Now showing items 1-20 of 22

    • Potential risks of contaminants with specific reference to mercury

      Campbell, L.M.; Balirwa, J.S.; Mugidde, R.; Ogutu-Ohwayo, R. (National Fisheries Resources Research Institute (NaFIRRI), 2004)
      Fresh water and fish are important to the people wholive in the Lake Victoria region therefore the quality ofthe water and fish is of major importance (Johnson &Odada, 1996). It is well known that dirty water and spoiltfish can lead to poor health and lower standards of living,and that quality can be affected by the pollution in theenvironment.Even though Lake Victoria is very large, it is relatively shallow and the water remains in the lake basin for a long time (Bootsma & Hecky, 1993). There are a number of environmental issues in Lake Victoria, including water hyacinth~over-population and increased farming causing problems with the lake ecosystem. All these factors combine to keep contaminants within the lake for long time, which will lead to gradually increasing concentrations in the lake.Pollution is a term that covers a wide variety of chemicals and physical changes and their adverse effects on the environment. Here we focus on contaminants, which are unwanted chemicals introduced to the environment. Contaminants include a very wide variety of chemicals, both man-made and natural, for example, mercury, pesticides and herbicides, heavy metals, and natural plant and algae toxins. Many contaminants do not always lead to adverse effects immediately, but can gradually induce long-term problems leading to chronic illnesses and physical damage. A few contaminants have very rapid impacts resulting in immediately obvious changes such as death or injury.Sources of contaminants are varied. Contaminants can get in the lake by the way of agricultural treatment of crops near the lake, industrial effluent, intentional introduction such as fish poisoning byfishermen, natural sources such as heavy metals from particular types of rocks, and even some plants naturally release their toxins. Contaminant sources are not always found near Lake Victoria.
    • Wetlands and riparian zones as buffers and critical habitats for biotic communities in Lake Victoria

      Balirwa, J.S.; Nsega, M.; Sekiranda, S.K.; Balirwa, J.S.; Mugidde, R.; Ogutu-Ohwayo, R. (National Fisheries Resources Research Institute (NaFIRRI), 2004)
      Despite their ecological and socio-economic importance,Lake Victoria's adjoining "swamps" and lake interface areamong the least investigated parts of the lake.The "swamps" a term commonly equated to "wastelands"and the difficult working environment they present incomparison to open water, are major factors for the lowlevel of attention accorded to shoreline wetlands. Moreover, definitions of wetlands highlighted for example in the Ramsar Convention as "areas of marsh, fern, peatland or water, whether natural or artificial, permanent or temporary, with water that is static or flowing, fresh or brackish, or salt, including areas of marine water, the depth of which does not exceed six metres" (Ramsar, 1971) were designed to protect birds (water fowl) of international importance. The Ramsar definition, which also includes oceans, has till recently been of limited use for Lake Victoria, because itdoes not fully recognise wetlands in relation to other public concerns such as water quality, biodiversity and the tisheries that are of higher socioeconomic priority than waterfowl. Prior to 1992, fishery research on Lake Victoria included studies of inshore shallow habitats of the lake without specific reference to distance or the type of vegetation at the shore. Results of these studies also conveniently relied heavily on trawl and gill net data from the 5-10 m depth zones as the defining boundary of shallow inshore habitats.In Lake Victoria, such a depth range can be at least one kilometre from the lake interface and by the 10m depth contour, habitats are in the sub-littoral range. Findings from these studies could thus not be used to make direct inferences on the then assumed importance of Lake Victoria wetlands in general.
    • Nutrient status and thermal stratification in Lake Victoria

      Mugidde, R.; Hecky, R.E.; Balirwa, J.S.; Mugidde, R.; Ogutu-Ohwayo, R. (National Fisheries Resources Research Institute (NaFIRRI), 2004)
      Worldwide, human activity in the watershed has beenfound to induce lake responses at various levels, includingat population and ecosystem scale. Recently, Carignanand Steedman (2000) reported on disruptions ofbiogeochemical cycles in temperate lakes followingwatershed deforestation and lor wildfire and Carignanet al., (2000 a, b) concluded that water quality and aquaticbiota are strongly influenced by disturbances in thewatershed. Similarly, Lake Victoria is no exception aspeople in its catchment have exploited it for the last hundred years or more, but have now begun to understand the extent to which they have thrown the lake into disorder and how their increasing activity in the watershed have driven some environmental changes within and around the lake.
    • Distribution of endangered native fish fauna and their conservation in Lake Victoria

