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Management issues in the Lake Victoria watershed
Abstract
Lake Victoria is the largest lake in Africa (68 800 km2) and is the eighth largest lake in the world by volume. The three East African countries of Tanzania, Uganda and Kenya share Lake Victoria and its resources. The total annual catch of fish from the lake ranges between 400 × 106 kg and 500 × 106 kg, bringing these riparian countries a combined annual income of approximately US$250 000–500 000 from exports alone. Approximately 30 million people live in the riparian region and the catchment, with about 2 million of these depending directly or indirectly on fishing activities. Tragically, Lake Victoria’s extremely diverse fauna was decimated in only 30 years following the introduction of non-native Nile perch in the early 1960s. An estimated 200 endemic cichlid species became extinct. Dramatic increases in overfishing, pollution from various sources, effects of noxious water weeds and other associated problems threaten the sustainability of the lake’s resources and the economies of the riparian governments and peoples. Regulations governing Lake Victoria’s resources are different in each country. The laws concerning treatment of effluents from point sources in the three countries are not harmonized, neither are implementation or enforcement provisions. The governments of Kenya, Uganda and Tanzania have begun to put in place regional mechanisms to address the lake’s many problems including the creation of a permanent regional international institution through the establishment of the Lake Victoria Fisheries Organization (LVFO). A strategic vision document and action plans have been developed. Efforts are being made at local, national and regional levels to control the water hyacinth, including manual pulling, mechanical harvesting and introduction of weevils that weaken hyacinth root systems. To address the problem of overfishing, fishermen committees at landing beaches have been put in place. Each country has committed to take all necessary measures including legislation to implement the decisions of the LVFO governing bodies. All three countries have agreed to adopt and enforce legislation and regulations prohibiting the introduction of non-indigenous species to the lake and to enforce existing regulations regarding fisheries. A Global Environment Facility project which provides funding to the Lake Victoria Fisheries Organization addresses land use management, catchment forestation, fisheries research and management, water hyacinth control, industrial effluent treatment and municipal waste treatment.
... The three governments began discussions about transboundary water management following the Rio Earth Summit (Muyodi et al., 2010). They submitted a biodiversity grant to the Global Environment Facility (Ntiba, Kudoja, & Mukasa, 2001). 19 ...
... A long drought began that lasted until 1984 (Mwiturubani & van Wyk, 2010). 14 The water hyacinth was introduced into the lake (Ntiba et al., 2001). 15 ...
... The countries are also obligated to legislatively implement decisions of the LVFO Steering Committee (Zilov, 2013). There have been criticisms that there is little financial investment by states in the LVFO and that there has not been harmonization of regulations signaling lack of commitment to constraints and costs affiliated with the organization (Ntiba et al., 2001). The Lake Victoria Environmental Management Project (LVEMP) was also agreed upon by the three riparian countries in 1994 to conduct research and address environmental management of the lake (Wirkus & Böge, 2006;Kolding et al., 2014). ...
... During the second half of the 1990s, after a decline of the Nile perch due to over-fishing (e.g. Ntiba et al., 2001), some haplochromine species recovered in the Mwanza Gulf ( Seehausen et al., 1997b;Witte et al., 2000). A similar pattern of faunal loss and recovery in relation to Nile perch upsurge and decline was observed in Lake Nabugabo ( Chapman et al., 2003). ...
... The catchment area of Lake Victoria covers 195,000 km 2 and has a human population of ca. 30 million people with a growth rate of 6% per annum in urban centres and over 3% in rural areas ( Ntiba et al., 2001). The people largely depend on the agriculture and cattle breeding and the use of firewood as fuel for cooking. ...
... Deforestation, coupled with bad agricultural practices, strongly increases land erosion. Rapid industrial development in the major urban centres contributes to pollution of the lake ( Scheren et al., 2000;Ntiba et al., 2001;Kishe & Machiwa, 2003). Unless adequate measures are taken, eutrophication and pollution of Lake Victoria is bound to increase rapidly. ...
During the past decades, dramatic changes were observed in the ecosystem of Lake Victoria. The introduced Nile perch ('Lates niloticus') boomed in the 1980s and many other fish species disappeared. The more than 500 haplochromine cichlid species, that originally made up more than 80% of the demersal fish mass, were most severely affected. Within 10 years, they had almost vanished from the catches in the sublittoral and offshore waters, and lakewide, some 200 species may have disappeared. In the same period, the native zooplanktivorous cyprinid dagaa ('Rastrineobola argentea') and the introduced Nile tilapia ('Oreochromis niloticus') strongly increased in numbers. Concomitant with the changes in fish species composition, other changes in the ecosystem were also observed. Most prominent was the increase in eutrophication that had started already in the 1930s when a strong increase of the human population was also observed. As a result of soil runoff, eutrophication and phytoplankton blooms, dissolved oxygen concentrations and water transparency in the lake declined in the 1980s.
In the 1990s, after a decline of the Nile perch due to over-fishing, some 20 haplochromine species recovered in the Mwanza Gulf. Apart from predation by Nile perch — which is still high when compared to predation in general before the ecological changes — the recovering species have to cope with environmental changes, such as increased hypoxia and decreased water clarity.
... Consequently, loss of water quality and biological diversity threaten the well-being of millions of lake side riparian communities. This is because studies have shown that portable water supply by relevant authorities is less than 60% hence, most people use the water directly without prior treatment (Ntiba et al., 2001;Njiru et al., 2008;Kobingi et al., 2009;Masese et al., 2009b). The major cause of degradation is increased intensity of agriculture and deforestation coupled with the rapid growth of urban centers and industrial activities that have been linked to increasing magnitude and frequency of run-off events (Mutie, 2006;Mati et al., 2008), pesticide contamination (Osano et al., 2003), reduced base flow (GEF, 2004), erosion and sedimentation of streams and rivers (Mutie, 2006). ...
... Overall, the hydrological characteristics of flow and water retention have been altered resulting in massive and destructive flooding in the lowlands during spates (UNEP, 2003;Kadomura, 2005). As a result, these activities have led to sedimentation and eutrophication that have not only affected domestic and industrial water supply (Ntiba et al., 2001), but also led to massive fish kills and proliferation of the water hyacinth (Eichhornia crassipes) (Gichuki, 2000;Lung'aiya et al., 2000;Mugidde et al., 2005;Wawire and Ochiel, 2005;Njiru et al., 2008). ...
... The lake is at an altitude of 1135 m above sea level and lies on the between latitude 0.7 • 'N-3 • 'S and longitude 31.8 • 'E-34.8 • 'E 6,7 . Annual rainfall in the lake area varies between 950 and 2450 mm and on the terrestrial part of the basin, it ranges from 450 to 950 mm. ...
... The contribution of haplochromines fish biomass in the lake decreased from 80% to less than 1% within a decade from 1970 and1980 47 11,49 . There are about 35 fish fillet processing factories operating within the lakeshore cities which have created high demands for fish landing 7,50 . Artisanal fishermen cannot compete with commercial fishers because of the poor fishing gear they use 51 . ...
For the countries within the Lake Victoria basin, sustainably managing it is critical to the harmonious survival of a vast array of biodiversity. The abundance of resources in and around the lake provides various vital ecosystem services (like food, transport, nutrient cycling, tourism, climate regulation as well as disease and flood control) for humans and countless other species. However, decades of unsustainable development practices combined with unchecked population growth are diminishing the lakes' productivity and threatening its very existence. Eutrophication, proliferation of alien species, water pollution, inappropriate fishing techniques, and climate change are among some of the anthropogenic and natural threats that are besieging Lake Victoria. In light of recent exploration and exploitation of minerals, oil, and gas further degradation of the watershed is not only eminent but a surety. However, to date the institutions mandated with the regional management of the basin have fallen short of their expectations and literature pertaining to the basin's management is quite outdated. There is urgent need to draw attention to the cause-effect relationship between the driving forces-pressures-state-impacts-responses, that diminish sustainable utilization and development of Lake Victoria. Using this indicator-based approach clearly highlights the nexus between the environmental metrics and anthropogenic interactions making decisions for practice and policy-making more sustainable. Overall, the need for robust integrated water management policies within the riparian countries is critical to simultaneously address conservation and development which are paramount in ensuring sustainable development and enhancing the lake's productivity. Sensitization and capacity building within the communities utilizing the lake as a primary source of income will mitigate detrimental impacts from unsustainable usage. More so, appropriate incentives and fines to deter pollution and illegal reclamation of wetlands and forests will promote regeneration of the ecosystem and recovery in the long term.
... The lake is shared by three of the East African countries: Uganda (45%), Kenya (6%) and Tanzania (49%). With approximately 30 million people living within its catchment area (Ntiba et al. 2001), people carry out a number of economic activities (fishing, agriculture, forestry, transport and tourism). The lake's natural resources in terms of its waters and immense biodiversity base, serve not only the people of East Africa, but also the world in general. ...
... They comprise beaches, resorts, hotels, camping sites, botanical gardens and conservation areas with activities ranging from water jet skiing and canoeing to sun bathing and nature walks. Tourism, like the other economic activities, (fishing and agriculture) is threatened by unsustainable use of natural resources which has led to overfishing, water pollution (from industries, urban waste and agriculture sources), wetland reclamation, invasion of noxious waterweeds and other associated problems (Ntiba et al. 2001, LVEMP 2005. To address these challenges, trans-national bodies have been set up to coordinate resource use and management among the three countries. ...
