The Great Lakes Belt of Africa cuts across five major drainage basins: The Nile, Congo-Zaire, Rift Valley, Coastal and Zambezi basins. The region contains the earth's largest aggregation of tropical lakes. Three of these lakes–Victoria, Tanganyika and Malawi—hold one quarter of the earth's total surface water supply, and are home to rich and diverse assemblages of fish. Apart from the diversity and endemicity of their biota, properties that distinguish the African Great Lakes from their North American counterparts include their great age, sensitivity to climate change, long residence times, persistent stratification, continuously warm temperatures at all depths, major ion composition, and propensity for nitrogen limitation. Current management problems include over-fishing, increased input of sediment and nutrients, and in the case of Lake Victoria, loss of endemic fish species and the proliferation of the introduced water hyacinth. The harmonization of research programmes and management strategies among the various riparian countries is a challenge. Among the other challenges currently facing the African Great Lakes, perhaps none is more important, nor more often overlooked, than the ecosystem-based management. Ecosystem integrity is beginning to receive acknowledgement in some quarters as a foundation upon which sound management must be built. Recent changes in the African Great Lakes have resulted in an increased realization that individual components of these systems cannot be understood in isolation, and that effective management must expand beyond conventional fisheries management to account for the interaction of physical, geological, chemical and biological processes at the ecosystem scale. Although specific processes in tropical aquatic ecosystems, such as hydrodynamics, plankton production and fisheries production have received some attention, there remains a need to integrate these processes in order to gain a better understanding of ecosystem functioning. One means of achieving this is through the development of conceptual and numerical models, which can facilitate both the theoretical understanding and applied management of these ecosystems. As management problems move from the relatively simple issue of fishery control to the more complex issues of climate change and land use, models will play an important role in decision-making processes regarding sustainable utilization of these vital natural systems.

Introduction

The East African Rift Valley region contains the tropics' densest aggregation of lakes (Figure 1). Although many of these lakes can be considered large (sensuHerdendorf, 1982), Lakes Victoria, Tanganyika and Malawi stand out, with surface areas and volumes comparable to those of the Laurentian Great Lakes. For the purposes of this paper these three lakes are referred to as the African Great Lakes.

Figure 1.

The East African Great Lakes. Dashed lines represent drainage basin boundaries. Bathymetric Contour depths are given in meters, and are based on Tiercelin and Mondeguer (1991: Tanganyika), T. C. Johnson and B.M. Halfman (unpublished data for Malawi), and Lake Victoria bathymetry data collected during the IDEAL project, as given in Talbot and Laerdal (2000).

Figure 1.

The East African Great Lakes. Dashed lines represent drainage basin boundaries. Bathymetric Contour depths are given in meters, and are based on Tiercelin and Mondeguer (1991: Tanganyika), T. C. Johnson and B.M. Halfman (unpublished data for Malawi), and Lake Victoria bathymetry data collected during the IDEAL project, as given in Talbot and Laerdal (2000).

With a surface area of nearly 69,000 km2, Lake Victoria is second largest freshwater lake on earth. Lake Tanganyika is second only to Lake Baikal with regard to depth, followed by Lake Malawi (Table 1: Lake Malawi is referred to as Lake Nyasa in Tanzania, and Lake Niassa in Mozambique). The lakes were formed by tectonic activity associated with the formation of the East African rift valley, a slowly widening divide that extends from the Red Sea in the north to Botswana in the south. Lakes Malawi and Tanganyika are located within the rift valley; hence their long, narrow, deep morphometry and mountainous shorelines. The shallower Lake Victoria basin occupies an uplifted region between the western and eastern arms of the rift valley. In addition to these three large lakes, the East African rift resulted in the formation of a number of other water bodies, including Lakes Edward and Albert in the western rift branch along the border between Uganda and the Democratic Republic of the Congo, Lake Turkana (formerly Lake Rudolf) which straddles the Kenya -Ethiopia border, and smaller Ethiopian, Kenyan and Tanzanian lakes in the eastern rift branch.

Table 1.

Physical characteristics of the African Great Lakes. Morphometric data for the African Lakes are from Rzoska (1976), Gonfiantini et al. (1979), Bootsma and Hecky (1993), and a bathymetric map for Lake Malawi (T.C. Johnson and B.M. Halfman, unpublished).

VictoriaTanganyikaMalawi
Surface Area (km268,800 32,600 29,500 
Maximum Depth (m) 79 1,470 700 
Mean Depth (m) 40 580 264 
Volume (km22,760 18,900 7,775 
Drainage Area (km2195,000 220,000 100,500 
Altitude (m amsl) 1,134 774 474 
River inflow (km3 yr−1)* 20a 14b 29c 
River Outflow (km3 yr−120a 2.7b 12c 
Rainfall (km3 yr−1100a 29b 39c 
Evaporation (km3 yr−1100a 50d 57e 
Residence Time (years) 23 440 114 
Flushing Time (years) 138 7,000 648 

aRzoska (1976).

