THE AFRICAN RIFT LAKES, PART 1
LAKE VICTORIA: Troubled Waters
By Jason Jenkins
From July 2005 Underwater, Iowa Aquarium Society
Aquarticles.com
Lake Victoria is located in Eastern Africa, resting between the countries of Uganda,
Kenya, and Tanzania. Covering approximately 68,800 km squared (about the size of
Ireland)(3.), Lake Victoria is among the largest of freshwater bodies in the world, second
only to Lake Superior. Although the lake has a massive surface area, the depth of the lake
is relatively shallow. With an average depth of 40 meters, and a maximum depth nearing 80
meters Lake Victoria contains only about 15% of the total volume of water that is found in
its neighboring lake, Lake Tanganyika.
Speaking in geographical terms, Lake Victoria is extremely young. The lake was formed
when a recent up-thrust of the Western side of the Victorian Basin reversed the flow of
the rivers that once flowed away from the basin. Scientists are saying that the lake could
have been formed as early as 25,000 to 35,000 years ago. Within that time, it is believed
that the lake may have dried up entirely between 10,000 to 14,000 years ago. This means
that the 300+ know Haplochromines that evolved in Lake Victoria did so in an astoundingly
short period of time. Even more amazing, they have all evolved from a single species, and
have "less genetic variation than the human species." (Coleman)
Discovered by John Speke in 1858, Lake Victoria was believed to be the source of the
Nile River. Lake Victoria started to experience drastic changes once "Henry Stanley
circumnavigated the lake to confirm Speke's claim" (TED Case Studies) in 1875. Within
a few decades the English had built a railroad through the area, and started to clear
large areas of the lake's forest for farming teas, sugar, tobacco, and cotton. As local
populations grew, the people turned to the lake as means to satisfy a growing demand for a
tilapia known as Ngege. With the new English gill nets being used, the population of Ngege
was quickly decimated to a commercially unsustainable level.
At that point, in the early 1950s, it was decided that the lake would have to be
stocked with nonnative fish to sustain the growing fisheries. The first stocked species to
thrive was the Nile Tilapia, Oreochromis Niloticus, a plankton feeder. A few years later
the idea of establishing a population of the Nile Perch, Lates Nicloticus, came about.
Ecologists, knowing the dangers of introducing such an invasive species, strongly opposed
the idea. Regardless, in 1954 the Nile Perch started to show up in commercial catches. It
is suspected that homesick, English anglers released them into the lake for sport fishing.
With the Nile perch already introduced, the governments decided to actively stock Lake
Victoria with them in the early '60s. For the next twenty years the population of the
enormous predatory Perch, reaching lengths over six feet, and weighing over 390 pounds,
remained in check. It wasn't until the early 1980s that a troubling change appeared. The
perch population exploded from comprising of less than 2% of the lake's biomass to an
astounding 80%. In the meantime, the native Haplochromine populations dropped from 80% of
the lake's biomass to just 1%. It is estimated that 150-200 of the 300 indigenous
Haplochromines are believed to be extinct.
The Nile Perch industry brings about three to four billion U.S. dollars a year to the
fisheries, and supports around 25 million people (a third of the combined populations of
the involved countries). No part of the Perch goes unused. The fillets are sold for food.
The skins are tanned and used to make belts, purses, and boots. The swim bladders go to
breweries to use as filters, and to Asia for use in soups. A large swim bladder alone can
fetch as much as $6 a pound.
Still, the local fishermen are harmed by the industry. With Haplochromine populations
decimated, the fishermen are forced to purchase the Perch scraps from the large fisheries
that have the technology and boats to fish from the open waters of the lake. Not only are
the heads and tails of the perch less tasty than the native Haplochromines, the high oil
content of the perch makes processing for sale much more difficult. Instead of letting the
Haplochromines dry in the sun, the fishermen must go through the process of smoking and
cooking the filleted carcasses of the perch. While local populations suffer from protein
deficiencies, the large Nile Perch exporters sell approximately 200,000 tons annually to
local hotels, as well as European countries. The price fetched for theses filets is well
beyond the average local's budget. Unemployed, and too poor to afford the prices demanded
of Perch meat, the Victoria Basin has experienced the loss of livelihood and food of
approximately 30 million people.
Nile Perch are not the lake's only problem. Pollution has become rampant as booming
populations have settled in the basin. Approximately 2 million liters of untreated raw
sewage get dumped into the lake on a daily basis. On top of that, industrial wastes from
companies like breweries, fish processors, and agricultural processors are discharged into
the lake as well. Gold mining is also on an upswing causing the levels of mercury, used in
the mining process, to rise. Although the local waterways are becoming contaminated with
heavy metals, the problem has not become out of control.
Nutrient levels have tripled since 1950, as a result of the industrializing of the
area. The concentration of phosphorous has increased five times the level they were since
1960. This has caused a massive bloom of blue-green algae. When algae decays, it takes a
great deal of oxygen to complete the process. This depletion of oxygen is causing huge
parts of the lake to be devoid of life.
The nutrient rich waters have also given rise to a water hyacinth infestation. Water
Hyacinth is a rapidly growing, floating weed that clumps together in large bunches. Absent
from the lake as late as 1989, the Water Hyacinth has begun to choke off important
waterways and landings as the growths are too thick for most boats to traverse. Uganda has
been hit the hardest so far. While the Hyacinth blankets the surface, it robs the waters
below of light. This in turn prevents the development of plankton, robbing the already
stressed populations of cichlids, of food. Water Hyacinth also serves as the perfect
breeding ground for disease-carrying snails. As the growth of Hyacinths continues to rise,
so does the frequency of diseases reported in the area of infestation.
As grim as all the problems Lake Victoria is currently facing seem, measures are being
taken to ensure that the lake doesn't become the largest body of dead water on the planet.
Groups like the Lake Victoria Environmental Management Program are planning ways to manage
and restore the land surrounding the Basin. They are also working on controlling the Nile
Perch and Water Hyacinth. Test zones have shown successful, and the tactics discovered
there will be implemented on increasingly larger scales.
Perhaps all is not lost for Lake Victoria. On the bright side, stocks of more than 40
different Haplochromines are being maintained in genetic isolation from other species at
more than 30 different aquariums in the U.S. and Europe under the watch of the World
Conservation Program. There has recently been a return of several species in the wild that
were believed to be extinct, and many more species' status is being re-evaluated. To lose
such an amazing example of species radiation (remember 300+ species evolved in 10-14,000
years) would not only be a great loss to Africa, or even aquarists, but the whole planet.
Sources:
1. Rabi, Marcela. TED Case Studies: Lake Victoria. Fall 1996.
2. Coleman, Ron. Cichlid News. Vol. 6 No. 1, pp. 14-15. How Old is Lake Victoria.
January 1997
3. Chege, Nancy. Lake Victoria: a sick giant. people&theplanet.net. 1/6/04
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