The Declining Fish Numbers In Lake Victoria Environmental Sciences

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Lake Victoria is an international water body that offers the riparian communities a large number of extremely important environmental services. Lake Victoria is the world's second largest fresh water lake with a surface of 68,000km2 and a catchment area of 284,000km2. the lake Victoria basin is arguably the most important of Africa's water basins which is shared immediately by 3 countries which are Kenya, Uganda, and Tanzania each controlling 6%, 45% and 49% respectively of the lake surface. Lake Victoria faces considerable stress due to environmental damage to catchments areas, industrial and human pollution, excess algae proliferation and hyacinth infestation which has led to a great decline in fish stock.


The current decline in fish catches in the Kenya as well as in the world, in addition to an increasing Kenyan population has exacerbated the scarcity of fish. Competition for fish between the domestic and export market is rather unequal and the drive to sell fish overseas has resulted in reduced local availability. Lake Victoria's renewable resources are in steep decline most notably the quality of water and the quantity of various species of fish. Over the past three decades or so, the lake has come under increasing and considerable pressure from a variety of interlinked human activities such as over fishing, species introductions, industrial pollution, eutrophication, and sedimentation. In this paper we examine the root causes for, attack by hyacinth, over fishing that has led to increase in export market over domestic market and industrial pollution in Lake Victoria. The fish catch in the lake has exploded in the last 3 decades with the rise of export oriented commercial fishing where the overall number of fishermen grew by 30% between 1973 and 1999 and the number of boats increased by 266%. The weed hyacinth which is a dangerous free floating weed reproducing rapidly and covering any uncovered territory. It blocks sunlight for organisms below depleting the low concentrations of oxygen and also allowing poisonous gases such as ammonia and hydrogen sulphide to accumulate and this has led to great reduction of fish stock in Lake Victoria.

OBJECTIVESGeneral objective

The general objective of the research is to identify the extent to which fish in Lake Victoria basin has reduced to in the past few years.

Specific objective

The specific objectives of the research are?

To identify the extent to which hyacinth has led to the reduction of fish stock in Lake Victoria basin.

To identify the extent to which increase in export demand for fish has led to the decline in fish stock in Lake Victoria basin.

To identify the extent to which industrial pollution has led to the decline in fish stock in Lake Victoria basin.


This chapter contains past studies in the area of study.

The East African Community (EAC) has raised fresh concerns over increasing pollution and diminishing resources in the Lake Victoria basin. Environmentalists are unanimous that threats on the Lake's flora and fauna have stressed its ecosystems. The increased population density of the riparian communities, estimated at 33 million from 30 million less than five years ago, is adversely affecting the basin. The annual population growth rate, which stands at 3 %, has resulted in over-fishing. Fisheries researchers are concerned about the decrease in fish biodiversity and altered food webs in the world's second largest fresh water lake. Most alarming is the disappearance of over 300 fish species that had previously dominated the lake. Nile perch, Tilapia and omena are the only remaining species, yet they too are under constant threat of extinction. Over 200 environmentalists attending a three-day regional workshop in Kisumu are unanimous that the noxious water hyacinth has affected the Lake's ecosystem. The weed, which doubles in 11 to 18 days, occupies over 17,000 hectares and nearly 90 per cent of the shoreline in Kenya, interfering with fishing and transport services. The hyacinth has led to increased water loss, destruction of fishing grounds and and also leading to a decline in the fish stock in the Lake Victoria.

Kenya Marine and fisheries research Institute researchers- Dr, Richard Abila, Andrew Asila, Kenneth Werimo and Dr. john Gichuki- says the decline in biodiversity in Lake Victoria is alarming. "There is a concern over widespread loss of biodiversity most affected are fisheries, forestry and range of wild flora and fauna." says Abila. In a study, applied Research Programme for the Lake Victoria Basin, the researchers have raised alarm over water levels and climatic changes, open access policy to most natural resources and invasive new species.

"Over-fishing, invasion of exotic species and assorted human activities are among the major factors threatening decreased biodiversity of the basin", says Abila. "Insufficient scientific knowledge of how fish species may adapt to the changing environment of the lake contributes to the decline," he adds.