Tourism in Uganda has over the years witnessed an increase in tourist arrivals which has resulted in the development of a number of tourist facilities and destinations. Although studies have been conducted to examine the development of tourism in Uganda, limited attention has been given to Lake Tourism, especially with respect to tourism planning from a spatial and temporal perspective. This paper focuses on the Lake Victoria shore region where it identifies the tourism establishments, analyses their spatial and temporal trend and examines the implication on tourism planning of the lakeshore region. Using qualitative, quantitative and geo-spatial techniques data was collected and analysed using nearest-neighbour tool, Chi Square and ANOVA tests. The results indicate that: the
lakeshore region has a variety of tourism sites, majority of whom are beach resorts (without accommodation facilities); they have been increasing in number and size over the years; and attract an increasing number of visitors. Spatial analysis revealed that there is a tendency of the sites clustering near the urban than in the peri urban areas. This implies that tourism planning of the lakeshore should ensure that resources are sustainable utilised as tourism ‘hot spots’ begin to develop around the clustering areas, which are already experiencing an increasing number of sites and visitors. The study
recommends a pro-active planning approach, which incorporates spatial and temporal aspects to ensure sustainable tourism development along the lakeshore region.
... Consequently, loss of water quality and biological diversity threaten the well-being of millions of lake side riparian communities. This is because studies have shown that portable water supply by relevant authorities is less than 60% hence, most people use the water directly without prior treatment (Ntiba et al., 2001;Njiru et al., 2008;Kobingi et al., 2009;Masese et al., 2009b). The major cause of degradation is increased intensity of agriculture and deforestation coupled with the rapid growth of urban centers and industrial activities that have been linked to increasing magnitude and frequency of run-off events (Mutie, 2006;Mati et al., 2008), pesticide contamination (Osano et al., 2003), reduced base flow (GEF, 2004), erosion and sedimentation of streams and rivers (Mutie, 2006). ...
... Overall, the hydrological characteristics of flow and water retention have been altered resulting in massive and destructive flooding in the lowlands during spates (UNEP, 2003;Kadomura, 2005). As a result, these activities have led to sedimentation and eutrophication that have not only affected domestic and industrial water supply (Ntiba et al., 2001), but also led to massive fish kills and proliferation of the water hyacinth (Eichhornia crassipes) (Gichuki, 2000;Lung'aiya et al., 2000;Mugidde et al., 2005;Wawire and Ochiel, 2005;Njiru et al., 2008). ...
The degradation of freshwater systems is on the increase due to anthropogenic activities. In the recent past, there has been a rapid shift of assessment and monitoring from the conventional methods to biomonitoring of these ecosystems globally. Although, an organism's response to degradation varies, little is known as far as their sensitivities are concerned. The aim of this study, therefore, was to assess the life cycle responses of the midge of Chironomus species (Diptera: Chironomidae) to sugarcane and paper pulp effluents exposure. This is in order to ascertain their use in the monitoring of freshwater ecosystems. Fourth instar of Chironomid midges were sampled at two locations on the Rivers Nzoia and Mbogo. River Mbogo is a tributary joining River Nyando within the Lake Victoria Basin. All midges were taken to the laboratory on the same day of collection and acclimatized in a controlled climate room for 24 hours. They were then exposed to the effluent dilutions (i.e. 100%, 50%, 25%, 12.5% and lastly 6.25%) collected from Webuye Paper Mill Factory and Chemelil Sugar Factory treatment ponds/lagoons. A completely randomized experimental design was employed in which ten midges were placed in each of the treatments replicated four times and the experiment ran for 28 days. It was found that emergence of the Chironomus species decreased with an increase in the effluent concentration. An increase in effluent concentration, led to a delay in emergence of chironomids over time. However, there was no significant difference (p<0.05) between the emergence of Chironomus species exposed to the two effluents. Emergence is one of the most sensitive endpoints in toxicological studies. This is because effects on emergence involve three moultings and the very complex pupation process. Therefore, not all surviving larvae would have managed to undergo all the four stages of their life cycle due to adverse effects of the effluents. The study concluded that pulp paper and sugar cane effluents delayed the development of life cycle stages of Chironomus species and it was recommended that life cycle stages of the midges, Chironomus species can be a good indicator of environmental degradation.
... It is prevalent in tropical and sub-tropical water bodies where nutrient levels are often high due to agricultural runoff, deforestation, and insufficient wastewater treatment. The weed has a very high growth rate such that it doubles in area within five day (Ntiba et al., 2001) [3] . Nutrients and temperature are considered the strongest determinants for its growth and reproduction (Wilson et al., 2007) [4] . ...
... It is prevalent in tropical and sub-tropical water bodies where nutrient levels are often high due to agricultural runoff, deforestation, and insufficient wastewater treatment. The weed has a very high growth rate such that it doubles in area within five day (Ntiba et al., 2001) [3] . Nutrients and temperature are considered the strongest determinants for its growth and reproduction (Wilson et al., 2007) [4] . ...
This study compared water quality parameters, fish species diversity and abundance in the water hyacinth infested and non-infested areas. The mean (±SD) water temperature of the infested and non-infested areas were 25.60±4.39 0 C and 24.62±4.94 0 C respectively. Dissolved oxygen 2.44±1.14 mgl-1 of the infested area was significantly lower than non-infested (4.24±0.96 mgl-1) (p<0.05). The mean pH of infested and non-infested areas were 6.05±1.04 and 7.62±0.42 respectively. The lowest (6.97±01.83 mgl-1) nitrate was recorded in infested and the highest (11.34±1.46 mgl-1) in non-infested areas. Infested areas had high fish species diversity (2.00) and evenness (0.93). In the infested areas, Protopterus aethiopicus (35%) had the highest relative abundance, followed by Clarias gariepinus (28%), while in the non-infested areas, Lates niloticus had the highest abundance (23%) followed by Oreochromis niloticus (18%). The abundance of haplochromines, C. gariepinus and P. aethiopicus in the infested areas is attributed to their ability to tolerate low oxygen levels. However, the Lates niloticus is very sensitive to low oxygen levels.
... East African inland fisheries predominantly rely on major freshwater bodies, notably Lake Victoria, the world's secondlargest freshwater body (Getabu et al. 2003). The capture fisheries from Lake Victoria alone contribute US$250 000-US$500 000 annually to three greater East African states (Uganda, Kenya and Tanzania) from exports alone (Ntiba et al. 2001;Scullion 2007). ...
The Nile tilapia (Oreochromis niloticus) is the second-most economically important fish species in East African countries (EAC), surpassed only by the Nile perch (Lates niloticus). It is the most-farmed freshwater fish species in EAC and the second-most-farmed worldwide. Currently, in EAC, through direct stocking activities and likely indirectly via aquaculture escapees, Nile tilapia are present in waterbodies where it is not native and where it is thought to have contributed to the fish biodiversity loss observed in recent decades. Introduced Nile tilapia may hybridise with native, congeneric species, promoting genetic introgression that can be detrimental to the sustainability of biodiversity. Moreover, the translocation dynamics and escapes from aquaculture can contribute to artificial geneflow between Nile tilapia stocks, compromising their gene pool and the sustainability of the species as a fishery resource. In the current work, we review some examples of these phenomena in EAC. Additionally, we explore the importance of collecting genetic data to define baseline knowledge for native and non-native Nile tilapia populations that can be used in monitoring programmes for development, management and conservation of tilapia genetic resources.
... It is part of depression within the East African Great Rift Valley, between two mountain ranges, generally running north-south, on both sides and one of Africa's great lakes. The lake is bounded by latitudes 0.5o N and 2.5o S and longitudes 32o E and 34o E covering an area of 69,000 km2 (Semazzi, 2011), but it is also one of the shallowest; the bathymetry within the lake Many people in the region rely on the lake for food, water, income, and energy (World Bank, 2015), and it has long served as a convenient method to travel between the three nations via boat transport (Ntiba, Kudoja, and Mukasa, 2001). ...
The objective of this study was to explore lake and land breezes over the Lake Victoria basin based on 2 years (2019 to 2020). Hourly and daily data of wind speed and direction, precipitation, 2-meter air temperature over land, and Lake mix-layer depth obtained from Era 5 re-analysis were utilized. The method employed was based on the characteristics of the lake breeze with the elimination of the days with strong synoptic winds. According to the results, the main drivers for the breeze development at the meteorological stations were the thermal gradient between the lake and the surroundings and the low-level winds. The breezes mainly occur between 9:00 h and 15:00 h characterized by divergence over the lake and reduction in temperature and they move over land. The study calls for a look at the factors that may contribute to the formation of the breezes.
... Freshwater tropical lakes in Africa are among the most biologically productive lakes globally [9]. Equatorial Lake Victoria is the second-largest freshwater lake globally by surface area and the largest freshwater lake in Africa, with a surface area of 69,000 km 2 [10] and a catchment area of 284,000 km 2 [11]. Lake Victoria is large enough to create its weather system and influence regional climate [10; 12]. ...
Lake Victoria is the second-largest freshwater lake in the world, with an eco-system critical to 25-30 million inhabitants of Kenya, Uganda, Tanzania, Rwanda, and Burundi who live in the lake basin. The lake provides several ecosystem services from inland waterway transport, fisheries to hydropower and supports many different industries such as tourism, trade, and wildlife. However, Lake Victorias ecosystem management has been highly extractive; hence its water resources are either inefficiently or overused. This is because the value of this resource is either unknown or underestimated. The main purpose of the research was to contribute to Lake Victorias conservation efforts by providing the best techniques that can be used to assess the value of this resource and develop appropriate policies for the sustainable management of the lake. The study reviewed relevant literature on the economic assessment methods of environmental resources in the context of water management. Search engines such as Google Scholar, Web of Science, and ScienceDirect were used for it. The study suggests methods for economic valuation of Lake Victoria water ecosystem for each service. The proposed techniques can be used for assessing the value and benefits of conservation and restoration of Lake Victoria ecosystem.
... The lake fisheries are important livelihood sources that provide food and employment (Ntiba et al., 2001). Lake Victoria is the principal inland fishery, with a five-year cycle average production of about 90,000 tonnes landed and valued at about US$ 90 million in Kenya alone Njiru et al., 2018). ...
