Deo Kujirakwinja, who manages the Eastern DRC program for WCS as well as working within the Albertine Rift Program, made a survey of hippos on Lake Edward for his MSc thesis. He undertook one of the most comprehensive surveys of this species anywhere, obtaining correction factors for aerial survey counts by undertaking waterborne counts at the same time. His estimates for the number of Hippos in Virunga Park in 2010 was about 1,000 individuals.
Estimates made by UWA in Queen Elizabeth Park are around 5000 individuals from ground/waterborne counts. In the 1960s Lake Edward and George had supported 30,000 hippos. Today there are only about 6000 hippos. What impact this decline in hippo biomass has on the ecosystem is uncertain but it could be significant. Hippos feed on grass at night within 3-5 km of a lake or river and then defaecate during the day in the lakes. The nutrients they add to the lakes support Tilapia which are the main species harvested by fishermen on the lake and the decline in the fisheries on these lakes, formally some of the most productive in the World, may be in part due to the decline in hippo numbers as well as over fishing.
In the same study that assessed the impacts of elephants on vegetation in Queen Elizabeth Park we also assessed the impacts of hippos on vegetation. The results showed that hippos had more impact on the composition of the habitat with species such as Euclea racemosa, Rhus natalensis, and Azima tetracantha increasing in cover where hippo density has been high. Dichrostachys cinerea a woody shrub or small tree has also increased in cover where hippo density has been high because it is not fed upon by the hippos and is has no competition. Large areas along the Kazinga Channel in Queen Elizabeth Park are dominated by this plant now. It is likely that with time elephants will knock the species back to a more natural density.
We support anti-poaching efforts in Virunga Park to control the poaching of hippos and are working to improve fisheries management on Lake Edward in Virunga Park to reduce the level of illegal activities on the lake. We will also continue to support monitoring of hippos on Lake Edward.