The Nile perch (Lates niloticus),2 was reportedly transplanted into the Ugandan waters of Lake Victoria in the late 1950s and early 1960s (EAFFRO 1960; Hamblyn 1960).3 The question of whether or not to introduce this large, predatory fish sparked considerable controversy (Anderson 1961; Fryer 1960; Jackson 1971; Ogutu-Ohwayo 1985; Ribbink 1987; van Someren 1963). Opponents pointed out that such a step made little ecological sense: the theoretical potential sustained harvest from predatory fish (at the top of the food/energy pyramid) is significantly less than from their prey (typically represented at the middle or lower levels of the pyramid). Others argued that Nile perch, feeding on the huge but relatively unexploited and unpopular species stocks of haplochromine cichlids, would eventually provide the Lake with an important new fishery. Indeed, certain reports give the impression that Lates was first introduced with just such an objective in mind (e.g. Acere 1985). However, the circumstances of its original appearance in the Uganda part of the Lake, first noticed in May 1960 even as the debate on transplantation continued, still seem somewhat mysterious (Achieng' 1986; Beadle 1981; Hughes 1983). The fish was subsequently introduced deliberately on two occasions, in 1962 and 1963 (Gee 1965).4
From its points of introduction in Uganda waters, Lates gradually dispersed in a mostly “clockwise” (east-south-west-north) movement around the lakeshore. In the early 1970s it began to colonise the fertile, multispecies fishing grounds of the Nyanza Gulf in Kenya. Here, in less than a decade, it established itself as a major component of the fish population. This process of gradual incursion and trace occurrence followed by explosive growth has been repeated elsewhere. A few Nile perch were reported further to the south in Tanzanian waters as early as 1964 (EAFFRO 1965; Gee 1965). Catches remained incidental around Musoma and Mwanza through the 1970s, but by the early 1980s it was obvious that Lates was rapidly proliferating all along the southern lakeshore (cf. Acere 1985; Arunga 1981; Barel et al. 1985; Bwathondi 1985; Goudswaard and Witte 1985; HEST 1986; Hughes 1983; Mainga 1981; Ogutu-Ohwayo 1985; Okemwa 1981, 1984; Ssentongo and Welcomme 1985; Wambayi 1981).
The controversy over the role of Lates in the Lake has intensified with its proliferation across ever wider areas. Developments have also been popularised in the press, sometimes in rather exaggerated terms. Lines of argument are not always hard and fast, but observer opinion can be roughly divided between those who regard the Nile perch introduction as a great calamity, and those who take a milder or more positive view, noting certain benefits that the new population of fish may bring over time.
B.2. IMPACT OF NILE PERCH: DISRUPTIVE EFFECTS
Some authorities consider that disastrous and irreparable harm has been caused to the Lake fisheries by Lates. Its voracious habits have drastically reduced the stocks of a rich and varied indigenous fish fauna, especially amongst cichlid herbivores and detritus feeders. It is argued that these latter species represented important subsistence and commercial resources for lakeside population and provided ecologically efficient fisheries, since short food chains were involved (Barel et al. 1985; Fryer 1972, 1986; cf. Haines 1985; Payne 1987; Ribbink 1987).
The spread of the new predator amounted to an extremely rapid succession. One veteran critic of the Nile perch transplantation has described this succession in terms of the sudden loss of “enemy-free space” for endemic species, indicting at the same time those responsible for this loss:
The importance of enemy-free space is sometimes unequivocally demonstrated when it is lost; that is when predators are introduced. In some cases extinction follows. The arrival of enemies to whose form of attack prey species have had no time to adapt also sometimes indicates that enemy-free space exists in complex communities. A dramatic example is provided by the depredations of the criminally introduced Nile perch, Lates niloticus, on the endemic haplochromine cichlid fishes of Lake Victoria, many species of which have virtually disappeared from areas in which this predator has become established [Fryer 1986:290-1].
Barel et al. (1985:20) have summed up the negative consequences of Lates in terms which suggest that the fish is a veritable curse for the Lake:
The establishment of Lates is not only an economic and ecological tragedy but an enormous loss to evolutionary biology. Lake Victoria is the site of a remarkable radiation of cichlid fishes which has given rise to several hundred endemic species….and the loss of these fishes, often before their biology has been elucidated, is incalculable [1985:20; cf. Coulter et al. 1986].
