Assessment of the Impact of Dam Construction on Upstream Fisheries in Shiroro Dam Reservoir, Niger State

Large dam construction creates impoundments that alter riverine fish habitats and transforms the structure of aquatic communities, with complex long-term implications for fisheries that are often inadequately documented in Nigerian river systems. This study assesses the long-term impact of the Shiroro Dam on upstream artisanal fisheries by comparing catch composition, catch per unit effort, and community-reported changes in fishing conditions between the reservoir zone and a comparable unimpounded upstream reach of the Kaduna River in Niger State. Data were collected over five months through catch monitoring at three landing stations and structured interviews with 80 fishers who have fished in both zones. Physicochemical parameters, phytoplankton biomass, and macrophyte coverage were measured at all stations. Results showed that total species richness was higher in the unimpounded reach (28 species) compared to the reservoir zone (21 species), though total biomass per unit of effort was higher in the reservoir, dominated by pelagic clupeids and Lates niloticus. Fishers reported the complete disappearance of migratory species including Brycinus nurse from the reservoir zone following dam closure. Macrophyte coverage was extensive in the upper reservoir zones, reducing net fishing access. The study provides baseline comparative data on dam impacts in the Shiroro system and recommends the evaluation of downstream fish passage infrastructure to partially mitigate barriers to fish migration.

Keywords: dam impact, fisheries, Shiroro Reservoir, fish community, Niger State