Fisheries governance uses policy and statutory documents to improve governance on fish ecology, harvesting, trade and consumption by identifying and addressing gaps regarding inefficiencies, inequity and post‐harvest losses. The current study examines existing policies and institutional documents on fisheries, health and trade to assess the level of inclusion of small indigenous fish species (SIS), especially Omena, as a means of guiding governance interventions for sustained livelihoods of fishing communities in Lake Victoria. A content‐analysis review was conducted on all the fisheries and nutritional policy documents related to Lake Victoria fishery to ascertain the need for their integration into fisheries governance. From the scoring scale, where zero (0) implies no integration and three (3) implies high integration, the study results indicated very low levels of integration across health, fisheries and trade relating to small fish species. Further, the management plans and regulations/guidelines exhibited a relatively higher level of integration than did policies and laws. There is need for a more targeted approach for streamlining the existing policy documents to realize the untapped potential contribution of SIS towards food and nutritional security.
... Although the Lake Victoria Fisheries Organization (LVFO) has tried to harmonize regulations for fisheries management in Lake Victoria, differences do occur across the three riparian countries. For instance, closed season for Rastrineobola argentea (dagaa) is only observed in Kenya from 1st April to 31st July (Ntiba et al., 2001), and monofilament gill nets are banned in Kenya and Tanzania, but allowed in Uganda (Njiru et al., 2008). ...
... As represented in Figure 3, the total capacity of Africa's river basins, freshwater bodies, riparian areas, wetlands and groundwater reservoirs is approximately twice that of North America [21][22][23][24]. With a total land area of roughly 68,800 km 2 , Lake Victoria, Africa's widest lake, the second-largest globally freshwater lake, ranked after Lake Superior, is vast in size (with a water volume of approximately 2500 km 3 even though it is a little shallow. ...
Human activities mostly impact the trend and direction of rainwater, groundwater, and other river basin resources in the watershed in Africa. These activities alter river flows and the quality of usable water supplies at both highlands and lowlands. A watershed is indeed a conserved area of land that collects rain, sleet and snow, and empties or penetrates groundwater sources. The act of managing the activities around the watershed is integrated watershed management, which considers the social, economic, and environmental issues in tandem with the human, institutional, natural, and sustainability systems, which are the key drivers as identified in this study, as well as community interests and participation, to manage groundwater resources sustainably. These watersheds, river basins, and groundwater resources provide important services for communities and biodiversity. This paper reveals that the best way to protect groundwater resources is on a watershed basis using sustainable management measures. This technique enables us to handle a variety of concerns and objectives while also allowing us to plan in a complicated and uncertain environment. Sustaining a regional and sub-regional watershed involves cooperation and participation from a wide range of community interests and water users, including municipalities, companies, people, agencies, and landowners, for stakeholders’ input to be successful. All of the strategies and plans are produced with regard to one another, as well as the overall conditions of the watershed, local land uses, and specific regional transboundary issues.
... Fishers' income is determined by the quantity of fish they catch and the price obtained for it; thus, if the fishery is managed well, it will contribute to driving income poverty down (Nyeko 2004;Bavinck 2009;McGregor 2009;Coulthard et al. 2011;Weeratunge et al. 2014). Building on these facts, Lake Victoria provides open access to anyone to fish in it, subject to existing fishery regulations (Ntiba et al. 2001;Eggert & Ellegård 2003;Ogello et al. 2013). This study therefore conceptualises that the existing income poverty among communities in Lake Victoria will lead to Nile perch overfishing because of the open-access nature of the lake and the lack of income diversification activities. ...
Despite the crucial role played by Nile perch in the income of fishers around Lake Victoria, Tanzania, fishing pressure has increased in recent years and has led to overfishing and, consequently, a risk to the lake’s future sustainability and the fishers’ livelihoods. This study used data collected in 2018 from 268 randomly selected sample fishers at 10 landing sites across Lake Victoria. In conjunction with the endogenous switching regression model, the potential impact of Nile perch overfishing on the fishers’ income per fishing trip in Lake Victoria was evaluated. The results show that there is a significant difference in the socio-economic, institutional and fishing effort characteristics of Nile perch fishers who overfish and those who do not. In particular, Nile perch fishers who overfish earn significantly higher incomes per fishing trip than fishers who do not overfish. The study recommends the need for policy makers to develop policies that acknowledge the dynamics of socio-economic, institutional and fishing effort factors. In addition, more flexible fish quota restrictions and consistent fishing patrols need to be enforced to ensure compliance with fishery regulations. These measures should promote a balance between the sustainability of fishery resources and an improved income for Nile perch fishers in Lake Victoria.
... T A B L E 6 Pearson correlation matrix generated using 11 measured parameters and WQI as parameter (a: p The remarkable variation in turbidity between stations highlighted the effect of human disturbance in the lake's watershed and along the shores of Lake Kivu. These variations in turbidity, the only parameter that showed a highly significant negative correlation with the WQI, are related to the observations made along the shores of other lakes of the Albertine Rift, such as Lake Victoria (Ntiba et al., 2001;Odada et al., 2004;Odada et al., 2006) and Lake Tanganyika (Hecky, 1993). In fact, high population growth and associated activities not only increase domestic water uses, but also contribute to an increase in discharges of waste and pollutants of all kinds that affect water quality in lake littoral areas (Bootsma & Hecky, 1993;Busch et al., 2018;Cohen et al., 1993;Palacios-Fest et al., 2005). ...
en Freshwater ecosystems provide many services such as moderation of the local microclimate and a source of water and food for riparian communities. It is also a preferred habitat for many organisms such as plankton, benthic macroinvertebrates and fish. However, these ecosystems are among the most affected by various anthropogenic threats that modify water quality and ecological processes, thus affecting biodiversity. The objective of this study was the spatio-temporal characterization of physico-chemical littoral water parameters and the assessment of anthropogenic disturbance on the littoral zone by a water quality index (WQI). Physico-chemical water quality data including temperature, dissolved oxygen, conductivity, pH, TDS, turbidity, SiO2, PO4³⁻, NO2⁻, and NH4⁺ were collected from January to December 2018. They were used to calculate the WQI to assess water quality according to aquatic life, using limits values of Canadian Council of Ministers of the Environment (CCME), United States Environmental Protection Agency (USEPA) and Australian and New Zeland Environment and Conservation Council (ANZECC). PO4³⁻ is out of range in all the stations while NO2⁻ and Turbidity are out of range in some of the anthropized stations according to ANZECC, CCME, and USEPA recommended values for aquatic life. The WQI values range from medium to good and the high WQI values obtained in the non-anthropized stations that reflect the negative influence of human disturbance on water quality in the Lake littoral zone. The results suggest the need for an integrated lake watershed management system in order to maintain the ecological functions of the lake and support livelihoods from the lake.
摘要
zh 淡水生态系统为河岸社区提供了许多服务, 例如调节当地微气候和提供水源及食物。它也是许多生物所偏好的栖息地, 例如浮游生物、底栖大型无脊椎动物和鱼类。不过, 这些生态系统也是最受人类活动威胁所影响的群体之一, 人类活动威胁改变水质和生态过程, 因此影响生物多样性。本文目的是发现沿湖水的物理-化学参数的时空特征, 并通过水质指标 (WQI)对沿湖区的人类影响进行评估。2018年1月至12月收集了一系列物理-化学水质数据, 包括温度、溶解氧、电导率、pH、总溶解固体、浊度、SiO2、PO4³⁻、NO2⁻ 和NH4⁺ 。数据被用于计算WQI, 以期根据水生生物评估水质, 数据使用了加拿大环境部长理事会 (CCME)、美国环境保护署 (USEPA)以及澳大利亚和新西兰环境与保护理事会 (ANZECC)的限制值。根据ANZECC、CCME 和USEPA的水生生物推荐值, 发现PO4³⁻在所有采集点都超出检测范围, NO2⁻和浊度在部分受人类影响的采集点 (anthropized stations)超出检测范围。WQI值处于中等到良好之间, 并且在不受人类影响的采集点获得的高WQI值反映了人类活动对沿湖区水质产生的消极影响。研究结果暗示, 需要一个综合性流域管理系统, 以期维持该湖的生态功能并保护河岸社区的生计。.
Abstract
es Los ecosistemas de agua dulce brindan muchos servicios, como la moderación del microclima local y una fuente de agua y alimentos para las comunidades ribereñas. También es un hábitat preferido para muchos organismos como el plancton, los macroinvertebrados bentónicos y los peces. Sin embargo, estos ecosistemas se encuentran entre los más afectados por diversas amenazas antropogénicas que modifican la calidad del agua y los procesos ecológicos, afectando así la biodiversidad. El objetivo de este estudio fue la caracterización espacio-temporal de los parámetros físico-químicos del agua litoral y la evaluación de la perturbación antropogénica en la zona litoral mediante un Índice de Calidad del Agua (WQI). Los datos fisicoquímicos de la calidad del agua que incluyen temperatura, oxígeno disuelto, conductividad, pH, TDS, turbidez, SiO2, PO4³⁻, NO2⁻ y NH4⁺ se recopilaron de enero a diciembre de 2018. Se utilizaron para calcular el WQI para evaluar la calidad del agua. Según la vida acuática, utilizando valores límites del Consejo Canadiense de Ministros de Medio Ambiente (CCME), la Agencia de Protección Ambiental de los Estados Unidos (USEPA) y el Consejo de Conservación y Medio Ambiente de Australia y Nueva Zelanda (ANZECC). La PO4³⁻ está fuera de rango en todas las estaciones mientras que el NO2⁻ y la turbidez están fuera de rango en algunas de las estaciones antropizadas según los valores recomendados por ANZECC, CCME y USEPA para la vida acuática. Los valores de WQI van de medio a bueno y los valores altos de WQI obtenidos en las estaciones no antropizadas que reflejan la influencia negativa de la perturbación humana en la calidad del agua en la zona litoral del lago. Los resultados sugieren la necesidad de un sistema integrado de manejo de cuencas del lago para mantener las funciones ecológicas del lago y sustentar los medios de vida del lago.
