Colombia begins sterilizing its invasive hippos: what scientists think – Nature.com

Wild hippos spend most of the day immersed in water and can be difficult to capture.Credit: Fernando Vergara/AP Photo/Alamy

Colombia has begun a new campaign to sterilize its invasive hippos, showing signs that it is taking the threat the animals pose to the countrys biodiversity and local communities seriously. The plan is to capture, anaesthetize and sterilize an initial 20 hippos by the end of 2023 as part of a three-pronged approach the government is taking to reduce the rapidly expanding population that has established itself along the countrys Magdalena River.

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The other prongs involve shipping hippos abroad to sanctuaries and zoos, and more contentiously culling some of the animals. Colombias environment minister, Susana Muhamad, announced the plan at a press conference on 2 November.

Earlier this year, researchers feared that Muhamad would not take the action needed to curb the hippo population after she met with animal-rights groups and created a new division of animal protection within the ministry, and the publication of a government-commissioned study on the hippos was delayed. Although some still have concerns, they are glad the ministry is taking action.

There are questions around how all this will be carried out, particularly the euthanasia, but it seems that the government is generally going in the right direction, says Jorge Moreno-Bernal, a biologist at the University of the North in Barranquilla, Colombia.

We are in a race against time in terms of permanent impacts to the environment and ecosystem, Muhamad said at the press conference.

Colombias hippos considered the largest invasive animals in the world flourished in the countryside after escaping from drug-cartel leader Pablo Escobars estate. Escobar illegally imported four hippos (Hippopotamus amphibius) in the 1980s. Left alone after he died in 1993, the male and three females reproduced rapidly thanks to a lack of droughts and predators, factors that normally keep hippo populations in check in their native sub-Saharan Africa.

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A study commissioned by Colombias environment ministry and published in April estimated that there are now 181215 hippos in the country. One model of their population growth estimated that, by 2050, they could number more than 1,000 if measures arent taken to control them1.

Ecologists have been concerned that the highly territorial animals, which can weigh up to 3 tonnes, are altering the composition of Colombias main river with their excrement, and are outcompeting other species, such as the capybara (Hydrochoerus hydrochaeris), for habitat and resources.

Following the April release of the study, which detailed evidence of the damage being caused by the hippos and recommended solutions, the government decided to take action, Muhamad said.

One of the key conclusions is that there is not a single strategy to control the hippos population and their environmental impact, Muhamad told Nature.

The first step is the sterilization campaign, for which the government has put aside 808 million pesos (US$200,000) this year. Each surgical castration will take a team of eight including veterinarians, technicians and support staff between six and eight hours. So far, three sterilizations have been completed, according to David Echevveri, head of biodiversity management, protected areas and ecosystem services at Cornare, the regional environment authority tasked with the campaign. In the coming years, the goal is to ramp up to sterilizing 40 hippos a year.

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Researchers have pointed out that this will be a slow and costly endeavour. Sterilization is only a prerequisite for the other strategies. They must execute the three simultaneously, says Rafael Moreno, an ecologist who participated in the ministry-commissioned hippo study while at the Alexander von Humboldt Biological Resources Research Institute in Bogot.

Muhamad told Nature that a more effective strategy would be to export the animals. During the press conference, she said that the ministry has had a concrete offer from a buyer in India willing to take 60 of the animals, and that Indias environmental authorities are considering it.

Researchers who spoke to Nature are sceptical about the exportation plan because they think it could be costly and logistically challenging. According to Ernesto Zazueta, the owner of the Ostok Sanctuary in northern Mexico who has expressed interest in taking some of the animals, to export 60 hippos to India and another 10 to Mexico would cost a total of about $3.5 million.

The Colombian government will cover the costs of sterilization, and probably the costs of euthanasia, but exportation would be paid for by the zoos or sanctuaries importing the hippos, Muhamad told Nature.

Although the researchers Nature spoke to are glad the government is moving ahead with its plan to control the hippo population, they are concerned that it will rely too heavily on sterilization, because fewer details have been offered about the other two, more effective strategies. After sterilization, the animals would ideally be confined or exported, Moreno says. Returning them to the countryside to roam would allow them to continue to inflict damage on the environment, he says. In the past, sterilization efforts havent been effective, because the hippos bred faster than they could be caught and operated on.

Moreno is also concerned by the ministrys announcement that it will consult citizen groups about the process of euthanizing the animals. It is a technical matter that should be taken by experienced professionals, he says.

Ecologists say that culling will be necessary. But that part of the initiative will probably be met by legal challenges, says Elliot Doornbos, a senior lecturer in criminology at Nottingham Trent University, UK. A public outcry occurred after a photo of a dead hippo was shared online in 2009 and caused efforts to rein in the population to be halted.

Muhamad told Nature that the environment ministry is working with experts to draw up an ethical euthanasia protocol that will be consulted in different expert committees to ensure its efficiency and rigour.

Depending on how many we export and how many we can sterilize, we will see how many we will have to cull, she added.

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Colombia begins sterilizing its invasive hippos: what scientists think - Nature.com