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Nile perch and Lake Victoria - Counting on EEC research for their survival

by Andreas LAGGIS *

Lake Victoria, shared by Kenya, Tanzania and Uganda, is the largest freshwater body in the tropics and the third largest in the world, with a surface area of approximately 69 000 km2 and a shoreline which exceeds 3 200 km at 1 130 metres above sea level. Considering its size and biological productivity potential, Lake Victoria is not only an important fishery resource: according to recently published evidence, the lake seems to interact with certain large scale climatic phenomena and it may be proven to be a 'barometer' for changes reported as far away as Latin America.

Historically, the lake hosted a dynamic multiple-species fishery until the late 1970s in the form of the tilapline and haplochromine cichlids (60-80% of the catch composition) but also with important subsidiary fisheries of more than 20 genera of non-cichlid fish, such as mormyrids, catfish, anadromous cyprinids, lungfish, etc. The naturally occurring fish fauna was modified during the 1950s following the introduction of four non-indigenous tilapias and was further altered around the 1960s by the introduction of Nile perch (Lates niloticus). The objective of the introduction was to increase fish production for the increasing human population after the collapse of the fisheries of the endemic tilapias since Nile perch could feed on haplochromines, which were in abundance, commercially unimportant and almost regarded as a 'bash fish'. Of late, fish stocks in many parts of the lake are tending to be dominated by the two introduced species of Nile perch and Nile tilapia and one endemic cyprinid Rastrineobola argentea. Most of the traditional fish species, including the once abundant haplochromines, have either declined or almost disappeared from the commercial catch of the lake (Okaronon, 1990).

Despite all the above events, developments continue to take place with a view to increasing the exploitation of the fish resources of Lake Victoria, especially those of Nile perch. A number of fish processing and handling plants have been constructed a]ong the shores of the lake in order to supply appreciable quantitites of Nile perch to both internal and export markets. The liberalisation measures of July 1990 on trade, especially border trade between Uganda and Kenya, have further increased demand for fish and increased pressure on the stocks (Okaronon, 1990). During the 1960s and 1970s, the bulk of commercial catches (which, however, did not exceed 50 000 tonnes in total) was contributed by tilapline cichlids. Nile perch landings started to appear in the statistics only in the early 1970s and amounted to just a few hundred tonnes in 1977. A remarkable change in the fisheries of the lake occurred thereafter, with catches of Nile perch alone amounting to some 300 000 tonnes in the early 1990s and with tilapline landings inversely affected. The species which were introduced, though they have been in Lake Victoria for less than 40 years, have contributed to the highest catches ever recorded (total production from the lake now exceeds 500 000 tonnes of fish, more than 50% of which comes from Nile perch and approximately 15% from tilapias). In terms of greater availability of food, employment opportunities and financial return to the industry, the new fisheries regime has proved to be of tremendous value to lakeside populations and fish consumers within the three riparian states and the neighbouring region (Twongo, 1992).

The controversy over me introduction of Nile perch

According to some scientists the introduction of Nile perch into Lake Victoria has caused an ecological catastrophe. Others, investigating the effects of introducing alien species into established ecosystems, believe that it is never easy in ecology to ascribe cause and effect to provide a straightforward reply to this particular question. In fact, there have been successful introductions of alien species of fish into lakes in Africa: Limnothrissa introduced into the artificial Lake Kariba in Zimbabwe is a well-documented example.

Trying to determine precisely the effects of Nile perch on the other fish of Lake Victoria is extremely difficult, partly because many of the endemic species have never been accurately described, very little being known of their biology. Some may already have disappeared from the lake before the introduction of Nile perch without it ever being known to science. Certainly, the Nile perch cannot be blamed unreservedly for the decline of the haplochromine stocks in Lake Victoria. Haplochromines, according to the FAO, were already overfished in the lake. No-one denies, however, that the interlopers have had at least some effect and common sense suggests that their effect has been very great indeed as more than 90% of the haplochromine ichthyomass, which was recorded in 1974, is now missing from the lake.

