Across the world, there are thirteen known species of otter. As its name suggests, the giant river otter (Pteronura brasiliensis) is the world’s largest otter, more than twice the size of the world’s smallest otter, which lives in Asia. Giant otters live across South America’s Amazon basin, including Tambopata National Reserve, in southeastern Peru.
As one the Amazon forest’s top predators, along with the jaguar, puma, caiman and anaconda, the giant river otter is the largest member of the weasel family (Mustelidae). It can grow up to 1.80 meters (six feet) in length and weigh more than 30 kilograms (70 pounds). As one of the Amazon’s few exclusively diurnal species, the otter’s excellent eyesight serves as its principal hunting tool, together with its long and extremely sensitive whiskers.
The giant river otter is highly adapted to its watery environment. Its fur is so dense that water never penetrates as far as the skin, and its ears and nostrils close when the animal submerges. Its considerable size and remarkable agility mean that it has few natural predators. In Spanish, the giant river otter is known as the “river wolf” (“lobo del río”), and using its powerful tail it hunts the Amazon rivers and lakes that form its preferred habitats, eating up to four kilograms (8.8 pounds) of fish every day, and supplementing its diet with other river-dwelling creatures, such as crustaceans and even snakes.
Giant river otters are highly social animals. They live in family groups of up to nine or ten individuals, composed of a monogamous breeding pair and their offspring from several breeding seasons. The females of this highly aquatic species leave the water to give birth and nurse their litters of between one and six young, withdrawing to their underground dens. Giant river otters give birth during the dry season (usually in August and September), and the cubs tend to emerge from their dens for the first time in November.
The social interaction of these extended family groups involves grooming, collaborative hunting expeditions, rest and constant communication. Their broad range of up to nine vocalizations is believed to include predator warnings and contact calls. Otters will engage in “periscoping” behavior: lifting their heads and necks out of the water to reveal the unique white throat markings through which individuals can be identified. Young otters will remain with their family groups for around three years, before venturing out to establish their own territory and search for a mate.
For many years, otters were hunted for their pelts. Today, giant river otters are threatened by habitat loss, contamination and degradation, overfishing of their prey and conflicts with fishermen, and infrastructure such as roads and hydroelectric dams. The species is now classified as "endangered" on the International Union for Conservation of Nature (IUCN) Red List.
Populations of giant otters are now highly fragmented and widely dispersed, and Tambopata National Reserve is one of the few protected areas of South America’s forests where they are guaranteed safe refuge, making it home to one of Peru’s last viable otter populations. In Tambopata, the giant river otter’s preferred habitat is the series of oxbow lakes that exist within the boundaries of the National Reserve, including Lake Sachavacayoc, which it shares with the black caiman. The clear waters of oxbow lakes offer ideal hunting conditions in which the otter can employ its excellent eyesight.
Picture credits: ©André Baertschi