What To Do With Pablo’s Hippos?

Hippos in water

The fall of a Colombian drug lord’s empire left behind a growing problem.

A luxurious estate built by Colombian drug lord Pablo Escobar has become home to another infamous inhabitant.

When Escobar’s empire crashed in the early ’90s, many of the exotic animals he owned, such as rhinos, giraffes and zebras, were safely relocated. But not the hippopotamuses—notoriously difficult to catch and dangerous to confront. Left to fend for themselves on over 4,000 acres, what was once four hippos has become more than 80.

Scientists at UC San Diego and colleagues in Colombia have made the first scientific assessment of the impact this invasive animal has had on local aquatic ecosystems. Over two years, the research team tested water quality values, oxygen levels and stable isotope signatures, comparing lakes with hippo populations to those without.

“This unique species has a big impact on its ecosystem in its native range in Africa, and we found that it has a similar impact when you import it into an entirely new continent with a completely different environment and cast of characters,” says Jonathan Shurin, professor of biological sciences.

The study revealed that the hippos are changing the area’s water quality by consuming large amounts of nutrients and organic material from the surrounding landscape. And since the nocturnal hippos feed on land most of the night and spend their days cooling off in lakes, their large outputs of waste are altering the chemistry of those waters.

“We found that lakes are soupier if they have hippos in them. This can change the kinds of algae and bacteria, leading to ‘pond scum’ and problems like eutrophication, or excess algae production, and harmful algal blooms similar to red tides,” says Shurin.

In the next couple of decades, Shurin warns, there could be more hippos exacerbating the problem. “This study suggests that there is some urgency to deciding what to do about them. The question is: What should that be?”

Shurin is working with the Colombian Ministry of the Environment to devise a strategy for hippo population control via immunocontraception or vaccinating the animals against pregnancy. Such methods have worked with feral horses and other wildlife.

But any solution, Shurin notes, will be easier to implement when there are 80 hippos, rather than thousands.