Some of the characteristics of the African Great Lakes are the numerous species of fish, crustaceans, mollusks, plankton, and other phyla, most of them endemic. The usual sources of perturbation when speaking about Great Lakes also have their impacts on the African Great Lakes, such as overfishing, dumping of untreated sewage, pebble and sand mining, agricultural run-off and other threats. Should this biodiversity be protected in times of sheer poverty of the riparian populations? Should it be exposed to exploitation for food security? What are the values of these endemic species in economic terms? This article reviews the impacts on biodiversity by human-induced factors like exotic fish introductions and the invasive water hyacinth, but also by indirect factors like climate change. Lake Victoria has a long history of fish introductions and invasive weeds, but on Lake Tanganyika the original species composition of many taxa can still be preserved and protected, at a cost. The Great Lakes surrounding these countries, by means of conventions and regional management bodies, sought to protect the environments and called for international collaboration to improve management of the natural resources, both terrestrial and aquatic. The way forward will be to involve local fishing communities in nature conservation and management, but there are many communities and many fishermen. How to reach them in areas where there is no municipal electricity supply, no portable phone network, nor internet facilities. In the 21st century, around the African Great Lakes the keyword is survival, not only of biodiversity, but also of the inhabitants of their basins.
Fisheries managers on the Great Lakes of Africa, but also on other African waterbodies, are confronted with a dilemma regarding the objectives of their fisheries management policies and plans. Often their plans, to be politically correct, contain the combination of conserving the fisheries resources as well as biodiversity of the lake (LVFO, 1999; LTA Secretariat, 2012a; LTA Secretariat, in preparation). The present article deals with this dilemma and attempts to describe the objectives and the management actions and recommendations for strengthening fisheries management for two case studies on Lakes Victoria and Tanganyika. Furthermore, the issue of responsibility is discussed, particularly when an invasive species is discovered in a lake basin, which is known to have wreaked havoc in other situations from the biodiversity point of view. The purpose of the present article is to find ways and means to overcome the impasse of conservation of biodiversity on one hand and the (over)exploitation of fishery resources on the other.
The three African Great Lakes: Victoria, Tanganyika, and Malawi/Nyassa (Figure 1) are characterized by large numbers of fish species, of which the majority are the Cichlidae family (Van der Knaap et al., 2008). Many of these species are under pressure due to siltation, pollution, invasive weeds, overharvesting of fish. It may well be that their existence is also threatened by climate change directly or indirectly (Langenberg et al., 2003; Descy et al., 2006; LTA Secretariat 2012a).
Fisheries and biodiversity in Lake Victoria
Lake Victoria has undergone a number of changes in the past half century. The lake has been subjected to various fish introductions, particularly Lates niloticus and Oreochromis niloticus (Barel et al., 1985; Ogutu-Ohwayo, 1990, 1992; Mkumbo, 2002; Goudswaard, 2006; Van der Knaap and Ligtvoet, 2010) willingly or unwillingly, as well as to an invasion of an aquatic weed species (Eichhornia crassipes) (Ogari and Van der Knaap, 2002; Njiru et al., 2005). The fish species composition of the lake as it was known in the early 1900s consisted of a wide variety of species of the Tilapia and Haplochromis groups, including Tilapia esculenta and T. variabilis, catfishes, Lungfish and cyprinids (Geheb, 1997).
The number of haplochromines has been estimated by the Haplochromis Ecology Survey Team (HEST) at more than 300 with a long list of descriptions of species new to science in the period 1980–1995 (Van Oijen et al., 1981; Witte et al., 1992a, 1992b). In that same period, a fish meal plant was established in Mwanza (Tanzania), which was expected to turn large quantities of haplochromine fish (also called Furu or Fulu) into fish meal. The nets of the bottom trawler R/V Kiboko of the Tanzania Fisheries Research Institute caught all these varieties of cichlids for years until the Nile Perch, Lates niloticus, started to form part of the catches, and gradually took over from the haplochromines and became the dominating species in the catches (Ligtvoet and Mkumbo, 1990; Abila, 2000; Goudswaard, 2006). It became immediately clear that the fish meal factory was not going to produce much meal as the Nile Perch was not suitable for this purpose. The riparian fishermen populations were distressed by the appearance of this species as their valued target species were replaced by a predator that could not be processed in traditional ways. Their beloved Furu were threatened and fishermen were desperate, until ways were introduced to fillet the Nile Perch for export, mainly to Europe. This came at an opportune time as Atlantic Cod (Gadus morhua) was under heavy exploitation by European fishing nations and the Nile Perch appeared a good alternative, and much less expensive as well (Van der Knaap and Ligtvoet, 2010).
