The giant river otter (Pteronura brasiliensis) is one the Amazon forest’s top predators, along with the jaguar, puma, caiman and anaconda. It is the largest member of the weasel family (Mustelidae), and 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 extremely good 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 itself.
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 forest rivers and lakes that are its natural habitat, 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 very 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 said 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 these family groups for around three years, before venturing out to establish their own territory and search for a mate.
For many generations, otters were hunted for their pelts, and in recent decades the principal threat they have faced is habitat loss. The species is now classified as "endangered" on the International Union for Conservation of Nature and Natural Resources Red List. Today, its small groups are widely dispersed, and Tambopata National Reserve is one of the areas of South America’s forests where it is 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, for example, Lake Sachavacayoc, which it shares with the black caiman. The clear water of oxbow lakes offers ideal hunting conditions in which the otter can employ its excellent eyesight.