Biomass and distribution of commercially important fish species in lake Victoria (Uganda), their exploitation and management

Until the 1970s, Lake Victoria had a multi-species fishery dominated by the tilapiine and haplochromine cichlids. There were important subsidiary fisheries for more than 20 genera of non-cichlid fishes , including catfishes (Bagrus docmak, Clarias gariepinus, Synodontis spp and Schilbe intermedius), the lungfish (Protopterus aethiopicus and Labeo victorianus) & Cordone 1974). Stocks of most of these species declined and others disappeared following the introduction of four tilapiines (Oreochromis niloticus, Oreochromis leucostictus, Tilapia rendalli and Tilapia zillil) and Nile perch (Lates niloticus) during the 1950s. Since then the commercial fishery in the Uganda portion of Lake Victoria has been dominated by the Nile perch , Nile tilapia (Oreochromis niloticus) and the native cyprinid species, Rastrineobola argentea (Mukene)

Trends in exploitation of the Lake Victoria fishes

Lake Victoria is the second largest lake in the world and is the largest fresh water body in the tropics lying across the equator (0021'N -3°0'S, 31°39' -34°53'E) at an altitude of1116 m above sea level. It is shared between Tanzania (51 %), Uganda (43%) and Kenya (6%). Its greatest length and breadth 400 and 320 km, and respectively; surface area is 68680 km2; mean depth is 40 m and the deepest zone is 60-79 m. The lake's shoreline is extremely irregular and totals some 3 300 km in length. There are a number of large islands (3.7% of the lake's area) especially in the northern half, whose shorelines are as varied as those of the mainland area. It has large expanses of open water, which during rough weather can be difficult to navigate especially by small boat

Large herbivore assemblages in a changing climate: incorporating water dependence and thermoregulation.

The coexistence of different species of large herbivores (ungulates) in grasslands and savannas has fascinated ecologists for decades. However, changes in climate, land-use and trophic structure of ecosystems increasingly jeopardise the persistence of such diverse assemblages. Body size has been used successfully to explain ungulate niche differentiation with regard to food requirements and predation sensitivity. But this single trait axis insufficiently captures interspecific differences in water requirements and thermoregulatory capacity and thus sensitivity to climate change. Here, we develop a two-dimensional trait space of body size and minimum dung moisture content that characterises the combined food and water requirements of large herbivores. From this, we predict that increased spatial homogeneity in water availability in drylands reduces the number of ungulate species that will coexist. But we also predict that extreme droughts will cause the larger, water-dependent grazers as wildebeest, zebra and buffalo-dominant species in savanna ecosystems - to be replaced by smaller, less water-dependent species. Subsequently, we explore how other constraints such as predation risk and thermoregulation are connected to this two-dimensional framework. Our novel framework integrates multiple simultaneous stressors for herbivores and yields an extensive set of testable hypotheses about the expected changes in large herbivore community composition following climate change

How rainfall variation influences reproductive patterns of African Savanna ungulates in an equatorial region where photoperiod variation is absent.

In high temperate latitudes, ungulates generally give birth within a narrow time window when conditions are optimal for offspring survival in spring or early summer, and use changing photoperiod to time conceptions so as to anticipate these conditions. However, in low tropical latitudes day length variation is minimal, and rainfall variation makes the seasonal cycle less predictable. Nevertheless, several ungulate species retain narrow birth peaks under such conditions, while others show births spread quite widely through the year. We investigated how within-year and between-year variation in rainfall influenced the reproductive timing of four ungulate species showing these contrasting patterns in the Masai Mara region of Kenya. All four species exhibited birth peaks during the putative optimal period in the early wet season. For hartebeest and impala, the birth peak was diffuse and offspring were born throughout the year. In contrast, topi and warthog showed a narrow seasonal concentration of births, with conceptions suppressed once monthly rainfall fell below a threshold level. High rainfall in the previous season and high early rains in the current year enhanced survival into the juvenile stage for all the species except impala. Our findings reveal how rainfall variation affecting grass growth and hence herbivore nutrition can govern the reproductive phenology of ungulates in tropical latitudes where day length variation is minimal. The underlying mechanism seems to be the suppression of conceptions once nutritional gains become insufficient. Through responding proximally to within-year variation in rainfall, tropical savanna ungulates are less likely to be affected adversely by the consequences of global warming for vegetation phenology than northern ungulates showing more rigid photoperiodic control over reproductive timing

Trends and spatial variation in water and land footprints of meat and milk production systems in Kenya

