Development of a Spatial Population Dynamics Model for Migrating Fish Species in the Niger River Basin within Nigeria

The long-distance migrations of diadromous and potamodromous fish species through the Nigerian reach of the Niger River Basin create a fundamental mismatch between the spatial extent of ecological processes and the jurisdictional boundaries of state-level fisheries management, a challenge that requires a spatially explicit population dynamics modelling approach not yet developed for this system. This study develops an original spatially explicit population dynamics model for three migratory species, namely Brycinus nurse, Alestes dentex, and Distichodus rostratus, in the Nigerian Niger River Basin, spanning the river reach from Kainji Lake in Niger State to the Niger Delta in Rivers State. The model framework integrates individual-based movement rules derived from acoustic telemetry data with stage-structured population dynamics and spatially referenced fishing mortality imposed by state-level artisanal fleets with independently estimated effort distributions. Model development required three years of original field data collection including tagging of 340 individual fish across the three species at five release stations, acoustic receiver network deployment at 28 sites, and catch monitoring at 22 landing sites. Simulation experiments using the calibrated model demonstrated that fishing mortality applied in the lower Niger reach, where immature migrants concentrate during the dry season, disproportionately affects recruitment to upriver spawning grounds, with a 10% increase in lower-reach fishing mortality producing a 23% reduction in spawning stock biomass basin-wide. The study introduces spatially referenced maximum sustainable yield as an original management concept applicable to migratory species in multi-jurisdictional river basins.

Keywords: spatial population dynamics, migratory fish, Niger River, acoustic telemetry, bass management