The Slow Death of Africa's Greatest Lake

Tuesday, May 1, 2007 | Mwanza, Tanzania (map)

Near Mwanza, local kids show off their share of the daily catch, which continues to dwindle under environmental pressures.
The Spring 2007 issue of the Georgetown University Journal of the Environment (Vol. III, pp. 42-47) includes a piece I wrote, drawing on much of the research I did last summer while studying the local ecology in Mwanza, Tanzania, on Lake Victoria's southern shore. I've reprinted it here; please enjoy:

The Slow Death of Africa’s Greatest Lake:
The Environmental and Social Impacts of the "Modernization" of Lake Victoria

by Andrew Farrand

In the past several decades, the ecosystem of Lake Victoria, Africa’s largest lake, has witnessed a dramatic decline. This transformation is the result of the so-called "modernization" of the lakeshore economies in Uganda, Kenya, and Tanzania and their integration into the global economy. As the region’s human population has expanded rapidly in recent decades—reaching over 30 million
individuals today—the process of industrialization has injected a wide range of foreign substances, including many toxins, into the ecosystem. Most disruptive to the natural environment, however, has been the introduction, both deliberate and accidental, of several particularly insidious invasive exotic plant and animal species.

These changes have fundamentally restructured the lake’s ecosystem and surroundings and have fostered equally dramatic structural shifts within the area’s human societies. While some may consider the overall result of such changes to be a positive case of economic development, the plight of many women, children, and even entire small fishing communities who continue to suffer from the human-induced environmental transformations cannot be ignored.

One environmental change in recent years which has impacted the health of the lake ecosystem—and the human population which relies upon it—is the introduction of the water hyacinth. This surface aquatic plant, a native of South American waterways, was first seen in northern Lake Victoria in the late 1980s.1 Since that time, it has spread rapidly throughout the lake, forming a thick mat of vegetation over large littoral areas, resulting in significant oxygen depletion, with far-reaching consequences.

By reducing the amount of dissolved oxygen in the water which fish, crustaceans, aquatic plants, and other marine organisms require to survive, the hyacinth renders large swaths of underwater habitat unlivable. As a result, human populations, which rely on such organisms for their livelihood and as a major source of protein in their diets, suffer from the decline in fish numbers. A family of fishes known as the cichlids, which traditionally feed off the rich, varied habitats of the lake’s shallows, is but one of many groups which has suffered greatly from the hyacinth’s arrival. The plant also presents a formidable obstacle for fishermen, who can no longer access now hyacinth-choked areas of the lake. In addition, its calming effect on waves improves the chances that malaria, sleeping sickness, bilharzia, and other diseases will breed and spread from still lake waters to human populations.2

Thanks to several projects funded by regional governments aimed at controlling the water hyacinth, the plant’s coverage area has declined significantly since its peak in the mid-1990s. As a result, today the hyacinth continues to cause many of the same problems, to a slightly lesser degree. And for all the damage it has done, water hyacinth may not be without its advantages: biologists single out the hyacinth’s thick mats as the last refuge of the beleaguered native cichlid fishes in their fight for survival against more deadly invasive species.

In the 1950s, Ugandan Game and Fisheries Department employees and local residents, eager to bolster Lake Victoria’s sport fishing potential, began introducing Lates niloticus, the Nile perch, into the lake and several of its tributaries. Previously prevented from reaching the lake from its natural habitat downstream because of several impassable waterfalls along the White Nile in Uganda, this aggressive, almost indiscriminate feeder was now unleashed on the indigenous species of Lake Victoria. Native populations of small cichlid fishes—an incredibly diverse family comprising (at that time) some 500 distinct species—were among the perch’s earliest victims. In 1961, when a perch was caught near the Mwanza, the major Tanzanian port on the Lake’s southern shore, several hundred kilometers from where the species was likely introduced, the extent of its rapid spread became clear.3 At the expense of the cichlid species, over half of which no longer exist today, the Nile perch conquered the lake, its population reaching its height in the 1980’s. In the process, the perch decimated populations of several catfish species,4 as well as many within the cichlid species flock, a group which would prove collectively to be the "keystone family" in Lake Victoria’s ecosystem.

The Nile perch boom also ushered in drastic changes in the structure of the local fishing economy. The total value of the local fishing sector increased fivefold in the 1980’s as larger ships and nets came into use and new companies began exporting fish to the lucrative markets of Europe and America.5 The fish being exported, however, was not a native cichlid, catfish, or Nile tilapia, but rather the Nile perch, which grows rapidly and to nearly limitless size in the rich waters of the Lake, at the expense of other species.

In recent decades, the disappearance of numerous cichlid species into the ruthless jaws of the Nile perch has been particularly noticeable in several ways. First, the current prevalence of the deadly bilharzia parasite, which relies on a certain snail to complete part of its life cycle, is in part due to the perch’s decimation of certain cichlid species adapted to feed on such snails. The cost of the parasite on the local health infrastructure due to hospitalizations and treatment is unknown but likely significant, as is the lost economic revenue due to workers’ suffering from the parasite’s infestation. Another unknown, but certainly significant, cost to the region is the potential tourism revenue lost due to foreigners’ fears of contracting bilharzia. The lack of adequate sewage treatment infrastructure in lakeshore communities both large and small compounds the effect of the Nile perch’s introduction by further contributing to the parasite’s persistence.

A second effect of the reduction of populations of cichlids is the sixfold increase in population of the lake sardine (Rastrineobola argentea, known locally as dagaa) in recent decades.6 The cichlids, some of which are a natural predator of the sardine and others a competitor with it for zooplankton, previously served to suppress the numbers of the nutrient-poor sardine. Today, in the absence of nutrient-rich cichlids, fishing communities’ reliance on the sardine likely has deleterious health effects on those communities.