      Namulemo, G.; Balirwa, J.S.; Mugidde, R.; Ogutu-Ohwayo, R. (National Fisheries Resources Research Institute (NaFIRRI), 2004)
      Lake Victoria in East Africa, supports socio-economicallyimportant fisheries for more than 30 million inhabitants inthe lake basin. The lake had until the 1970's a diverse fish assemblage dominated by haplochromines species whichformed at least 83% of the fish biomass (Kudhongania &Cordone 1974). The more than 500 haplochrominespecies in Lake Victoria, over 99% of them endemic,exploited virtually all the food sources in the lake (Witte and van Oijen 1990).Each species had its own unique combination of food and habitat preference (Goldschmidt et al., 1990).
    • Impacts of fishing gears, fishing methods and fishing effort in the fisheries of Lake Victoria and proposals for management

      Muhoozi, L.I.; Kamanyi, J.R.; Balirwa, J.S.; Mugidde, R.; Ogutu-Ohwayo, R. (National Fisheries Resources Research Institute (NaFIRRI), 2004)
      The initial subsistence fisheries of Lake Victoria were dominated by two indigenous tilapiines, Oreochromis esculentus (Graham 1929) and Oreochromis variabilisBoulenger 1906, exploited with simple fishing crafts and gears that had little impact on the fish stocks (Jackson 1971). Commercial fisheries, targeting the tilapia fishery,started at the beginning of the 20th Centurywhen cotton flax gillnets were first introduced in 1905 into the Nyanza Gulf in Kenya. Gillnets were quickly adopted around the whole lake and consequently, the native methods of fishing soon died out (Jackson 1971).Following the introduction of gillnets, fishing boats and their propulsion methods were also improved. These improvements in fishing capacity coincided with developmentof urban centres and increasing human population around the lake, which increased the demand for fishery products. To satisfy the increasing demand, fishing effort increased greatly during the 20th century, despite the decline of catch per unit of effort (CPUE) (Jackson 1971; Ogutu-Ohwayo 1990). The initial catch rates of 127mm (5 inch) mesh size gill nets in the tilapia-based fishery, in 1905, was in the range of 50 to 100 fish per gillnet of approximately 50 m in length. However, twenty years later, the catch rates of gillnets of the same mesh size had declined to about six fish per net and gillnets of smaller mesh sizes, which had better catch rates, had been introduced suggesting overfishing (Worthington and Worthington, 1933).
    • Implications of the industrial fish processing growth for the commercial fishery and fishers in Uganda

      Namisi, P.W.; Balirwa, J.S.; Mugidde, R.; Ogutu-Ohwayo, R. (National Fisheries Resources Research Institute (NaFIRRI), 2004)
      The study was undertaken to generate socio-economic information on fish market systems and performance of the industrial processing industry, which will guidethe processes leading to modernization of the fisheries sector and, sustainability of Lake Victoria fisheries.The main objective of this study was to evaluate the socio-economic implications of the fish marketing systems with particular emphasis on fish export market in Uganda. The study thus, analysed the socio-economic characteristics of fishers and examinined fish marketing systems and the impacts on the fishing activities, food security, employment opportunities and incomes of fisher-folk communities.
    • The status and significance of invertebrate communities