 
 
 
 

ebased on estimates of Eccles (1974) and Spigel and Coulter (1996).

 
VictoriaTanganyikaMalawi
Surface Area (km268,800 32,600 29,500 
Maximum Depth (m) 79 1,470 700 
Mean Depth (m) 40 580 264 
Volume (km22,760 18,900 7,775 
Drainage Area (km2195,000 220,000 100,500 
Altitude (m amsl) 1,134 774 474 
River inflow (km3 yr−1)* 20a 14b 29c 
River Outflow (km3 yr−120a 2.7b 12c 
Rainfall (km3 yr−1100a 29b 39c 
Evaporation (km3 yr−1100a 50d 57e 
Residence Time (years) 23 440 114 
Flushing Time (years) 138 7,000 648 

aRzoska (1976).

 
 
 
 

ebased on estimates of Eccles (1974) and Spigel and Coulter (1996).

 

The African Great Lakes are extremely old. Lakes Tanganyika and Malawi date back to the Miocene, with age estimates ranging from 10 to 20 million years (Haberyan and Hecky, 1987; Tiercelin and Mondeguer, 1991; Cohen et al., 1993). As a result of their great age, each of these two lakes is underlain by more than four kilometers of sediment (Rosendahl, 1987; Tiercelin and Mondeguer, 1991).

Environmental challenges

The large lakes of East African Rift Valley are unique natural resources that are heavily utilised by their bordering countries for transportation, water supply, fisheries, waste disposal, recreation and tourism. The large lakes as well as many smaller freshwater bodies (wetlands and rivers) in the region are under considerable pressure from a variety of interlinked human activities. Overfishing, siltation from the erosion of deforested watershed, species introductions, industrial pollution, nutrient eutrophication and climate change are all contributing to a host of rapidly evolving changes occurring in these lakes that seriously threaten both their ecosystem function and overall diversity (Hecky and Bugenyi, 1992; UNEP, 2004).

Lake Victoria basin

Lake Victoria basin is mainly (80%) an agricultural catchment (Majaliwa et al., 2000), and the current population pressure (more than 30 million people in the catchment) on forests, wetlands, rangelands and marginal agricultural lands as well as inappropriate cultivation practices, forest removal and high grazing intensities (that, in extreme cases, leave barren environments) lead to unwanted sediment and stream flow changes that mainly impact the downstream communities (Magunda and Majaliwa, 2000; Botero, 1986). Lake sediment core analysis indicates that landscape disturbance became significant from the 1930s onwards, and the resulting increase in soil erosion and sedimentation is the dominant cause of the ongoing eutrophication in Lake Victoria (Verschuren et al., 2002). Signs of overfishing in the lake were reported as early as 1927 when catch rates for tilapia dropped from 50–100 fish per 50 m long net with 127 mm stretched mesh to less than five fish (Worthington and Worthington, 1933; cited in Ssentongo, 1972). As recently as the 1960s, Lake Victoria supported an endemic cichlid fish species flock of 500+ species (Seehausen, 1996), but these have progressively disappeared from the catches to become poorly represented today. Many food fish species such as Oreochromis esculentus (Graham), Bagrus docmak Forsskåll, Clarias gariepinus (Burchell), Labeo victorianus Boulenger and the haplochromines (once important for fishmeal) have almost disappeared (Mkumbo, 1999). More recently, even L. niloticus, the most important fish in the fishery, shows signs of declining (Othina and Osewe-Odera, cited in Mkumbo, 1999). There are indications that the fishery yield (Uganda) has declined from 135,000 tons in 1993 to 107,000 tons in 1997 (Odongkara and Okaronon, 1999). The losses are attributed to habitat degradation in the catchment, introduction of exotic species (particularly Nile perch) and heavy fishing pressure (e.g. Ogutu-Ohwayo, 1990; Witte et al., 1999). For example, the extinction of several hundred species of haplochromine cichlid fish in the Lake Victoria following the introduction of the Nile Perch, a large voracious predatory species, ranks as the largest single recorded vertebrate extinction attributable to specific human actions on earth (Johnson et al., 1996).

Lake Tanganyika basin

In the Lake Tanganyika basin, increased deforestation and consequently erosion in the catchment has caused an increase in suspended sediment entering the rivers and the lake (Cohen, 1991; Bizimana and Duchafour, 1991; Tiercelin and Mondegeur, 1991). The dynamics and behaviour of river-borne and runoff sediment entering the lake are complex and not well understood but it appears that much sediment deposition occurs in the littoral zone, precisely where most of the lake's biodiversity is concentrated (West, 2001), and threatens the diversity of nearshore fishes (Cohen et al., 1996) and benthic organisms (O'Reilly, 1998). Analyses of sedimentation rates from 14C dated cores (Tiercelin and Mondegeur, 1991) confirmed the high sediment impact in the northern basin with the southern and central basins receiving < 1,500 mm/1,000 years and < 500 mm/1,000 years respectively, compared with the northern basin which received about 4,700 mm/1,000 years. In Lake Tanganyika, fishing activities include commercial fishing by both industrial and artisanal fishermen, subsistence fishing, and ornamental fish extraction for export: overfishing and fishing with destructive methods have led to loss of jobs and livelihoods even at country scale, e.g., the collapse of the Burundi industrial fishing fleet in the early 1990s (West, 2001). Sample surveys show that fishers and post-harvest operators are very pessimistic in their appraisals of catch trends over recent years: majorities in all the national sectors take the view that they have been on the decrease (FAO, 2001).