At present, the effects of the Nile perch’s introduction are most immediately apparent in Lake Victoria’s human communities. For all its conspiracy theories, the 2004 documentary Darwin’s Nightmare succeeded in illustrating, atthe very least, the degree to which ecological destruction had impacted human communities around the Lake. Unfortunately, since that time, the situation in the region has only deteriorated further.

The arrival of the Nile perch in Lake Victoria prompted an extensive reconfiguration of the local fishing economy. In Mwanza, a long-time town resident and local NGO employee named Suitbert Musiba described the socioeconomic stratification that resulted from the local economy’s realignment toward more large-scale, commercial export fishing: "It has made two types of fishermen— the rich and the poor. But before, they were all in the middle."7 Indeed, those locals now employed with the major fish exporters have benefited greatly from the Nile perch’s presence, while the rest—a vast majority of lakeshore residents—have suffered in several ways.

Women and children have been hit hardest by the introduction; it was they who previously relied most heavily on the now-depleted cichlid fishes as both the primary source of protein in their diets and as their source of income through the small-scale sale of fish catches. Unlike larger fish, the protein- and fat-rich cichlids could be harvested by women and children using small traps along the shoreline. Today, in the absence of the cichlids, women, desperate to feed their children and themselves, turn to new strategies. Some have adopted the less lucrative trade of agriculture, already practiced at maximum capacity along the lakeshore, such that further farming will only contribute to environmental degradation through erosion and habitat loss for many species. Some women even opt for prostitution, bringing in small amounts of fish in exchange for sex and helping to spread the deadly HIV/AIDS scourge wider.

Most important in the long run for the human populations reliant on Lake Victoria is the lack of biodiversity which has resulted from the cichlid decline at the hands of the Nile perch. Often dismissed as trivial by those without a fundamental understanding of ecology, the lack of biodiversity actually presents a critical long-term threat to the lake. Its resilience to future introductions of exotic invasive species, infectious diseases that could affect certain species within the ecosystem, and the ability of the ecosystem to support the growing nutritional demands of burgeoning human populations are all at risk as a result ofthe drop in species diversity.

One potential solution to the Nile perch’s reign of terror in Lake Victoria is a redefinition of fishing regulations, particularly those governing net usage. Some scientists have suggested that by decreasing the minimum size of holes permitted in gill nets, authorities could greatly increase the numbers of midsize fish being caught.8 These would include adolescents of the lake’s larger inhabitants, principally tilapia and the Nile perch, while having little effect on the smaller cichlids. By reducing the numbers of medium and larger species, authorities could prompt a drastic decline in the predation of cichlids by Nile perch, perhaps allowing their numbers to rebound, while also increasing fishing revenues in the short- to medium-term. Unfortunately, the potential decline in catch values in the long run may prompt significant political opposition from major fish exporters, but the idea is one which further study may prove to be the savior of Lake Victoria’s dwindling cichlid populations.

In the past half-century, the ecosystem of Lake Victoria has suffered from a series of severe human-induced shocks. The water hyacinth and Nile perch introductions have had a significant negative effect on many small fishing communities, particularly the more remote ones, which are less likely to be tied into the international fish export economy. The increasing human population continues to burden the lake’s ecosystem, which may not long prove capable of supporting such rapid growth. In addition, studies performed on pollution in the lake show troubling results, indicating that high mercury levels—due to regional mining operations, soil runoff, and the use of skin-bleaching creams— are likely contaminating fish.9 The reckless use of poisons in fishing, the environmentally disastrous effects of which are self-evident, also add toxins to the ecosystem which are ultimately consumed by humans.

The damage of introducing several exotic invasive species has already occurred. Coping with that damage is possible, however, as several successful programs designed to combat the hyacinth’s spread have shown, and as the gill net solution outlined above may yet prove as well. As development of the Lake Victoria coast and its watershed continues at a rapid pace, such solutions will be required if the lake’s ecosystem is to remain robust enough to continue to support biological and human communities of all sizes across the region.

Andrew Farrand (SFS ’07) graduated in December 2006 with a degree in Regional and Comparative Studies. His concentration was in Africa and the Middle East, and he earned a certificate in Arab Studies. Andrew submitted an earlier version of this paper in Ecology of the Great Lakes and the Savannah, taught by Mr. Dino J. Martins, at the St. Augustine University of Tanzania.

1 Wulf Klohn and Mihailo Andjelic, United Nations, Food and Agriculture Organization, Lake Victoria: A Case in International Cooperation (Water Resources Development and Management Service, 1997), 5 Mar. 2007.
2 Karl Vick, "Betting on Bugs, Machine-Like Weevils Rid Lake Victoria of Choking Weed," The Washington Post 22 Sept. 1999: A25.
3 Robert M. Pringle, "The Origins of the Nile Perch in Lake Victoria," BioScience 55.9 (Sept 2005): 781.
4 Kees Goudswaard and Frans Witte, "The Catfish Fauna of Lake Victoria after the Nile Perch Upsurge" Environmental Biology of Fishes 49.1 (May 1997): 22.
5 Pringle, 783.
6 Ibid, 786.
7 Suitbert Musiba, personal interview, 16 July 2006.
8 Daniel E. Schindler, James F. Kitchell, and Richard Oguto-Ohwayo, "Ecological Consequences of Alternative Gill Net Fisheries for Nile Perch in Lake Victoria," Conservation Biology 12 (Feb. 1998): 56.
9 Review of Mercury in Lake Victoria, East Africa: Implications for Human and Ecosystem Health," Journal of Toxicology and Environmental Health, Part B: Critical Reviews 6.4 (July-Aug. 2003): 325.

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