Matsés Indigenous People team with Acaté conservation biologists to protect large stronghold populations of endangered giant river otters in their ancestral lands!
Giant river otters (Pteronura brasiliensis), known in Peru as lobos del río or river wolves, are among the most endangered mammal species in the Neotropics, with a wild population estimated at fewer than 5,000 individuals. Reaching lengths of up to 6 feet, giant river otters are apex predators in the Amazon Rainforest. Giant river otters rely on healthy aquatic ecosystems with abundant fish populations for survival, and their diverse diet includes small caimans and anacondas.
The first-ever census of the local giant otter populations in the Matsés territory was successfully completed in 2018. The Matsés field teams counted a total of 296 giant otters across 97 family groups, demonstrating that the Matsés territory has one of the highest giant otter populations ever recorded! In the seasonally flooded forest, otters are more concentrated during the low-water period and establish feeding platforms on beaches and river banks. As the rivers rise, the otters disperse throughout the flooded forest in search of prey. This can make population surveys challenging in the rainy season. Before the start of this initiative, the population of giant river otters was unknown, but populations were thought to be robust due to the Matsés’ territorial protection, which deterred poachers, and their traditional wildlife management practices.
Giant river otters are known to the Matsés indigenous people as onina. Watercolor by Guillermo Nëcca Pëmen Mënquë, a talented and self-taught Matsés artist who illustrated the Matsés ecological texts, readers and apps developed with Acaté.©Acaté
Historical Decline
Giant river otters are highly vocal and conspicuous animals that live in family groups of 6 to 8 individuals. Unfortunately, these characteristics have made otters easy targets for poachers seeking their dense, waterproof pelts, which were processed into luxury garments and fashion accessories. From the 1940s to the 1970s, giant river otter populations plummeted, and the species verged on extinction. Today, the hunting of giant river otters is banned throughout their native range. The impact of commercial poaching, however, has been enduring, with the total extirpation of giant river otters in two countries and profound declines across the remainder of their range. Existing populations are often fragmented and isolated, creating significant challenges for the long-term survival of the species. Giant river otters are classified as Endangered by the IUCN; the species is listed on CITES Appendix 1.
Continued Threats
Even after the cessation of large-scale commercial poaching, the species has struggled to rebound, and the population declines continue in many areas. The current threats include deforestation, overfishing, entanglement in fishing nets, gold mining, the construction of hydroelectric dams, waterway contamination, excessive river traffic, noise pollution, and other forms of human disturbance. Mercury contamination from gold mining, rampant in many regions of Peru, Venezuela, Suriname, and Guyana, is particularly insidious because levels of the highly toxic element are biomagnified in fish species that comprise much of the otters’ diet.
Current global estimates suggest that only between 1,000 and 5,000 giant river otters remain in the wild. This number is alarmingly low, given their extensive range in South America, which historically spanned most of the Amazon and extended into the Pantanal and other tropical wetland ecosystems. To ensure the successful long-term management and conservation of this iconic Amazonian species, further studies on giant river otter populations are clearly needed.
Hope in the Matsés Ancestral Territory
The rainforests of the Matsés Ancestral Territory exist intact today because generations of Matsés fought against the encroachment of outsiders intent on resource extraction.©Acaté
The otter population monitoring methodology was developed by Dr. David Fleck, Acaté Amazon Conservation zoologist, who is a member of the IUCN Species Survival Commission Otter Specialist Group and has been working with the Matsés since 1998. It is important that the census be carried out during the dry season (June to August), because, as noted earlier, during the rainy season, giant otters forage in the flooded forest, travel up small streams, and their feeding platforms and maternity dens (known as holts) are submerged.
Giant otter maternity den – watercolor by Matsés indigenous artist Guillermo Nëcca Pëmen Mënquë.©Acaté
During the dry season, giant otters are concentrated along the major waterways, where they can be readily observed and quantified. Giant river otters have unique patterns of whitish throat patches, allowing for the identification of individual animals. The field teams, after reaching the furthest navigable points of the waterways, quietly paddled downstream, taking detailed notes on all otters they encountered.
They recorded signs of habitation, particularly feeding platforms—areas on riverbanks where giant otters have cleared vegetation for their regular feeding—and maternity dens. Each location was geo-referenced using handheld GPS receivers.
The 2018 census results serve as a baseline for long-term giant otter population monitoring and for assessing the effect of the conservation strategies. We found from the geo-referenced census data that giant otters are more numerous in lakes and large streams than directly along the Javari River, which forms the boundary between Peru and Brazil. Giant otters are less numerous in stretches of waterways where villages are located. In unpopulated stream headwaters, we found extraordinarily large otter family groups (as many as 10 individuals), indicating very healthy populations and ecosystems.
In certain areas of the Matsés’ territory, giant river otter populations are likely being affected by increased river travel, fishing, and the establishment of new settlements, although the exact extent of this impact remains unclear.
After the baseline census in 2018, Acaté personnel and representatives from all the Matsés villages in Peru gathered at the Matsés village of Puerto Alegre. They came together to strategize and develop plans to reduce the impact on local otter populations. The Matsés leaders emphasized the importance of protecting their territory’s boundaries, monitoring and safeguarding the giant otter populations within their region, and educating children about the value of preserving giant otters.
An excerpt from one of the 11 published readers developed by Acaté and Matsés authors to support bilingual education for Matsés children and transmission of traditional ecological knowledge.©Acaté
A follow-up census of giant river otters was conducted in 2020 and 2022. Comparing data from monitoring patrols in 2018, 2020, and 2022 indicates that overall otter populations in the Matsés territory are stable and may even be increasing. There are no areas within the Matsés territory where giant otters have been extirpated. In fact, a greater number of giant otters than anticipated were observed, especially in the more remote upper reaches of the waterways.
We concluded that measures should be taken to reduce human impact on otter populations near villages and areas of high riverine traffic. Measures proposed by the community were to 1) seek funding to provide the Matsés with noiseless, but more expensive, electric outboard motors 2) to evaluate fish populations in heavily fished areas, and 3) to sponsor the creation of fish farms near Matsés villages to reduce fishing pressure in natural waterways.
In 2022, the Matsés and Acaté launched a large scale integrated aquaculture initiative across their 19 communities that proved highly successful. One important benefit of this initiative with respect to otter conservation is a reduction of pressure on river fish stocks and reduction of motorized canoe travel.©Acaté
We are grateful for the foundations and individual donors supporting this initiative. The initial otter census in 2018 was funded by the Mohamed bin Zayed Species Conservation Fund. A second census in 2020 was funded by individual donors. The 2022 otter census, which was combined with a territorial demarcation and vigilance initiative, was funded by an International Union for Conservation of Nature (IUCN)-Save Our Species (SOS) grant. We are currently seeking funding to continue and advance the giant otter population conservation initiative.
If you would like to learn more about or contribute to this project please reach out here.
Giant river otters at their feeding platform – watercolor by Matsés indigenous artist Guillermo Nëcca Pëmen Mënquë.©Acaté
The headwaters of the Matsés Ancestral Territory contain extraordinary levels of biodiversity. Pictured here is the imposing, but rarely seen, King Vulture (Sarcoramphus papa).©Acaté
For over a decade, Acaté has worked directly with the Matsés indigenous people in a true and transparent partnership to support their communities as they strive to protect their cultural self-determination in a rapidly changing world. We operate through implementing strategic programs and real on-the-ground initiatives that help them protect their chosen way of life, traditions, their land, and, ecology from a position of strength and independence. All of Acaté’s field projects are led, coordinated, and undertaken by the Matsés people.
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