Lake Malawi basin

As early as 1960, the high population density of Malawi had led to extensive alteration of the natural vegetation of the catchment (Eccles, 1974), and catchment disturbance through land clearance has resulted in greatly increased sediment loads (Tweddle, 1992; Calder et al., 1995; Bootsma and Hecky, 1999; Irvine et al., 2001). The rocky shores harbour a wealth of invertebrates (e.g., harpacticoid copepods, chironomids, ostracods), molluscs and the crab Potamonautes lirrangensis while sandy shores support an almost entirely different invertebrate fauna (copepod and ostracod Crustacea, the prawn Caridina nilotica, chironomid larvae, gastropods, bivalve Mollusca) (Hughes and Hughes, 1992). These communities are under threat from sediment inundation of the habitats, and overfishing (Ribbink, 2001). By the 1930s, commercial fisheries had begun in Malawi (Ribbink, 2001), and in the 1940s the first concerns over overfishing were raised (Ricardo-Bertram et al., 1942). Fishing pressure increased in the 1960s when artificial twines replaced natural fibres, plank boats with outboard engines became popular and the first demersal trawlers were introduced (Tarbit, 1971). Fish production in Malawi rose dramatically from annual catches of 20,000 tons in 1965 to 84,000 tons in the 1970s and has declined since then to give fluctuating yields, sometimes dropping to 60,000 tons per annum (Mapila, 1998). Overfishing does not occur throughout the lake, and the deep pelagic waters of the lake are probably underexploited. Nearshore, shallow demersal communities are under greatest pressure, and deep water demersal communities (between 50–100 m depth) are harvested by offshore trawlers in particular and have shown changes in species composition and standing stock (Ribbink, 2001). An imminent threat, therefore, is the impact of fishing on the demersal fish community in the more inshore, but still relatively deep (to 200 m) areas of the lake; there is also sufficient evidence that many endemic fish species are being driven to extinction by commercial fisheries in the southern end of the lake (Irvine et al., 2001). There is no evidence of deliberate or accidental introductions of alien stocks or genetically modified species in Lake Malawi (Cohen et al., 1996). However, there have been many unintentional species translocations within the lake, mostly by the aquarium trade industry; this disrupts existing nearshore species, and may result in the extinction of species at certain locations, and/or homogenisation of the gene pool and loss of genetic diversity (H. Bootsma, pers. comm.).

Other cross-cutting issues

Water hyacinth is perhaps the best known invasive species in the Lakes. It is believed to have invaded Lake Victoria in the late 1980s (Freilink, 1991), through the Kagera River (Twongo, 1996). Its spread has disrupted fishing activities, transportation, and has threatened the functioning of various lakeshore-based installations such as water purification and hydroelectric power plants (e.g. Twongo, 1996). Proliferation of the water hyacinth leads to reduced oxygen levels, and hence reduced floral and faunal diversity (Kudhongania et al., 1996). A study in Lake Victoria (Uganda) has shown that, in the vicinity of the water hyacinth, fish species number, biomass and diversity are reduced, the former two very significantly (Willoughby et al., 1996). It, however, provides a protective habitat for some of the endangered haplochromine species, hippopotamus, crocodiles, snakes, bilharziasis carrying snails and mosquitoes. Invasive species exist in the Tanganyika Basin, including water hyacinth, Typha, Oreochromis and others, but there is currently no data to quantify their impact (West, 2001). The water hyacinth is now encroaching into Lake Malawi from a variety of sources, including its infested Shire outlet and rivers such as Bua and Linthipe, that drain the watershed (UNEP-IETC, 2003).

The lakes act as repositories for human, agricultural, mining and industrial waste. In Lake Victoria, pollution is a major problem. Several studies show that since the 1960s, Lake Victoria has experienced a serious decline in water quality (e.g. Wandiga and Onyari, 1987; Kansiime and Bugenyi, 1996; Kansiime and Nalubega, 1999; Scheren et al., 2000; LVEMP 2001). In Lake Tanganyika, untreated waste water discharge, including industrial waste from large cities, e.g., Bujumbura in Burundi, Uvira in D. R. Congo, Kigoma in Tanzania and Mpulungu in Zambia; agricultural runoff particularly from Malagarasi and Rusizi catchments due to increase in the use of agrochemicals concomitant with agricultural expansion; and mining waste containing mercury, are major chemical pollution sources but are mainly of local and not lakewide concern (Chale, 2000; West, 2001). A survey of the water resources of Malawi concluded in 1980 that industrial pollutants and partly treated wastes from sewage had reduced the quality of water in many streams too far below acceptable levels (UNEP-IETC, 2003). Today, with the rapidly rising population, lack of sanitation infrastructure, lack of sewage treatment facilities, increased numbers of informal settlements, rampant deforestation, etc., the situation is far worse in the rivers and lake (cf. Coulter and Mubamba, 1993; Bootsma and Hecky, 1999). In addition to sediment loading, another long-term threat to the Lake Malawi ecosystem arises from possible pesticide load from the catchment Irvine et al., 2001).

