Giant Otter

Giant Otter

Lobo de Rio (the River wolf), Los Lobos del Rio (Wolves of the River), Ariranha, Giant otter, Giant river otter

Pteronura brasiliensis
Population size
Life Span
8-19 yrs
Top speed
14.5 km/h
22-32 kg
1-1.7 m

The giant otter or giant river otter(Pteronura brasiliensis ) is a South American carnivorous mammal. It is the longest member of the weasel family, Mustelidae, a globally successful group of predators, reaching up to 1.7 metres (5.6 ft). Atypical of mustelids, the giant otter is a social species, with family groups typically supporting three to eight members. The groups are centered on a dominant breeding pair and are extremely cohesive and cooperative. Although generally peaceful, the species is territorial, and aggression has been observed between groups. The giant otter is diurnal, being active exclusively during daylight hours. It is the noisiest otter species, and distinct vocalizations have been documented that indicate alarm, aggression, and reassurance.

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The giant otter ranges across north-central South America; it lives mostly in and along the Amazon River and in the Pantanal.

Its distribution has been greatly reduced and is now discontinuous. Decades of poaching for its velvety pelt, peaking in the 1950s and 1960s, considerably diminished population numbers. The species was listed as endangered in 1999 and wild population estimates are typically below 5,000. The Guianas are one of the last real strongholds for the species, which also enjoys modest numbers – and significant protection – in the Peruvian Amazonian basin. It is one of the most endangered mammal species in the Neotropics. Habitat degradation and loss is the greatest current threat. The giant otter is also rare in captivity; in 2003, only 60 animals were being held.

The giant otter shows a variety of adaptations suitable to an amphibious lifestyle, including exceptionally dense fur, a wing-like tail, and webbed feet. The species prefers freshwater rivers and streams, which are usually seasonally flooded, and may also take to freshwater lakes and springs. It constructs extensive campsites close to feeding areas, clearing large amounts of vegetation. The giant otter subsists almost exclusively on a diet of fish, particularly characins and catfish, but may also eat crabs, turtles, snakes and small caimans. It has no serious natural predators other than humans, although it must compete with other predators, such as the neotropical otter, jaguar, and various crocodilian species, for food resources.

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The Giant otter, living in South America, and the largest of the otters in its total length, is the cousin of the sea and river otters in North America, Europe, and Africa. Known throughout much of their range as 'river wolf', they are amongst South America's top carnivores. Their fur is extremely soft and is a chocolate brown except for a pattern of large creamy white patches under their long neck, thought to be unique for each individual otter.



This species is a native of South America (except for Chile), east of the Andes. Currently, there are almost none in Argentina and Uruguay, and they are very rare in Paraguay. They are seen within the Amazon, Orinoco, and La Plata River systems and are found in slow-moving streams and rivers, lakes, swamps, and marshes, as well as flooded forests during the rainy season. Giant otters prefer habitats with non-floodable banks that have vegetation cover and where there is easy access to hunting places in relatively shallow waters.

Giant Otter habitat map

Climate zones

Giant Otter habitat map
Giant Otter
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Habits and Lifestyle

Giant otters are diurnal highly social animals; they live together in family groups numbering 2-20 individuals. A family has a home range of 12 sq. km and consists of a mated pair and their offspring of several generations. The family members clear an area beside a stream for their living quarters, of up to 50 sq meters, usually near feeding sites. Sizeable burrows are then built under fallen logs. One to five latrines for communal use are placed along the perimeter of the site. The established territory is then marked by the scent from the animals' anal glands. If intruders invade the family's territory, the parents will defend it and their family members. Within groups, otters are extremely peaceful and cooperative. They groom each other, rest, and may even hunt together. Giant otters are especially noisy and have a complex repertoire of vocalizations. Quick ‘hah’ barks or explosive snorts suggest immediate interest and possible danger. A wavering scream may be used in bluff charges against intruders, while a low growl is used for aggressive warning. They will also make hums and coos, and whistles. Newborn pups squeak to elicit attention, while older young whine and wail when they begin to participate in group activities.

Seasonal behavior

Diet and Nutrition

Giant otters are strictly carnivorous (piscivorous) and mainly fish such as cichlids, perch, characins (such as piranha), and catfish. If fish are unavailable, they will also take crabs, snakes, and even small caimans and anacondas.

Mating Habits

year-round, peak in late spring-early summer
65-70 days
1-5 pups
3-4 months
whelp, pup

This species is monogamous, and pairs stay together for life. Reproductive behavior has largely been documented by observations of captive animals. Although some breeding occurs throughout the year, the peak of the breeding season is from late spring to early summer. Gestation lasts 65-70 days and the altricial young are born in late August until early October. There are 1-5 pups in a litter (usually 2-3) and they stay in the family den until they are 2-3 weeks old. They can open their eyes after 1 month and start to regularly follow their parents out of the den. Young are weaned at the age of 3-4 months. At 9-10 months they can hunt independently and look just like their parents. Reproductive maturity is reached when they are 2 years old.


Population threats

Habitat fragmentation and loss, as well as pollution, are the current major threats to the Giant otter, as the areas where they live are degraded and destroyed by logging, mining, and damming. This species was excessively hunted up until the late 1970s for its valuable fur. Illegal killing still occurs, often at the hands of fishermen, who see Giant otters as competition for fish. Some pups in the wild are taken for pets and usually die because of the inexperience of caretakers.

Population number

The IUCN Red List has no current estimate for the total Giant otter population. There are estimates for the populations of a few areas: 2,000-5,000 individuals in the Brazilian Pantanal; 180-400 individuals in Madre de Dios, southeastern Peru; 31 individuals in Cantao State Park, Brazil; 75 individuals in Amana, Brazil; at least 130 individuals in Balbina Lake, Brazil; 54 individuals in Araguaia, above Bananal Island; 32 individuals in Yasuni National Park, Ecuador; and at least 35 individuals in Rewa Head, Guyana. Estimates have been provided for the following countries: 60 animals in Bolivia in the northwest in the Madre de Dios-Beni sub-basin; 50 individuals in 118,031 km² of the Pantanal (Paraguay river sub-basin), and 600 animals in the 186,460 km² of the northeast (Itenez sub-basin), totaling an estimated 700 individuals; less than 250 animals in Ecuador; at least 200 animals in French Guiana; and 24-32 animals in Paraguay. Overall, currently, Giant otters are classified as Endangered (EN) and their numbers today are decreasing.

Fun Facts for Kids

  • The Giant otter was discovered by Gmelin in 1788. It is also known as the Guiana flat-tailed otter, margin-tailed otter, and winged-tailed otter.
  • These animals are most active from 10-11 am and from 3-5 pm. They take a nap at mid-day during really warm weather.
  • Giant otters are able to swim 330 feet (100 meters) in less than 30 seconds.
  • Because of their size and speed of swimming, Giant otters are successful in competing for fish with Black caimans and jaguars.
  • Giant otters do not store food. They will seek a peaceful place (or "picnic spot") to eat their prey.
  • Giant otters can hunt singly, in pairs, and in groups, relying on sharp eyesight to locate prey. They prefer prey fish that are generally immobile on river bottoms in clear water. They chase prey rapidly and tumultuously, with lunges and twists through the shallows and few missed targets.


1. Giant Otter Wikipedia article -
2. Giant Otter on The IUCN Red List site -

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