It is claimed that Lates, insatiably dominating the food chain of the Lake, has achieved the untenable position of making up most of the fish biomass in some areas. Furthermore, having exhausted other food sources, they are reportedly turning to auto-predation to sustain themselves (Barel et al. 1985; Hughes 1983; Ogari 1985; Payne 1987).
In Kenya's Nyanza Gulf, for example, Nile perch is now said to be totally dominating the ecosystem, constituting something over 80% of the fish biomass: “The change is from a richly polyspecific, trophically diverse system to a virtually monospecific, trophically restricted system, dominated by Lates and its predatory and competitive interactions” (Hughes 1983:55; cf. Barel et al. 1985; Ogari 1985).
While the proliferation of Nile perch has led to enormous catch levels for local fisherfolk in many places, critics argue that prospects are poor because of: continued eradication of other fish stocks as food sources; increased removals of juvenile Lates due to beach seining operations; and the cannibalistic tendencies of large Lates (Hughes 1983; Barel et al. 1985).
Indeed, dire forecasts have been issued based on these interpretations of trends in the Lake Fisheries. Such “doomsday” thinking would simply have Lates eating all available prey in the Lake (ultimately including its own stock through autopredation) up to the point of its own disappearance. A process of increased trophic instability and breakdown attendant upon the demise of the speciose community of cichlid and other fishes - planktivores, detritivores, algal and other specialised feeders - would ultimately result in lacustrine ecological system collapse (Ribbink 1987; cf. CIFA 1985).
As a partial remedial measure, many experts have suggested that selective fishing for Lates be intensified. The idea would be to help reduce pressure on endemic stocks of small cichlids and allow some recovery of their fisheries. It is also proposed that such efforts be supplemented by the establishment of aquatic reserves or conservation sanctuaries (Coulter et al. 1986; cf. Jackson 1973), and by the captive propagation of endangered species to secure evolutionary continuity (Ribbink 1987).5
An array of further socioeconomic disruptions, both actual and potential, has been associated with the proliferation of Lates. Consumers and fishermen are said to resent Nile perch for devouring other fishes traditionally preferred around the lakeside, and for damaging nets set for smaller fish (Barel et al. 1985; HEST 1986; Mainga 1981; Oyugi Aseto 1979). Also, Nile perch is alleged to be locally unpopular as food because of its taste and texture, and possibly because of beliefs about its habits and associations (Barel et al. 1985; Bwathondi 1985; HEST 1986; Mainga 1981; Okemwa 1984, 1985; cf. Leemans and Kors 1985).
The further point is made that Nile perch, because of its comparatively big size and oily flesh, is difficult to preserve in the old ways (sun-drying and light smoking of whole fish) used for other, traditional species. Local processors have adopted the practice of cutting larger fish into pieces either for smoking or to be fried in their own fat. Such processing techniques require vast amounts of firewood, and are therefore leading to widespread deforestation and severe shortages of fuel supplies (Balarin 1986; Barel et al. 1985; Coulter et al. 1986; HEST 1986; Payne 1987; Vonk 1986).
Distribution and marketing problems are also cited. Lates catches are said to glut local markets and fetch poor prices (Barel et al. 1985). In addition, they are difficult to sell further afield since this involves arrangements beyond the means of most local operators and co-operative organisations (Hansen 1981; Kongere 1979; Roach 1974; cf. INFOFISH 1986; Payne 1987).
Fears are expressed that the Lates “boom” is threatening to displace poorer fisherfolk not only because of the loss of other fish stocks, but because production is tending to concentrate in the hands of wealthier entrepreneurs -- the ones who can best afford the heavier investments in gear needed for successful exploitation of Nile perch (Barel et al. 1985; Prazmowski 1987; cf. Payne 1987).
The projected expansion of capital-intensive, industrial-level operations in Nile perch processing and marketing could result in massive transfers of fish protein supplies away from food deficit areas to serve the lucrative urban and export markets (cf. Bwathondi 1985). This might also lead to heightened displacement of small-scale fish distributors, mostly women, who currently depend on the trade as an important source of income (cf. Jansen 1973; Kongere 1979). Finally, involvement of large firms directly in capture operations on an industrial scale (trawling) could severely marginalise artisanal fisherfolk, in addition to rapidly depleting fish stocks (Comte 1982; Mainga 1981; cf. Butcher and Colaris 1975).