The Nile perch is an opportunistic carnivore which can grow to over 100 kg in a few years and eats as much as would be expected for a fish of its size. It harmoniously co-exists with numerous other fish species in many African water bodies where it is endemic, like in Lakes Tanganyika, Turkana (Kenya), Albert (Uganda), Chad (Central Africa) and the River Nile starting from below the Murchinson Falls in Lake Victoria. These falls actually block its natural migration and colonisation into Lake Victoria's ecosystem (Acere, 1988).

Arguments against the introduction of Nile perch also have another scientific basis, namely that due to energy losses by the predatory fish, overall productivity in the lake will be down by some 60-80% of its potential if it were inhabited by plankton and detritus feeders such as haplochromines and tilaplines.

There is further room for discussion on this subject. However, what is most worrying of all is the hard scientific evidence that while the total catches from the lake appear to have been increasing during the 1980s, following the explosive increase in Nile perch stocks, the mean size of the individual fish caught from the lake has continued to decline during the same period. This means that the continued abundance of fish resources in the lake should not be taken for granted.

The need for further research

In view of this ambiguous situation, where there is an increased demand for fish and currently little knowledge as to the magnitude and potential of the available stocks from which this demand is to be met, it is increasingly necessary to establish a proper management system based on analysis of pertinent data with the aim of exploiting the fish resources of the lake whilst conserving the stocks.

Back in 1947, with the establishment of the East Africa High Commission and later its successor, the East African Community, some fisheries research and regulation programmes were organised on a lakewide basis under the East African Freshwater Fisheries Research Organisation (EAFFRO) based in Jinja. This organisation, with its fisheries research vessel IBIS; donated in 1968 by UNDP/FAO, was well equipped to be a good base of information on the ecology of the whole lake. Sadly, the East African Community collapsed abruptly in 1977 and all the research stations, equipment and vessels were taken over by the countries within whose boundaries they were positioned at the time of the collapse. This random distribution of assets, especially of the vessels, has been a source of discontent and mistrust ever since. In the subsequent difficult economic and political times much of the research infrastructure, including the IBIS vessel, has deteriorated and fallen into disuse, though the National Research Institutions still exist, even if they are ill-equipped.

As mentioned above, in about 1960, Nile perch was intentionally introduced into Lake Victoria in Uganda. Ironically, the explosive and controversial effects of this exotic introduction did not start to appear until about the time when the Community, and consequently the regional research programmes, collapsed. Information on the rapidly changing ecosystem came initially from the three poorly-equipped National Fisheries Research Institutes, while more recently the Dutch-aided HEST programme has been providing the only available data.

The EEC Lake Fisheries Research project was initiated in 1989, with a view, through financing and technical support in the fields of vessels, infrastructure, equipment, training etc, to helping the National Institutes around Lake Victoria fill this gap and carry on research projects.

National and international bodies agree that further research is urgently needed so as not only to understand but also to forecast the emerging changes in the fauna of the lake. The objective will be to establish a valid system of fisheries management.

While there is historical caution between Kenya, Tanzania and Uganda in terms of regional use of physical research infrastructure across state borders, there is demonstrable enthusiasm at the level of researchers for regionally planned research programmes and for regional cooperation in the sharing, analysing and interpretation of data. Recently, the neighbouring Lake Victoria governments have gone a step further in overcoming their differences by requesting the Commission of the European Communities to launch a new fisheries research project, and they have agreed to appoint Uganda's National Authorising Officer as the Regional Authorising Officer for the proposed project.

It is my personal view that this type of research project is an excellent area for regional cooperation with good prospects of being successful. It can demonstrate that scientists can revive the spirit of cooperation and coordination in relation to some of their common interests, which could bring identifiable benefits to all three countries. If fisheries research is continued and expanded, it will be possible to develop appropriate longterm policies and planning for the lake, which is of prime importance as a protein source to each of the three riparian countries. This will also embrace other shoreside development not restricted merely to fishing and fish processing.

Lake Victoria itself faces problems of asphyxia

Apart from its fishery aspects, Lake Victoria has a national and regional significance. There is industrial and urban development along the lake shores, agricultural activities, transport and so on. However, the development has been to a large extent badly planned and as a result there is widespread deforestation, soil erosion in the lake watersheds, agricultural pollution from pesticides and eutrophication from fertilisers and domestic and industrial effluents. There has also been mismanagment in the use of the fringe wetland zones and their reclamation for agricultural use. These have had, and will continue to have both direct and indirect effects on the lake environment and fisheries.

