Lake Victoria
Lake Victoria or Victoria Nyanza (also known as Ukerewe and Nalubaale) 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.
At 68800 square kilometres (26564 sq mi), Lake Victoria is Africa’s largest lake, and the largest tropical lake in the world. As Lake Michigan-Huron is connected at the same elevation pool and is thus treated as one lake by hydrologists and geographers, Lake Victoria is the world’s third-largest freshwater lake. In terms of volume, it is the world’s seventh-largest freshwater lake, containing 2,750 cubic kilometres (2.2 billion acre-feet) of water.
The lake receives most of its water from direct precipitation. Its largest influent is the Kagera River, the mouth of which lies on the lake's western shore. The only river to leave the lake, the White Nile (known as the "Victoria Nile" as it leaves the lake), leaves at Jinja, Uganda, on the lake’s north shore .
Lake Victoria occupies a shallow depression in the East African Plateau, and has a maxiumum depth of 84 metres (276 ft) and an average depth of 20 metres (66 ft). Its catchment area covers 184,000 square kilometres (71,040 mi2). The lake has a shoreline of some 4828 kilometres (3000 mi), with islands constituting some 3.7% of this length, and is divided between three countries: Kenya (6% or 4,100 km2), Uganda (45% or 31,000 km2) and Tanzania (49% or 33,700 km2).
Lake Victoria supports Africa's largest inland fishery.
Geology
Lake Victoria has, during its geological history, gone through successive changes ranging from its present shallow depression, through to what may have been a series of much smaller lakes. Cores taken from its bottom show that Lake Victoria has dried up completely three times since it formed. These drying cycles are probably related to past ice ages, which are times when precipitation declined globally. The lake last dried out 17,300 years ago, and filled again beginning 14,700 years ago. Geologically, the lake is relatively young - about 400,000 years old - and formed when westward-flowing rivers were dammed by an upthrown crustal block.
This geological history probably contributed to the dramatic Cichlid speciation that characterises its ecology, as well as that of other African Great Lakes, although there are researchers who refute this, arguing that while Lake Victoria was at its lowest between 18,000 and 14,000 calendar years ago, and it dried out at least once during that time, there is no evidence of remnant ponds or marshes persisting within the desiccated basin. If such features existed, then they would have been small, shallow, turbid, and/or saline, and therefore markedly different from the lake to which today’s species are adapted.
The lake's shallowness, limited river inflow, and large surface area relative to its volume make it vulnerable to the effects of climate changes.
Hydrology and Limnology
Lake Victoria receives almost all (80%) of its water from direct precipitation. Average evaporation on the lake is between 2,000 - 2,200 mm per annum, almost double the precipitation of riparian areas. In the Kenya Sector, the main influent rivers are the Sio, Nzoia, Yala, Nyando, Sondu Miriu, Mogusi and the Migori. Combined, these rivers contribute far more water to the lake than does the largest single in-flowing river, the Kagera, which enters the lake from the west. The only river flowing out of the lake is the White Nile.
The lake exhibits eutrophic conditions. In 1990-1991, oxygen concentrations in the mixed layer were higher than in 1960-61, with nearly continuous oxygen supersaturation in surface waters. Oxygen concentrations in hypolimnetic waters (i.e. the layer of water that lies below the thermocline, is noncirculating, and remains perpetually cold) were lower in 1990-1991 for a longer period than in 1960-1961, with values of <1 mg per litre occurring in water as shallow as 40 m compared with a shallowest occurrence of >50 m in 1961. The changes in oxygenation are considered consistent with measurements of higher algal biomass and productivity. These changes have arisen for multiple reasons: successive burning within its basin, soot and ash from which has been deposited over the lake’s wide area; from increased nutrient inflows via rivers, and from increased pollution associated with settlement along its shores.