... According to [5], in most developing countries including Nigeria, anthropogenic activi-ties of different kind such as bathing and washing, indiscriminate dumping and direct discharge of untreated waste including human feaces around the shoreline and into nearby rivers, streams and into creek, contaminate surface water directly and in turn contrib-ute to increase in microbial pollution. Other negative effects in-clude nutrient enrichment, deterioration of the water quality, and destruction of spawning grounds for aquatic and marine life [6]. ...
... The introduction of seven exotic fish species and the surge of clupeids that are originally marine fish, have become one of the biggest challenges to the lake management authorities and fisheries biologists in Bangladesh. This is somewhat similar to the case in Lake Victoria in East Africa, where despite an increased fish yield, over 200 fish species were lost after introducing Nile perch, Lates niloticus (Linnaeus, 1758) (Ntiba et al., 2001). Kohinoor et al. (1998) observed adverse effects on the overall growth and yield of carp in polyculture with mola carplet (A. ...
Kaptai Lake (KL), the largest artificial lake in Bangladesh, supports an important inland open water fishery. Nevertheless, detailed studies on its fish diversity and environmental threats are still limited. Hence, a study was conducted to evaluate the current fish management scenarios, fish production, relative abundance to improve the production and biodiversity of KL. Data were collected from stakeholders through personal observation, focus group discussions, and cross-check interviews from September 2018 to July 2019. The fish production of KL increased from 1,200 metric tons (MT) in 1965–1966 to 10,577 MT in 2018–2019. The output of the lake was dominated by small fish remarkably, Gudusia chapra (Hamilton, 1822), Gonialosa manmina (Hamilton, 1822), and Corica soborna Hamilton, 1822, accounting for 64 % of the total production in 2018–2019. A total of seventy-six fish species were observed under ten orders, including seven exotic fish species. According to the IUCN Bangladesh, 14 % of total species were identified as vulnerable, 11 % as endangered, 3 % as critically endangered, 11 % as near threatened and 51 % as least concern. The study also identified that climate change and various human-driven causes threaten the fish production and biodiversity of this lake. These findings suggest that community-based fisheries management, protection of natural breeding grounds of carps, control of pollution, amendment of existing fishing laws, and collaborative research would be a necessary approach for mitigating the negative environmental impact of this lake. The overall practical knowledge of this investigation could assist in policymaking and further research.
Keywords: management, threats, fish production, biodiversity, conservation
https://www.asianfisheriessociety.org/publication/abstract.php?id=1359
... The introduction of seven exotic fish species and the surge of clupeids that are originally marine fish, have become one of the biggest challenges to the lake management authorities and fisheries biologists in Bangladesh. This is somewhat similar to the case in Lake Victoria in East Africa, where despite an increased fish yield, over 200 fish species were lost after introducing Nile perch, Lates niloticus (Linnaeus, 1758) (Ntiba et al., 2001). Kohinoor et al. (1998) observed adverse effects on the overall growth and yield of carp in polyculture with mola carplet (A. ...
Kaptai Lake (KL), the largest artificial lake in Bangladesh, supports an important inland open water fishery. Nevertheless, detailed studies on its fish diversity and environmental threats are still limited. Hence, a study was conducted to evaluate the current fish management scenarios, fish production, relative abundance to improve the production and biodiversity of KL. Data were collected from stakeholders through personal observation, focus group discussions, and cross-check interviews from September 2018 to July 2019. The fish production of KL increased from 1,200 metric tons (MT) in 1965-1966 to 10,577 MT in 2018-2019. The output of the lake was dominated by small fish remarkably, Gudusia chapra (Hamilton, 1822), Gonialosa manmina (Hamilton, 1822), and Corica soborna Hamilton, 1822, accounting for 64 % of the total production in 2018-2019. A total of seventy-six fish species were observed under ten orders, including seven exotic fish species. According to the IUCN Bangladesh, 14 % of total species were identified as vulnerable, 11 % as endangered, 3 % as critically endangered, 11 % as near threatened and 51 % as least concern. The study also identified that climate change and various human-driven causes threaten the fish production and biodiversity of this lake. These findings suggest that community-based fisheries management, protection of natural breeding grounds of carps, control of pollution, amendment of existing fishing laws, and collaborative research would be a necessary approach for mitigating the negative environmental impact of this lake. The overall practical knowledge of this investigation could assist in policymaking and further research.
... The study was conducted along Lake Victoria shoreline in Magu district, Tanzania which is among the seven districts in Mwanza region involved in fishery activities along Lake Victoria (DADPs, 2009(DADPs, /2010 (Ntiba et al., 2001), is not mentioned in the refernces list occupying an area of about 15,000 ha. The data for this study was collected from Ihale, Nyamikoma and Nyakaboja landing sites ( Figure 1). ...
This study was conducted to assess body size distribution and Catch Per Unit Effort (CPUE) of Nile perch (Lates cf. niloticus) captured using three common fishing gears at Magu district in Tanzania. Three landing sites along Lake Victoria were selected for this assessment. Each site was visited twice per week for two months. At each site 10 boats were identified based on the gear used and randomly selected for fish count. Ten fish per boat were taken for weight and length measurements. The results show that the main fishing gears used to catch fish at all sites were gillnet (GN), long line (LL) and beach seine (BS). Mean length of captured fish recorded from each gear were 33.7, 41.5 and 43.8 for beach seine, gillnets and long lines respectively, which was below the minimal required length of 50 cm. Large proportion of small landed fish were observed in vessels fishing with beach seine, this was due to illegal nature of the beach seine, where by fishermen used small mesh sizes of 10 mm to 12 mm. However, beach seine had higher CPUE (kg/gear/day) (44.9) and gillnet had the lowest (22.6). This study revealed that the mean length from all sites were below the legal minimum size required by the Tanzanian government, suggesting that all beaches are involves in over exploration of fish.
... Although authorities in Kenya acknowledge the need to reduce sediment pollution, the linkages between land use change and changes in sediment dynamics in the headwater catchments are not well quantified (Nyssen et al., 2004;Vanmaercke et al., 2010Vanmaercke et al., , 2014. There are limited data on sediment export for montane catchments in Sub-Saharan Africa in general and in East Africa in particular (Ntiba et al., 2001;Walling & Webb, 1996). Clearly, this is a significant gap in our knowledge of these environments that requires empirical measurements to address it. ...
Land use change is known to affect suspended sediment fluxes in headwater catchments. There is however limited empirical evidence of the magnitude of these effects for montane catchments in East Africa. We collected a unique 4-year high-frequency data set and assessed seasonal sediment variation, water pathways, and sediment response to hydrology in three catchments under contrasting land use in the Mau Forest Complex, Kenya's largest tropical montane forest. Annual suspended sediment yield was significantly higher in a smallholder agriculture-dominated catchment (131.5 ± 90.6 t km −2 yr −1) than in a tea-tree plantation catchment (42.0 ± 21.0 t km −2 yr −1) and a natural forest catchment (21.5 ± 11.1 t km −2 yr −1) (p < 0.05). Transfer function models showed that in the natural forest and the tea-tree plantations subsurface flow pathways delivered water to the stream, while in the smallholder agriculture shallow subsurface and surface runoff were dominant. There was a delayed sediment response to rainfall for the smallholder agriculture and the tea-tree plantations. A slow depletion in sediment supply suggests that the wider catchment area supplies sediment, especially in the catchment dominated by smallholder farming. In contrast, a fast sediment response and depletion in sediment supply in the natural forest suggests a dominance of temporarily stored and nearby sediment sources. This study shows that the vegetation cover of a forest ecosystem is very effective in conserving soil, whereas catchments with more bare soil and poor soil conservation practices generated six times more suspended sediment yield. Catchment connectivity through unpaved tracks is thought to be the main explanation for the difference in sediment yield.
... Governance, too, is also a key factor around these issues. The Lake Victoria Basin is one of the regions in East Africa with the highest population density [29], averaging approximately 500 persons per km 2 , and, in some parts of Kenya, densities of up to 1200 persons per km 2 have been reported [1]. The basin is home to over 30 million people [30] whose livelihoods depend mainly on agriculture and livestock production, beekeeping, mining, trade, and fishing [9]. ...
The Lake Victoria Basin (LVB) is a significant resource for five states within East Africa, which faces major land use land cover changes that threaten ecosystem integrity and ecosystem services derived from the basin's resources. To assess land use land cover changes between 1985 and 2014, and subsequently determine the trends and drivers of these changes, we used a series of Landsat images and field data obtained from the LVB. Landsat image pre-processing and band combinations were done in ENVI 5.1. A supervised classification was applied on 118 Landsat scenes using the maximum likelihood classifier in ENVI 5.1. The overall accuracy of classified images was computed for the 2014 images using 124 reference data points collected through stratified random sampling. Computations of area under various land cover classes were calculated between the 1985 and 2014 images. We also correlated the area from natural vegetation classes to farmlands and settlements (urban areas) to explore relationships between land use land cover conversions among these classes. Based on our land cover classifications, we obtained overall accuracy of 71% and a moderate Kappa statistic of 0.56. Our results indicate that the LVB has undergone drastic changes in land use land cover, mainly driven by human activities that led to the conversion of forests, woodlands, grasslands, and wetlands to either farmlands or settlements. We conclude that information from this work is useful not only for basin-scale assessments and monitoring of land cover changes but also for targeting, prioritizing, and monitoring of small scale, community led efforts to restore degraded and fragmented areas in the basin. Such efforts could mitigate the loss of ecosystem services previously derived from large contiguous land covers which are no longer tenable to restore. We recommend adoption of a basin scale, operational, Earth observation-based, land use change monitoring framework. Such a framework can facilitate rapid and frequent assessments of gains and losses in specific land cover classes and thus focus strategic interventions in areas experiencing major losses, through mitigation and compensatory approaches.