Lake Victoria is a bowl-like basin with an average depth of 40 metres and a maximum depth of 90 metres in a few places in the centre. Nutrients in the lake initially support greater primary production (phytoplankton), which in turn is grazed by zooplankton and other phytoplankton feeders to feed planktivore organisms like haplochromines and tilaplines which ultimately feed Nile perch and other carnivorous species found at the top of the food chain.

Excess fertilisation (eutrophication) will result in blooms of phytoplankton and water pollution and will primarily affect the composition of phytoplankton and develop one-species types (sometimes toxic) of blooms of monstrous proportions which often 'get out of hand'. High-generation turnover results in vast amounts of these plankton blooms dying and sinking to the bottom where they are decomposed by bacteria before being taken by the planktivore or detrivorous species. In deep water, where oxygen transport through diffusion, vertical movement of water or photosynthesis is insufficient, dead organic matter accumulates at the bottom and provokes oxygen depletion from the bacterial action. Thus, oxygen is removed from the lower depths, creating a gradually expanding death zone of water now some 40 metres thick. Fish swimming in this zone are asphyxiated and die.

Although records of fish kills date back to the 1920s, these is evidence that they have been increasing in recent years. In 1987, a research study conducted by life scientists showed that thousands of fish, including the exotic Nile perch, had died in mass quantities in Lake Victoria, reportedly due to low levels of dissolved oxygen. Similar disasters occurred several times afterwards and thousands of different fish species died due to the same cause, oxygen depletion and/or pollution.

Quite recently, another unforeseeable event, closely associated with the nutrient enrichment of the waters, is having a direct influence not only on man's activities (e.g. fishing and transport) but also on the lake itself. Tremendous quantities of floating aquatic macrophytes (mainly the exotic water hyacinth) have proliferated at an enormous rate in the shallow sheltered inshore areas of the lake. Water hyacinth quickly reaches pest proportions, causing constriction of wind-induced water movements, buildup of anoxic levels below the plant mats, excessive losses of water through evapotranspiration, and then, as it dies and sinks as detritus to the bottom of the lake, increases the organic load and anoxic conditions in wide areas at the bottom of the lake. New approaches to reduce the problem in recent years, using biological control methods or other means, have shown good results. An accurate assessment of the extent of the problem, particularly for the artisanal fishing communities, followed by trials to develop control strategies in selected locations, may provide solutions.

The danger posed by the spread of water hyacinth in Uganda's lakes has attracted the interest of the authorities and a workshop was organised in Kampala in October 1991 under the auspices of the FAO. The aim of this workshop was to raise public awareness of the problem and draw on available expertise in the various fields to help develop a National Action Plan for water hyacinth control.

A new role for the public sector?

In conclusion, it is obvious that the problems associated with the introduction of exotic species into Lake Victoria or the pollution phenomena could in the near future have tremendous consequences for the 30 million human beings living around the lake. Facing up to these ecological changes is urgently needed if the ecosystem is to stand a chance of being stabilised. Measures should not only extend to the valuable fisheries resources but also include reafforestation programmes as well as the protection of the shoreline swamps and wetlands to halt the flow of sediments and to filter the pollutants from the runoff.

It is my feeling that tackling the problems of this aquatic environment presents a good opportunity for both national and international organisations to pursue their development objectives by stimulating fisheries and for other relevant departments to view the fisheries sector in a more holistic way having regard to its interactions with other sectors. Projects in this direction would assist the public sector in developing countries in finding a new role to play, in widening its interests beyond the production sector and looking at lakeshore, river or coastal fishing communities in a much broader community-based way.

A.L.

References

- Acere, T.O., The controversy over Nile perch Lates niloticus in Lake Victoria, Naga, The ICLARM Quarterly, October 1988.

- Okaronon, J.I., Future prospects of the fish stocks of Lake Victoria, Uganda, Food and Agriculture Conference, Kampala, 1990.

- Okaronon, J.O. and Wadanya, J., Fishery resource base for the Uganda sector of Lake Victoria; IFP Report RAF/87/099/TD/31/92 (En), 1992.

- Twongo, T., Management issues, options and strategies for Lake Victoria fisheries, IFIP Report RAF/87/099/TD/ 31/92, 1992.