It is considered very positive that HEST discovered and described so many fish species before some became extinct or, at least, greatly reduced in abundance. Without the upsurge of the Nile Perch, however, numerous tonnes of the hundreds of Furu species were planned to be turned into fish meal. The construction of the fish meal plant coincided with that of a boat yard to build trawlers to fish the haplochromine species. These trawlers were built nonetheless in the forthcoming years, targeting Nile Perch that had become the dominant species in the catches. Trawlers were eventually banned from operating (Van der Knaap et al., 2002).
Can conservation of biodiversity contribute to poverty alleviation? The most logical response is naturally to state that if the ecosystem-based management is applied, including the ecosystem approach to fisheries (FAO, 2003), then equilibrium will be achieved and poverty alleviation as well as biodiversity issues addressed. Sustainable fisheries, rationally managed, including the conservation of biodiversity, will result in poverty alleviation, whereas, overexploitation will reduce the possibility to escape from the poverty trap. It may be concluded that transportation, fisheries, water supply, recreation and tourism, among others, may certainly contribute to poverty alleviation.
Willoughby et al. (1993) investigated the fish biodiversity underneath water hyacinth mats on Lake Victoria. The dissolved oxygen concentration below these mats appeared too low for the Nile Perch to forage and, thus, the floating weeds, although considered noxious by many, formed refugia for many a species threatened by the voracious predator. A total of 43 Haplochromis species were recognized at the time as hiding there, but also other fish species appeared abundant in this environment, particularly Tilapia, catfishes and Lungfish (Willoughby et al., 1993). Remnants of the original species flocks may still exist in the satellite lakes near Lake Victoria, where the Nile Perch had not been introduced yet (Katunzi and Kishe, 2009).
Balirwa et al. (2003) concluded that the heavy fishing pressure exerted on the Nile Perch may have enhanced biodiversity as some indigenous species resurged and that this, in turn, renewed the interest in combining fisheries sustainability and biodiversity conservation in management measures.
Institutions responsible for the collection of catch statistics for the Lake Victoria fisheries, faced many difficulties in terms of access to financial and human resources, and their data series were not always consistent, e.g. Kenyan data from the Fisheries Department and the Kenya Marine & Fisheries Research Institute were quite different (Cowx et al., 2003). Despite the suggestions for improvement and harmonization, the LVFO designed its own data collection system and sampling frequency, which resulted in some very high fish harvest figures. The production figures from the last decade show that the group of haplochromines re-appeared massively in the catch data, amounting to over 113,000 tonnes in 2005 and 146,000 tonnes in 2006, while the production in 2003 was little over one thousand tonnes (LVFO, 2013). This is quite likely due to a sampling inconsistency, albeit that the pelagic haplochromines may have recruited abundantly to the offshore waters of the lake.
At the time Nile Perch catches were increasing in the 1980s, nobody knew how to process or make use of this species. It was seen as a noxious animal eating away the unique biodiversity of the lake. By the time that almost all the haplochromine species susceptible to trawl nets were described, the Nile Perch had become so dominant that trawl catches were practically becoming mono-specific (Goudswaard, 2006; Witte et al., 2007). A trawl fishery developed rapidly in the three riparian countries, exploiting the Nile Perch. A group of scientists concerned about the potential loss of biodiversity encouraged the fishermen to fish out the perch (Barel et al., 1985). This appeared more complicated than envisaged and three decades later the Nile Perch still occurs in Lake Victoria despite the high fishing pressure (Van der Knaap et al., 2002; Njiru et al., 2005; Goudswaard, 2006; Johnson, 2010).
The three countries around Lake Victoria export ornamental fishes (Figure 2). Monticini (2010) does not provide any details on the waterbodies from where the species originated, but it is very likely that marine fishes are included as well. It may be concluded, however, that the countries around Lake Tanganyika export larger quantities of ornamental fishes, although this should be interpreted with caution as again, no details were presented on the originating waterbodies. It should be stated, however, that exporting firms exist along Lake Tanganyika's shores in Burundi, Tanzania, and Zambia.