Eutrophication is a problem in all the lakes, but is significantly more widespread in Lake Victoria (e.g. Hecky, 1993; Calder et al., 1995; Hecky et al., 1996; Cohen et al., 1996; Bootsma and Hecky, 1999). Nutrient loads to the lakes are associated mainly with atmospheric deposition (natural and biomass burning) and land runoff (e.g. agriculture) (Scheren et al., 2000; Hecky et al., 2002). The very large volumes of Lakes Tanganyika and Malawi may provide temporary buffers against deterioration of water quality in the two lakes. In Lake Victoria, eutrophication has increased drastically within the last three decades due to high levels of nutrients (Hecky, 1993). Some consequences of this include: increased algal blooms since the 1960s (Mugidde, 1993; Hecky, 1993; Verschuren et al., 2002); dominance of filamentous and colonial blue green algae, known for causing hypoxia conditions that occasionally lead to fish kills (Kling et al., 2001; LVEMP, 2001); and increased and prolonged anoxia in nearly half of the lake floor compared with the 1960s when anoxia was localized and sporadic (Talling, 1965, 1966; Hecky, 1993; LVEMP, 2001).

All the lakes are sensitive to climate change as their water balance is dominated by rainfall on the lake and evaporation, with river inflow and outflow making minor contributions (Spigel and Coulter, 1996). Several studies indicate that the lakes are known to have fluctuated between closed and open status several times in the recent and far past (e.g. Scholz and Rosendahl, 1988; Cohen et al., 1997), and indeed, about 10,000 years ago Lake Victoria was completely desiccated (Johnson et al., 1996). Lake Victoria, is now one-half a degree (°C) warmer than in the 1960s (Hecky et al., 1994; Bugenyi and Magumba, 1996), in harmony with changes in surface temperature at tropical elevations above 1000 m world-wide, but not much is known about the effect of present climate change on this lake. In Lake Tanganyika, recent studies show that local temperature rises, less windy conditions and climate change have dramatically altered the nutrient balance of the lake (O'Reilly et al., 2003; Verburg et al., 2003): the surface of the lake is getting warmer, reducing mixing of essential nutrients such as nitrogen and sulphur between the epilimnion and hypolimnion, and thus cutting off fish production. Catches per unit effort of the main pelagic fishes were partially correlated with ENSO for the last 30 years in two stations of Lake Tanganyika, and changes in hydrodynamic and upwelling intensity were presented to explain this. The observed decline of primary productivity by about 20% implies that the fish yields have decreased by about 30% over the past 30 years or so (O'Reilly et al., 2003). This suggests that the impact of regional effects of climate change on the aquatic ecosystem functions and services can be larger than that of local anthropogenic activity or overfishing (O'Reilly et al., 2003).

Monitoring and management practices

Each of Africa's three largest lakes is shared among several countries. Lake Malawi is bordered by Malawi, Mozambique and Tanzania; Lake Tanganyika by Zambia, Tanzania, Burundi and the Democratic Republic of the Congo; and Lake Victoria by Tanzania, Kenya and Uganda. As a result, water quality and fisheries management face challenges similar to those in the Laurentian Great Lakes, such as the coordination of research activities, the dissemination of data, and the harmonization of management strategies. There is a long history of collaboration on Lake Victoria, where the British colonial government established the East African Freshwater Fisheries Research Organization (EAFFRO) in 1947. In addition to promoting collaborative research and management efforts, EAFFRO established the African Journal of Tropical Hydrobiology and Fisheries, which is published intermittently. EAFFRO collapsed in 1977, when the treaty that had established the East African Community was officially dissolved. In 1971, the UN Food and Agriculture Organization (FAO) established the Committee for Inland Fisheries of Africa (CIFA), with the stated purpose of promoting research, education, training and management of inland waters throughout Africa. With the recognition of emerging problems and the increasing value of the fisheries in the Lake Victoria region, the Lake Victoria Fisheries Organization was formed by the three riparian countries in 1994, and its head office in Jinja, Uganda, became operational in 1997.

Unlike the countries around Lake Victoria, those around Lakes Tanganyika and Malawi were not previously linked by a common colonial government, and therefore international collaboration on these two lakes does not have as long a history. Some coordination is provided by the Southern African Development Community (SADC), established in 1979, of which Malawi, Mozambique, Zambia, Tanzania and the DRC are members. However, although SADC includes a fisheries sector, the SADC mandate is very broad, and communication between researchers and managers in the various riparian countries has been limited.

