Hippo Dung Threatens Fish in Kenya River Studied With Crocodile Boats

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Hippo pools are virtual cesspools in the Mara River, with each two-and-one-half ton animal producing an estimated 22 pounds of dung each day. Small boats disguised to look like crocodiles are being used by scientists to study levels of hippo dung that they think is affecting water quality and threatening the fish population in the Kenya river. The boats are being used by researchers from Yale University and the Cary Institute of Ecosystem Studies who have been studying Mara water since 2008. They are using the boats to scan the river bottom for deposits of hippo poop and water quality measurements.

The robotic boats were disguised as crocodiles upon the suggestion of a local Maasai guide. They are approximately two feet long and weigh 13 pounds. They are decorated with green fabric and foam crock heads. Hippos, considered one of the most dangerous in Africa, seem to be buying into the deception, with the exception of one who decided to chase one of the boats for an exciting 30 seconds. The animals kill close to 3,000 people every year according to the African Wildlife Foundation. In addition to killing people they also are known to attack boats, leading to the crocodile-disguised craft.

The boats were developed by the Robotics Institute at Carnegie Mellon University. They are designed to navigate autonomously, and use Android smartphones for onboard computing. Sonar sensors on the boats measure the depth of fecal deposits in the water, and also measure water temperature and oxygen content. The researchers spent three weeks in Kenya recently, and used the boats in 10 different hippo pools, hoping that the crocodile craft can help them verify the theory that dung is what is threatening fish in the river.

During times that the river is running high the hippo dung washes down river, but during times that the river is running low it settles to the bottom of the pools, attracting bacteria and threatening fish habitat. The bacteria use up a great deal of oxygen, killing fish as high water later flushes the feces out of the pools and downriver, where the oxygen content becomes dangerously low.

Studying the problem has been difficult, as hippos are not only dangerously aggressive but also territorial. They have been known to attack boats, a particular danger in one of their pools. It is estimated that about 4,000 hippos live, and poop, in the river. It has been suspected that fish die-offs downstream from hippo pools have been caused by decaying dung being washed into those areas, but the theory has never been confirmed. If the researchers are able to determine that the animals’ dung is causing the problem with the fish habitat then plans can be made to try and reduce the impact on downstream fish.

Hippos and crocodiles tend to peacefully coexist in the Kenya river, threatening each other much less than fish and hippo dung do, and the boat experiment seems to have been successful in exploiting this relationship. The researchers’ data is not yet published so no definite conclusions have been drawn yet.

By Beth A. Balen

NBC News