... Fisheries are a vital industry in the Lake Victoria Basin, being a major source of income for the population and a driver for many regional economies (Njiru et al. 2008). However, the lake is under severe pressure due to overfishing and pollution (Ntiba et al. 2008). Promoting a shift from wild catch fisheries to sustainable aquaculture is vital (Bostock et al. 2010) for safeguarding the lake ecosystem and the provision of a reliable protein supply for the region's ever-expanding population. ...
Lake Victoria, regionally important both as a food and income source, is under pressure due to overfishing and severe pollution. Currently, the vast majority of east African aquaculture is open pond based. The adoption of modern, sustainable, aquaculture technologies and practices – in this case study recirculating aquaculture systems (RAS) – will aid the region to increase food security and decrease the current reliance on imported fish and stressed wild stocks. To this end, VicInAqua, a project under the EU Horizon 2020 programme, has developed a pilot Nile Tilapia (Oreochromis niloticus) hatchery in Kisumu, Kenya using RAS adapted to local conditions. The hatchery is designed as a flexible, scalable and modular system. An online monitoring system enables the farmers to access farm data both from fish tanks and the supporting renewable energy systems allowing around the clock monitoring and control. The hatchery is linked to a 14.3 kWp Photovoltaic system including 30 kWh lithium‐battery storage to supply sustainable electricity. Treated by a membrane bioreactor (MBR), water for the RAS, certified for use in aquaculture and agriculture, comes chiefly from Kisumu's municipal sewage reducing the farms reliance on an expensive and occasionally intermittent potable water supply. The coupling of these technologies represents a first for the industry and offers a working example for larger scale future developments. The purpose of the project is to demonstrate the possible technologies and practices in situ as well as providing a template for future development and investment. The hatchery is used by the Department of Livestock, Agriculture and Fisheries, Kisumu County, Kenya, as a training and demonstration facility to promote the aquaculture sector and increase awareness, knowledge and skills for fish farmers as well as providing high quality fingerlings to cage farmers within the lake. This article is protected by copyright. All rights reserved.
... Eutrophication tends to affect shallow lake systems more than deeper tropical lakes (Kemka et al., 2006). Population growth, intensified agriculture (including the use of agrochemicals) and deforestation are the main drivers of nutrient-rich inflows into shallow tropical reservoirs (Ndebele-Murisa et al., 2010;Ntiba et al., 2001). ...
Man-made reservoirs are important inland ecosystems that provide food and livelihoods in many countries. Due to the dispersed nature of inland fisheries, most individual systems are rarely adequately assessed or monitored, therefore reliable data on the target stocks are largely unavailable to implement management strategies. This thesis focuses on Tono, Bontanga and Golinga reservoirs in northern Ghana which contribute significantly to food nutrition and community livelihoods. The thesis presents studies that demonstrate how differences in reservoir use patterns, reservoir morphometry and physicochemical characteristics influence ecosystem structures and fisheries resource productivity. The thesis includes (i) an assessment of empirical models for reservoir harvest estimations, (ii) a study relating morphometric characteristics of the reservoirs to fish production, (iii) assessments of the exploitation levels and stock status of the reservoirs’ target species and (iv) a holistic description of the reservoirs’ biological interactions through a food web modelling approach (Ecopath with Ecosim). To improve the estimation of current harvest potential of West African reservoirs, the relationship between total annual fish catch and reservoir surface area was modelled, which compared to a previous model, indicated that catches from reservoirs in the region have more than doubled over the last two decades. While the analysis indicated that fisheries productivity is inversely correlated with both mean depth and surface area, no significant correlation was found with reservoir age. The exploited resources in the small-scale fisheries of the Tono, Bontanga, and Golinga reservoirs were assessed based on length frequency samples. Growth, mortality, exploitation status, stock size, and relative yield per recruit reference points were determined using bootstrapping fish stock assessment (BFSA), a novel framework that allows for the estimation of uncertainties around the life-history parameters and reference levels (e.g., L∞, K, and F0.1). A complementary assessment approach based on length-based indicators was used to calculate the species’ spawning potential ratios under the current exploitation regime. Tono, Bontanga and Golinga reservoirs provide a total fish catch of 10.1, 15.5 and 17.1 t km−2 yr−1, respectively. The reservoir fisheries are dominated by two cichlid species (Sarotherodon galilaeus and Oreochromis niloticus). The cichlid species Oreochromis niloticus, Sarotherondon galilaeus, and Coptodon zillii were found to be heavily exploited in all three reservoirs. The giraffe catfish, Auchenoglanis occidentalis was found only in Tono and Bontanga reservoirs. In Bontanga, the catfish stock is fully exploited. While in Tono, the giraffe catfish is underexploited, the current fishing mortality could be doubled to increase yield. The length-based indicators suggested all the species at Bontanga and O. niloticus and S. galilaeus populations at Golinga have spawning stock biomasses below 40% of the unfished biomass. This points to a situation of a possible ongoing recruitment overfishing of those species in the two reservoirs and suggests that a further increase in fishing effort is not advisable. To support the construction of reservoirs’ food web models, a study was conducted on the feeding characteristics of the giraffe catfish with the expectation that the population in Reservoir Tono, which has an extensive macrophyte coverage, feeds more on plant material and associated insects than their counterparts in the Reservoir Bontanga. The study showed that fish food items did not differ significantly between the two reservoirs. Insect larvae and algae dominated the stomach contents. Comparative analysis of the reservoirs showed interesting differences: the mean trophic level of the catch was lowest in the largest and deepest reservoir (Tono), likely due to higher trophic level species occupying less accessible deep ‘refuge’ habitats. In the medium-sized (Bontanga) and small shallow (Golinga) reservoirs, in contrast, a larger catch portion resembles high trophic level species. Lake Bontanga differs from the other reservoirs by having a lower human population impact, a significantly lower Total Primary Production to Total Respiration ratio, a higher Total Biomass to Total System Throughput ratio, a higher Finn Cycling Index, a higher Detritivory to Herbivory ratio as well as the highest gross efficiency of the catch, all indicative for a more developed ecosystem. The smallest shallow (Golinga) reservoir is more impacted by anthropogenic activities than the other two reservoirs as indicated by the high levels of dissolved organic carbon, total dissolved nitrogen bonded, nitrite-nitrogen and turbidity in the reservoir. While the smallest lake had the highest fish production (per unit area) under optimal conditions of water supply, it is most vulnerable when used for both irrigated agriculture and fisheries production. The findings of this thesis suggest that the use of man-made lakes and respective catchment areas should be assessed and managed carefully to prevent the loss of nutrition and livelihoods contributions. Finally, this thesis serves as a broad template for the development of sustainable ecosystem-based management measures not only for the three studied ecosystems but for other reservoirs exposed to human activities around the world.
... Eutrophication tends to affect shallow lake systems more than deeper tropical lakes ( Kemka et al., 2006 ). Population growth, intensified agriculture (including the use of agrochemicals) and deforestation are the main drivers of nutrient-rich inflows into shallow tropical reservoirs ( Ndebele-Murisa et al., 2010 ;Ntiba et al., 2001 ). ...
A major constraint to science-based fish stock management in West Africa is the lack of reliable data on target stocks. This especially holds true for inland fisheries, such as those that operate in reservoirs. Due to the low availability of resources and population data, and the limited number of fisheries experts in the region, state institutions and investigators rely heavily on simple catch statistics and empirical models for their estimations of fish production and potential yields. This paper reviews data from the FAO, and published articles and reports on West African reservoirs, with special reference to their morphometric and environmental features in relation to fish catch. In addition, we analyse primary data on three focus reservoirs. First, to improve and update available models of potential harvests from reservoirs, we regress fish catch data against reservoir surface area data for 30 reservoirs in West Africa, yielding the following equation: Catch (tonnes/year) = 17.3 × Area (km2)0.8626. The equation accounts for 95.7% of the variation observed in the fish catches. Analysis of covariance of small (<2 km2) and large (>2 km2) reservoirs shows no significant difference (F = 0.5895, p = 0.45) in the slopes of the two groups. Second, we apply multiple regressions to a sub dataset of 15 reservoirs with surface area and mean depth as predictors; and we also explore reservoir age as a further variable. We find that fisheries productivity is inversely correlated with both mean depth (r = -0.49) and surface area (r = -0.32), but there is no significant correlation found with reservoir age (r = 0.03).
... Other threats to freshwater that are exacerbated by climate change include increased river siltation resulting from high soil erosion in the basin, recurrent destructive floods in the low-lying areas, riparian land encroachment, degradation of river banks, eutrophication, and proliferation of the invasive water hyacinth [23,24]. Increasing intensity and frequency of extreme climatic events pose additional threats to the future ecological and community well-being in the Lake Victoria Basin (LVB) [25]. ...
Rivers in the Lake Victoria Basin support a multitude of ecosystem services, and the economies of the riparian countries (Kenya, Tanzania, Uganda, Rwanda, and Burundi) rely on their discharge, but projections of their future discharges under various climate change scenarios are not available. Here, we apply Vector Autoregressive Moving Average models with eXogenous variables (VARMAX) statistical models to project hydrological discharge for 23 river catchments for the 2015–2100 period, under three representative concentration pathways (RCPs), namely RCPs 2.6, 4.5, and 8.5. We show an intensification of future annual rainfall by 25% in the eastern and 5–10% in the western part of the basin. At higher emission scenarios, the October to December season receives more rainfall than the March to May season. Temperature projections show a substantial increase in the mean annual minimum temperature by 1.3–4.5 °C and warming in the colder season (June to September) by 1.7–2.9 °C under RCP 4.5 and 4.9 °C under RCP 8.5 by 2085. Variability in future river discharge ranges from 5–267%, increases with emission intensity, and is the highest in rivers in the southern and south eastern parts of the basin. The flow trajectories reveal no systematic trends but suggest marked inter-annual variation, primarily in the timing and magnitude of discharge peaks and lows. The projections imply the need for coordinated transboundary river management in the future.