While a common past facilitated international collaboration on Lake Victoria, exchange between the lake's bordering countries has also been fostered out of necessity in the past two decades as a result of the dramatic ecosystem-scale changes that have occurred in the lake. Although different views are held on the desirability of Nile perch in the lake, the invasion of the water hyacinth (Eichhomia crassipes) was an undisputed disaster. The plant entered the lake in the early 1980s, and by the early 1990s its numbers had increased to the point of covering much of the lake's shoreline, affecting water supply, fish distribution, transportation, and public health (Twongo, 1996; Willoughby et al., 1996). In the last two years, there has been a dramatic decline in the abundance of the hyacinth, which is attributed at least in part to a weevil (Neochetina eichoniae) that was introduced in 1995. However, meteorological conditions and nutrient supply may have also played a role and there is continued concern that the weed could make a comeback.

Recent changes in Lakes Tanganyika and Malawi have been less dramatic, but the combined effects of overfishing and deteriorating water quality in the lakes and their tributaries have raised concerns about the future of these species-rich systems (Bootsma and Hecky, 1993; Cohen et al., 1996). As a result, there has been closer collaboration among the riparian countries, with support from international organizations such as the FAO, UNEP, and various European, North American and Asian development organizations. In particular, collaborative projects to foster research, management and training have been facilitated by the Global Environmental Facility (GEF), a facility that was born out of the 1992 UN Conference on Environment and Development (Earth Summit) in Rio de Janeiro. GEF programs have been in operation on all three of the African Great Lakes for the past several years, and much of the research data used in this paper was conducted as part of these programs.

Monitoring programmes

Lake Victoria

Prior to the 1960s, most agreements (except the 1929 Nile Waters Agreement) dealing with development and uses of the Nile waters have been on bilateral basis (UNECA, 2000). In 1967, the United Nations Development Programme (UNDP) and the World Meteorological Organisation (WMO) initiated the Hydromet Project for the hydrometeorological survey of the equatorial lakes basin. This project was initially endorsed by Egypt, Sudan, Kenya, Uganda and Tanzania, and later on included Rwanda, Burundi and the Democratic Republic of Congo, with Ethiopia as an observer (UNECA, 2000). The Kagera River Basin Agreement was signed by Burundi, Rwanda and Tanzania, with establishment of the Kagera Basin Organisation (KBO) in 1977. Other international conventions and agreements that Kenya, Uganda and Tanzania are signatories to or subscribe to are summarised in Bwathondi et al. (2001). The relevant regional agreements include: Technical Cooperation for the Promotion of the Development and Environmental Protection of the Nile Basin (Tecconile), Initiative for Nile Basin Management, the Convention for the Establishment of the Lake Victoria Fisheries Organisation (LVFO), the Agreement on the Preparation of a Tripartite Management Program for Lake Victoria, and the Treaty establishing the EAC. The international conventions and agreements include: the Convention on Wetlands of International Importance, the Convention for International Trade in Endangered Species of Wild Fauna and Flora, the Convention on Conservation of Biological Diversity, and the Code of Conduct for Responsible Fisheries (CCRF).

Overwhelmingly, the politics of management and ownership of Lake Victoria falls into the larger context of the establishment and development of the East African Community (EAC, 2001). The need for fisheries collaboration in Lake Victoria was realized already in 1928 (Klohn and Andjelic, 2006). More recently, the three countries collaborated through the FAO Committee for Inland Fisheries of Africa (CIFA) Sub-Committee for Lake Victoria. A Convention for the Establishment of the Lake Victoria Fisheries Organization (LVFO), drafted with FAO assistance, was signed by all three countries in 1994 (Klohn and Andjelic, 2006). Within the Community, two institutions on Lake Victoria have therefore been established. These are Lake Victoria Fisheries Organisation (LVFO-which is specific for fisheries) and the Lake Victoria Development Programme (LVDP-covering general development matters of the Basin).

During the 1990s, two other projects were established, namely, the Lake Victoria Fisheries Research Project (LVFRP) financed by the European Union, and the Lake Victoria Environmental Management Project (LVEMP) financed by the World Bank and the Global Environmental Facility (GEF) (Bwathondi et al., 2001). The LVFRP Phase II, implemented by the research institutes of the riparian countries of Kenya, Uganda and Tanzania, started in June 1997. Its main objectives were to encourage sustainable development of the Lake Victoria basin by assisting the LVFO in the creation and implementation of a viable regional management of the lake fisheries (Bwathondi et al., 2001). The Lake Victoria Regional Local Authorities Cooperation (LVRLAC) was set up in 1997 to begin to collaborate in addressing the region's socio-economic concerns in relation to the deteriorating conditions of Lake Victoria and its surroundings (Kiyaga-Nsubuga, 2002). The Nile Basin Initiative was formally launched in 1999 by the Council of Ministers of Water Affairs of the Nile Basin States, and it includes all Nile countries and provides an agreed basin-wide framework to fight poverty and promote socio-economic development in the region. Its vision is “to achieve sustainable socio-economic development through the equitable utilization of, and benefit from, the common Nile Basin water resources.” Core support for the Initiative, whose early partners included UNDP, the Canadian International Development Agency, and the World Bank, is provided by the Nile countries.

