Hippopotamuses in Colombia

Hippopotamuses are an introduced species in Colombia. Four hippopotamuses were kept by Pablo Escobar in the late 1970s, and upon his death in 1993 they were allowed to wander his unattended estate. By 2019 their population had grown to approximately one hundred individuals, causing concerns for harming the native flora and fauna in the area; as well as posing significant threat to the human population in the area. They are also referred to as "cocaine hippos".

History
In the late 1970s, Colombian drug lord Pablo Escobar kept four hippopotamuses in a private menagerie at his residence in Hacienda Nápoles, 100 km east of Medellín, Colombia. They were deemed too difficult to seize and move after Escobar's death, and hence left on the untended estate.

By 2007, the animals had multiplied to 16 and had taken to roaming the area for food in the nearby Magdalena River. In early 2014, there were reported to be 40 hippopotamuses in Puerto Triunfo, Antioquia.

The estimated population in December 2019 was around 90–120, with their range covering around 2250 km2 and now extending into Santander; it was expected that the population would almost certainly increase to more than 150 individuals within a decade and could reach up to more than 200 hippos, while the range eventually could cover more than 13500 km2. Population projections estimate that there could be thousands within a few decades. The Colombian hippos reach sexual maturity earlier than African hippos. Another study in 2023 revealed the number of existing hippos to be even higher than previously estimated, with already between 181–215 individuals.

Hippopotamuses represent a serious threat to fishermen and other locals. There have been attacks on humans, but as of 2017 none had been fatal.

Conservation concerns
Being non-native introductions, most conservationists considered them problematic and invasive in Colombia, as they have the potential to change the ecosystems, feeding heavily on plants and displacing native species like the West Indian manatee, Neotropical otter, spectacled caiman and turtles. The critically endangered Dahl's toad-headed turtle and Magdalena River turtle are largely restricted to the Magdalena River basin, as are many threatened fish. In 2020, a study showed that there was an increase in the nutrient levels and cyanobacteria in Colombian lakes inhabited by hippos. Cyanobacteria can cause toxic algae blooms and die-offs of aquatic fauna. Despite the limited magnitude of the observed change, it was noticeable since the species' population was still quite small.

In contrast to the opposition by most conservationists, some ecologists have argued that they should remain and might even have a positive effect on the local environment. It has been suggested that the nutrients they introduce to the water and the occasional fish kills caused by them are overall positive, but this was based on a study in their native Africa. Alternatively, the introduced hippos could be a form of Pleistocene rewilding project, replacing species like Toxodon that became extinct in prehistoric times, but Pleistocene rewilding itself is highly controversial. Others have argued that the Colombian hippos should be regarded as a safe population, isolated from the threats faced by African hippos, and that they could be beneficial to the local ecotourism industry.

Control efforts
In 2009, one adult hippopotamus (called "Pepe") was killed by hunters under authorization of the local authorities. When a photo of the dead hippo became public, it caused considerable controversy among animal rights groups both within the country and abroad, and further plans of culling ceased.

Alternative methods have been considered, but they are unproven, or difficult and expensive. In 2017 a wild male hippo was caught, castrated and released again, but it cost about US$50,000.

In 2020, there were no plans by the local government to manage the population, but further studies on their effect on the habitat have been initiated. Because of the fast-growing population, conservationists recommended that a management plan needed to be rapidly developed.

By October 2021, the Colombian government had started a program to sterilize the hippos using a chemical to make them infertile. The approach uses an anti-GnRH vaccine known as GonaCon. Such vaccines turn the immune system against GnRH, a hormone important for sex organ function. During this time alongside both national and international animal rights movements surrounding the hippo population had increased. As such, in an effort to protect the hippos, a lawsuit was filed which explored the interests of the hippos in relation to their management.

In March 2023, it was announced that the Colombian government is proposing transferring at least 70 hippopotamuses to India and Mexico as part of a plan to control their population. Authorities estimate that 170 hippos currently inhabit Colombia and there is a potential for the population to increase to 1,000 by the year 2035.

In November 2023 the Colombian Environment Minister, Susana Muhamad, announced plans to manage the invasive hippo population. This strategy involves three measures, the sterilization of around 40 hippos a year, in addition to translocation and culling measures which were still being explored, citing environmental concerns.

Media
In 2013, the National Geographic Channel produced a documentary about the species in Colombia titled Cocaine Hippos.

In series 3 of The Grand Tour, the presenters went to Colombia to photograph wildlife, including hippos.