Transboundary Survey Reveals Declining Hippo Population Along Zambezi River

Ndanatsiwa Tagwireyi

The first transboundary hippo survey between Zimbabwe and Zambia, conducted along the Zambezi River, has revealed a significant decline in hippopotamus populations due to droughts and human activities.

In October 2022, the African Wildlife Foundation (AWF) supported a survey along a 262-kilometer stretch of the river. The survey documented 1,424 hippos in Zimbabwe and 1,769 in Zambia. Despite having fewer hippos, the Zimbabwean side recorded a higher number of hippopotamus pods (138) compared to the Zambian side (123).

Hippos on the Zambezi River where their population is declining owing to drought and human activities

The 2022 survey was conducted by boat within the Mid Zambezi Valley Region, an AWF priority landscape. This method allowed researchers to approach hippopotamus pods closely for better observation and helped establish more accurate data on the shared hippo population.

The last hippo census in Zimbabwe, conducted in 2002, covered the Zambezi River from below the Kariba Dam Wall to the Mozambique border at Kanyemba, opposite the Luangwa/Zambezi River confluence. Previous surveys showed a population range between 5,763 and 6,320.

The study, published in the International Journal of Environmental Studies in March 2024, provides insights into the population and distribution of the hippopotamus in the Zambezi River. It offers valuable recommendations for the management and sustainable utilization of the Zambezi River hippo population and explores the factors affecting the distribution of these large mammals between Zambia and Zimbabwe.

According to the study, the mid-Zambezi region experiences a severe shortage of grazing areas for four months annually, forcing hippos to migrate and congregate in certain habitats. Additionally, persecution from poaching, hunting, and human-wildlife conflict puts pressure on hippos, leading to a population decline.

The report attributes the hippo population decline to two major factors: droughts and persecution. Droughts affect the availability of grazing areas and reduce water flow, while persecution from poaching, hunting, and human-wildlife conflict puts pressure on hippos.

Most hippos were located in the shallow waters on the Zambian side of the Zambezi River, where siltation challenges have created numerous shallow areas. Throughout the day, hippos seek rest in these shallow waters, with calving hippos favoring these areas to safeguard their calves from drowning.

The report notes that hippos tend to migrate from areas with high persecution to more secure places. Hippos are aggressive, they charge unprovoked, and in Africa, more people are killed by hippos than by any other animal.

The study recorded more hippos, crocodiles, and other wildlife species on the Zimbabwean side than on the Zambian side within protected areas. It also recorded low numbers of hippo pods in communal areas on both sides of the countries.

The joint hippo survey was conducted by ecologists and technical experts from the Zimbabwe Parks and Wildlife Management Authority (Zimparks) and the Zambia Department of National Parks and Wildlife.

The study helps to inform the management of protected areas’ carrying capacities and the management of Human-Wildlife Conflicts. It recommends more studies on hippopotamus migration, population demography, variation in home ranges, and regular population surveys in both rivers and inland waterholes.

AWF Country Director Olivia Mufute expressed satisfaction with the report’s completion, stating, “The survey is crucial in understanding the hippo population and how it changes over time, which will help conservation players make better decisions about the animals.”

She added, “This will also aid Zimbabwe in developing and implementing national action and recovery plans for key species in line with Goal number 3 of AWF Zimbabwe’s 10-year Conservation Strategy.”

Ndanatsiwa Tagwirei is a Public Relations and Communications Specialist based at African Wildlife Foundation (AWF) in Harare.

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