      Ndawula, L.M.; Kiggundu, V.; Pabire Ghandi, W.; Balirwa, J.S.; Mugidde, R.; Ogutu-Ohwayo, R. (National Fisheries Resources Research Institute (NaFIRRI), 2004)
      Invertebrates constitute a major link in energy flowculminating into fish production in aquatic ecosystems. Intropical water bodies relatively little research has been done on invertebrate ecology especially their role in fishery production.European scientists through periodic expeditions to Africa in the last quarter of the 20th century carried out the earliest research on zooplankton. Rzoska (1957) listedthese early workers including Stuhlmann (1888), Weltner (1897) and Mrazek (1897-1898).Daday (1907), Verestchagin (1915) and Delachaux (1917) undertook further work during the early twentieth century. These earlyworks provide a useful basis for tracking community changes by comparison with modem investigations. Worthington (1931) provided the first quantitative account of the zooplankton of Lake Victoria along with information on diurnal vertical migrations, compared to a temperate lake. The establishment of the East African Freshwater Fisheries Research Organisation (EAFFRO) at Jinja in 1947 enabled investigations on the fisheries, algae, invertebrates and water quality aspects of the lake (EAFFRO Annual Reports 1947-1977) to be regularly carried out. Macdonald (1956) made the first detailed observations on the biology of chaoborids and chironomids (IakefJies) in relation to the feeding of the elephant snout fish, Mormyrus kannume. A detailed study of the biology of the mayfly, Povilla adusta Navas with special reference to the diurnal rhythms of activity was carried out by Hartland-Rowe (1957).The search to unravel the ecological role of aquatic invertebrates in the production dynamics of the lake has taken invertebrate research to greater heights through recent investigations including Okedi (1990), Mavut
    • Management of water hyacinth, Eichhornia crassipes, in Lake Victoria Basin

      Twongo, T.K.; Wanda, F.M.; Balirwa, J.S.; Mugidde, R.; Ogutu-Ohwayo, R. (National Fisheries Resources Research Institute (NaFIRRI), 2004)
      Water hyacinth is a free-floating waterweed native to theAmazon River Basin in South America. In its native range,water hyacinth is not an environmental problem, althoughthe weed is one of the most invasive alien plants infreshwater environments. Water hyacinth has the potentialto become invasive through fast vegetative reproductionand rapid growth to accumulate huge biomass and extensive cover in freshwater environments.Over the last 150 years water hyacinth has invaded most countries in the tropics and sub-tropics, introduced by man, mainly for ornamental purposes. Such introductions led to the infestation of most freshwater-ways in the southern United States of America, parts of Australia, the pacific islands, and most countries in Asia and Africa.The extensive tightly packed mats of water hyacinth are often associated with devastating socio-economic and environmental impacts. Invasion by the weed has, therefore, often generated urgent costly problems associated with the weed biomass and its management. A classic example of such problems was triggered by the invasion and proliferation of water hyacinth in the Lake Victoria Basin during the 1980s (Freilink 1989, Taylor 1993, Twongo et al., 1995). The weed infestation marked the beginning of a decade of intensive and systematic campaign by the three riparian states (Kenya, Tanzania and Uganda) to bring weed proliferation under control. The discussions in this Chapter span over ten years of dealing with the challenges paused by the imperative to manage infestations of water hyacinth in the Lake Victoria Basin. The challenges included the need to understand the dynamics of water hyacinth infestation; its distribution, proliferation and impact modalities; and the development and implementation of appropriate weed controlstrategies and options. Most specific examples were taken from the Ugandan experience (NARO, 2002).
    • Epidemiology of bilharzia (Schistosomiasis) among fishing communities of Lake Victoria

      Kadama, A.B.; Magumba, K.M.; Balirwa, J.S.; Kyangwa, I.J.; Odongkara, K.; Balirwa, J.S.; Mugidde, R.; Ogutu-Ohwayo, R. (National Fisheries Resources Research Institute (NaFIRRI), 2004)
      The study was done in six districts of Mukono, Jinja, Iganga, Bugiri, Busia and Kalangala. At both mainland shoreline and islands, 271 adult respondents were randomly selected from 17 landing sites of Lake Victoria over a four months period between October 2000 and January 2001. A questionnaire was administered for symptoms of schistosomiasis and samples of stool, urine and blood were taken from respondents. Stool and urine were analysed for schistosome eggs and blood.Blood was analysed for increased eosinophils. Snail samples were collected from various depths along the shoreline of study sites identified and screened for schistosome cercariae.
    • The potential for co-management in fisheries

