principal components and FST-based clustering identifying genetically differentiated management units. A sex-and age-structured stock assessment model integrating biological parameters, population genetic stock boundaries, and a 20-year commercial catch time series estimates current spawning stock biomass relative to reference points and projects the response of the stock to alternative harvest control rules. Findings document two genetically distinct management units (western and eastern) and estimate the eastern stock to be at 45 percent of unfished biomass. Keywords: Ethmalosa fimbriata, bonga shad, stock structure, population dynamics, stock assessment