Freshwater biodiversity in the Lake Victoria Basin: Guidance for species conservation, site protection, climate resilience and sustainable livelihoods

Abstract

Key messages ■ The Lake Victoria Basin has exceptionally high diversity and endemism of freshwater species. The Lake Victoria Basin supports a diverse set of freshwater species and habitats, which provide a wide variety of ecosystem services. Of the 651 species of freshwater decapods (crabs, crayfish and shrimps), fishes, molluscs, odonates (dragonflies and damselflies) and selected aquatic plants considered in this project, 204 species (31.3%) are endemic to the region. Levels of endemism are particularly high amongst the fishes, of which 78.2% are endemic to the basin. This richness is due largely to the presence of the large haplochromine cichlid species flock of Lake Victoria and would increase further if the large number of undescribed endemic haplochromine cichlids were considered. ■ Freshwater species in the basin are highly threatened, primarily by pollution, biological resource use (chiefly overfishing), agriculture and invasive species. These threats have resulted in 19.7% of freshwater biodiversity in the region being assessed as threatened and a staggering 76.0% of the region’s endemic freshwater species being assessed as threatened. Levels of threat vary widely amongst the taxonomic groups assessed, with fishes being the most threatened (55.1% of species assessed), followed by molluscs (25.5%), decapods (8.3%), plants (9.0%) and odonates (1.9%). ■ We lack sufficient information on freshwater species to effectively inform environmental and development decision making within the basin. The current lack of basic information on the status and distribution of freshwater species, and the absence of long-term monitoring of freshwater biodiversity were noted as major failings. It was not possible to assess the extinction risk of 13.4% of freshwater species native to the basin (i.e. these species were assessed as Data Deficient (DD)) and this increases to 38.2% when considering only endemic species. Of the taxonomic groups assessed, the highest percentage of DD species was for the fishes (33.3%), followed by the decapods (7.7%), molluscs (6.0%), odonates (1.8%) and plants (0.7%). Additionally, 8.0% of freshwater species native to the basin and 25.5% of endemics, all of which are fishes or molluscs, are assessed as Critically Endangered and tagged as Possibly Extinct. Detailed field assessment is required to confirm whether these species are still extant. ■ Freshwater biodiversity in the basin is suffering ongoing decline and the risk of species extinctions is increasing. The situation is particularly dire for the native haplochromine cichlid species flock of Lake Victoria, which has experienced significant declines attributed in large part due to the introduction of the predatory Nile Perch (Lates niloticus) and environmental changes, such as eutrophication, and for which the Red List Index (RLI) value declined by 63% between 1960 and 2010. ■ Lake Victoria itself supports the greatest richness of freshwater species overall and of threatened, endemic and Data Deficient species in the basin. It is known that species are not evenly distributed across the lake, but at the time of assessment there was insufficient information on the distribution of species within the lake, or on the distribution of habitat types, to present meaningful patterns of intra-lake species richness. However, lake-wide fish surveys were completed in 2017 and the results of these will help to elucidate spatial patterns in the richness of freshwater fishes native to the lake. ■ The ongoing decline in freshwater biodiversity is impacting livelihoods of the rural poor in the basin. Freshwater fishes are particularly important for provision of food (human and animal), and the Lake Victoria fishery supports household livelihoods of millions of people in the basin. Freshwater plants have diverse uses, including for medicine, food, construction and handicrafts, and constitute an important resource, since many communities either lack access to or cannot afford market goods. ■ The region’s freshwater fishes are highly vulnerable to climate change, having high sensitivity, seemingly poor adaptive capacity and an expected high exposure to change. Given the high importance of this group in supporting human livelihoods, freshwater fishes should be a priority for monitoring and, as appropriate, conservation action to reduce the negative impacts of climate change. Freshwater molluscs, odonates and plants of the region all have a medium degree of vulnerability to climate change. ■ Management of water resources needs to take freshwater biodiversity into consideration. Integrated River Basin Management and Environment Flows methodologies need to be adopted to ensure that freshwater ecosystems can sustainably provide water and other ecosystem goods and services in the long term, while at the same time supporting biodiversity. This in turn will maintain social and economic benefits. ■ Site-scale conservation, focussed on freshwater Key Biodiversity Areas (KBAs), can help to guide conservation of freshwater species in the region. Thirty-nine important river, lake and wetland sites have been delineated as KBAs for freshwater biodiversity, including two Alliance for Zero Extinction (AZE) sites. It is now important to raise awareness of their status as validated KBAs and to develop plans for conservation action at these sites. Eighty-two potential KBA site champions have been identified as individuals or organisations well placed to raise awareness of the existence of the KBAs and the issues faced with respect to threats to biodiversity, and to help implement the required actions to safeguard these globally important sites. ■ A critical sites network for freshwater biodiversity in the Lake Victoria Basin has been identified using a systematic conservation planning analysis. We recommend this is used as a scientific basis for potential development and expansion of the existing protected areas network in the Lake Victoria Basin to better represent threatened, endemic and climate change vulnerable freshwater species.