      Odongkara, K.O.; Nyapendi, A.T.; Kyangwa, M.; Balirwa, J.S.; Mugidde, R.; Ogutu-Ohwayo, R. (National Fisheries Resources Research Institute (NaFIRRI), 2004)
      Concerns have been raised over the sustainability ofthe fisheries resource base of Lake Victoria for sometime. The draft National Fisheries Policy states: "Thekey issues in the fisheries sector are resourcedepletion through overfishing aggravated by use ofdestructive fishing gear and methods" (MAAIF 2000).A fishery is said to be degraded if any or all of the indicators begin to show including decline in catches from the fishery, higher proportion of immature fish in the catch and reduction in the species composition of the catch. Inadequate implementation of fisheries management is considered the main cause of resource degradation. One of the factors identified as constraints to fisheriesmanagement has been lack of involvement of the resource users.
    • The status of legal framework for management of fisheries

      Odongkara, K.O.; Balirwa, J.S.; Mugidde, R.; Ogutu-Ohwayo, R. (National Fisheries Resources Research Institute (NaFIRRI), 2004)
      The success of fisheries management depends very much on the effectiveness of the legal framework in use. A historical perspective of the fisheries of Lake Victoria, Uganda, suggests that fisheries management has not been very successful. This chapter reviews the legal framework with a view to assessing its impact on fisheries management on Lake Victoria, Uganda
    • The nutritional status of fishing and non-fishing communities of Lake Victoria basin

      Nyapendi, A.T.; Odongkara, K.; Kyangwa, M.; Balirwa, J.S.; Mugidde, R.; Ogutu-Ohwayo, R. (National Fisheries Resources Research Institute (NaFIRRI), 2004)
      We examined socio-economic variables that contribute to malnutrition in selected communities in the Lake Victoria basin during 2001. The study was carried out innine districts and hinterland communities up to 25 km awayfrom the beach were used as the reference population. The main variables examined were: feeding habits, income and intra-household food distribution and living standards. Others included disease and health, sanitation and hygiene, childcare and mothers' age and workload, weaning practices, agricultural production and food availability, careduring pregnancy and food taboos.
    • Changes in phytoplankton communities and primary production

      Mugidde, R.; Balirwa, J.S.; Mugidde, R.; Ogutu-Ohwayo, R. (National Fisheries Resources Research Institute (NaFIRRI), 2004)
      Lake Victoria is the second largest lake in the world(69000km2) by surface area, but it is the shallowest (69mmaximum depth) of the African Great Lakes. It is situatedacross the equator at an altitude of 1240m and lies in ashallow basin between two uplifted ridges of the easternand western rift valleys (Beadle 1974). Despite theirtropical locations, African lakes exhibit considerableseasonality related to the alteration of warm, wet andcool, dry seasons and the accompanying changes inlucustrine stratification and mixing (Tailing, 1965; 1966;Melack 1979; Hecky& Fee 1981; Hecky& Kling,1981;1987; Bootsma 1993; Mugidde 1992; 1993).Phytoplankton productivity, biomass and species composition change seasonally inresponse to variations in light environment and nutrient availability which accompanychanges in mixed layer depth and erosion or stabilization of the metalimnion /hypolimnion (Spigel & Coulter 1996; Hecky et al., 1991; Tailing 1987). Over longer,millennial time scales, the phytoplankton communities of the African Great Lakes haveresponded to variability in the EastAfrican climate (Johnson 1996; Haberyan& Hecky,1986) which also alters the same ecological factors (Kilham et al., 1986). Recently, overthe last few decades, changes in external and or internal factors in Lake Victoria and itsbasin have had a profound inlluence on the planktic community of this lake (Hecky,1993; Lipiatou et al., 1996). The lake has experienced 2-10x increases in chlorophylland 2x increase in primary productivity since Tailing's observations in the early 1960s(Mugidde 1992, 1993). In addition to observed changes in the lake nutrient chemistry(Hecky & Mungoma, 1990; Hecky & Bugenyi 1992; Hecky 1993; Bootsma & Hecky 1993), the deep waters previouslyoxygenated to the sediment surface through most ofthe year are now regularly anoxic(Hecky et al., 1994).
    • The socio-economic and cultural structures of the fisherfolk communities

