Population Dynamics of Brackish Water Fish in the Calabar Estuary, Cross River State

This study investigated the population dynamics of commercially important brackish water fish species in the Calabar Estuary, Cross River State, South South Nigeria. Estuarine systems in Cross River State support productive artisanal fisheries, yet population-level data necessary for rational management are scarce. Monthly fish samples were collected from artisanal landings and supplemented by direct netting over six months. Target species included Pseudotolithus elongatus, Lutjanus agennes, Ethmalosa fimbriata, and Mugil cephalus. Age-structured data were derived from otolith readings and length-frequency analysis. Von Bertalanffy growth parameters were estimated using ELEFAN methodology, and total mortality rates were computed using length-converted catch curves. Results indicated that Pseudotolithus elongatus exhibited the fastest growth, with a von Bertalanffy growth coefficient (K) of 0.56 per year and an asymptotic length (L-infinity) of 68.4 centimetres. Fishing mortality (F) exceeded natural mortality (M) in all four species, yielding exploitation ratios above 0.5, suggesting that populations are being harvested beyond sustainable levels. Recruitment patterns showed two annual cohorts for Ethmalosa fimbriata coinciding with wet season inflows. Size-at-first-capture was below size-at-first-maturity for Lutjanus agennes in 71 percent of sampled individuals, indicating growth overfishing. The study recommends the implementation of minimum landing size regulations, seasonal fishing restrictions, and regular stock assessment surveys to rebuild overexploited populations in the Calabar Estuary. Keywords: population dynamics, brackish water fish, estuarine fisheries, stock assessment, Calabar Estuary