Lake Tanganyika

Lake Tanganyika's riparian nations agreed upon a set of principles and values in their quest to ensure the conservation and sustainable use to the lake's resources. Many of these principles are embodied in existing Conventions to which the four riparian countries are signatories, in particular the environmental and social principles that underlie the Convention on Biological Diversity, Agenda 21 and the Dublin principles. These principles include the: Precautionary Principle, Polluter Pays Principle, Principle of Preventive Action, Principle of Participation, Principle of Equitable Benefit Sharing, and Principle of Gender Equality. Recognising that Lake Tanganyika is a special system that it is threatened by a variety of destructive behaviours, and that existing national legislation regarding the lake is inadequate, Tanganyika's riparian countries drafted the Convention for the sustainable of the lake (West, 2001). This Convention was signed by the Ministers of the four countries on 12 June 2003, and was to be ratified within 90 days following the signing. The convention is the result of five years of technical studies and expert evaluation, and charges member countries with controlling pollution, overfishing and other human activities in their territories that threaten the lake, which supports the livelihoods of up to 10 million people in the four countries. The Convention provides the necessary rights, responsibilities, institutions and framework in international law which compel the countries to cooperate in managing Lake Tanganyika. Specifically, it creates a binding legal framework ensuring certain standards of protection, establishes the institutions for implementing the Convention, establishes the mechanisms for implementing the Strategic Action Programme and establishes procedures for settling disputes. Simply stated, the Strategic Action Programme (SAP) is a participatory strategic planning process to enable scientists and natural resource managers to identify and prioritise their management initiatives for the Lake. The SAP is mandated to “establish clear priorities that are endorsed at the highest levels of government and widely disseminated. Priority transboundary concerns should be identified, as well as sectoral interventions (policy changes, program development, regulatory reform, capacity-building investments, and so on) needed to resolve the transboundary problems as well as regional and national institutional mechanisms for implementing elements of the SAP.”

Lake Malawi

Projects that have been carried out on Lake Malawi include: the Joint Fisheries Research Organisation of Northern Rhodesia that was carried out in the 1950s and that provided information on the limnology of the lake; the United Nations Food and Agricultural Organisation Project from 1977 to 1981 that was designed to estimate fish stocks and yields in the open water pelagic zone; the UK/SADC Lake Malawi Fish Resource Assessment carried out in the 1990s to investigate offshore processes, as well as the SADC/GEF Lake Malawi Biodiversity Project (Irvine et al., 2001 and references therein). Open access conditions prevail in most circumstances in the three countries as the right to use natural resources is synonymous with survival (WWF, 2003). At the international level, some environmental conventions have been endorsed, e.g., Malawi is signatory to the Convention on International Trade in Endangered Species of Fauna and Flora, Convention on Biological Diversity, Convention on the Conservation of Migratory Species of Wild Animals, and the Ramsar Convention. At the regional level, there are a number of policies which guide the conduct of State Parties in relation to the use of natural resources: SADC Protocols on Fisheries, Shared Watercourse Systems, Mining, Wildlife Conservation, and Law Enforcement (Kasweswe-Mafongo, 2003; WWF, 2003). However, due to the voluntary nature of their application and a lack of effective enforcement institution at regional level, they do not have notable impacts (Kasweswe-Mafongo, 2003; WWF, 2003).

Also, all three countries have passed a number of policies and legislation on fisheries, forestry, water, and soil, but these have been developed independently and without consultation, and they are, therefore, disjunct. In Malawi, the major statute for the regulation and control of fisheries is the Fisheries Act 1974 that is administered by the Department of Fisheries. The Act is charged with the prevention of depletion of fish resources and making harvesting of fish sustainable through licensing, gear restriction and seasonal closing of fisheries. Policing of these regulations however is constrained by lack of trained staff and patrol equipment also inadequate penalties for non-compliance. In Tanzania and Mozambique, the fisheries policies focus more on marine fisheries rather than on inland water bodies such as Lake Malawi (WWF, 2003). There is also some disagreement over political boundaries between Tanzania and Malawi.

The Lake Malawi Ecosystem Management Project (LMEMP) is an ecosystem management programme that is being prepared by the three riparian countries and is funded by GEF and other bilateral agencies. It aims to maximize the benefits to the riparian communities from improved fisheries management and the sustainable use of soils, forests, wetlands and other resources within the basin to generate food, employment and income, while sustaining the ecosystem from which these benefits arise. There is, however, some uncertainty as to the current status of this project.

