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Giant Otter (Brazilian, Flat-tailed or Margin-tailed Otter)

The longest otter in the world

Order: Carnivora

Family: Mustelidae

Genus & Species: Pteronura brasiliensis


The giant otter is the longest of all the otter species, with a length of 6 ft (1.8m), including the tail, and a weight of 76 lbs (34 kg). The females are smaller and weigh only 57-60 lbs (26-27 kg). The tail is, on average, 2 ft (56 cm) in length, with 2/3 of it flattened. The fur is dense, thick, and velvety, and is highly sought after by fur traders. The guard hairs are short, 5/16 in (8 mm) long, twice as long as the underfur. The fur is water repellent and is a deep chocolate brown in colour. A unique white mark is located on the throat that can be used to distinguish between individuals. The head is round and the ears are small. The nose is completely covered in fur, with only the two slit-like nostrils visible. The eyes are large and acute, perfect for hunting underwater. The legs are short and stubby and end in large webbed feet tipped with sharp claws. The giant otter is well suited for an aquatic life, and can close its ears while underwater.

Giant otters have a life span of 12 years in the wild, 21 years in captivity.


The giant otter is found in the lakes, slow-moving forested rivers, creeks, reservoirs, and swamps of South America. They are absent from Argentina, Chile, and Uruguay. They are highly social animals found in extended family groups of 10-20 individuals. They share roles within the group, which is structured around the dominant, breeding pair.


Giant otters are one of the largest predators of their region, and so can choose from a wide variety of animals to feed on. They feed mainly on fish, such as catfish and perch, but will also feed on crabs, caimans (related to the alligators) and snakes. They can hunt in either groups or alone, tending to head towards the deeper waters while in groups. They consume up to 10 lbs (4.5 kg) of food each day, using mostly their sense of eyesight to capture it.

In the zoo, they are fed bass, carp, tilapia, catfish, trout, and vitamin supplements.


Giant otters are at the top of the food chain, and therefore have few natural predators. Jaguars are some of the few that have been known to hunt them. Humans are their main enemies, at one time exclusively hunting them for their fur. One pelt was worth a year's wages in South America, and so giant otters were hunted by most everybody, driving them nearly to extinction by the 1970's. Today they are very rare, with an estimated population of only 2000-5000. Factors besides the fur trade are keeping their numbers down. Ignorant fishers sometimes shoot them, as they are thought to compete with the fishing industry. Other factors include mercury poisoning caused by gold mining; habitat loss; and the disturbance of waterways by boaters.


Much is being done to protect the giant otter. In 1973, CITES classified the giant otter as endangered and banned all trade in pelts. The Philadelphia Zoo opened up the first North American exhibit of giant otters in order to increase public awareness. Finally, a sanctuary for giant otters and other native endangered species was created in 1995. It is an 81510 acre lot on the Duroche Ranch, and was created by the Nature Conservancy with Ecotropica.


Giant otters have a gestation period of 65-70 days, after which a litter of 1-5 pups is born. The mothers give birth in underground dens near the shore. The pups are taught to swim after 2 months and leave to fend for themselves after 2-3 years. Giant otters are very sensitive to human activity, and tourists boating too close to a nursing mother can cause her so much stress that she stops producing milk; the pups starve. Giant otters give birth annually.


There are 13 species of otters found throughout the world, with the exception of Australia and Antarctica. The giant otter is a river otter and is closely related to the North American river otter and the European otter.