B.3 PRESS REPORTS
Concern raised about Lates in scientific circles has been echoed and amplified in press accounts and the publications of various conservation organisations. Numerous articles on the subject have appeared in newspapers the world over (see Appendix D for a partial listing), though much of what is printed consists of extracts and reiterations of information from a few basic sources. Because these are generally the same sources which have provided alarming descriptions of Lates' destructive impact on the ecological and human welfare settings of the Lake, the weight of testimony given in press reports on Nile perch has been overwhelmingly in the negative.
Thus, for example, tropical fisheries experts are quoted as saying that the introduction of the fish into Victoria waters amounts to “…the biggest disaster to affect the Lake since the Pleistocene era, when it dried up” (P.H. Greenwood (1966) as cited by Ngaiza and Timberlake 1985). Scientific studies are invoked in order to project Lates as a kind of aquatic harbinger of doom:
The idea that this enormous predator could co-exist with other species native to the lake has proved tragically faulty. [Nile perch] are now cannibalising their own kind, having reduced populations of most of the lake's 300-plus other species to a fraction of their pre-1970 size. There is no reason to suppose this trend will ease before most of Lake Victoria's native fish species (many of which are unique to this one water) have been wiped out [Lamb and McHugh 1986]
Nile perch have been damned in the press with such epithets as “the scourge of Lake Victoria,” “elephants of the water,” “vacuum cleaners,” and the “piranha of Africa.” They are treated as “monsters” (specimens close to 200 kg. have been reported), eating their way through the Lake waters at the expense of everything else. Headlines proclaim such news as “Nile perch devours smaller species out of existence,” “The fish that is eating out a lake,” “The glutton of Lake Victoria,” or “Nile perch causing death and decay in Lake Victoria.”6 Finally, press accounts repeat the allegations reviewed above about how life in local communities is being disrupted and ruined by Nile perch due to consumer dislike of the fish, deforestation caused by the preservation techniques that must be used, distribution and marketing problems, and the marginalisation of small-scale fishing operators.
B.4 IMPACT OF NILE PERCH: ALTERNATIVE VIEWS
Other assessments of the situation are less catastrophic in outlook, and credit the introduction of Lates as a positive development for the Lake area.
Lates may not be solely responsible for declining catches of certain popular fish species over recent years. Over-exploitation with small-mesh nets is often cited as the principal cause. Additional factors include the impacts of other sorts of human intervention and various natural phenomena. Episodes of sudden mass fish mortalities, for instance, have been attributed to pollution, algal blooms, and/or rapid deoxygenation following the mixing of stratified water layers during violent storms (Bwathondi 1986; cf. Ochumba 1985; Wandera 1986). Flooding, agricultural activities and attendant destruction of fish breeding grounds, and the introduction of other tilapiine cichlids may have played some role in fish stock declines as well (Bwathondi 1986; cf. Acere 1985; Fryer 1973; Jackson 1971; Kibaara 1981; Kongere 1979; Mainga 1981; Marten 1979; Okemwa 1984; Ssentongo and Welcomme 1985; Wambayi 1981; Wandera 1986; Wanjala and Marten 1974; Welcomme 1969; Whitehead 1958, 1959).
Such developments were noticeable before the presence of Nile perch became significant. In some cases signs of decline, principally blamed on overfishing, were reported as early as the 1920s (Graham 1929; cf. Beauchamp 1955; Beverton 1959; Garrod 1960, 1961; Mann 1970; Ogutu-Ohwayo 1988; Wambayi 1981).
Whereas some previously important commercial and subsistence target species have recently declined, sometimes drastically, the total yield in parts of the Lake at least has shown an increasing trend. This is due to greater catches of Lates, the small shoaling fish known locally as dagaa or omena, i.e. Rastrineobola argentea (=Engraulicypris argentea), and the introduced Oreochromis niloticus (=Tilapia niloticus) (Arunga 1981; Balarin 1986; Coche and Balarin 1982; Kongere 1979; Mainga 1981, 1985; Okedi 1981; Ssentongo and Welcomme 1985).
While it is clear that the introduction of Lates has wrought serious disruptions on the fisheries, it would now be virtually impossible to eradicate them from Lake Victoria waters (cf. Barel et al. 1985; Bwathondi 1985; Ribbink 1987). However, the eventual resolution of predator-prey relationships may be quite a long-term process; furthermore, even though this process would almost certainly involve a decline of Nile perch from the present high levels, the outcome might still be such as to provide for the sort of multispecies fisheries as exist in other waters where Lates species are endemic (Acere 1985; Arunga 1981; Coche and Balarin 1982; Okemwa 1984).
