Boundaries

The ecoregion spans parts of southern Mauritania, Senegal, southwestern Mali, Gambia, Guinea-Bissau, and Guinea, and includes the Senegal, Saloum, Casamance, Gébe, and Gambia river basins. 

Freshwater habitats

During the rainy season (between June and October - duration depending on location), the ecoregion’s major rivers often experience pronounced flooding. For example, historically, the Senegal River flooded 5,000 km² of land during its peak flood (Welcomme 1979). However, since the construction of two dams (Manantali and Diama dams) and along the river, flooding has been significantly curtailed (Hamerlynck & Duvail 2003). In the dry season, saltwater moves into the deltas of the lowland coastal rivers (including the Saloum, Casamance and Gébe), forcing strictly freshwater fish species to move inland. The penetration of seawater far inland permits the growth of mangrove forests 70-100 km inland in the southern portion of the ecoregion.

Terrestrial habitats

Terrestrial vegetation ranges from semi-desert Sahelian grassland and shrubland in the north to progressively moister Guinea savanna in the south. In the wetter, southern portion of the ecoregion, seasonally inundated swamp forests line the rivers. Floodplain vegetation includes perennial grasses and sedges, in addition to reedmace (Typha domingensis) in the main channels.

Description of endemic fishes

The rivers of this ecoregion support a moderately rich aquatic fauna, but levels of endemism are low, with only three endemic frogs and one endemic fish species. The desiccation of the basins and relatively recent re-colonization by a Nilo-Sudanian fauna explains the low level of endemism.

Justification for delineation

This ecoregion is defined by the Senegal and Gambia river basins and supports a Nilo-Sudanian freshwater fauna (Roberts 1975; Lévêque et al. 1990, 1992; Lévêque 1997). Uplifting of the earth’s crust during the late Jurassic created the central Fouta Djallon Mountains, which became the source of the Gambia and Bafing (now a tributary to the Senegal) Rivers. Further uplifting of these mountains occurred in the late Miocene (Lévêque 1997). In low-lying areas north of the mountain range, the Niger and Senegal Rivers occasionally became connected during wet periods and Nilo Sudanian fishes are thought to have reached the Gambia from the Senegal by crossing low-lying country in between their lower courses. The Senegal and Gambia Rivers are thought to have been nearly dry during the last interpluvial from about 27,000 to 12,000 years ago (Roberts 1975). Thus, Nilo-Sudanian fish from the Niger River likely re-colonized the Senegal-Gambia catchments during the last pluvial about 12,000 to 8,000 years ago (Lévêque 1997).

Level of taxonomic exploration

Good