Researchers identify 22 key areas for protecting struggling giant otters

“They’re big, like an overweight Peruvian dog,” is how photographer Santiago Romaní describes giant otters (Pteronura brasiliensis). In 2022, on his trip to the Imiría Regional Conservation Area, a protected area in the Ucayali region of Peru’s east-central Amazon, he observed the aquatic river giants.

That same year, the area’s administration confirmed the presence of this species in a canal leading to Lake Chauya, a wetland that is part of the Imiría protected area. The species had not been documented in the area since 2017.

At present, the species is endangered, according to the International Union for Conservation of Nature (IUCN) Red List of Threatened Species; its primary threats are habitat destruction, overfishing and pollution of water sources by agricultural and extractive industries.

In response to the otter’s plight, a team of experts from 12 South American countries set out to identify and prioritize where conservation efforts should be focused in order for the species to have the highest chance of continued survival. Their results highlight 22 areas and were published in a report earlier this year by the Wildlife Conservation Society (WCS).

“Prioritizing conservation areas is a strategy used to identify the distribution of a threatened species and determine protection actions. This has already been done with other animals, such as the jaguar, the tapir and the spectacled bear,” says Rob Wallace, director of the Greater Madidi-Tambopata Landscape Conservation Program for WCS Bolivia, and who led the team that produced the report.

The giant otter is the largest of the world’s 13 otter species. They grow up to 2.4 meters (nearly 8 feet) in length and can reach 32 kilograms (70.5 pounds). The species is endemic to South America and lives primarily in rivers, lakes and wetlands.

“As a predator, the giant otter plays a role in maintaining fish populations and is also a tourist attraction, as it is one of the most charming species for visitors,” says Juvenal Silva, program coordinator of the Frankfurt Zoological Society in Peru.

According to the WCS report, the giant otter’s historical distribution is 9 million square kilometers (3.5 million square miles), spanning 12 countries in South America: Argentina, Bolivia, Brazil, Colombia, Ecuador, French Guiana, Guyana, Paraguay, Peru, Suriname, Uruguay and Venezuela — with 35.3% of its distribution protected by law.

“In Peru, the giant otter is found in Amazon regions, but primarily within protected natural areas,” says Silva, who was part of the giant otter research team. “The areas with the highest number of sightings are Manu National Park, the Tambopata National Reserve and the Bahuaja-Sonene National Park. However, in some areas, mainly in Tambopata and Bahuaja-Sonene, family groups are being displaced by gold mining.”

To identify priority conservation areas for the giant otter, researchers use historical data, local accounts and field visits to determine the species’ presence in rivers. After three years of data collection, from 2015 to 2018, and an in-person meeting to systematize the data, the researchers determined the existence of 36 areas in South America where the giant river otter is found. The team condensed these 36 to 22 priority areas, which together encompass more than 80 river basins in 12 countries.

These areas vary in size, ranging from 1,367 km2 (528 mi2) to 829,152 km2 (320,000 mi2). Wallace explains that the conservation areas have been determined based on the identification of family groups of otters.

Researchers established three population size categories for giant otters: Type I, with more than 250 breeding adults; Type II, with more than 50 breeding adults; and Type III, with fewer than 50 breeding adults.

“One of the largest is in Peru, with 250 giant otters observed in one location,” he tells Mongabay Latam.

The researchers found giant otter presence in less than 43% of the area they surveyed. However, they were only able to obtain data for 63% of the giant otter’s historical range.

Wallace says more research is needed to fill this gap.

“We need more studies on the giant otter,” Wallace says. “We haven’t been able to determine whether the species exists in that range or whether there simply aren’t enough experts to conduct the assessment.

Wallace adds that gaps are particularly notable in Argentina, Bolivia, Brazil, Colombia and Peru, and that it will be a challenge for the scientific community to work in areas where the presence of giant otters needs to be assessed.

“Otters are known for overturning boats. If you see them, you shouldn’t approach them. You should either move away or scare them away. They move in groups and aren’t very affectionate,” photographer Romaní says.

The giant otter has faced several threats to its survival. In the 1960s, hunting for the fur industry was its main problem, nearly driving the species to extinction. The implementation of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) in 1973 has significantly reduced hunting.

Today, however, threats to the species are more closely linked to the loss of forest cover and the pollution of water bodies with heavy metals, petrochemicals and agricultural runoff.

“The study will be presented to the 12 governments [of the nations where giant otters are found] so they can identify priority areas and make decisions that support the giant otter’s conservation,” Wallace says.

Banner image: The presence of giant otters is indicative of an aquatic ecosystem’s health. Image courtesy of Daniel Rosengren/Frankfurt Zoological Society.

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This story was first published here in Spanish on April 1, 2025.