Ecosystem-based management approach

Recent changes in all the three African lakes have resulted in an increased realization that individual components of these systems cannot be understood in isolation, and that effective management must expand beyond conventional fisheries management to account for the interaction of physical, geological, chemical and biological processes at the ecosystem scale (Molsa et al., 1999). It is likely that sustainability can be achieved when there is compatibility between both human benefits and ecosystem health (Coulter and Irvine, 2002). Although specific processes in tropical aquatic ecosystems, such as hydrodynamics, plankton production, and fisheries production have received some attention, there remains a need to integrate these processes in order to gain a better understanding of ecosystem functioning. One means of doing this is through the development of conceptual and numerical models, which can facilitate both the theoretical understanding and applied management of these ecosystems (Crisman and Streever, 1996), including testing different scenarios (Coulter and Irvine, 2002). As management problems move from the relatively simple issue of fishery control to the more complex issues of land use and climate change, models will play an important role in decision-making processes. For the developing riparian countries, it is critical that management strategies have maximum positive impact with minimal expense. Predicting the efficacy of various management options is obviously more cost effective than a trial and error approach. To this end, initial models that simulate physical and biogeochemical processes in the lakes and their catchments have been developed for Lakes Malawi and Victoria (e.g. Lam et al., 2002). The hope is that these models will serve as a basis for informed discussions about the present and future state of the lakes, and eventually be applied as decision-support tools for management of the lakes.

An understanding of ecosystem functioning and the development of integrated physical and biogeochemical models are also critical for the interpretation of sediment records. The sediment records available from the African Great Lakes, as well as smaller African lakes, are invaluable to our understanding of the magnitude and timing of global climate variation (Johnson, 1996; Gasse, 2000). Interpretation of many of the climate proxies measured in these sediments requires an understanding of the mechanisms that link meteorology, hydrodynamics, chemistry and biology. For example, the interpretation of diatom microfossil records (Stager et al., 1986; Haberyan and Hecky, 1987; Gasse et al., 2002) relies on a general understanding of diatom autecology (Hecky and Kling, 1987; Kilham et al., 1986; Owen and Crossley, 1992). But there remains a need to better quantify the effects of physical and chemical conditions on diatom species composition (Kilham et al., 1986; Gasse et al., 2002) and biogenic silica deposition. While some empirical data is available to indicate how the lakes' plankton communities respond to meteorological changes over time scales of months to years, these observations do not necessarily reflect steady state conditions in these slowly flushing lakes and therefore they must be used with caution when trying to interpret the climatic significance of long-term changes in the microfossil record. For this purpose, hydrodynamic and biogeochemical models that simulate over time scales of decades to centuries are necessary.

The need for tropical lake ecosystem models goes beyond lake management. The study of large tropical lakes can increase our general understanding of the mechanisms that control the physical, chemical and biological functioning of large, aquatic ecosystems. Paradigms that help to direct research and management priorities, such as in the Laurentian Great Lakes, are constrained by the geological, meteorological and biological conditions that exist in those lakes. When those conditions change (e.g. following exotic species invasions or a change in climate), the paradigms often are of limited use in predicting ecosystem response. Thienemann (1932) observed this over half a century ago, when he discovered that the measurement of hypolimnetic oxygen deficit could not be used to trophically classify tropical lakes, as it was for temperate lakes. Currently there is much concern and uncertainty about potential impact of climate change on temperate aquatic ecosystems (Mortsch and Quinn, 1996; Nicholls, 1999). While the effects of a given change in climate on lake physical processes can probably be predicted with a good degree of certainty, potential changes in chemical cycles and biological properties are much more difficult to predict, due to the number and complexity of interacting processes that link meteorology to chemical and biological dynamics. By viewing the African Great Lakes as endpoints along a climatic gradient, we may be able to acquire insight into how physical changes such as warmer temperatures, prolonged stratification and hydrologic shifts will affect biota and ecosystem functioning in other lakes.

Following accelerated species extinction rates around the world, the implications of species losses for ecosystems has become a concern, and the question of how organisms are influenced by their environment has been turned around to ask what role species composition and biodiversity play in ecosystem functioning (Tilman, 1999; McCann, 2000). Already several decades ago, Fryer and IIes (1972) discussed the possible relationship between cichlid diversity and ecosystem stability in the African Great Lakes. However, despite the recognition that fish diversity might play a role in ecosystem processes such as energy transfer and nutrient cycling, and that the cichlid communities of the African Great Lakes present a unique opportunity to examine these relationships, the role of diverse fish communities in ecosystem functioning has received little attention in the African Great Lakes (Leveque, 1995). Some recent papers on this topic (Higgins et al., 2001) and others strongly support the need for continued research, within the lakes and their catchments, on the biophysical processes, anthropogenic impacts and socio-economic factors, in order to gain a better understanding of these inter-related issues to guide on the sustainable management of the lakes and their resources. Both the great biological diversity in these lakes, and the recent loss of much of this diversity from Lake Victoria, present opportunities to examine the relationships between community structure and ecosystem functioning in natural settings.