Other thinkers on the subject blame the lake's eutrophication on the mass extinction of the Haplochromis species 'flock'. The fertility of tropical waters depends on the rate at which nutrients can be brought into solution. The influent rivers of Lake Victoria provide few nutrients to the lake in relation to its size. Because of this, it is thought that most of Lake Victoria’s nutrients are locked up in lake-bottom deposits By itself, this vegetative matter decays slowly. Animal flesh decays considerably faster, however, and therefore the fertility of the lake is dependent on the rate at which these nutrients can be eaten up by fish. There is little doubt that Haplochromis played an important role in returning detritus and plankton back into solution With some 80% of Haplochromis species feeding off detritus, and equally capable of feeding off one another, they represented a tight, internal recycling system, moving nutrients and biomass both vertically and horizontally through the water column, and even out of the lake via predation by humans and terrestrial animals and humans. The removal of Haplochromis, however, may have contributed to the increasing frequency of algal blooms, which may in turn be responsible for mass fish kills.
Biology and Ecology
Before 1954, Lake Victoria’s ecology was characterised by enormous biodiversity. It was inhabited by over 500 species of fish, 90% of which were Cichlids belonging to the Haplochromis species ‘flock’. They are known for their extraordinary ability to evolve rapidly to suit extremely localised and diverse environments, a characteristic termed ‘evolutionary plasticity’ . This ability has made the cichlid species of Lake Victoria an extremely successful fish. Haplochromis species accounted for some 80% of the fish biomass of the lake, an abundance which led Graham to believe that this species flock could support a trawler fishery of up to 200 boats. It also meant that Lake Victoria at one time boasted one of the most diverse fish environments on earth . With such diversity, the cichlids of Lake Victoria managed to exploit virtually every food source available, including most detritus, zoo- and phyto-plankton.
On the whole, however, Haplochromis species are a small and bony species, and were generally not favoured in catches. Riparian populations preferred the lake’s two endemic species of tilapia (Oreochromis esculentus and O. variabilis). Hence, by the late 1940s, British colonial authorities were debating the overall ecological efficiency of the lake. For many authorities at this time, the lake needed a large and efficient predator to turn Haplochromis fish stocks into something more economically valuable. The prime candidate was the Nile perch (Lates niloticus). This argument is central to what would eventually occur on Lake Victoria, and is therefore considered in some detail. Evidence in favour of introducing a predator was as follows:
(a)Evidence from other African lakes suggested that the Nile perch could do well commercially, and if the fish were introduced into Lake Victoria, it would no doubt eat the Haplochromis, and hence improve the overall value of the fishery. In addition, it was suggested that by introducing such a fish, fishers might turn their attentions to catching it, so easing some of the pressure on tilapia stocks. Because the Nile perch can weigh as much as 200kg, it was argued, fishers would be encouraged to use large mesh-sizes to capture it. Furthermore, the perch was said to prefer off-shore habitats, and this would serve to relieve pressure on the in-shore tilapia fishery. (b)In those lakes where the Nile perch was a native it co-existed with tilapia species, and therefore it posed no great danger to commercially important tilapia stocks in Lake Victoria. (c)The potential size of the perch made it a fine sports fish, and this might attract sports fishers and tourists to the lake region. (d)Finally, archaeological findings close to Lake Victoria suggested that an ancestor of the Nile perch had been native to the Miocene predecessor of Lake Victoria, Lake Karunga. It was reasoned, then, that if the perch had once been native to the lake, there was little reason why it could not be a native again.
The arguments against its introduction were as follows:
(a)Predators can never be as abundant as non-predators because of their nutritional requirements. In other words, the amount of fish a Nile perch has to eat to produce a single kilo of flesh is far greater than the amount of vegetative matter an tilapia has to eat to produce an equal amount of flesh. In ecological terms, the Nile perch is inefficient. The fertility of tropical waters depends on the rate at which nutrients are brought back into solution. Because the nutritional contribution of in-flowing rivers is small in relation to Lake Victoria’s size, it was reasoned that most of its nutritional value must therefore be locked up in its bottom deposits. This vegetative matter decays slowly by itself, and the rate at which these nutrients are brought back into solution depends on the rate at which they were eaten. The Nile perch, however, does not eat this detritus, and it was argued that its introduction would do little to improve the over-all ecological efficiency of the lake. If any fish should be introduced, it should be a herbivore or a detrivore. (b)It would be wishful thinking to suppose that the Nile perch would exclusively consume Haplochromines. (c)Given the complexity of tropical ecosystems, it is impossible to predict what might happen should the Nile Perch be introduced.
