An ecological experiment goes wrong
In the 1950s, the Nile perch (Lates niloticus), a large freshwater fish, was introduced into Lake Victoria. The goal was to establish a commercial fishery and provide a bigger fish for local communities to catch. Unofficial introductions began as early as 1954, with more official stocking programs by fisheries officials in Uganda and Kenya following in the early 1960s. For decades, the perch population remained small. Then, in the late 1970s and early 1980s, its numbers exploded.
Before the perch, Lake Victoria contained an diversity of more than 350 species of cichlid fish found nowhere else on Earth. These small fish, particularly the group known as haplochromines, formed the backbone of the lake's ecosystem and local fisheries. In 1978, cichlids made up about 80% of the lake's total fish biomass. By the late 1980s, that number had plummeted to less than 1%, while the Nile perch biomass surged to over 80%. The voracious perch, a predator that can grow up to two meters long and weigh 200 kilograms, had systematically consumed the native fish. This event led to the extinction of an estimated 200 cichlid species, a loss of biodiversity E.O. Wilson called "the most catastrophic extinction episode of recent history".
A cascade of consequences
The disappearance of the cichlids triggered a series of destructive changes throughout the lake. Many of the extinct cichlids were specialized algae-eaters. Without them, algal blooms became more frequent, clouding the water and reducing visibility. When this massive amount of algae died and decomposed, it consumed large amounts of oxygen, creating "dead zones" in the deeper parts of the lake where other fish could not survive. The entire food web was reconfigured, leaving the perch to prey upon a small species of shrimp and even its own young.
The socio-economic impacts were complex. A massive commercial fishing industry developed around the Nile perch, with exports to the European Union reaching 169 million euros in 2003. This boom came at a cost. The smaller cichlids could be preserved by sun-drying, a simple and inexpensive method. The oily Nile perch required smoking or frying, which created a huge demand for firewood. This led to significant deforestation in the areas surrounding the lake, increasing soil erosion and harmful runoff into the water. The new industry also displaced many artisanal fishermen and local traders who had depended on the native cichlid fishery.