The Cichlids of Lake Victoria
At one time it was estimated that lake Victoria was home to in excess of 400 different cichlid species. That number is now down to 200 or less species due in part to the introduction of Nile Perch and other problems being encountered at the lake. Of the remaining species many are critically endangered while others are headed in that direction. Lake Victoria or Victoria Nyanza (also known as Ukerewe, Nalubaale, Sango, or Lolwe) is one of the African Great Lakes. The lake was named after the United Kingdom's Queen Victoria, by John Hanning Speke, the first European to see the lake. Lake Victoria fisheries have traditionally been dominated by a large number cichlid fish species (particularly Haplochromine cichlids and Tilapiine cichlids)which have evolved rapidly from a few species that were present in the rivers that helped fill the lake 14,700 years ago. It is estimated that the number of Haplochromine cichlids species may have been in excess of 500 while current estimates are at least 150 species (out of over 200 cichlid species overall), most endemic to the lake.
A 1971 UN survey reported that Haplochromine cichlids constituted about 80% of the total fish biomass of the lake. Cichlids were also a significant food source for the rapidly expanding population living around the lake. By the 1950s, growing lakeside populations began to have a noticeable impact on the water quality and fisheries of Lake Victoria. Changes in land use resulted in increased flows of silt, and chemicals into the lake, which, combined to reduce fishing capacity, thus, leading to a decline in catch, even as the demand for fish was rapidly increasing. In the 1950s, the Nile perch (Lates niloticus) was first introduced into the lake's ecosystem in an attempt to improve fishery yields of the lake. Introduction efforts intensified during the very early-1960s. However, the species was present in small numbers until the early to mid-1980s, when it underwent a massive population expansion and came to dominate the fish community and ecology of the world's largest tropical lake. Also introduced was the Nile tilapia (Oreochromis niloticus), now an important food fish for local consumption.
The most recent data for fish catch show the dramatic change in the Lake Victoria fishery:
63% - Lates Niloticus (Nile Perch)
19% - Astrineobola Argentea (Silver Cyprinid, Dagaa, Mukene, Omena)
09% - Oreochromis Niloticus ( Nile Tilapia)
-1% - Haplochromine Cichlids
The abrupt change in fisheries is rather startling. The Nile perch is a predator and has devastated Haplochromine cichlids populations to a point where many species are becoming extinct in the wild or extinct totaly. Some species are being maintained in zoos and aquaria, e.g. as part of the Association of zoos and aquarium's Species Survival Plan for these species. Some species which were extirpated from Lake Victoria itself, are known to survive in nearby smaller so-called satellite lakes, such as lake Koyota, lake Edward and lake Albert. The damage is not limited to Haplochromine cichlids. For example, the Singidia tilapia (also called ''ngege'' - Oreochromis esculentus) is also assessed as critically endangered and is found only in a few satellite lakes.
The Nile perch has become the most important commercial species and is exported for consumption worldwide. The impact of perch fishing upon the local economy is the subject of the documentary Darwin's Nightmare. However, Nile perch catches have diminished dramatically in recent years due to overfishing and poor enforcement of fisheries regulations.
The overfishing of the Nile perch maybe having the side effect of allowing the populations of a few endemic cichlid species to increase again, particularly one to three species of zooplankton-eating, herring-like cichlids (''Yssichromis'') that school with the abundant native Rastrineobola argentea.
In 1996, The World Bank funded a project to restore and sustain the ecology of lake Victoria and its fisheries, called LVEMP (Lake Victoria Environmental Management Project). Meanwhile, the European Union invested another large sum in fisheries infrastructure and monitoring. One product of these foreign aid programmes has been the training of a new generation of East African aquatic ecologists, conservation professionals, and fisheries scientists. There has also been an increase in the fishery research institutes of the lake.
Another exotic species introduced to lake Victoria has also caused major environmental problems, the Water Hyacinth (Eichhornia crassipes), a plant native to the tropics of South America. It appears to have been been introduced to the region by Belgian colonists to Rwanda in the nineteenth century to beautify their holdings and then advanced by natural means to lake Victoria where it was first sighted in 1988.
In ten years, it had spread along the shorelines in thick mats that covered an estimated 77 square miles (200 km2) impacting fishers, transportation and hydroelectric power production. Agressive efforts to halt its spread included the introduction of the mottled water hyacinth weevil (Neochetina eichhorniae) which ate the plant. After initial succes, when the plants coverage was dramatically reduced, it has returned.
Photograph © Kevin Bauman Used with Permission. http://www.african-cichlid.com/index.html