The great lakes of Africa, Lakes Victoria, Malawi, and Tanganyika, are located in East Africa in the vicinity of the Great Rift Valleys and hold approximately 27% of the world’s freshwater. Lake Victoria is set between the Rift Valleys and is bounded by uplifted mountains and highlands associated with rifting. Compared to the other lakes, it is geologically younger (less than half a million years) and much shallower with markedly lower water clarity.
Fish are important as a source of food and income across the African Great Lakes. Total annual fish catches in Lake Victoria are approximately 1 million tonnes, consisting of 230,000 tonnes of Nile perch and 500,000 tonnes of dagaa (Kolding et al., 2008). Fishing employs approximately 2 million people around Lake Victoria (Gudmundsson et al., 2006). Harvested fish supplies more than 22 million people locally with a substantial portion of their protein source (LVFO, 2009). Landed value of the catch is$590 million US, with $250 million US of this total from the export of Nile perch (LVFO, 2009).
Lake Victoria was once inhabited by more than 500 species of endemic cichlids (Seehausen, 1996) but the onset of eutrophication and the introduction of Nile perch (Lates niloticus) in the early 1950s have been attributed with a rapid and radical change in the Lake Victoria fish community (Kolding et al., 2008), resulting in the loss of an estimated 200 cichlid taxa (Verschuren et al., 2002; Witte et al., 2007; Witte et al., 1992).
Commercial catches in Lake Victoria are dominated by Nile perch, Nile tilapia (Oreochromis niloticus), and dagaa (Rastrineobola argentea), a small native cyprinid (Kolding et al., 2008). Prior to the introduction and expansion of Nile perch, total catch in Lake Victoria during the 1970s averaged 100,000 tonnes (Fig. 1). Today, total catch of the three key species is approximately 1 million tonnes annually. Nile perch catches reached their maximum of 300,000 tonnes in 1990 but have fallen since and range between 200,000 and 250,000 tonnes annually (Balirwa, 1998; Kolding et al., 2008). Since the early 1990s there has been evidence of overexploitation of Nile perch (Balirwa, 1998), although declining catches have also been attributed to eutrophication (Kolding et al., 2008). Nile tilapia is a nearshore species found in waters less than 20 m deep. They are opportunistic feeders and readily change their diets from planktivorous to omnivorous. Dagaa are pelagic fish and now comprise the largest proportion of the catch (Kolding et al., 2008).
Population Growth and the Economy
The human population around the East African Great Lakes has been steadily increasing. Over 30 million people reside in the Lake Victoria watershed with an estimated increase of 3% per annum (UNEP, 2006). In the Lake Victoria watershed, population density is one of the highest in the world, averaging more than 500 persons/km2 and exceeding 1000 persons/ km2 in parts of Kenya (UNEP, 2006).
Across the African Great Lakes, poverty levels are high and a majority of the population living along the lake shores rely directly or indirectly on the fisheries. The gross economic product in the Lake Victoria catchment is $3−4 billion US with annual per capita less than $1,200 US (World Bank, 1996). In this region, fisheries, agriculture and manufacturing comprise the majority of contributions to the GDP.