While the argument continued, it was agreed that tilapia stocks needed bolstering largely as a result of increasing fishing pressure on indigenous species, associated with the expansion of the market for fresh fish in the 1940s. Tilapia introductions started in the early 1950s with Oreochromis leucostictus from Entebbe, and followed by Tilapia zillii (Winam Gulf, 1953), T. rendalli (Winam Gulf 1953/54), O. niloticus (Kagera River 1954) and O. mossambicus (Entebbe 1961/62). Because tilapia are detrivores and herbivores, these introductions were regarded as less threatening than the introduction of any carnivore. Nevertheless, while the argument over the introduction of the Nile perch raged throughout the early 1960s, it seems that it had already been surreptitiously introduced in 1954 from Uganda. Once it had been discovered to be in the lake, further official introductions occurred in 1962 and 1963.
Introduced tilapia species were unable to establish themselves in the lake between the 1950s and 1963. Following unusually heavy rainfall in the early 1960s, however (the so-called ‘Uhuru Rains’), the lake-level rose considerably, flooding large areas of shore-line, and opening up new breeding areas to fledgling tilapia stocks, so creating the opportunities for these exotic species to compete with indigenous stocks. Of the six exotic species introduced, two - Oreochromis niloticus and O. zillii - were to firmly establish themselves in the lake, so that by the early 1980’s, these two species comprised the main-stay of tilapia catches. Of the indigenous species, O. esculentus was extirpated from the lake as a consequence of competition with introduced tilapiids, while O. variabilis populations declined significantly.
The Nile perch is a magnificent and substantial predator. One specimen, preserved at the Kisumu Museum in Kenya, weighed 184 kg when landed. Populations of the fish established themselves in a clockwise motion around the lake, starting in Uganda, followed by Kenya and ending in Tanzania. Initial catches were minimal, but grew rapidly in the 1980s, heralding the start of the so-called 'Nile perch boom'. “On the face of it...the lake after the debut of Lates [Nile perch] has turned into a fish producer that can only be described in Gargantuan terms”.
The introduction of the Nile perch, had a decisive impact on Haplochromis stocks which it favoured as its prey, affecting both their abundance and diversity. It is believed that the contribution of this species flock to the fish biomass of the lake has decreased from 80% to less than 1% since the introduction of the Nile perch, and that some 65% of the Haplochromis species were driven to extinction in the process, an event which may well represent the largest extinction event amongst vertebrates in the 20th Century.
Freed from their evolutionary predators, populations of the diminutive endemic Silver cyprinid Rastrineobola argentea (omena in Dholuo, mukene in Luganda and dagaa in Kiswahili), flourished, developing into huge shoals. In turn, Pied kingfisher (Ceryle rudis) populations, that had hitherto fed on Haplochromines, exploded in response to this new food source. Similar and other impacts have reverberated throughout this previously unique ecosystem.
Given it's famed 'evolutionary plasticity', it follows that Haplochromis should adapt rapidly to the new environmental conditions generated by the Nile perch 'boom' (see below) and eutrophic conditions. Evidence from studies on the lake does suggest that this is happening. One Haplochrimine, H. (Yssichromis) pyrrhocephalus, a zooplanktivore, was almost driven to extinction by the Nile perch. A recent study of this specie found that it has recovered alongside increased exploitation of the Nile perch, at a time (the 1990s) when water clarity and dissolved oxygen levels had declined as a consequence of eutrophication. Over a period of just two decades, H. pyrrhocephalus responded to raised hypoxia (oxygen deficiency) by increasing its gill surface area by 64%. Head length, eye length, and head volume decreased in size, whereas cheek depth increased. The former morphological changes may have occurred to accommodate this increased gill size. Other morphological changes suggest adaptations in response to the availability of larger and tougher prey types.
