Lake Tana



ID

526

Author(s)

Michele Thieme and Ashley Brown, World Wildlife Fund-US

Countries

Ethiopia

Reviewer(s)

Leo Nagelkerke, Wageningen University Wageningen, The Netherlands


Major Habitat Type

Montane freshwaters

Main rivers to other water bodies

Lake Tana was formed by a volcanic blockage that reversed the previously north-flowing river system (Beadle 1981). The total area of the Lake Tana basin is 16,500 km2 and the lake itself covers about 3,150 km2. Numerous seasonal streams and four perennial rivers feed the lake, while only one—the Blue Nile—leaves it (Nagelkerke 1997).



Description

Boundaries

Lake Tana, a lake in the highlands of Ethiopia lies in the north of Ethiopia and is the source of the Blue Nile. The Blue Nile descends from Lake Tana to Tissisat Falls (c. 40 m high), effectively isolating the lake’s freshwater fauna from the rest of the Nile. 

Topography

The lake is situated in the highlands of Ethiopia at about 1,800 m, and experiences a tropical highland climate.

Freshwater habitats

Because evaporation exceeds rainfall, the hydrology of this shallow lake depends largely on the local climate (Burgis & Symoens 1987). Lake level varies depending on seasonal rains. The average difference between the lowest lake level (May-June) and the highest (September-October) is 1.5 m (Nagelkerke 1997). The lake has a mean depth of 8 m, and is well mixed due to relatively strong winds in the evenings (Nagelkerke 1997). The water of the lake is clear, and in places at the lake bottom volcanic peaks form reefs (Sibbing et al. 1998). Cyperus papyrus and other Cyperus spp. line the shores of the lake (Beadle 1981).

Terrestrial habitats


Description of endemic fishes

About 70% of the fish species in this highland lake are endemic, including eighteen endemic cyprinids. The fifteen large barb species of the subgenus Barbus (Labeobarbus) and the 3-4 small barb species of the subgenus Barbus (Enteromius) are currently under revision (Nagelkerke, Agricultural University, Wageningen, Netherlands, pers. comm.). The tilapia (Oreochromis niloticus) of Lake Tana belongs to a widespread species but is described as an endemic subspecies, Oreochromis niloticus tana (Seyoum & Kornfield 1992). The only river loach (family Balitoridae) known from Africa, Nemacheilus abyssinicus, was described from Lake Tana in 1902 and rediscovered in 1992 in the lake and in the upper Omo River (Dgebuadze et al. 1994).

Other noteworthy fishes

The large catfish, Clarias gariepinus, widespread throughout Africa, also lives in the lake and forms an important part of the fishery.

Justification for delineation

The ecoregion is isolated from the rest of the Nile by Tissisat Falls (c. 40 m high); and this isolation has played a role in the evolution of the endemic fauna of the lake.  This ecoregion is distinguished by the only extended cyprinid fish species flock in Africa; at present fifteen species of large barbs have been described from this endemic flock. 

Level of taxonomic exploration

Fair


References

  • Beadle, L. C. (1981). "The inland waters of tropical Africa" England: Longman Group Limited.
  • Burgis, M. J.;Symoens, J. J. (1987). "African wetlands and shallow water bodies" Paris, France: ORSTOM.
  • De Graaf, M., Dejen, E., Sibbing, F. A., et al. (2000). "Barbus tanapelagius, a new species from Lake Tana (Ethiopia): its morphology and ecology" Environmental Biology of Fishes 59 (1) pp. 1-9.
  • Dgebuadze, Y. Y., Golubstov, A. S., Mikheev, V. N., et al. (1994). "Four fish species new to the Omo-Turkana basin, with comments on the distribution of Nemacheilus abyssinicus in Ethiopia" Hydrobiologia 286 pp. 125-128.
  • Manconi, R., Cubeddu, T. and Pronzato, R. (1999). "African freshwater sponges: Makedia tanensis gen. et sp. Nov. From Lake Tana, Ethiopia" Memoirs of the Queensland Museum 44 pp. 361-367.
  • Mina, M. V., Mironovsky, A. N. and Dgebuadze, Y. Y. (1996). "Lake Tana large barbs: Phenetics, growth and diversification" Journal of Fish Biology 48 (3) pp. 383-404.
  • Nagelkerke, L. A. J.;Sibbing, F. A. (1997). "A revision of the large barbs (Barbus spp., Cyprinidae, Teleostei) of Lake Tana (Ethiopia), with a description of a new species, Barbus osseensis" Nagelkerke, L. A. J. (Ed.) The barbs of Lake Tana, Ethiopia: morphological diversity and its implications for taxonomy, trophic resource partitioning, and fisheries ( pp. 179-214 ) Wageningen, The Netherlands: Wageningen Agricultural University.
  • Nagelkerke, L. A., Mina, M. V., Wudneh, T., et al. (1995). "In Lake Tana, a unique fish fauna needs protection" BioScience 45 (11) pp. 772-775.
  • Nagelkerke, L. A. J. and Sibbing, F. A. (1998). "The ‘Barbus’ intermedius species flock of Lake Tana (Ethiopia): I. the ecological and evolutionary significance of morphological diversity" Italian Journal of Zoology 65 (suppl.) pp. 3-7.
  • Nagelkerke, L. (1997). "The barbs of Lake Tana, Ethiopia: Morphological diversity and its implications for taxonomy, trophic resource partitioning, and fisheries" Wageningen, The Netherlands: Special edition, Agricultural University.
  • Seyoum, S. and Kornfield, I. (1992). "Identification of the subspecies of Oreochromis niloticus (Pisces: Cichlidae) using restriction endonuclease analysis of mitochondrial DNA" Aquaculture 102 (1-2) pp. 29-42.
  • Sibbing, F. A., Nagelkerke, L. A. J., Stet, R. J. M., et al. (1998). "Speciation of endemic Lake Tana barbs (Cyprinidae, Ethiopia) driven by trophic resource partitioning; a molecular and ecomorphological approach" Aquatic Ecology 32 pp. 217-227.
  • Thieme, M. L.,Abell, R.,Stiassny, M. L. J.,Skelton, P.,Lehner, B.,Teugels, G. G.,Dinerstein, E.,Kamdem-Toham, A.,Burgess, N.;Olson, D. (2005). "Freshwater Ecoregions of Africa and Madagascar: A Conservation Assessment" Washington, D.C., USA: Island Press.