Get ready for a giant-sized Monday Mustelid!

The Giant Otter (Pteronura brasiliensis) can be found in the Amazon and Pantanal regions of South America. It is the largest otter and the longest of all mustelids, and it is one of the main carnivorous mammals in its range. Indeed, some of its local names include hadami, wankanim, lobo de rio (river wolf), perro de agua (water dog, although that is also used to refer to other animals), onça d’água and ariranha, which both translate to “water jaguar.” For some indigenous cultures, Giant Otters play a role in their mythology, being perceived as water spirits.

Giant Otters have elongated bodies, wing-like tails, and large webbed feet. They have dark brown coats, with short dense fur. Many of them have a pale patch with brown spots on their chins and chests, which look like bibs. The pattern of the patch and spots is unique to each individual. Their coats are extremely soft, and made them a target for fur trappers and led to a significant decline in their population. The Giant Otter’s whiskers are long and sensitive, and allow them to detect the presence of prey underwater. Adult males can grow up to 5.9 feet (1.8 meters) in total body length, from nose to tail. Females are slightly shorter at 5.6 feet (1.7 meters). Males can weigh up to 71 pounds (32 kg), while females weigh around 57 pounds (26 kg).


Within its ecosystem, the Giant Otter is an apex predator and crucial to the ecosystem’s health. Its diet consists primarily of different types of river fish, like piranha, cichlids, catfish and characins. Giant Otters are opportunistic hunters, however, and while they prefer fish they will also take crustaceans, snakes (including anacondas) and small caimans. They are social creatures who live in family groups, and are able to hunt by themselves and in groups. Coordinated hunting can bring down some of the larger animals on the menu, like the caimans and anacondas. The amazing agility and speed of the otters means that hunts can be chaotic and quick, and are largely successful. When the prey is caught, the Giant Otter holds it in its front paws and begins to eat immediately, starting with the head.

During the dry season, Giant Otters start to dig their dens along the exposed river banks. They give birth in these dens, usually around August or September, and the pups do not emerge for a couple of months. The gestation period of Giant Otters is approximately 65 days, after which they will give birth to a litter of one to five pups (the average litter size is two). The entire family group participates in raising the cubs, including the adult males, and they form strong bonds with each other. After the pups reach sexual maturity at the age of two or three years, they will leave their birth families to find new territory and start families of their own. Though Giant Otters are social, they are also territorial, and will defend their patch of the river from other rival groups.


Giant Otters are among the most vocal of all otter species (or at least their calls are the most audible to human hearing), and their rich vocabulary of vocalizations is important in their communication with each other. Different calls are used to mean anything from warnings, interest, aggression, or pleas for attention. The main predator of Giant Otters is humans. They are not generally hunted by jaguars, caimans or anacondas, although the pups are the most vulnerable to predation by other animals. Giant Otters are still poached for their pelts, and their habitat is threatened by deforestation and pollution. They are considered to be an endangered species by the IUCN.

Source for all images used in this post.