Also in a more positive vein, it has been noted that certain valuable food fish have avoided predation by Lates apparently by occupying separate niches in the Lake environment (O. niloticus), or have thus far proved less sensitive to predation (R. argentea), perhaps due in part to heavier fishing pressure on Lates itself (Arunga 1981; Okemwa 1981, 1984; cf. Witte and Goudswaard 1985).
It may also be that the use of heavier and larger mesh size nets by some local fishermen for capture of Nile perch is having the effect of permitting the escape of the smaller endemic species of traditional food fishes and hence rebuilding these stocks (Achieng' 1986; Arunga 1981; Ssentongo and Welcomme 1985).
Such “retooling” of gear and mesh sizes is one way in which local fishermen have adapted to the changes in Lake fisheries and started to exploit the new opportunities available. New methods of fish processing, the filleting and frying of Lates before marketing, are other indications of such adaptation (cf. Arunga 1981; Coche and Balarin 1982; HEST 1986). Furthermore, contrary to what is widely publicised, some observers contend that Nile perch has become a more acceptable item in local diets, (Arunga 1981; Coche and Balarin 1982; Ogutu-Ohwayo 1988). It is also noticed that the use of Nile perch by-products for cooking fat, medicines, and soap-making has become common (Bwathondi 1985). Finally, it is emphasised that local fisherfolk have enjoyed much-enhanced levels of income through Lates sales (Arunga 1981; Balarin 1986; HEST 1986; Ogutu-Ohwayo 1988).
As for long-term prospects, several observers in recent years have taken the view that the Nile perch fishery offers considerable scope for expansion (Arunga 1981; HEST 1986; INFOFISH 1986; Kongere 1979; Mainga 1981; Ogutu-Ohwayo 1988; Okemwa 1984). In this connection, however, it has been recognised that (a) there are inefficiencies in present methods of capture and marketing (Mainga 1981) and (b) some balance will need to be struck between the interests of an expanded and improved artisanal fishery for Nile perch and the larger scale operations which are beginning to make their presence felt in the Lake (Comte 1982; Mainga 1981; cf. Butcher and Colaris 1975 for earlier comment).
B.5 SUMMARY: THE CONFLICTING TESTIMONY ON NILE PERCH
It can be appreciated from the above review of fisheries literature and press articles that there are different, and at points, markedly conflicting assessments of the Lates presence in Lake Victoria. Opinion is broadly split between two camps, and can be briefly summarised as follows.
Those who censure the Nile perch introduction argue that the fish has proved to be an unmitigated disaster for the Lake.
Ecological balances have been thrown into severe disarray and endemic fish stocks, representing crucial subsistence and commercial resources for human communities as well as invaluable objects of biological study, have been wiped out.
Local people resent Nile perch for destroying traditional and preferred food fish stocks, ruining fishing gear, being an unpleasant food in itself, and having a poor market value.
The preservation techniques which are commonly used on Nile perch to prolong the storage life (smoking and frying) are leading to widespread fuelwood shortages and deforestation around the lakeshore.
Nile perch is displacing or threatening to displace huge numbers of small-scale fishermen and traders due to the damage it causes to other fish stocks and because richer and bigger operators are coming to dominate its fishery.
In alternative readings of the situation, Lates is certainly recognised as a disruptive element but its fishery is judged to have positive attributes.
The decline of endemic species stocks is not necessarily due only to the introduction of Nile perch. Overfishing has been especially significant as a cause of such decline. Other factors that need to be taken into account include fluctuating water levels, episodes of mass fish mortalities brought on by sudden environmental changes, damage to breeding grounds, etc.
Overall fish yields have not declined. They have in fact increased for local fisherfolk due to a switch to other target species, including Nile perch.
It is not certain how fish stock balances will adjust themselves in the long term, but a multispecies fishery may still be maintained. In the meantime, increased selective fishing for Lates may actually be helping to conserve and rebuild other species stocks.
Nile perch has developed into an important fishery in its own right, and lakeshore communities are benefitting from higher catch levels and greater economic returns. Also, the fish and its by-products are proving more acceptable to local people than previously reported.