Truly large freshwater systems that immediately invite the epithet “great” are rare on the present earth. Studies of these large systems are logistically and intellectually challenging. These characteristics of rarity and challenge impose a special onus upon Great Lakes researchers to share and promote the results of these studies for the benefit of all the Great Lakes.

Conclusions

Among the challenges currently facing the African Great Lakes, perhaps none is more important, nor more often overlooked, than the ecosystem management. Ecosystem integrity is beginning to receive acknowledgement in some quarters as the foundation upon which sound management must be built. Still, much research needs to be done both in order to understand the changes that have already occurred in these ecosystems and to establish baseline data by which future changes can be evaluated. If policy and management decisions are to have any hope of ensuring the sustainable use of the African Great Lakes resources, they will have to be informed by sound scientific research.

In the African Great Lakes region, the main problem is management. It is typical for a number of different agencies to be responsible for the numerous lake resources in a given country. Fisheries issues, agricultural issues, industrial waste issues, and drinking water issues, for example, have been addressed separately and without co-ordination. Government policies have generally emphasised exploitation for development at the expense of conservation and sustainability. In most countries there is no single agency responsible for lakes management, as there tends to be for agriculture or forestry. To complicate matters further, the major lakes in the region are shared by multiple nations; if co-ordination within a country is difficult, the task is all the more daunting across political boundaries.

Recent changes in all the three African lakes have resulted in an increased realisation that individual components of these systems cannot be understood in isolation and that effective management must account for the interaction of physical, geological, chemical and biological processes at the ecosystem scale. In addition, scientific information is of no effect without supporting policies and the ability to address the underlying issues that restrict or prevent meaningful application of the concepts of sustainability (Coulter and Irvine, 2002). Some policy options have been proposed (Table 2; UNEP, 2004), recognising that although specific processes in tropical aquatic ecosystems such as hydrodynamics; plankton production, and fisheries production have received some attention, there remains a need to integrate these processes in order to gain a better understanding of ecosystem functioning.

Table 2.

Recommended policy options for ecosystem management with respect to Lake Victoria (UNEP, 2004).

IssueRecommended policy option(s)
Overexploitation Fish processing quota. 
Destructive Fishing Practices Provide civic education and awareness, empower and involve more communities in management. 
Microbiological pollution Liberalisation of waste disposal activities to involve the private sector and communities. 
Eutrophication Improve natural resource management, farming practice through training governance and technologies in agriculture. 
Chemical pollution Strengthen enforcement of regulations requiring effluent treatment in municipalities and industries. 
Suspended solids Improve natural resource management, soil conservation, farming practice through training, governance and technologies in agriculture, improve road construction design to minimize erosion. 
Cross-cutting ▪ Integration of institutional framework at two levels: national and regional. 
 ▪ Integration of regulations and laws at two levels: national and regional. 
 ▪ Enforce compliance to international conventions e.g. RAMSAR, CITES, and the Biological Diversity Convention of Agenda 21. 
 ▪ Strengthening of capacity of National Environmental Protection Authorities in order to be able to be more effective. 
 ▪ Provide economic incentives for use of clean technologies. 
 ▪ Promote self regulation in fisheries and pollution management. 
IssueRecommended policy option(s)
Overexploitation Fish processing quota. 
Destructive Fishing Practices Provide civic education and awareness, empower and involve more communities in management. 
Microbiological pollution Liberalisation of waste disposal activities to involve the private sector and communities. 
Eutrophication Improve natural resource management, farming practice through training governance and technologies in agriculture. 
Chemical pollution Strengthen enforcement of regulations requiring effluent treatment in municipalities and industries. 
Suspended solids Improve natural resource management, soil conservation, farming practice through training, governance and technologies in agriculture, improve road construction design to minimize erosion. 
Cross-cutting ▪ Integration of institutional framework at two levels: national and regional. 
 ▪ Integration of regulations and laws at two levels: national and regional. 
 ▪ Enforce compliance to international conventions e.g. RAMSAR, CITES, and the Biological Diversity Convention of Agenda 21. 
 ▪ Strengthening of capacity of National Environmental Protection Authorities in order to be able to be more effective. 
 ▪ Provide economic incentives for use of clean technologies. 
 ▪ Promote self regulation in fisheries and pollution management. 

One means of doing this is through the development of conceptual and numerical models, which can facilitate both the theoretical understanding and applied management of these ecosystems. As management problems move from relatively simple issues of fishery control to the more complex issues of land-use and climate change, models will play an important role in decision-making processes. For the developing riparian countries, it is critical that management strategies have maximum positive impact with minimal expense. To this end, initial models that simulate physical and biogeochemical processes in the lakes and their catchments have been developed for Lakes Malawi and Victoria. The hope is that those models will serve as a basis for informed discussions about the present and future state of the lakes, and eventually be applied as decision support tools for management of the lakes.

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