The experts warned of a looming environmental disaster following unfriendly land use patterns impacting negatively on forest covers, wetlands and riverbanks. Uncontrolled destruction of vegetation, human settlements, forest fires, mining activities, and overgrazing raise environmental concerns.

Lake Victoria Vision feedback consultant, Gertrude Kopiyo, who presented a paper on behalf of EAC, raised the red flag on over-fishing. "More than 500,000 tonnes of Nile Perch and other species from East Africa are exported or supplied to local markets annually despite the decline in catches," She said

"Fishermen go to the extent of using poison to catch fish, which is detrimental to declining stocks and breeding areas," she added. The EAC studies reveal perpetual decline of fish stocks, sizes and species due to illegal fishing practices in the 1950s," said Kopiyo. "Water quality, nutrient cycling and altered food web structures consequently lead to a decrease in fish quality."

Experts say poverty impacts negatively on the Lake as half the population of the riparian communities live on an income of less than a dollar a day.. "High levels of illiteracy, inappropriate skills for production and income generating activities remain impediments to efforts to improve the lake's ecosystem, "says Kopiyo.

(Powell 1977) In Lake Victoria, several important fish species have declined recently, particularly tilapia, Protopterus aethicopicus, Clarias, mossambicus, and Bagrus docmac.

(Maten 1979). Further decline of fish species such as Sarotherodon esculentus, Barbus, labeo, Alestes and Mormyrus have been reported.

(Hynes 1963). The need for baseline data on pollution studies to the aquatic biota of Kenya lakes and rivers is therefore of utmost importance. Baseline data is prerequisite to pollution evaluation. Since even "natural" streams may show the characteristic signs of pollution, that is, "natural" pollution may also faithfully reproduce the effect of the addition of industrial pollutants to water.

(Tellefson 1961) Statistics on fish catches, both commercial and sport, have often been used to show that pollution is the cause of declining catches. Fisheries statistics indeed are valuable tools in assessing the effects of pollution, but they must be complete and must be considered along with other factors in order to avoid unreliable conclusions.

(Camp and Meserve 1974). Elsewhere, excessive pollution of rivers, lakes, and tidal estuaries by sewage and industrial wastes has resulted in deterioration of commercial fishing, fish kills, and injury to water fowl. The damage to water fowl results from the destruction by pollution of the feeding and breeding grounds. This may be brought about by soils, greases, foams, insecticides, and excessive depletion of dissolved oxygen by decomposing organic wastes.

(Beetin 1965) In some parts of the world, the tonnage of commercially important fish has been reduced drastically over the past 50 years. This has been attributed to the more desirable fish species being unable to spawn in the glossily polluted tributaries.

(Ethan 1970) In Lake Victoria, several important fish species have been showing a declining trend. Scientific literature is replete with reports of studies of the aquatic environment and its inhabitants. Fish are usually employed as sensitive indicators of toxic pollution. The dissolved oxygen is of utmost importance to aquatic life, since it determines whether or not the water can sustain a desirable variety of aquatic organisms.

(Bukenyi 1979) Quite a large number of potentially harmful metals and elements are known pollutants. Heavy metals are very rapidly trapped in biological systems and many accumulate in the sediments. Aquatic plants (e.g., algae) are also known to accumulate heavy metals.

(UNESCO 1972) The discharge of domestic sewage with varying degrees of treatment into lakes and rivers may lead into major qualitative and quantitative changes in the biota. The water may become a health hazard, uninhabitable by desirable fish or aesthetically unpleasant. The symptoms of stress in fresh water bodies caused by loading with treated or untreated sewage are outlined below:

1. Low dissolved oxygen levels caused by biological oxidation of organic matter and increased concentrations of refractory organic matter in this water.

2. Stimulation of algae growth and shift of algal type to obnoxious blue greens. This may lead to large accumulations of algae, often characterized with massive production of floating algal scum. Later as these decompose, and dissolved oxygen levels will be lowered.

(UNESCO 1972) The appearance of new synthetic compounds such as poly-chlorinated biphenyls (PCB) and changes in distribution, concentration and form of naturally occurring substances, e.g., zinc and cyanides in the environment due to the disposal of industrial wastes has led to increased and differential mortality of populations, impairment of reproduction and disruption of species composition and balance.