      Namisi, P; Kyangwa, M.; Balirwa, J.S.; Mugidde, R.; Ogutu-Ohwayo, R. (National Fisheries Resources Research Institute (NaFIRRI), 2004)
      Fishing communities that have exploited the resource forgenerations constitute the main stakeholder groups in thefisheries of Lake Victoria. Several studies have examinedUganda's Lake Victoria fishing communities andcharacterised key stakeholders at community level over thelast decade (SEDAWOG 1999a and b; Geheb 1997;FeSEP 1997; Kitakule 1991).The communities are made up of scattered settlements at the shores and on islands.The categories of people living in these communities include fishers who consist primarily of large numbers of male youths who provide labour to boat and gear owners.There are resident and non-resident fish traders who after securing their supplies at the beaches, depart for their market destinations. In addition, there are fish processors,mostly operating traditional and improved smoking kilns. Many other people, dealing in provisions and supplies also stay at the beaches, their activities depending on thelevel of fish catch. The fishing communities of Lake Victoria, Uganda, include auxiliary livelihood activities such as boat building, net repairing and transportation; bait supply and beachside kiosks, video halls and retail shop business. Other economic activities are brick making, charcoal burning/wood trade, farming and livestock keeping.
    • Implications of changes in trophic diversity and food webs on fisheries and the environment

      Mbabazi, D.; Ogutu-Ohwayo, R.; Hecky, R.E.; Campbell, L.M.; Balirwa, J.S.; Mugidde, R.; Ogutu-Ohwayo, R. (National Fisheries Resources Research Institute (NaFIRRI), 2004)
      Most of the earth's ecosystems are experiencing slight tocatastrophic losses of biodiversity, caused by habitatdestruction, alien species introduction, climate change andpollution (Wilcove et al., 1998). These human effects haveled to the extinction of native fish species, the collapse of their populations and the loss of ecological integrity and ecosystem functioning (Ogutu-Ohwayo & Hecky, 1991;Witte et al. , 1992a; Mills et al., 1994; Vitousek et al., 1996).Food webs are macro-descriptors of community feedinginteractions that can be used to map the flow of materialsand nutrients in ecosystems (Jepsen & Winemiller, 2002).Comparative food web studies have been used to address theoretical questions such as 'does greater trophic connectivity increase stability?' (Cohen et al., 1990), and 'does the number of trophic levels increase with productivity?' (Briand & Cohen, 1987). Answers to such questions have obvious applications for natural resources management. From a multi-species fisheries standpoint, there is a need to understand consumer-resource dynamics within complex trophic networks.
    • Evolution and management of the mukene (Rastrineobola argentea) fishery

      Wandera, S.B.; Balirwa, J.S.; Mugidde, R.; Ogutu-Ohwayo, R. (National Fisheries Resources Research Institute (NaFIRRI), 2004)
      Rastrineobola argentea locally known as mukene inUganda, omena in Kenya and dagaa in Tanzania occursin Lake Nabugabo, Lake Victoria, the Upper VictoriaNileand Lake Kyoga (Greenwood 1966). While its fisheryis well established on Lakes Victoria and Kyoga, thespecies is not yet exploited on Lake Nabugabo.Generally such smaller sized fish species as R. argentea become important commercial species in lakes where they occur when catches of preferred largersized table fish start showing signs ofdecline mostly as a result of overexploitation.With the current trends of declining fish catches on Lake Nabugabo, human exploitation of mukene on this lake is therefore just a matter of time. The speciesis exploited both for direct human consumption and as the protein ingredient in the manufacture of animal feeds.
    • Composition, biomass, distribution and population structure of the fish stocks