Does Lates ultimately amount to a boon or a bane for Lake Victoria and the people who rely on its fisheries? Obviously controversy over the “Nile Perch Question” involves a complex of issues, perspectives, and interests. This background discussion is intended to set the context for the more detailed country reviews presented in the main part of the mission report. The various arguments are weighed further in the concluding section (5.1) which follows these accounts of experiences within each of the riparian states, and of the findings from the mission field visits around the lakeshore.
Some parts of this report draw upon material presented in an earlier document submitted to the FAO through the Kenya Lake Basin Development Authority in February 1987 (Reynolds 1987).
Nile perch is commonly known as mbuta in Kenya, mputa in Uganda, and sangara or chengu in Tanzania. The Victoria Lates is treated as Lates niloticus in most of the literature, but questions about taxonomic status -- whether more than one species is represented -- have been raised (Bwathondi 1985; Goudswaard and Witte 1985; Ribbink 1987).
It has been suggested by some commentators that the placing of Nile perch in Lake Victoria actually constituted a re- introduction. Miocene fossil deposits of Lates have shown up on Rusinga Island at the entrance to Nyanza Gulf, indicating that the genus had an ancient occurrence in the region. The claim of continuity is tenuous. The former Lates inhabited a prehistoric and totally different lake or lake system which existed before the formation of the present basin structure. The modern lake is thought to have been created as a result of tectonic upheavals and hydrological changes over a period extending until the late Pleistocene, perhaps 25,000 – 35,000 years B.P. (Acere 1985; Arunga 1981; Beadle 1981; Greenwood 1966).
While then contemporary official sources indicate that introduction took place in the late 1950s-early 1960s timeframe, it is more recently claimed by the writer of a letter appearing in the Kenya Standard newspaper (22 July 1986) that Nile perch were actually introduced to Victoria waters as early as 1954. The writer, a former government fisheries officer then stationed in Uganda (pers. comm.), asserts that he himself assisted in the original transplant operation, which he says was carried out with the clearance of the Uganda fisheries authorities at the time. Elsewhere there is testimony to the effect that senior Uganda Department of Game and Fisheries officers transplanted Lates from Lake Albert to points above the Murchison Falls at various times in 1954, 1955, 1956 and 1957 (Kinloch, 1972). Stockings took place in the upper Nile below the Owen Falls Dam (completed in 1954) where Lake Victoria spills out into the river, as well as lower down on Lake Kyoga. It would have been quite easy to introduce Lates into Lake Victoria at the same time as the upper Nile stockings were taking place.
The Cichlid Workshop group of the Fifth Congress of European Icthyologists (August 1985, Stockholm) formulated several resolutions about steps to be taken to save the native fish communities of Lake Victoria (Balon and Bruton 1986). These are noted as follows.
Recognizing that never before, man in a single ill advised step placed so many vertebrate species simultaneously at serious risk of extinction and also, in so doing, threatened a food resource and traditional way of life of riparian dwellers, we, of the Cichlid Workshop, resolve to engender support through the Secretary to the Union of European Ichthyologists and by individual endeavour to conserve the fishes of Lake Victoria.
To win time for those species which are at present facing extinction, as many species as possible should be placed in gene banks (using cryopreservation techniques and holding these species in aquaria).
To reduce drastically the populations of the introduced Nile perch, intensive selective fishing should be carried out and, simultaneously through research a practical biological control method for the Nile perch should be sought.
The species held in gene banks should be reintroduced in the Lake when the Nile perch stock has been reduced to levels at which native populations may be maintained substantially.
Recognizing that the goal achievement outlined above is dependent on an ability to identify exactly the species which are currently threatened, it is clear that a greatly increased research effort is essential. The meeting resolved to recommend that funding and personnel for such research be found as soon as possible.
Recognizing the extreme vulnerabiltiy of species within the Lake and realizing that gene banks are not entirely safe refuges for species, the meeting recommended that comprehensive museum collections should be made as soon as possible to form permanent records of the existing diversity in Lake Victoria.
6. See the listing of press articles in Appendix D for a selection of epithets and depictions such as those noted. An account entitled “Nile Perch Causes Death and Decay in Lake Victoria” (“Nijlbaars Zaait Dood en Verderf in Victoriameer”) appeared in the Netherlands newspaper De Telegraaf of 4 January 1986. The same paper printed a piece on “The Glutton of Lake Victoria” (“De Veelvraat van het Victoriameer”) in its issue of 30 August 1986.