Ground-Breaking Hippo Research in Tanzania’s Ruaha River

Few species are as evocative of Africa as the hippopotamus (Hippopotamus amphibious). Entirely dependent on healthy aquatic ecosystems, hippos were once widespread in every freshwater system in sub-Saharan Africa. But in recent years some hippo populations have gone into decline, largely as a result of changes to their habitat.

Tanzania’s Great Ruaha River is the life source for the vast Ruaha-Rungwa ecosystem.  But the Ruaha River, as project partner Dr. Douglas McCauley of the University of California, Santa Barbara, said, “…has been transformed from a river that flowed year-round to a river that now dries for multiple months every year.”  Without free-flowing water, stagnant pools create toxic conditions that aren’t suitable for life.

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Safari Club International Foundation, in collaboration with Dr. McCauley and Dr. Keenan Stears, our partners at the University of California Santa Barbara, began research and conservation efforts in Tanzania’s Ruaha River in the fall of 2015.  Our focus was on hippo populations and their place within Ruaha National Park, one of the largest national parks in the world, around the size of New Jersey.  As water-dependent species, hippos are the ideal indicators of water condition in this ecosystem.  Unlike many large herbivores, the hippo spends most of its time in the water. In the heat of the day, hippos retreat into the deepest pools.

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Our study had three main objectives: 1) What is the average home range of the hippopotamus; 2) What habitats are most preferred and consequently most important to the hippopotamus; and 3) How does habitat use and home range size of the hippopotamus differ when river flow changes?

Brave researchers blazed new ground by fitting one of the largest creatures in the world with a GPS collar.  With a GPS tracker designed to be worn on the hippo’s ankle rather than the neck, hippos were collared at the end of the dry season when water levels were at their lowest and hippos were easier to find. Capturing and collaring one of the most dangerous mammals in Africa is no small feat. A veterinarian from Tanzania National Parks Authority (TANAPA) immobilized all hippos to allow collars to be fitted. Collars were only placed on male hippos since females usually stay in large groups.

One advantage of Ruaha National Park is that it has a strong cell phone network, allowing daily downloads of GPS locations from the hippos’ collars, even while submerged in water.

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The Tanzania hippo project documented that when humans alter the hydrology of a river like the Ruaha, it can seriously and negatively affect animal populations downstream. Upstream irrigation for rice farming is seriously impacting the Ruaha downstream, and causing water that normally flows freely to stagnate and become polluted much more quickly. As herbivores, hippos consume large quantities of grass at night, which is deposited as dung directly into the river where the hippo spends most of its time by day.  Fish, aquatic insects, vegetation and other wildlife depend on hippo compost as a source of nutrients. However, without a regular flush from a flowing system, stagnant pools can easily become toxic from too much hippo dung.

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Because the Ruaha River does not flow freely year-round as it used to, hippos have altered their movements to patterns that didn’t originally exist.  Tracking these movements enables SCI Foundation and its partners in East Africa to better manage this important species, but more importantly, to develop the scientific knowledge base needed to manage the entire freshwater ecosystem.  Going forward, our investments in science-based research and management will give managers the most detailed picture of what is happening and what needs to happen in order to preserve one of the most wonderful ecosystems on earth.

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