The Giant Otter or Giant River Otter (Pteronura brasiliensis) is a species of otter that ranges across north-central South America; it lives mostly in and along the Amazon River and in the Pantanal. It is the longest member of this family, although the sea otter is heavier. Unlike most mustelids, giant otters are highly social animals. They live in cohesive family groups, typically consisting of 3–8 members, including parents, siblings, aunts, and uncles. These groups are led by a dominant breeding pair and exhibit strong cooperation and coordination. They are known as the noisiest otter species, utilizing distinct vocalizations to communicate alarm, aggression, or reassurance within their groups. While generally peaceful within their groups, giant otters are territorial. They will exhibit aggression towards rival groups to defend their territories. They lack significant natural predators, but they do compete for food with other apex predators in their habitat, including jaguars, anacondas, caimans, and bull sharks. Family groups employ cooperative hunting strategies to capture prey and defend against potential threats. When excited or threatened, they may snort and expel mucus as a defensive or communicative response. The giant otter's diet primarily consists of fish, including characins, piranhas, and catfish. They will also supplement their diet with crabs, turtles, snakes, and small caimans when fish are scarce. Decades of poaching for their valuable pelts, particularly in the 1950s and 1960s, drastically reduced their population. As a result, they were listed as endangered in 1999. Current wild populations are estimated to be below 5,000 individuals. Key refuges for the species include the Guianas and the Peruvian Amazonian basin, where conservation efforts have helped stabilize populations.