The Fisheries of Lake Victoria
By the end of the 1940s, fish stocks were under severe pressure, occasioned by (a) the growth in the fish market and associated transport infrastructure that saw fish being transported down the railway line towards the East African coast and growing urban centres in between; and (b) the arrival of improved fishing technologies, which saw boats (and, indeed, whole fleets) being used to catch fish, and flaxen gill nets introduced. As described above, British colonial authorities set out to remedy this through the introduction of exotic species, including new species of Tilapia and the Nile perch. These introductions had five main impacts. The first of these was the rise of the Nile perch. The fish took some time to establish itself, and only began to appear catch statistics in the mid-1970s. By the 1980s, the ‘explosion’ of this species was being referred to as the Nile perch ‘boom’. Catches climbed from about 335 mt in 1975, to a peak of 380,776 mt in 1990. The second impact was the Nile perch’s devastation of the Haplochromis species flock, its main food source. Catches of this species crashed. The third impact related to the lake’s diminutive endemic Silver cyprinid, the dagaa. Freed from competition (with Haplochromis species) for food sources, this species thrived. It was not the main target of the Nile perch, and catches increased spectacularly from 13,000 mt in 1975, to an all time high 567,268 mt in 2006. The fourth main impact of the introductions related to the exotic tilapia species. One of these, the Nile tilapia (Oreochromis niloticus), was to establish itself firmly in the fishery. Tilapia catches from the lake rose from about 13,000 mt in 1975, to an all time high of around 105,000 mt in 2000. There can be little doubt that these introductions saved the fishery from collapse. With such staggering increases, so too the entire production system on the lake changed, the fifth and final key change. Prior to the arrival of the colonial administration, the fishery was dominated by fishermen (mainly, although certain fishing techniques were reserved for women) who owned their labour and their fishing gear. Contributing to the near-collapse of the fishery in the 1940s and 1950s was the reorganisation of the fishery into fleets drawing on hired labour and much improved gear . The Nile perch ‘boom’ was to accelerate and massively expand this process. It coincided with an emerging European market for high-quality white fish meat, prompting the development of industrial fish processing capacity along the lake’s shores in Kisumu, Musoma, Mwanza, Entebbe and Jinja. The export of Nile perch has since expanded away from the European Union (EU) to the Middle East, the United States and Australia, and now represents large foreign exchange earnings to the lake’s riparian states. In Uganda, indeed, its export is second only to coffee in the rankings of export earnings. In 2006, the total value of Nile perch exports from the lake was estimated to be US$ 250 million. The main market for the perch remains the EU, and the industry is, therefore, subject to the worries of EU health and safety inspectors. The EU has frequently closed its doors to the export for reasons ranging from unsatisfactory hygiene at factories to cholera outbreaks on the lake shores.
With such high demands for Nile perch, the value of the fishery has risen considerably. Labour inflows into the fishery have increased along with growing demand. In 1983, there were an estimated 12,041 boats on the lake. By 2004, there were 51,712, and 153,066 fishermen. The fishery also generates indirect employment for additional multitudes of fish processors, transporters, factory employees and others. All along the lakeshore, ‘boom towns’ have developed in response to the demands of fishing crews with money to spend from a day’s fishing. These towns resemble shanties, and have little in the way of services. Of the 1,433 landing sites identified in the 2004 frame survey, just 20% had communal lavatory facilities, 4% were served by electricity and 6% were served by a potable water supply.
The Nile perch fishery has proved controversial, not least between conservationists keen to see the preservation of the lake's unique ecology; and others who recognise the fish's importance to regional economies and poverty alleviation. In the 1990s, one group of thinkers argued that the export of this fish represented a net loss of fish proteins to riparian fishing communities, hence explaining high incidences of malnutrition amongst them. ‘Empirical evidence. . .vividly show that the growing export of the Nile perch and the commercialisation of the dagaa are undermining the survival of households’. Malnutrition amongst these communities are indeed high. One study estimates that 40.2% of children in fishing communities are stunted. Rates of childhood malnutrition are, however, lower around the lake than they were in the agricultural hinterland. 5.7% of mothers at fish landing sites were found to be chronically malnourished. The latter study, however, argues that these malnutrition levels do not arise from the Nile perch export, but rather as a consequence of gender relations, that tilt income distributions in favour of men, while undermining women's economic status. As the children's primary care givers, this economic status translates directly into the malnutrition rates observed. This economic disparity arises for multiple reasons, including the lack of access that women have to the fishery (very few women actually fish, although some do own fishing boats and gear); children force women to be sedentary (staying close to schools, health facilities and/or social networks), and so are unable to take advantage of the opportunities that emerge through migration, and which are available to men. Women, the authors argue, are forced to exploit peripheral economies, such as the small-scale fish trade, where they must compete against (male) buyers and the fish factories. Women, the study claims, often use sex as a means of developing relationships between fishermen, and so securing a steady supply of fish. While women devote all or most of their income to their children, men have different spending priorities, such as investing in their fishing capacity, drinking and prostitution.
