Aquatic Ecology of the Tropics (Spring 2011) - EEES 4980-008/6980-008
Gottgens: Example of fact sheet
Lake Victoria (East Africa)
Objective:
Introduce aspects of the ecology and management of Lake Victoria (East Africa) with special emphasis
on the changes in its endemic fish fauna.
Introduction:
 Lake Victoria, the largest tropical lake in the world, is of tectonic origin and located near the
equator in eastern Africa (bounded by Tanzania, Uganda, and Kenya).
 Morphometric data (from Serruya and Pollingher 1983, unless otherwise noted): mean depth =
40m, maximum depth = 79m, surface area = 68,800 km2, basin size = 263,000 km2 (Verschuren et
al. 2002) with a population of 27.7 million (United Nations 1995), altitude = 1,134m, shoreline
development index = 3.7.
 83% of the water gain in the lake is due to rainfall (Talling 1966) and the lake characteristically
mixes once per year (at the onset of the rainy season) with partial mixing at other times. The
thermocline depth varies from 30 to 50m.
 During the last several decades, deforestation, industrial waste and intensive agriculture have
contributed to increased nutrient loading and primary production. Cyanobacteria are now the
dominant producers of the open water (Kling et al. 2001) and indigenous fish stocks of
haplochromine cichlids have collapsed (see below). Extensive swamps, dominated by papyrus
(Cyperus papyrus), are especially common in the northern portion of the basin.
Selected Publication:
Recently, Verschuren et al. (2002) documented the history and timing of human impact on Lake Victoria. In
the absence of historical data on this ecosystem, Verschuren et al. used the paleolimnological record
preserved in offshore sediments to reconstruct the chronology of these changes over the past 180 years.
Increased phytoplankton production, starting in the 1930s, paralleled growth in human population and
agricultural activity. Cyanobacteria replaced diatoms and anoxia-intolerant benthic midge larvae were
replaced by anoxia-tolerant taxa. Loss of deep-water oxygen may have contributed to the 1980s collapse of
indigenous fish species. Conservation of Lake Victoria depends, in part, on large-scale implementation of
improved land-use practices.
Selected Management Problem:
Following the introduction of the piscivore Nile perch (Lates niloticus) in the 1950s, Lake Victoria's
haplochromine cichlid species assemblage was reduced by massive extinctions (ca. 65% of more than 400
species or 5% of the world's known freshwater fishes). This assemblage encompassed a remarkably wide
trophic spectrum and constituted 83% of the lake's total fish biomass (Gophen et al. 1995). The fish
industry changed to favor large-scale fisheries for the Nile perch, tilapia, and the endemic zooplanktivore
Rastrineobola argentea. Both top-down (Nile perch piscivory) and bottom-up (nutrient changes) have
enhanced eutrophication of the lake.
Glossary:
Cyanobacteria: Photosynthetic prokaryotes formerly known as blue-green algae.
Endemic: Confined to a specific, relatively small geographical area.
Eutrophication: Nutrient enrichment of aquatic systems.
Cichlids: Large family of tropical fish species characterized by a broken lateral line, brilliant colors and
specialized breeding behavior (Haplochromis is a genus in this family).
Paleolimnology: Interdisciplinary study of physical, chemical, and biological information preserved in the
sediments to reconstruct past environmental conditions.
Shoreline development index: A measure of the degree of irregularity of the shoreline.
Thermocline: A layer of water where temperature changes rapidly over depth.
References:
Gophen, M., P.B.O. Ochumba and L.S. Kaufman, 1995. Some aspects of perturbation in the structure and
biodiversity of the ecosystem of Lake Victoria (East Africa). Aquat. Living Resour. 8: 27-41.
Kling, H.J., R. Mugidde, and R.E. Hecky. 2001. Recent changes in the phytoplankton community of Lake Victoria
in response to eutrophication. In: The great lakes of the world: food web, health and integrity (ed. M.
Munawar & R.E. Hecky). Backhuys Publ., Leiden, The Netherlands: 47-65
Serruya, C. and U. Pollingher. 1983. Lakes of the warm belt. Cambridge University Press, London: 569 pp.
Talling, J.F. 1966. The annual cycle of stratification and phytoplankton growth in Lake Victoria (East Africa). Int.
Rev. Ges. Hydrobiologie 51: 545-621.
United Nations. 1995. World population prospects: the 1994 revision. New York, The United Nations.
Verschuren, D., T.C. Johnson, H.J. Kling, D.N. Edgington, P.L. Leavitt, E.T. Brown, M.R. Talbot, and R.E. Hecky.
2002. History and timing of human impact on Lake Victoria. Proc. Royal Society London 269: 289-294