Rift Valley Lakes

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Lake Tanganyika in the Mahale Mountains National Park, Tanzania.
© WWF-Canon / James W. THORSELL

About the Area

The Great Rift Valley, created by the moving of tectonic plates beneath the crust of Africa, is home to many lakes that harbour extraordinary endemic species.

Some such as Lakes Malawi (more than 800m deep) and Tanganyika (more than 1400m deep) have formed in the rifts, but the vast Lake Victoria is actually located in a shallow depression between the two rifts.

Several small soda lakes in the eastern rift represent a globally rare habitat type with upwards of 800 cichlids living in them and many more species yet to be discovered. The species radiations of cichlids in the Rift Valley lakes rival radiations of terrestrial fauna in the Galápagos and serve as a classic example of evolutionary adaptation.
Size:
780,000 sq. km (300,000 sq. miles)

Habitat type:
Large Lakes

Geographic Location:
East-central Africa: Burundi, Democratic Republic of Congo, Ethiopia, Kenya, Malawi, Mozambique, Rwanda, Tanzania, Uganda, and Zambia

Conservation Status:
Critical/Endangered

Local Species

The Rift Valley lakes are primarily known for the extensive radiations of fish species in the family Cichlidae. Endemic species of the Clariidae, Claroteidae, Mochokidae, Poecilidae, Mastacembelidae, Centropomidae, Cyprinidae, Clupeidae and other families are also found in these lakes.

A unique pelagic fish community has evolved in Lake Tanganyika including two endemic clupeids, Limnothrissa miodon and Stolothrissa tanganicae, that feed on zooplankton in the pelagic zone and, in turn, provide food for the four predatory centropomids, Lates angustifrons, L. mariae, L. microlepis, and L. stappersii.

Large numbers of cichlid species live adjacent to one another along the edges of the lakes. For example, one researcher caught 7,000 fish representing 38 families in one 4,300 square foot (400 sq. m) sampling area in Lake Tanganyika.

The cichlids have evolved specialisations to take advantage of their environment and to limit competition for resources. For example, one unusual group of fish, the scale-eaters, feed exclusively on the scales of other fish.

Most cichlids spend a lot of time caring for their young, but the young of mouth-brooders swim into their parent's mouth for protection in the face of imminent danger. It is not only the fish that are unique to these lakes.

Copepods, ostracods, shrimps, crabs, and mollusks are also represented by high numbers of endemic species. Lake Tana supports a group of cyprinid fish that are all descended from a common ancestor (called a "species flock"). This cyprinid species flock is one of only two known in the world, and the only one that is still intact.
Do lakes influence the weather?

Answer:
Lakes may be relatively quiet and still, but some are powerful enough to change the weather. Within a 31-49 mile (50-80 km) zone around Lake Victoria, the climate is different from that in places farther away.

Rainfall is heavier and droughts don't affect the water level as much. And even though this part of Africa can get very hot, the temperature around Lake Victoria is rarely higher than 27° C.

Featured species

Limnothrissa miodon

It is a non-migratory fish. Its size is about 17 cm. Body fairly slender. Pre-pelvic scutes not strongly keeled, beginning behind base of last pectoral fin ray. Lower gill rakers long and slender. A distinct silver stripe along flank. Snout broad with tapering sides, not concave when viewed from above. It has a large air bladder which is responsible for its ability to move great vertical distances.

Forms large schools. Mainly nocturnal and feeds on plankton (especially atyid shrimps, also copepods, prawns), but larger individuals take larval Stolothrissa. Cannibalism does occur. Breeds close to shore throughout the rainy seasons, but with peaks in May to June and December to January.

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Threats

Deforestation as a result of commercial agriculture and industrial logging, which leads to increased erosion and altered hydrologic regimes, poses one of the most significant threats. Road building in association with logging has opened up new lands to shifting agriculture. Pollution from mining, industrial logging, agricultural processing, and urban sewage is a serious problem.

Exotics such as Tilapia (Oreochromis mossambica) and Water hyacinth (Eichhornia crassipes), whose population is growing rapidly, place additional stresses; overfishing both for subsistence use and the commercial trade, threatens native species. Additionally, wildlife trade threatens reptiles such as the saltwater crocodile (Crocodylus porosus) - heavily hunted in the Sepik River region and elsewhere for its skins and live export.

WWF’s work


Lakes of the Rift Valley
The project aims to contribute to the conservation of the Lake Malawi/Shire catchment area. The Lake Malawi/Shire catchment and freshwater ecosystem, which extends into Mozambique and Tanzania has been identified as a priority conservation area because of the high biodiversity of wildlife; high endemism of fishery resources; the high number of threatened species and a high degree of threat to the wildland.

The proposed projects include creation of a Peace Park on the Lake, development of a Tourism and Biodiversity Corridor linking the Lake Malawi/Niassa to the coast.

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