Water Hyacinth Invasion
The water hyacinth Eichhornia crassipes, a native of the tropical Americas, was introduced by Belgian colonists to Ruanda to beautify their holdings and then advanced by natural means to Lake Victoria where it was first sighted in 1988. There, without any natural enemies, it became an ecological plague, suffocating the lake, diminishing the fish reservoir, and hurting the local economies. By forming thick mats of vegetation it causes difficulties to transportation, fishing, hydroelectric power generation and drinking water supply. By 1995, 90% of the Ugandan coastline was covered by the plant. With mechanical and chemical control of the problem seeming unlikely, the mottled water hyacinth weevil Neochetina eichhorniae was bred and released with good results.
In the late 1990s, the surface area covered by the Hyacinth reduced dramatically. It is unclear why. It is probable that the introduced weevils did serve their purpose, although El Niño weather in 1997/1998 was probably also a contributory factor. It is thought that an improved light climate, an ever increasing supply of nutrients and a potentially unstable weevil population will allow a resurgence of this plant.
Exploration History
The first recorded information about Lake Victoria comes from Arab traders plying the inland routes in search of gold, ivory, other precious commodities and slaves. An excellent map, known as the Al Idrisi map from the calligrapher who developed it and dated from the 1160s, clearly depicts an accurate representation of Lake Victoria, and attributes it as the source of the Nile.
The lake was first sighted by a European in 1858 when the British explorer John Hanning Speke reached its southern shore while on his journey with Richard Francis Burton to explore central Africa and locate the Great Lakes. Believing he had found the source of the Nile on seeing this vast expanse of open water for the first time, Speke named the lake after Queen Victoria. Burton, who had been recovering from illness at the time and resting further south on the shores of Lake Tanganyika, was outraged that Speke claimed to have proved his discovery to have been the true source of the Nile, which Burton regarded as still unsettled. A very public quarrel ensued, which not only sparked a great deal of intense debate within the scientific community of the day, but much interest by other explorers keen to either confirm or refute Speke's discovery.
The famous British explorer and missionary David Livingstone failed in his attempt to verify Speke's discovery, instead pushing too far west and entering the River Congo system instead. It was ultimately the Welsh-American explorer Henry Morton Stanley, on an expedition funded by the New York Herald newspaper, who confirmed the truth of Speke's discovery, circumnavigating the lake and reporting the great outflow at Ripon Falls on the lake's northern shore.
The three countries bordering Lake Victoria — Uganda, Kenya and Tanzania — have agreed in principle to the idea of a tax on Nile perch exports, proceeds to be applied to various measures to benefit local communities and sustain the fishery. However, this tax has not been put into force, enforcement of fisheries and environmental laws generally are lax, and the Nile perch fishery remains in essence a mining operation.
Nalubaale Dam
The only outflow for Lake Victoria is at Jinja, Uganda, where it forms the White Nile. The water 12,000 years ago drained over a natural rock weir. In 1952, British colonial engineers blasted out the weir and reservoir. A standard for mimicking the old rate of outflow called the "agreed curve" was established, setting the maximum flow rate at 300 to 1,700 cubic meters per second (392 - 2,224 cu yd/sec) depending on the lake's water level.