      Okaronon, J.O.; Balirwa, J.S.; Mugidde, R.; Ogutu-Ohwayo, R. (National Fisheries Resources Research Institute (NaFIRRI), 2004)
      Until the 1970s, Lake Victoria had a multi-species fisherydominated by the tilapiine and haplochromine cichlids.There were important subsidiary fisheries for more than20 genera of non-cichlid fishes, including catfishes(Bagrus docmak, Clarias gariepinus, Synodontis sppand Schilbe intermedius), the lungfish (Protopterusaethiopicus) and Labeo victorianus) (Kudhongania andCordone 1974). Stocks of most of these speciesdeclined and others disappeared following theintroduction of four tilapiines (Oreochromis niloticus,Oreochromis leucostictus, Tilapia rendalli and Tilapiazillit) and Nile perch (Lates niloticus) during the 1950s.Since then the commercial fishery in the Uganda portion of Lake Victoria has been dominated by the Nile perch, Nile tilapia (Oreochromis niloticus) and the native cyprinid species, Rastrineobola argentea (Mukene).
    • Evolution of the tilapia fishery with specific reference to the Nile tilapia (Oreochromis niloticus Linne)

      Balirwa, J.S.; Nsega, M.; Roijackers, R.; Nkalubo, W.; Balirwa, J.S.; Mugidde, R.; Ogutu-Ohwayo, R. (National Fisheries Resources Research Institute (NaFIRRI), 2004)
      As a fishery, the immensely large (c. 68,800 km2 ) LakeVictoria is a unique ecosystem which together with ariverine connection to the Lake Kyoga basin share acommon endemic "Victorian" fish fauna (Greenwood1966). Until the 1950s, the single socio economicallymost important species of fish in these two lakes wasthe native Oreochromis esculentus Graham (Graham1929) even though the lake also contained a secondnative tilapiine, 0reochromis variabilis , and over 300 other fish species (Beauchamp, 1956).
    • Geographic and economic setting of Lake Victoria

      Balirwa, J.S.; Bugenyi, F.W.B; Odongkara, K.O.; Chapman, L.J.; Chapman, C.A.; Balirwa, J.S.; Mugidde, R.; Ogutu-Ohwayo, R. (National Fisheries Resources Research Institute (NaFIRRI), 2004)
      Lake Victoria, besides being the second largest in theworld after Lake Superior, is the largest tropical lake. Itswaters are shared by Kenya (6% of the surface area),Uganda (43%), and Tanzania (51%). Before dramaticstructural and functional changes manifested in the lake'secosystem especially in the 1980s, fish life flourished inthe lake's entire water column at all times of the year.Currently, the situation is much more different from what it was in the past. The exponential increase in the introduced Nile perch (Lates niloticus) and Nile tilapia (Oreochromis niloticus) stocks, siltation, wetland degradation and eutrophication have characterised the lake ecosystem. The two exotic species and the small native cyprinid (Rastrineobola argentea) form the basis of the commercial fishery that was once dominated by two native tilapiines (Oreochromis esculentus and Oreochromis variabilis) and five other large-bodied endemic fishes. Severe deoxygenation observed at shallow depths (Ochumba 1990; Hecky et al., 1994) indicates that a large volume of the lake is unable to sustain fish life.The Lake Victoria catchment is one of the most densely populated areas in East Africa, encompassing a population of about 30 million people. Widespread poverty resulting from high inflation rates, lack of opportunities and general unemployment have characterised the lakeside communities over much of the last two decades.The biophysical environment in which Lake Victoria exists makes the lake particularly susceptible to changes that occur as a result of human modification to the watershed or the lake itself, thus rendering benefits from the lake unsustainable.
    • Fisheries research in Uganda

      Balirwa, J.S.; Ogutu-Ohwayo, R.; Balirwa, J.S.; Mugidde, R.; Ogutu-Ohwayo, R. (National Fisheries Resources Research Institute (NaFIRRI), 2004)
      Evolution of fisheries research and FIRRIThe earliest approach to fisheries research in Uganda dates from the first fisheries survey of Lake Victoria by Michael Graham between 1927 and 1928 (Graham,1929). Based on references to the rich fisheries that were reported to Graham, itappears that during the 18th Century, catch per net per night averaged 300 tilapia,a revelation that led Graham to conclude that Lake Victoria is a tilapia lake. The"tilapia" later came to be known as Tilapia esculenta and T variabilis(Oreochromis esculentus and O. variabilis) respectively.