Changes in Fish Assemblages after Completion of the Bumbuna Hydroelectric Dam in Sierra Leone, West Africa

The Bumbuna hydroelectric dam is a run-of-river facility on the Seli/Rokel River 200km northeast of Freetown, Sierra Leone. Located upstream of a large natural falls (Bumbuna Falls), the project impounds a 30 km long reservoir (445 m³).  We documented changes in the fish community in the river as part of a comprehensive assessment of the project’s effects.  We sampled fish at eight sites during pre- (2006) and post-impoundment (2012) wet and dry seasons with cast and gill nets, baited traps, and hand dip-nets as well as purchasing from local fishermen. We documented 87 species (1807 fish) pre-impoundment; 63 species were found only in freshwater, while 24 species were euryhaline or marine species. We caught 40% fewer species and 19.3% fewer fish in the river post-dam construction, with 33% fewer species captured in the impounded area. Prior to impoundment construction, Bumbuna Falls created a barrier to fish distribution and migration,  with 21 species collected 30 km upstream and 41 captured below the falls.  The reservoir fisheries is now dominated by Cichlidae (e.g.,Tilapia louka and T. joka), reflecting an increase in spawning habitat and presence of predators such as Clarias laeveceps, Heterobranchus isopterus, Hepsetus odoe, Hydrocynus forskalii and Hemichromis fasciatu.