... Located on the banks of Lake Victoria in Kenya, Kisumu has encountered many food-system shifts, from the depletion of a key protein resource in the Lake, as a result of the introduction of the Nile Perch [49], to more recent ecological challenges driven by increased effluent and agricultural run-off into the lake and the increase in water hyacinth [50]. The land-based resource has also seen significant change where traditional and more localised crops have been replaced with cash crops such as sugar. ...
Global food insecurity levels remain stubbornly high. One of the surest ways to grasp the scale and consequence of global inequality is through a food systems lens. In a predominantly urban world, urban food systems present a useful lens to engage a wide variety of urban (and global) challenges—so called ‘wicked problems.’ This paper describes a collaborative research project between four urban food system research units, two European and two African. The project purpose was to seek out solutions to what lay between, across and within the different approaches applied in the understanding of each city’s food system challenges. Contextual differences and immediate (perceived) needs resulted in very different views on the nature of the challenge and the solutions required. Value positions of individuals and their disciplinary “enclaves” presented further boundaries. The paper argues that finding consensus provides false solutions. Rather the identification of novel approaches to such wicked problems is contingent of these differences being brought to the fore, being part of the conversation, as devices through which common positions can be discovered, where spaces are created for the realisation of new perspectives, but also, where difference is celebrated as opposed to censored.
... The water prevents the wood from cracking. Boats not-in-use are normally stationed ashore [6,12] during months when fishing is illegal [4,56,57], when fish catches are significantly low, when actors are off duty and during tumultuous party times when fishermen revel after receiving cash bonuses from their cooperative societies. That aside, it is unlikely that the larvae found in boats were introduced through the maintenance process. ...
Background
Everyday hundreds of people, mainly men, set out to take part in a vibrant artisanal capture fishing (ACF) industry on Lake Victoria. It is not known whether actions of artisanal fishers, in their unrelenting quest for existence, surpass ecosystems’ sustainability thresholds with potentially negative repercussions on human health with respect to malaria transmission potential. This article sought to fill this information gap.
Methods
This study used an ecosystem approach to find out how ACF processes facilitate the breeding of mosquitoes. The observational study adopted a cross-sectional design and was carried out on Mageta Island situated inside Lake Victoria in western Kenya.
Results
Of the 87 mosquito larval habitats identified 27 (31%) were created through ACF activities. The ACF-related habitats, hereafter collectively referred to as ‘fishing habitats’, included fishing boats (24), trenches (1) and fish bait mines (2). About half (48%) of Anopheles larvae were recovered from fishing habitats. The mean larval density in the fishing habitats (35.7 ± 1.15) was double that in non-fishing habitats (17.4 ± 0.539). Despite being the most common ‘non-fishing habitat’ type (N = 32), the mean number of Anopheles larvae present in rock pools (30.81 ± 10.54) was significantly less than those found inside fishing boats (N = 24; 40.08 ± 10.16). Overall, man-made habitats and those used to support livelihoods contained significantly more Anopheles larvae.
Conclusions
These data show that artisanal capture fishing is a key driver of malaria epidemiology on Mageta Island. This suggests that larval source management strategies in the global south should pay attention to the heterogeneity in Anopheles breeding habitats created through livelihood activities.
... According to FAO [14], "The effective management of natural resources requires engagement of the resource users and attendant communities through sensitization as a starting point to achieve successful enforcement operation". People's lack of knowledge of their responsibilities in bringing about a favourable environment for a sustainable fishery may also weaken their effective participation in the management of natural resources and fisheries in particular [15]. Therefore, empowering the communities through sensitization on the fisheries regulations is the first step toward effective management and consequently sustainable utilization of fisheries resources. ...
... Pollution from tanning, fish processing and abattoirs has also been reported in the rivers and streams draining to the lake. As demand for land increases because of population growth, urbanization and agricultural expansion, forests and wetlands have been cleared, leading to environmental degradation and increased sediment deposition in rivers and lakes (Ntiba et al. 2001). This observation suggests sediments may be an additional sink and/or source of pesticides and heavy metals. ...
... According to FAO [14], "The effective management of natural resources requires engagement of the resource users and attendant communities through sensitization as a starting point to achieve successful enforcement operation". People's lack of knowledge of their responsibilities in bringing about a favourable environment for a sustainable fishery may also weaken their effective participation in the management of natural resources and fisheries in particular [15]. Therefore, empowering the communities through sensitization on the fisheries regulations is the first step toward effective management and consequently sustainable utilization of fisheries resources. ...
... Thus, to combat illegal fishing methods, the community should be involved in the management of the resources to ensure its sustainability. Participatory strategies should be employed as the government alone may not be able to control all the activities taking place in the resources [34]. For any conservation program to be successfull, it must get a support from the government but with the active participation of the beneficiaries of the resources [35]. ...
... Water hyacinth has a high growth rate as it can double its area coverage in only 5 days [11]. According to the opinion of nine of the FGDs, the area under water hyacinth has increased in their vicinities. ...
... It is particularly important to increase sites attractiveness and support lake-based tourism industry. In such scenarios development, determining lands viability and suitability to enhance sustainable lake-based tourism area becomes important [6] [7]. ...
The objective of the research is to identify and classify soil in an area surrounding Linow Lake, North Sulawesi for agrotourism development purposes. Result of the study confirm that lands surrounding Linow Lake can be classified into nine lands unit. The landform of these units dominated by hilly volcanic and soils were varies namely Aquic eutrudept, Humic dystrudept, Typic dystrudept, humic hapludult, Typica sulfudept and sulfic endoaquept. Soils in area surrounding Linow Lake can be classified into two orders namely Inceptisols and Ultisols. Inceptisols is characterized by cambic horizon as shown on soil profile 1,2,6 and 7. Ultisols is characterized by the existence of argillic B horizon, as shown on soil profile 4,5 and 8. The possibility for agrotourism development lies on the opportunities to plant some fruit trees, i.e. Rambutan, Lansat, Avocado, Durian, Guava, Papaya and Banana in policulture systems, or technically called agroforestry. The planting arragement and management should be meets the landcapability and suitability.
... Despite direct discharge of untreated municipal waste and sewerage in different parts of Lake Victoria catchments in Kenya (Ntiba et al. 2001) and Uganda (Bugenyi 1991;Naiman et al. 1995), the observed variance in the condition of B. altianalis between the systems were due to among others environmental quality fluctuations partitioned by the barriers created as result Fig. 3 Mean relative condition of B. altianalis derived after pooling data from all the landing sites sampled in River Nile, Lake Edward and Kazinga Channel. Vertical bars represent ±1 standard error. ...
Environ Biol Fish DOI 10.1007/s10641-016-0540-7
Condition factor, Length – Weight relationship, and the fishery of Barbus altianalis (Boulenger 1900) in Lakes Victoria and Edward basins of Uganda’
C. C. Ondhoro., C. Masembe., G. E. Maes., N. W. Nkalubo., J. K. Walakira., J. Naluwairo., M. T. Mwanja & J. Efitre.
Abstract
The condition, fishing effort and environmental parameters signify health of fish populations. This study characterized differences in water quality and fishing effort in the lacustrine and riverine systems of the River Nile, Lake Edward and Kazinga channel in Uganda. One-way Analysis of Variance (ANOVA) was used to test for differences in mean relative condition among populations in the water bodies exposed to different levels of fishing effort and water quality conditions. There were significant differences in the mean relative condition (Kn) of Barbus altianalis between River Nile (mean dif 0.0880, P < 0.001). No significant difference in the mean relative condition between Kazinga channel and Lake Edward (mean diff. 0.0840, P < 0.95). Lake Edward had the highest condition (1.05), while Kazinga channel and River Nile had 1.04 and 0.96 respectively. The relationship between weight and length for each population, obtained by pooling individuals across systems was significant (P < 0.001), the
length-weight allometry between the populations was also ignificantly different (F (2, 237) = 9.73, P < 0.001). River Nile had the highest number of fishers of 311 ± 0.88 while the number of fishers in Lake Edward and Kazinga channel were 75 ± 2.45 and 33 ± 9.12, respectively. Catch rates varied between River Nile (1.92 ± 0.59 Kg boat-1 day-1) and the rest of the systems, 6.20 ± 1.86 and 6.85 ± 1.49 Kg boat-1 day-1 in Lake Edward and Kazinga channel respectively. Water quality varied greatly across all the water bodies. Dissolved oxygen was below the minimum of 5 mgl-1 required for the physiology of freshwater fish. Conductivity was highest in Lake Edward (312 µS cm-1), followed by Kazinga channel and least in River Nile. The consistent variation in condition, fishing effort and water quality, indicates differential selective pressures faced by B. altianalis in the systems and therefore calls for concerted efforts for appropriate management measures.
Keywords: Relative condition . Populations. Fishing effort . Frame survey. Water quality
... Despite direct discharge of untreated municipal waste and sewerage in different parts of Lake Victoria catchments in Kenya (Ntiba et al. 2001) and Uganda (Bugenyi 1991;Naiman et al. 1995), the observed variance in the condition of B. altianalis between the systems were due to among others environmental quality fluctuations partitioned by the barriers created as result Fig. 3 Mean relative condition of B. altianalis derived after pooling data from all the landing sites sampled in River Nile, Lake Edward and Kazinga Channel. Vertical bars represent ±1 standard error. ...