Fisheries and biodiversity on Lake Tanganyika
Estimates suggest that Lake Tanganyika harbours at least 1,500 animal species (LTA Secretariat, 2012a), although species numbers vary from one taxonomic authority to the other. Approximately 600 species are endemic to the lake, including 245 morphologically diverse and colourful cichlid fish species (LTA Secretariat, 2012a). Lake Tanganyika is unique in harbouring endemic species clusters of bagrids, cyprinids, mastacembelids, and mochokids. Fish species of commercial interest are the Lake Tanganyika Sprat (Stolothrissa tanganicae), the Lake Tanganyika Sardine (Limnothrissa miodon) and the Sleek Lates (Lates stappersii) (LTA Secretariat, 2012a). An aquarium fish export sector exists but, due to limited numbers of international flight connections, this has not (yet) further developed. Also, the status of the many ornamental fish species remains unknown. Figure 3 presents the values of fishes exported from the four riparian countries in thousands of US dollars (compiled from Monticini, 2010). The database does not exclusively show that the fish originate from Lake Tanganyika. Fishes from other waterbodies may perturb the picture for Lake Tanganyika (e.g. the values for Tanzania are identical for Figures 2 and 3). Marine fishes may have also been included. The supply chain from Lake Tanganyika to the countries where ornamental fish are in demand is not well developed. In addition it should be noted that Thailand and the Czech Republic produce enormous quantities of cichlids from the African Great Lakes for the ornamental fish trade (Monticini, FAO, pers. comm.).
The ornamental fishes exported by the above countries originate from the wild and may contribute to the local economy. It should, however, be observed that breeding these species and exporting their offspring may be economically and environmentally a viable alternative to capturing fishes from the wild. Breeding programs of certain species may be of use to maintain the existence of threatened species for conservation, but also of endemic tilapia species for exploitation, e.g. the Tanganyikan Tilapia (Oreochromis tanganicae).
The main question remains how conservation of biodiversity and exploitation of fisheries resources can be combined. Due to the increased human population in the Lake Tanganyika basin, the number of fishermen has doubled in the past 15 years (Paffen et al., 1995; LTA Secretariat 2012b; Van der Knaap et al., in review 1). The main fishing effort is aimed at the pelagic fish resources but, in case the yields of these fishes are insufficient, then the effort will be directed to other species, mainly demersal ones including the endemic Oreochromis tanganicae.
The effects of fisheries may be observed from the species composition of catches. The Tiger Fish (Hydrocynus spp.) used to be common in the catches in the southern part of the lake and the African Tiger Fish (H. vittatus) and the Goliath Tiger Fish (H. goliath) were caught regularly. Particularly the latter, which may reach a weight of up to 50 kg, measuring 150 cm, has not been spotted in the catches from the lake for a long time. The river where H. vittatus spawns is heavily fished and long rows of nets prevent the fish from entering the lake. The removal of top predators from the lake definitely has its impact on the species composition and abundance of the lake (Coulter, 1991), although this is not easily measurable as data collection has been inadequate for many years. Another predator that has strongly reduced in abundance is the Lates mariae. The other two Lates species (L. microlepis and L. angustifrons) have become rare in the northern part of the lake, not only according to the fishermen, but this may also be concluded from the Burundian fisheries statistics. The relatively more abundant L. stappersii is under high pressure also and many fishermen resort to fishing gears exploiting the small-sized immature fish of this species. Coulter (1991) stated that with the reduction of Lates species, the abundance of the clupeid species increased.
Irrespective of the management measures that will be taken, it will be of paramount importance to involve the riparian fishing communities into co-management and through outreach programs (for instance through radio programs, mobile video presentations, flyers, etc.). Obvious management measures would be to limit the fishing capacity or to limit the access to the fishery resources. Banning the importation of illegal fishing gears is equally important. A specifically damaging gear is the beach seine. FAO (1999), Mölsä et al. (1999) and Reynolds et al. (1999) warned against the negative impacts of the beach seine. Since then the number of beach seines increased considerably (LTA Secretariat, 2012b) and, in case the authorities could efficiently ban the use of this gear, whose number is estimated to be of the order of 2000 (Van der Knaap et al., in review 2), then between 20 and 30 thousand fishermen and assistants would become jobless. Before such a measure can be implemented, sufficient alternative employment possibilities must be available (Van der Knaap et al., in review 1).
The Strategic Action Programme (LTA Secretariat, 2012a) mentions a total of 325 fish species that occur in the lake; however, there are some differences with other sources, e.g. Thieme et al. (2005) reported 287 formally described fish species in the lake itself out of 470 fish species in the entire Lake Tanganyika basin (Darwall et al., 2011).
It is of interest what the riparian countries of these two Great Lakes have accomplished in protecting the biodiversity in the lakes and their basins. The management of biodiversity is closely linked with that of fisheries resources and for these purposes the governments established the Lake Victoria Fisheries Organization (LVFO) (Mkumbo, 2002), the Lake Victoria Basin Commission (LVBC), and the Lake Tanganyika Authority (LTA) (LTA Secretariat 2012a). The conventions that established the above intergovernmental organizations have a strong emphasis on the conservation of biodiversity, including the control of exotic species. On Lake Victoria, the fish biodiversity could not be protected from the Nile Perch and Nile Tilapia (Oreochromis niloticus), as they were introduced before the conventions were put in place.