(Stumm and Morgan 1970). Industrial effluents comprises of several pollutants including heavy metals, some of which are extremely toxic.

(Hynes 1973) Industrial effluents which contain only chemical reducing agents, e.g., ferrous salts or sulphides, take up oxygen by purely chemical action. They do this rapidly exerting what is sometimes known as immediate oxygen demand.

Mailu's (2001) report Water hyacinth mats invaded fishing grounds and blocked waterways. For the individual fisherman, the hyacinth mats reduced their catch by covering fishing grounds, delaying access to markets due to loss of output, increasing fishing costs due to the time and effort spent clearing waterways, forcing translocation, and causing loss of nets.


Through its contribution to the literature and research on decline of fish stock case study of lake Victoria, this study was anticipated to present better knowledge on how the fish stock in lake Victoria has declined and could be used to help the fisheries ministry in coming up with ways in which to curb the current crisis in Lake Victoria.


The economic that is adopted is that the decline in fish stock is the dependent variable, which depends on the amounts of hyacinth weed, export demand for fish and the industrial pollution in lake Victoria.


Where: Y- decline in fish stock

b0 - hyacinth weed

b1 - export demand for fish

b2 - industrial pollution

error term

The framework:





In this framework, the independent variables were the factors leading t o decline in fish stock in Lake Victoria and the dependent variable was the fish stock in Lake Victoria.


This chapter presents the research methodology used in this study. It describes the research, design, and the data method.

Research design

The survey method was used in carrying out the research in the form of a case study. In this study, an attempt w as made to find out how the hyacinth weed, the export demand and the industrial pollution affects the fish s tock in Lake Victoria.

Data collection method

In this study, secondary information was used to collect the data used. The researcher sought information from books, journals and the internet.


Many fish stocks have now been depleted to very low levels or are now under threat of extinction all over the world fisheries. The world fisheries are threatened with over exploitation, threats of externalities from human, economic as well as social activities. When one thinks of environmental resources that are under threat, fish comes into mind because of t he following reasons:

Fish can be destroyed despite being a renewable resource and hence overexploitation and environmental change such as pollution and loss of wetlands threaten the survival of fisheries.

fish are the major source of protein for a large proportion of the world's population particularly the poor.

This paper presents the study on factors leading to the decline in fish stock case study of Lake Victoria. These factors include:

The amount of hyacinth weed

The demand of fish export

The amount of industrial pollution.

The presence of water hyacinth has been cited in Lake Victoria as far back as 1989. by early 1990, the adverse effects arising from water hyacinth were alarming. Water hyacinth mats invaded fishing ground s and blocked water ways. For the individual fisherman, the water hyacinth reduced their catch by covering fishing grounds delaying access to market due to loss of output, increased fishing costs due t o the time and effort spent clearing water ways, forcing translocation and causing loss of nets. It was noted that hyacinth mats sealed off breeding, nursery feeding and fishing grounds for various inshore fish species like Tilapia and Young Nile Perch. The hyacinth mats also have detrimental effects by blocking light and severely reducing oxygen levels. The hyacinth weed mats also allow poisonous gases such as ammonia and hydrogen sulphide to accumulate in the lake which are harmful to the fish leading to the reduction in the fish stock.

The increased export demand of fish in Lake Victoria has adversely affected the fish stock in the lake. This has led to overexploitation and over fishing in Lake Victoria. The commercial fishers in Lake Victoria are in conflict with t hose who entirely depend on fishing to feed their families because of declining fish stock and thus their ability to feed their families is compromised. As a result of increased export demand, their is increased total fishing effort, efficiency of fishing gear, and extension of fishing grounds to maintain the yield which has resulted to a decline in catch per unit effort. In all the 3 countries, Kenya, Uganda and Tanzania, efforts in terms of boats and fishermen have more than doubled in the past 10 years. With increased fishing pressure, increase in export demand , predation and competition among species, the multispecies fishery of Lake Victoria has changed to only 3 species: the Nile perch, the cyprinid -dagaa, and the introduced Tilapia. Recently, the total Nile Perch catches were half those at the beginning of the decade.