The condition, fishing effort and environmental parameters signify health of fish populations. This study characterized differences in water quality and fishing effort in the lacustrine and riverine systems of the River Nile, Lake Edward and Kazinga channel in Uganda. One-way Analysis of Variance (ANOVA) was used to test for differences in mean relative condition among populations in the water bodies exposed to different levels of fishing effort and water quality conditions. There was significant differences in the mean relative condition (Kn) of Barbus altianalis between River Nile (mean dif 0.0880, P <0.004) and Lake Edward and between River Nile and Kazinga channel (mean dif. 0.0796, P < 0.001). No significant difference in the mean relative condition between Kazinga channel and Lake Edward (mean diff. 0.0840, P < 0.95). Lake Edward had the highest condition (1.05), while Kazinga channel and River Nile had 1.04 and 0.96 respectively. The relationship between weight and length for each population, obtained by pooling individuals across systems was significant (P < 0.001), the length-weight allometry between the populations was also significantly different (F (2, 237) = 9.73, P < 0.001). River Nile had the highest number of fishers of 311 ± 0.88 while the number of fishers in Lake Edward and Kazinga channel were 75 ± 2.45 and 33 ± 9.12, respectively. Catch rates varied between River Nile (1.92 ± 0.59 Kg boat-1 day-1) and the rest of the systems, 6.20 ± 1.86 and 6.85 ± 1.49 Kg boat-1 day-1 in Lake Edward and Kazinga channel respectively. Water quality varied greatly across all the water bodies. Dissolved oxygen was below the minimum of 5 mg/l required for the physiology of freshwater fish. Conductivity was highest in Lake Edward (312 µS cm-1), followed by Kazinga channel and least in River Nile. The consistent variation in condition, fishing effort and water quality, indicates differential selective pressures faced by B. altianalis in the systems and therefore calls for concerted efforts for appropriate management measures.
... This region of sub-Sahara African hosts the most vulnerable populations to water stress [Rekacewicz, 2009], an alarming fact given that water scarcity is projected to increase [Meigh et al., 1999] due to climate change [UNEP, 2008], population growth and development [Falkenmark, 1990[Falkenmark, , 1997Fischer and Heilig, 1997;Wallace, 2000]. East Africa encompasses a number of surface lakes ( Figure 1) that significantly contribute to the productivity of the area by supporting a number of activities including fishing, agriculture, transport, and hydropower generation [Molsa et al., 1999;Ntiba et al., 2001;Awange et al., 2007;UNEP, 2008;Swallow et al., 2009;Maitima et al., 2010]. Lake Victoria, the largest regional lake, is known for generating great amounts of hydro-electricity for the entire region [Awange and Ong'ang'a, 2006], supplying over 30% of food to communities in its basin through fishing [Song et al., 2004] and supporting the livelihoods of over 70% of its basin communities through agriculture [Kayombo and Jorgensen, 2005]. ...
Although the use of the Gravity Recovery and Climate Experiment (GRACE) satellites to monitor groundwater storage changes has become commonplace, our evaluation suggests that careful processing of the GRACE data is necessary to extract a representative signal especially in regions with significant surface water storage (i.e. lakes/reservoirs). In our study, we use cautiously processed datasets, including GRACE, lake altimetry and model soil moisture, to reduce scaling factor bias and compare GRACE-derived groundwater storage changes to in-situ groundwater observations over parts of East Africa. Over the period 2007-2010, a strong correlation between in-situ groundwater storage change and GRACE-groundwater estimates (Spearman's ρ = 0.6) is found. Piecewise trend analyses for the GRACE-groundwater estimates reveal significant negative storage changes that are attributed to groundwater use and climate variability. Further analysis comparing groundwater and satellite precipitation datasets permits identification of regional groundwater characterization. For example, our results identify potentially permeable and/or shallow groundwater systems underlying Tanzania and deep and/or less permeable groundwater systems underlying the Upper-Nile basin. Regional groundwater behaviors in the semi-arid regions of Northern Kenya are attributed to hydraulic connections to recharge zones outside the sub-basin boundary. Our results prove the utility of applying GRACE in monitoring groundwater resources in hydrologically complex regions that are under-sampled and where policies limit data accessibility.
... The existence and size of a wetland can be dynamic, and depends on the balance between water input from precipitation and surface and ground water supplies and water losses through evaporation and run off (Woo 1992). The changes in wetland extent are influenced by a variety of factors including climate change, sedimentation in wetlands and the rivers feeding the wetlands (Ntiba et al. 2001;Ganjali and Ildoromi 2012;Wang et al. 2014), overexploitation of wetlands and the rivers coming to the wetlands for agricultural and fishery activities, agricultural wells (Ghazali 2012;Ibanez and Caiola 2013), dams, channel drainage, mining practices and urban development (Cowan 1995). The degradation and loss of wetlands can lead to serious consequences such as flood damage, erosion and dust storms, habitat loss and extinction of species (Carter 1996;Shine and De Klemm 1999). ...
Temporal changes in the area of 10 significant wetlands in Iran were determined using the remote sensing image of TM and ETM+ band 5 for a period of 15 years (1998–2012). The relationship between the annual time series of the area and the difference of precipitation and potential evaporation (P-E) was obtained for the wetlands using three evaporation methods. The area of the wetlands was predicted for 2050 using the best-fitting model and seven global climate models under four representative concentration pathways (a total of 28 climate scenarios). The area of five wetlands had a significant positive correlation with the P-E (R2 > 0.72). The area of one wetland (Ghoorigol) is predicted to increase and the area of four wetlands (Bakhtegan, Chaghakhor, Parishan and Gavkhooni) is predicted to decrease in 2050 in comparison to the maximum area of the wetlands from 1998 to 2012 under all the climate scenarios. In comparison to the mean area of the wetlands (1998–2012), one wetland (Ghoorigol) is predicted to be larger and two wetlands (Gavkhooni and Parishan) are predicted to be smaller under all the climate scenarios. Two wetlands (Bakhtegan and Chaghakhor) are predicted to be larger under most of the climate scenarios in 2050. The Uromia wetland, the largest wetland in Iran, is predicted to become completely dry by 2032 if anthropogenic impacts continue similar to what occurred from 1998 to 2012.
This datasheet on Lates niloticus covers Identity, Overview, Distribution, Dispersal, Diagnosis, Biology & Ecology, Environmental Requirements, Natural Enemies, Impacts, Uses, Further Information.
Understanding the factors that contribute to transboundary water conflict and cooperation is critical to improve governance and protect water resources. State interactions are shaped by multiple pressures and multi-scalar actors. This research assesses how local stakeholders influence the state through an analysis of power, water quality-related vulnerability and risk. Based on the findings, local stakeholders directly and indirectly support high-intensity cooperation over transboundary lakes and can foster low-intensity conflict to enable a greater representation of needs. Local actors also mutually influence state and international processes causing a multi-scalar impact and response to the states’ transboundary water quality interactions.
The ongoing global warming has caused unprecedented changes in the climate system, leading to an increase in the intensity and frequency of weather and climate extremes. This study uses the sixth phase of Coupled Model Intercomparison Project (CMIP6) data to investigate projected changes in drought events over East Africa (EA) under four Shared Socioeconomic Pathway (SSP) emission scenarios (SSP1-2.6, SSP2-4.5, SSP3-4.0, and SSP5-8.5). The CMIP6 data are bias-corrected using a quantile mapping method, with the Climatic Research Unit's precipitation dataset as reference. Drought is quantified using the standardized precipitation index and different measures of drought are estimated: drought duration, drought frequency, drought severity, and drought intensity. Evaluating the accuracy and reliability of historical data before and after bias correction demonstrates the importance of the approach. The overall distribution after bias correction depicts a close agreement with observation. Moreover, the multi-model ensemble mean demonstrate superiority over individual Global Circulation Models. Projected future changes show enhancement in precipitation over most parts of EA in the far future under different SSP scenarios. However, the arid and semi-arid regions are expected to receive less amount of precipitation, whereas the highlands and lake regions are expected to receive a larger amount of precipitation increase. Furthermore, the dry areas of EA are likely to experience more frequent drought events with longer duration, stronger intensity, and severity in the far future. Overall, this study identifies possible drought hotspots over EA, enabling early preparation for such events.
Supplementary information:
The online version contains supplementary material available at 10.1007/s11069-022-05341-8.
The changing climatic patterns and increasing human population within the Lake Victoria Basin (LVB), together with overexploitation of water for economic activities call for assessment of water management for the entire basin. Based on the work of [8], this chapter focuses on the analysis of a combination of available in-situ climate data, Gravity Recovery And Climate Experiment (GRACE), Tropical Rainfall Measuring Mission (TRMM) observations, and high resolution Regional Climate simulations during recent decade(s) to assess the water storage changes within LVB that may be linked to recent climatic variability/changes and anomalies.
Background and Objective: Human-induced physical and environmental barriers especially hydropower dams and dense anoxic
vegetation along riverine-lacustrine connectivity are known to isolate and fragment fish populations, leading to variation. This study
explored possible morphological variations among populations of Barbus altianalis from Uganda with the intent to provide a more costeffective and reliable platform for elucidating the stocks under combined environmental and anthropogenic influence as a tool for
improved fisheries management and conservation. Materials and Methods: Multivariate analysis of morphometric variables was
performed to determine the morphological variation and discreteness among three populations of B. altianalis (N = 251) from the
lacustrine (Lake Edward) and riverine (River Nile and Kazinga channel) systems in Uganda. Morphological variation was determined using
a multivariate analysis of advanced truss and non-truss network systems on all individuals collected from commercial catches.
Results: There was a significantly (p<0.001) higher level of heterogeneity among populations. Group means on the DFA1 showed that
River Nile (-0.89) separated furthest from Lake Edward (0.79) and the Kazinga channel (0.68). River Nile had the highest number (80.5%)
of individuals correctly classified while Lake Edward (67.2%) and Kazinga channel (60.5%) had more misclassifications between them, an
indication that they could be much harder to separate. Conclusion: The observed patterns of variation were consistent with the
geographical locations of the different water bodies, that the isolating mechanisms are subjecting the different populations to different
selection pressure hence different phenotypic responses by the populations.