Global consumption of livestock products is increasing steadily due to human population growth, poverty reduction and dietary changes raising the demand for already scarce freshwater and land resources. Here, we analyze the changes associated with direct and indirect use of freshwater and land for meat and milk production in three production systems in Kenya between the 1980s and 2000s. We use two resource use indicators, the water footprint (m3/year) and land footprint (ha), to assess changes in freshwater and land use for cattle, goats, sheep and camels in arid, semi-arid and humid production systems. We estimate actual water and land use using Kenya-wide data for yields, feed composition and feed conversion efficiencies. Our results show that the amounts of freshwater and land resources used for production are determined mainly by production volumes and feed conversion efficiencies. Total water and land footprints of milk production increased for goats, sheep and camels but decreased by half for cattle in arid and semi-arid production systems, in correspondence with similar changes in the total numbers of each livestock species. Green water and grazing land footprints dominated in all production systems due to the predominance of indirect use of water to support forage production. The per unit meat footprint for cattle increased significantly between the 1980s and 2000s in all production systems, due to adverse trends in feed conversion efficiency, while changes in the water and land footprints of other animal products were small, due to modest changes in all influencing factors. In contrast, national average footprints per unit of beef and milk show a modest decrease due to a relative shift of production to the more resource-efficient humid production system. Given the potential increase in demand for livestock products and limited freshwater and land availability, feed conversion efficiencies should be improved by rehabilitating degraded rangelands, adopting improved breeds and using appropriate feed compositio

Meat and milk production scenarios and the associated land footprint in Kenya

Increasing demands for meat and milk in developing countries and the associated production growth are driving the expansion of agriculture at the expense of environmental conservation and other land uses. While considerable attention has been directed at improving crop yields to alleviate the pressure on land, there has been far less attention on the implications of the expected intensification of livestock production. Here, we present and analyse the land availability and land footprints of livestock intensification for five scenarios representing various degrees of intensification of meat and milk production by cattle, sheep, goats and camels in arid, semi-arid and humid production systems in Kenya. The first three scenarios are defined by increasing levels of input and management, ranging from low (scenario S1), intermediate (S2) to high (S3) input feed crop cultivation and livestock production. Reference scenario S1 has production practices and output of meat and milk similar to current production practices. In scenarios S2 and S3, the total land used for livestock production remains the same as in S1. Two additional scenarios, S4 and S5, explore opportunities for lessening environmental pressure through reduction of the land footprint of meat and milk production. For each scenario, we quantify the potential availability of grassland and cropland for meat and milk production by cattle, sheep, goats and camel in the arid, semi-arid and humid production systems. A resource use indicator, land footprint (ha), is used to assess changes in land use associated with livestock production. We estimate that the potential increase in production due to intensification from scenario S1 to S2 is 51% for milk and 71% for meat. The potential increase due to improving production from scenario S1 to S3 is 80% for milk and 113% for meat. The area of grazing land, as a percentage of the total potentially available grazing land, decreases from 10% to 6% as productivity increases from scenario S1 to S5. Cropland usage increases from 4% in scenario S1 to 11% in scenario S5. Reduced land demand in scenarios S4 and S5 indicates the possibility that intensification may help reduce the pressure on land and hence promote environmental conservation. Overall, the results suggest that it is possible to increase production to meet increasing demands for meat and milk while also gaining land for environmental conservation through intensification. Realizing the potential presented by the intensification scenarios will be contingent upon successfully establishing and operationalizing enabling policies, institutional arrangements and markets and ensuring that relevant information, services, inputs, and other essential requirements are available, accessible and affordable to herders and farmers

Adaptation opportunities for smallholder dairy farmers facing resource scarcity: Integrated livestock, water and land management

Dairy intensification is a widely used means of achieving food security, improving farmer incomes and enhancing overall economic growth. However, intensification is dependent upon the availability and suitability of natural resources to sustain growth in production. Here, land and water footprints of milk production in three contrasting agro-ecological zones ranging from humid to semi-arid across nine counties of Kenya are quantified. Water and land use footprints across three potential intensification pathways are also outlined and evaluated against the baseline scenario, the currently prevailing practices or the S1 Futures scenario, treated as the benchmark. Intensification pathways focusing on improving livestock breeds, feed provisioning and milk output per cow and distinguished by contrasting management practices perform differentially across the three agro-ecological zones. Total water and land footprints increase for all scenarios relative to the baseline scenario. In particular, all the breed improvement scenarios, have much larger total water footprints than the baseline scenario. Improvement in breed to pure bred cattle across all production systems has the largest total water footprint across all the production systems. Across all the scenarios, the largest reduction in water footprint of milk production (75%) occurs with improvement in breed and feeding practices from two scenarios in the lowlands. Milk production by the cross-bred cattle is most efficient in the lowlands system whereas milk production by the pure breed Ayrshire is most land use efficient in the midlands system. Across the three agroecological zones, improving breeds, feed provisioning and milk production per cow may achieve production intensification but concurrently exacerbates resource limitation. Consequently, the heterogeneity inherent in resource availability across dairy production zones should be considered when developing strategies for increasing dairy production