The marketing of Lake Victoria's fish was localized within the riparian states during the pre-Nile perch era, but a s most fish filleting factories were established in the 1990's , both the regional and international trade expanded. The high demand fro processed fish products is, therefore, drive n mainly by the large export market for Nile perch fillets that emerged in the early 1990's. increasing human populations within the lake basin, poor governance in the fishing industry, and the restricted access status of the lake are secondary drivers. This has led to the decline in the fish stock in the lake.

Root causes for industrial pollution: in Tanzania and Uganda, industrial waste water treatment facilities are generally absent, but in Kenya a majority of factories operate a treatment plant. Some recent studies have shown that fish in Lake Victoria contain varying levels of organochlorine pesticide residue, reflecting the transport of agrochemical residues from farms within the catchment through rivers into the lake. Only a few industries a re connected to an urban sewage system. Growth in industries has taken place against a backdrop of no infrastructure development for disposal of effluents. The currently existing sewage infrastructure has not been expanded or improved for decades. However, some industries are being allowed to establish their operations in areas that have been designated "non- industrial", so they lack the infrastructure to handle their waste products. There is no enforcement of existing regulations regarding chemical use and their disposal. Lack of monitoring and poor scientific knowledge has led to the use of inappropriate or obsolete technologies to the detriment of the environment. The governments of t he 3 riparian countries have not taken deliberate actions to put in capital resources to meet the economic development needs of the region.

The appearance of new synthetic compounds such a s poly- chlorinated biphenyls (PCB) and changes in distribution, concentration and form of naturally occurring substances e.g zinc and cyanides in t he environment due to the disposal of industrial wastes has led to increased and differential mortality of populations, impairment of reproduction and disruption of species composition and balance.

Industrial effluents which contain chemical reducing agents for instance, ferrous salts or sulphides take up oxygen by purely chemical action . they do this rapidly exerting what is sometimes known as immediate oxygen demand. In Kenya we have reasonable industrial establishments manufacturing a wide spectrum of goods, for instance, sugar, textile and paper. Furthermore, new ones are coming up, for instance, the molasses industrial complex which produce power alcohol besides other products such a s citric acid, vinegar, dry and fish baker's yeast, sulphuric acid, methane and gypsum .All these industrial effluents have adversely affected the fish stock in Lake Victoria.


The governments of Kenya Uganda and Tanzania should come up with a project in which they should involve scientists who will come up with a remedy to eliminate the hyacinth weed.

The increased export demand for fish.

Quota for over fishing.

This has a high probability of success in a particular number or years like 5 years. There should be involvement of stake holders with change of attitude from government driven to community driven management and ownership of t he process. The process should be initiated in areas where the environment favours self- regulation and sustainability. A conducive environment for the success of the instruments that need to be put in place which include scientific basis for decision making, education and training, financial and technological assistance as w ell as revision of by laws, should be created. This measure should be able to control the number of entrants and efforts to a sustain able level at minimum cost.

Civic education and awareness.

It is important to increase public participation in order to enhance effective decision making and compliance by self- regulation. There is political will at the regional level a s demonstrated by the EAC treaty document and implementation of the intended objectives so far. This option will lead to more popular participation of t he communities in the environmental, economic and development issues that affect their livelihoods. It would also be more inclusive in terms of sharing accruing costs and benefits.

The industrial pollutionIn corporate all stake holders in drafting of regulations and in monitoring and en forcing agreed upon regulations.

Participatory approaches have been found to be effective in implementation of policies and decisions which require the input of t he community and where the communities in turn stand to benefit from the process. This is because involvement of t he beneficiaries inculcates a sense of responsibility and ownership among others. Because the cost of implementation and the benefit accrues to them, they be come effective partners ensuring proper and successful implementation. This solution has a high probability of success. It has been experienced across the region in several project implementations.

Liberalization of waste disposal activities to involve the private sector and communities.

Private sector participation in waste disposal activities is obviously important in order to fill the void left by the public institutions which have failed to render these services. The feasibility and effectiveness of t his policy option is that a business venture with the capability of generating income. There are, for instance, environmental and sanitation companies in Dar es Salaam and other towns that are carrying out the enterprise profitably. In some places there are established community youth groups that engage in waste collection and disposal from residential areas.

Article name: The Declining Fish Numbers In Lake Victoria Environmental Sciences essay, research paper, dissertation