The Giant Otter, Pteronura brasiliensis, (also known as the river wolf) is the longest of the world's otters, as well as the largest mustelid. It is native to South America but is endangered and is also very rare in captivity. A group of giant otters is called a romp, a bevy, a family, or a raft.
Physical characteristics
The River Wolf can reach up to 6 ft (1.8 m) in length, and weigh up to 76 lb (34 kg). The females are smaller and weigh only 57–60 lb (26–27 kg). It has a lifespan of 12 years in their natural habitat, and 21 years in captivity. Its 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 under-fur. The fur is water repellent and is a deep chocolate brown in color. 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 they have acute vision, an adaptation for hunting underwater. The legs are short and stubby and end in large webbed feet tipped with sharp claws. The River Wolf is well suited for an aquatic life, and can close its ears while underwater. River Wolfs can also close their nostrils when they swim under water. o_O
Feeding ecology
The River Wolf is one of the largest predators of its region, and so can choose from a wide variety of animals to feed on. It feeds mainly on fish, such as catfish, piranha, and perch, but will also feed on crabs, small caimans, and snakes, including small anacondas. It can hunt both in groups and alone, tending to head towards the deeper waters while in groups. It consumes up to 10 lb (4.5 kg) of food each day, using mostly its eyesight to locate its prey. The giant otter has very few natural predators. Caimans and large anacondas prey upon both young and adult otters by ambush. On land jaguars are also a threat to otters when they are in search of more suitable water reserves in the dry season.
Social and reproductive biology
The River Wolf is a highly social animal and lives in extended family groups of between 4-8 members. Group members share roles within the group, structured around the dominant breeding pair. The females have a gestation period of 65-70 days, giving birth to 1-5 young. Mothers give birth in an underground den near the river shore. Otter pups are taught to swim after two months and left to fend for themselves after two to three years. The River Wolf is 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, causing her young to starve. The Giant Otter gives birth annually. The River Wolf is the only species of mustelid that is monogamous.
The Giant Otter is known locally in Guyana as "Lobo del Rio" ("the river wolf") and in Brazil as "Ariranha".
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