7/21/11
Environmental problems in Lake Victoria
Lake Victoria is home to a large number of popular aquarium species, many of them endemic to the lake. Unfortunately, the native wildlife in Lake Victoria is under constant threat from introduced species, pollution, and over fishing. Deforestation of nearby regions is also a problem for the lake, and global warming might also pose threats to this ecosystem.
Lake Victoria facts and figures
Lake Victoria is known under several different names, since many different languages are spoken along its shores. In addition To Lake Victoria, it is for instance known as Victoria Nyanza, Nalubaale and Ukerewe. A surface area of 68,800 square kilometers makes it the largest of the Great Lakes of Africa. Lake Victoria is also the biggest tropical lake in the world.
Lake Victoria is located in the western part Africa's Great Rift Valley and was formed 400,000 years ago by an upthrown crustal block that prevented rivers from the east from running any further. It is the source of the White Nile, which is the longest branch of the famous River Nile. Lake Victoria is shared by three different countries: Kenya, Tanzania and Uganda. The shoreline is over 3,400 km long and home to numerous rock dwelling cichlids. Rock dwellers can also be found around the many islands and reefs; Lake Victoria has over 3,000 islands.
Lake Victoria and climate change
Since Lake Victoria is a comparatively shallow lake, it is sensitive to climate changes and can dry out quite easily. The river inflow is quite limited and the surface area is very large compared to its volume. The maximum depth in this lake is no more than 84 meters and the mean depth is only 40 meters. Throughout its 400,000 year long history, Lake Victoria has dried out completely three times. Samples retrieved from the bottom indicate that the droughts were related to previous ice ages, and ice ages are known to cause a reduction of global precipitation. 17,000 years ago, Lake Victoria did not exist. The lake began to fill up again 14, 700 years ago and the endemic species in Lake Victoria has therefore developed during a comparatively short period of time.
Lake Victoria cichlids and invasive species
Invasive species has caused a lot of problems for the native species in Lake Victoria. The introduction of Nile perch (Lates niloticus), Nile tilapia (Oreochromis niloticus) and Water hyacinth (Eichhornia crassipes) has proven especially hard to handle for the ecosystem.
The Nile perch (Lates niloticus) was deliberately introduced in 1954, since it is an appreciated food fish. During the 1960's, introduction efforts intensified, but it wasn’t until the mid 1980's that the Nile perch population began to really dominate the fish community in Lake Victoria. The Nile perch is believed to be responsible for the extinction or severe decline of several hundred cichlid species in Lake Victoria, many of them endemic Haplochromine chiclids that can be found nowhere else in the world. Some species do however still exist in captivity due to breeding programs orchestrated by aquarists.
The introduction of Nile tilapia (Oreochromis niloticus) is believed to have played a vital role in the near disappearance of one of Lake Victoria’s two native tilapia species, Negege (Oreochromis esculentus). Ngege is considered a more delicious food fish than Nile tilpai, but has a slower growth rate and do not reproduce as rapidly as the Nile tilapia. Today, Ngege is only found in small swampy ponds and minor lakes adjacent to Lake Victoria. A severe decline of the Nile tilapia population in Lake Victoria is believed to be necessary if we want this species to survive.
Positive news?
Sometime, over fishing can actually be a good thing. Since Nile perch is such a popular food fish, it is currently being severely over fished in Lake Victoria. This has led to a population reduction, and several populations of endemic cichlids species have actually shown signs of increasing numbers. The situation is especially hopeful for the Yssichromis chiclids. It is naturally impossible to know whether or not this trend will continue, and foreseeing what will happen to a disturbed eco-system is very difficult. It is also hard to know what will happen when fishermen begin to find less and less Nile perch in their nets.
The money derived from Nile perch sales is poorly distributed and a lot of the proceeds do not benefit the local populations. Kenya, Tanzania and Uganda has therefore agreed to create a Nile perch export tax and use the money to promote local communities and sustainable fishery. Unfortunately, this tax has still not been enforced, and even if the countries do decide to start collecting it, the entire region is known for political instability. Enforcement of environmental laws in general and fishery laws in particular are renowned for being lax.
The European Union has invested a major sum in fishery infrastructure and monitoring, and a Lake Victoria Environmental Management Project was launched by The World Bank in 1996. Even though a lot of money has been spent by these entities, the results are minor if any. One the positive side, the funding has made it possible for many east Africans to become conservation professionals, aquatic ecologists and fishery scientists. On the negative side, it is hard for this skilled labor force to find suitable employment. Quite a few of them end up employed by fisheries that have no real interested in committing to long term preservation of Lake Victoria.
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