In the Lake Tanganyika basin, however, the Nile Tilapia had been recorded already, which is apparent from a species catalogue for Tanzanian freshwater fish, Burundian catch statistics and the author's observations in Zambia (Eccles, 1992; Fisheries Department, Burundi). Mulimbwa et al. (2010) described the presence of this species in the Nyangara wetlands in the Rusizi Delta in the Democratic Republic of Congo. The Lake Tanganyika Convention may permit access of exotic species under certain conditions, but the Nile Tilapia is already widely used in the Lake Tanganyika basin for aquaculture purposes and this may be further intensified. The LTA could, however, restrict the introduction of genetically modified Nile Tilapia strains. Sukmanomon et al. (2012) described interspecific introgression among GIFT (Genetically Improved Farmed Tilapia) and the introduction of such strains depend on the concurrence of all Member States of the LTA.
The Governments of Tanzania and Zambia have established national parks along the shores of Lake Tanganyika: Gombe and Mahale in Tanzania, and Nsumbu in Zambia, respectively (LTA Secretariat, 2012a). To assure the collaboration of the neighbouring fishing communities, certain access may be given to the fishing grounds adjacent to the parks. The communities in Tanzania are involved through the Beach Management Units; however, in Zambia, fishermen are expected to get special licenses to fish in the park area, but this system is not always adhered to and some poaching has been observed.
Van der Knaap et al. (2002) described the management measures that have been applied on Lake Victoria until 2002, including the successful banning of trawling on the lake. Although the destructive beach seine is officially forbidden on the lake, during the recent fisheries frame survey a strong increase in the number of this illegal fishing gear was observed, affecting negatively the recruitment of juvenile Nile Perch and destroying the breeding pits of tilapias and other cichlids (LVFO, 2013), thus shaping the biodiversity, which is different from and not richer than the original.
The governments of the countries around lakes Victoria and Tanganyika showed clear political will and commitment to protecting the environment of the lakes and their basins by signing conventions and by adjusting and harmonizing their legislations and fisheries management measures, all in the light of their commitment to assuring food security and reducing poverty. To achieve these objectives simultaneously, the entire lake ecosystem, including the watershed, should be managed and conserved. Ecosystem services are required to become sustainable for maximum benefit to the environment and the economy.
Various factors have contributed to reduction in the number of species in Lake Victoria. To bring the decline to a halt, the solution could be in treating the lake as a single ecosystem. The Nile Perch certainly played an important role in the disappearance of the native Haplochromis species but a number of other factors accelerated their demise also. In the period that the Nile Perch became dominant in the fish catches, taxonomic research on the haplochromine species flock was in full swing. It will never be known how many species disappeared from Lake Victoria due to the perch. Despite the high fishing pressure exerted on the Nile Perch, some haplochromine species considered extinct, reappeared in particularly the catches of small pelagics (Coulter et al., 2006; Van der Knaap et al., 2008; Njiru et al., 2010). Van der Knaap et al. (2008) and Njiru et al. (2010) recommended that proper taxonomic studies be resumed to obtain a complete inventory of the fish biodiversity in Lakes Victoria and Tanganyika.
It is recommended that the LVFO and LTA continue to encourage the implementation of fisheries management measures, involving fishing communities, particularly as far as the use of beach seines is concerned. For improved collaboration with the communities, continued outreach should be organized. It is also recommended to reduce the post-harvest losses of clupeid catches during the rainy season, particularly in D. R. Congo, to increase food security as well as revenues. It is further recommended to study the possibility of culturing the local Tanganyikan Tilapia, Oreochromis tanganicae, to prevent the Nile Tilapia (O. niloticus) from being used in cage culture on Lake Tanganyika thereby contributing to the conservation of endemic tilapia species. To increase the knowledge of (fish) biodiversity, it is recommended to prepare inventories of the aquatic taxa occurring in the lakes and their basins. It is also recommended that the research results be translated into conservation and exploitation policy for sustainable ecosystem service management.
The author expresses his gratitude to the Aquatic Ecosystem Health and Management Society in general and to its President, Dr. Mohiuddin Munawar, in particular for the invitation to deliver an Honorary Lecture on the occasion of the 20th anniversary of AEHMS, during the 10th AEHMS Conference in Sienna, Italy, from 13 to 15 June 2011. He is also grateful to the staff of the AEHMS for their continuing support in organizing the AEHMS and GLOW conferences.