In 2002, Uganda completed a second hydroelectric complex in the area, with World Bank assistance. By 2006 the water levels in Lake Victoria had reached an 80-year low, and Daniel Kull, an independent hydrologist living in Nairobi, Kenya, calculated that Uganda was releasing about twice as much water as is allowed under the agreement, and was the primary culprit in recent drops in the lake's level. At 55,372 cubic meters per second (35,000 cu yd/s), more than double the maximum agreed curve, it would take a year to drain 110.75 cubic kilometres (89.5 million acre-feet) from the lake. That is approximately 4% of the lake's volume.
Transportation
Since the 1900s Lake Victoria ferries have been an important means of transport between Uganda, Tanzania and Kenya. The main ports on the lake are Kisumu, Mwanza, Bukoba, Entebbe, Port Bell and Jinja. The steamer MV Bukoba sank in the lake on October 3, 1995 with a loss of nearly 1,000 lives in one of Africa's worst maritime disasters.
Movie
The impact of perch fishing upon the local economy is the subject of the documentary Darwin's Nightmare.
Lake Victory in Popular Culture
In the anime series Mobile Suit Gundam SEED, Lake Victoria is a spaceport for the Earth Forces and home to one of their Mass Driver facilities.
In the anime series Mobile Suit Gundam Wing, Lake Victoria is the main training facility for the Specials (and later OZ), their training being overseen by Lieutenant Lucrezia Noin.
Translation
The phrase "Lake Victoria" occurs as such in the following languages: English, Fiji Hindi, Simple English.
Translation(s) in other languages: Arabic: بحيرة فكتوريا, Aragonese: Laco Bitoria, Asturian: Llagu Victoria, Bengali: ভিক্টোরিয়া হ্রদ, Belarusian: Возера Вікторыя, Belarusian (Taraškievica): Вікторыя (возера), Bosnian: Viktorijino jezero, Breton: Lenn Victoria, Bulgarian: Виктория (езеро), Catalan: Llac Victòria, Czech: Viktoriino jezero, Welsh: Llyn Victoria, Danish: Victoriasøen, German: Victoriasee, Estonian: Victoria järv, Greek: Λίμνη Βικτόρια, Spanish: Lago Victoria, Esperanto: Viktoria-lago, Basque: Victoria Lakua, Persian: دریاچه ویکتوریا, French: Lac Victoria, Galician: Lago Vitoria, Korean: 빅토리아 호, Hindi: विक्टोरिया झील, Croatian: Viktorijino jezero, Ido: Lago Viktoria, Indonesian: Danau Victoria, Icelandic: Viktoríuvatn, Italian: Lago Vittoria, Hebrew: אגם ויקטוריה, Javanese: Tlaga Victoria, Kannada: ವಿಕ್ಟೋರಿಯಾ ಸರೋವರ, Swahili: Victoria (ziwa), Latin: Lacus Victoria, Latvian: Viktorijas ezers, Lithuanian: Viktorijos ežeras, Hungarian: Viktória-tó (Afrika), Macedonian: Езеро Викторија, Malayalam: വിക്ടോറിയ തടാകം, Marathi: व्हिक्टोरिया सरोवर, Egyptian Arabic: بحيرة فيكتوريا, Mongolian: Виктория нуур, Dutch: Victoriameer, Japanese: ヴィクトリア湖, Norwegian (Bokmål): Victoriasjøen, Norwegian (Nynorsk): Victoriasjøen, Western Panjabi: جھیل وکٹوریہ, Polish: Jezioro Wiktorii, Portuguese: Lago Vitória, Romanian: Lacul Victoria, Quechua: Ñansa qucha, Russian: Виктория (озеро), Albanian: Liqeni Viktoria, Slovak: Viktóriino jazero, Slovenian: Jezero Ukerewe, Somali: Harta Fiktooriya, Serbian: Викторијино језеро, Serbo-Croatian: Jezero Victoria, Finnish: Victoriajärvi, Swedish: Victoriasjön, Tagalog: Lawa ng Victoria, Tamil: விக்டோரியா ஏரி, Thai: ทะเลสาบวิกตอเรีย, Turkish: Victoria Gölü, Ukrainian: Вікторія (озеро), Venetian: Lago Vitoria, Vietnamese: Hồ Victoria, Waray-Waray: Danaw Victoria, Samogitian: Viktuorėjė (ežers), Chinese: 維多利亞湖.
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