Key words: Discriminant function analysis, Lake Victoria, Edward basins, phenotypic variation, stock identification
The present study demonstrates the declining state of the major commercial fisheries of Lake Victoria, Kenya, a situation threatening sustainability of the lake's fishery. Data in the present study were derived from resource monitoring programmes that included hydro‐acoustics (2009–2018), trawl net fishing (2011–2018), frame surveys (2000–2016) and catch assessment surveys (2000–2015). The activities provided information on fish stocks and supported advice for fisheries management. The average fish stock densities for Tanzania, Uganda and Kenya of 8.92, 8.25 and 8.19 t/km2, respectively, were relatively similar. Diplomatic and sustainable efforts for harmony in fish harvesting among the fishers of the riparian countries are encouraged given the interdependence of the lake. The Kenyan and River Kagera regions had a higher proportion (≈ 4% each) of big‐sized Nile perch (≥50 cm total length) in 2018, signifying the critical breeding areas for Nile perch. To sustain the fishery, there is need to enforce a 36%–44% effort reduction for all the major fisheries, and enforcement of gear limits to avoid harvesting of immature fish and destruction of the lake ecosystem.
The past subsistence of the Lake Victoria fishery was dominated by rich, diverse haplochromine cichlids. This multispecies fishery has undergone a decline over the past four decades, evolving into a commercial fishery consisting mainly of Nile perch (Lates niloticus), Nile tilapia (Oreochromis niloticus) and cyprinid (Rastrineobola argentea species). To better understand Lake Victoria fisheries, studies dating as far back as the 1920s have been carried out to assess the status of the fish stocks. These past studies indicated the lake fisheries were declining because of numerous major challenges, including intense fishing, invasive species, loss of biodiversity, ecological alterations, climate change, inadequate information to inform management and unharmonized policies. Numerous policies and regulations have been developed and implemented over the years to address these issues and manage the fisheries sustainably. Most of the interventions have been sectorial, disjointed and unharmonized and have not reduced the declining fish catch rates. With reestablishment of the East Africa Community (EAC) with several institutions in 1994, the Lake Victoria riparian states initiated an ecosystem approach to manage the Lake Victoria fishery resources in a sustainable manner. This study reviews the development of the Lake Victoria fisheries, outlines major past and present management challenges and provides a set of new strategies to manage the lake's fisheries resources, with emphasis on an ecosystem approach.
Nile perch were secretly introduced into Lake Victoria in the 1950s, and officially in the 1960s, amid unresolved controversy. Proponents were of the view that the introduction would improve fisheries production and sport fishing. Although the former objective was achieved, the side effects were dire, including extinction of many native species, especially the ecologically important haplochromines, because of predation. The introduction also changed the habitat, trophic dynamics and water clarity. The change in water clarity is thought to be responsible for hybridization of haplochromines, further contributing to the loss of species diversity among cichlids. The establishment and expansion of the Nile perch also altered the fishery and socio-economic settings characterizing the lake. A local economy which, until the early 1980s, was based on native fish species has been replaced by an export-oriented exotic fish processing industry that destroyed the once-cherished traditional resource. Other socio-economic issues associated with Nile perch include the high HIV/AIDS prevalence among fishers, and border conflicts attributable to the migratory and transboundary nature of the fishery resource. Conservation measures for the fishery should include establishment of co-management units that have so far registered both successes and challenges. Other efforts include establishment of the Nile perch Fisheries Management Plans that focus on curbing overfishing and eradicating illegal fishing.
Globally, anthropogenic activities continuous to pose wide spread pollution into the aquatic ecosystems
such as rivers. This study set out to assess the sensitivity of Chironomus species to justify their use in
monitoring of riverine ecosystems in the Lake Victoria Basin, Kenya. Chironomid midges sampled from
upstream and downstream of paper mill factory in the River Nzoia and sugar cane factory in the River
Mbogo for toxicity tests in the laboratory. In the laboratory, midges were exposed to different dilutions of
paper-mill factory effluents and sugar cane factory effluents. Results for all the tests were evaluated for
variability among treatment effects and control using analysis of variance (ANOVA). There were
significant effects (p<0.05) of effluents on sensitivity. The study, therefore, concluded that Chironomus
species are sensitive to pollutants emanating from sugar cane processing and paper mill effluents, hence
can be used as test organism in monitoring the health of riverine ecosystems in LVB. It was recommended
that on-field toxicity tests for the Chironomus species be done, studies on expanded toxicity testing
monitoring to spatially and temporally characterize toxic conditions not only on the catchments of L.
Victoria but on the entire aquatic ecosystems in the country be carried out, expanded toxicity testing and
chemical analysis be done on other organisms and lastly studies to be carried out in establishing whether
Chironomus species at contaminated sites have a tolerance that is genetically passed on or acquired.
India has a coastline of about 7500 km and it supports almost 30% of Indian population for their livelihood. The Bay of Bengal and the Arabian Sea are the rich fishing grounds. India continues to be the 7 th largest marine fishing nation in the world. Now-a-days there is a change in the physical, chemical and biological characteristics of coastal water and sediments. It causes degradation of the natural quality of the coastal environments and affects the health and survival of all forms of life. It is a major problem in developing countries and the trends are expected to increase. The main causes of coastal pollution are population growth, urbanization and industrialization. Coastal pollution in India arises mainly from land-based sources like domestic waste, industrial effluents, agricultural runoff, shipping activity, offshore exploration and infrastructural development. Coastal ecology like coral reef loss due to anthropogenic stress, collection and recreational activities, mangroves are also getting degrade due to overexploitation, decline of fish catch rate due to overfishing and overdependence on trawlers. Beaches also get damage and reflect reduction in benthic organisms due to oil pollution. To reduce the impact of coastal threats, industries are encouraged to set up waste treatment plants, adopt measures to minimize waste, recycle waste and recovery and reuse of waste water. To protect the coastal environment must give practice in public awareness, cleaning programme, set standards for effluent discharge, minimal use of pesticides, strict implementation of laws pertaining to prevention and coastal zone management before establishing new industrial units on the coast.
Our study headwater ecosystem is the Lake Victoria basin of East Africa. This ecosystem holds world leading status for freshwater lake size, vertebrate diversity elaboration, species extinctions, exotic species invasions, and freshwater fishery production. It is high in elevation, the source of the Nile River, situated at the centre of the tropics, mostly enclosed by highlands and mountain ranges, and nearly a closed hydrologic system. The ecosystem is old but erratic in persistence on the scale of evolutionary time. Humans may have emerged in the basin, persisted there throughout human history, and recently increased to substantial density. However, the region remains undeveloped with meagre means of transportation, energy production, and industrial activity. Finally, this ecosystem is presently receiving heavy international development assistance including one of the largest and most costly ecosystem study programmes on earth. Lake Victoria has displayed massive ecosystem change in the relatively short three decade period thought to span an original intact system to one still foundering in unanticipated ways (Kaufman, 1992; Goldschmidt et al., 1993; Goldschmidt, 1996; Verschuren et al., 2002).
The Lake Victoria fish fauna included an endemic cichlid flock of more than 300 species. To boost fisheries, Nile perch (Lates sp.) was introduced into the lake in the 1950s. In the early 1980s an explosive increase of this predator was observed. Simultaneously, catches of haplochromines decreased. This paper describes the species composition of haplochromines in a research area in the Mwanza Gulf of Lake Victoria prior to the Nile perch upsurge. The decline of the haplochromines as a group and the decline of the number of species in various habitats in the Mwanza Gulf was monitored between 1979 and 1990. Of the 123+ species originally caught at a series of sampling stations ca. 80 had disappeared from the catches after 1986. In deepwater regions and in sub-littoral regions haplochromine catches decreased to virtually zero after the Nile perch boom. Haplochromines were still caught in the littoral regions where Nile perch densities were lower. However, a considerable decrease of species occurred in these regions too. It is expected that a remnant of the original haplochromine fauna will survive in the littoral region of the lake. Extrapolation of the data of the Mwanza Gulf to the entire lake would imply that approximately 200 of the 300+ endemic haplochromine species have already disappeared, or are threatened with extinction. Although fishing had an impact on the haplochromine stocks, the main cause of their decline was predation by Nile perch. The speed of decline differed between species and appeared to depend on their abundance and size, and on the degree of habitat overlap with Nile perch. Since the Nile perch upsurge, the food web of Lake Victoria has changed considerably and the total yield of the fishery has increased three to four times. Dramatic declines of native species have also been observed in other lakes as a result of the introduction of alien predators. However, such data concern less speciose communities and, in most cases, the actual process of extinction has not been monitored.
The equatorial Lake Victoria is unique in its loss of an estimated two-thirds of its more than 300 endemic cichlid species within the last two or three decades. Great international and local concern has spawned a bibliography of over 2000 references. Based on studies in which PH. Greenwood and the author participated, this contribution selects the key events affecting changes to the fish communities and limnological conditions in the lake since the establishment of the East African Fisheries Research Organization in 1947.
After the disappearance of the haplochromine species in the Nyanza Gulf of Lake Victoria as a result of predation by Lates niloticus, the latter has turned its attention to aquatic invertebrates and other fish. Changes in the diet of the Nile perch with increase in its size have been observed: young L. niloticus preyed mostly on invertebrates, including crustaceans and various small aquatic insects; large, immature L. niloticus supplemented the invertebrate diet with both young and small fish; adults above 80 cm total length were mainly piscivorous. L. niloticus feeds on fish prey of about one third its own length.
The tendency of L. niloticus to switch from one prey item to another, depending on availability, is reported; e.g., in the Nyanza Gulf, the prey diet has shifted from the haplochromine to Caridina nilotica and L. niloticus juveniles.
The haplochromine cichlids in Lake Victoria: An assessment of biological and fisheries interests
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