Giant otter (Pteronura brasiliensis) are, as the name would suggest, the largest living otters and the largest representatives of the Mustelidae. As anyone who has seen these animals in captivity or the wild can attest, they are also among the most gregarious of all mustelids and emit ear-piercing squeaks, squeals, and barks as they move around together. Groups are typically centered around a dominant breeding pair, residents defending territories against transients, and average group size is between 3 to 8 individuals.