Bio Facts: Otter, Giant
The Orinoco, Amazon, and La Plata River systems of north-central South America - Bolivia, Brazil, Colombia, Ecuador, French Guiana, Guyana, Paraguay, Peru, Suriname, and Venezuela
Freshwater rivers and streams, which are generally seasonally flooded; other water habitats include freshwater springs and permanent freshwater lakes (in the Guianas - Rupununi, Essequibo, Abary and Mazaruni Rivers)
Males are between 4.9 – 5.9 ft (1.5 - 1.8 m) in length and females 4.9–5.6 ft (1.5 - 1.7 m); the animal’s well-muscled tail can account for as much as 27 in. (69 cm) of total body length. Early reports of skins and living animals suggested exceptionally large males of up to 7.9 ft (2.4 m); intensive hunting likely reduced the occurrence of such massive specimens. Weights 55 - 70 lbs. (25 - 32 kg) for males and 48 – 57 lbs. (22 - 26 kg) for females. The giant otter has the shortest fur of all otter species; it is typically chocolate brown but may be reddish or fawn, and appears nearly black when wet. Unique markings of white or cream fur color the throat and chin, allowing individuals to be identified from birth. Muzzles are short and sloping and give the head a ball-shaped appearance. The ears are small and rounded. The nose (or rhinarium) is completely covered in fur, with only the two slit-like nostrils visible.
In the wild, the longest documented lifespan was 8 years; in captivity they may live up to 17 years.
About 2 years of age (730 days)
In the wild, they feed on mainly on fish, including cichlids, characins (such as piranha), catfish, and perch; in the Zoo they are fed trout, catfish and tilapia.
IUCN – Endangered; CITES – Appendix I; US - Endangered
Unusually for a mustelid, 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. They sleep, play, travel, and feed together. Although generally peaceful, the species is territorial and aggression has been observed between groups. Groups mark their ranges with latrines, gland secretions, and vocalizations. The giant otter is diurnal, being active exclusively during daylight hours. The giant otter seems to be opportunistic, taking whatever species are most locally abundant. If fish are unavailable it will also take crabs, snakes, and even small caimans and anacondas.
They hunt singly, in pairs, and in groups, relying on sharp eyesight to locate prey. In some cases, cooperative hunting may be incidental, a result of group members fishing individually in close proximity; truly coordinated hunting may only occur where the prey cannot be taken by a single giant otter, such as with anacondas and the black caiman. The giant otter seems to prefer prey fish that are generally immobile on river bottoms in clear water. Prey chase is rapid and tumultuous, with lunges and twists through the shallows and few missed targets. The otter can attack from both above and below, swiveling at the last instant to clamp the prey in its jaws. Giant otters catch their own food and consume it immediately; they grasp the fish firmly between the forepaws and begin eating noisily at the head.
The giant otter is an especially noisy animal, with a complex repertoire of vocalizations. All otters produce vocalizations, but by frequency and volume, the giant otter may be the most vocal. Duplaix identified nine distinct sounds, with further subdivisions possible, depending on context. 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. Hums and coos are more reassuring within the group. Whistles may be used as advance warning of non-hostile intent between groups, although evidence is limited. Newborn cubs squeak to elicit attention, while older young whine and wail when they begin to participate in group activities.
The giant otter seems to choose clear black waters with rocky or sandy bottoms over silty, saline, and white waters. Areas adjacent to rivers are used for the construction of dens, campsites, and latrines. Giant otters clear significant amounts of vegetation in constructing their campsites. One report suggests maximum areas 92 ft (28 m) long and 49 ft (15 m) wide, well-marked by scent glands, urine, and feces to signal territory. Carter and Rosas find average areas a third this size. Communal latrines are adopted adjacent to the campsites, and dens with a handful of entrances are dug, typically under root systems or fallen trees. One report found between three and eight campsites, clustered around feeding areas. In seasonally flooded areas, the giant otter may abandon campsites during the wet season, dispersing to flooded forests in search of prey. Preferred locations may be adopted perennially, often on high ground. These can become quite extensive, including “backdoor” exits into forests and swamps, away from the water. Not every site is visited or marked daily, but all are usually patrolled, often by a pair of otters in the morning.
Details of giant otter reproduction and life cycle are scarce, and captive animals have provided much of the information. Females appear to give birth year ‘round; although in the wild births may peak during the dry season. The estrous cycle is 21 days, with females receptive to sexual advances between 3 and 10 days. Study of captive specimens has found that only males initiate copulation. At Tierpark Hagenbeck in Germany, long-term pair bonding and individualized mate selection were seen, with copulation most frequently taking place in water. Females have a gestation period of 65 to 70 days, giving birth to one to five pups, with an average of two. Research over five years on a breeding pair at the Cali Zoo in Colombia found that the average interval between litters was six to seven months, but as short as 77 days when the previous litter did not survive. Other sources have found greater intervals, with as long as 21 to 33 months suggested for the wild.
Mothers give birth to furred and blind cubs in an underground den near the river shore and fishing sites. Males actively participate in rearing cubs and family cohesion is strong; older, juvenile siblings also participate in rearing, although in the weeks immediately after birth they may temporarily leave the group. Cubs open their eyes in their fourth week, begin walking in their fifth, and are able to swim confidently between 12 and 14 weeks. They are weaned by nine months and begin hunting successfully soon after. The animal reaches sexual maturity at about two years of age and both male and female cubs leave the group permanently after two to three years. They then search for new territory to begin a family of their own.
The fur is extremely dense, so much so that water cannot penetrate to the skin. Guard hairs trap water and keep the inner fur dry; the guard hairs are approximately 1/3 in. (8 mm) in length, about twice as long as the fur of the inner coat. The highly sensitive whiskers (vibrissae) allow the animal to track changes in water pressure and currents, which aids in detecting prey. The legs are short and stubby and end in large webbed feet tipped with sharp claws. Well suited for an aquatic life, it can close its ears and nose while underwater.
The giant otter moves through the water using different body parts according to its swimming speed. When swimming slowly, it paddles with all four feet and leaves the tail stationary. When moving quickly, it undulates its tail and leaves its feet stationary.
Senses: field observations show that the animal primarily hunts by sight; the fact that it is exclusively active during the day further suggests its eyesight should be strong, to aid in hunting and predator avoidance. In other otter species vision is generally normal or slightly myopic, both on land and in water. The Giant Otter’s hearing is acute and its sense of smell excellent.
Adult giant otters have no serious natural enemies, beyond human beings. “Possible and occasional” predation by the jaguar, cougar, and anacondas has been suggested by Duplaix, but based on historical reports, no direct observation. Cubs are more vulnerable, and may be taken by the black caiman and other large predators, although adults are constantly mindful of stray young. The spectacled caiman is another potential competitor, but Duplaix found no conflict with the species in Suriname. When in the water, the giant otter faces danger from animals that are not strictly preying upon it: the electric eel and stingrays are potentially deadly if stumbled upon, and piranha may be capable of at least taking bites out of a giant otter, as evidenced by scarring on individuals.
Even if without direct predation, the giant otter must still compete with other predators for food resources. Duplaix documented interaction with the Neotropical otter. While the two species are sympatric (with overlapping ranges) during certain seasons, there appeared to be no serious conflict. The smaller Neotropical Otter is far shyer, less noisy, and less social; at about a third the weight of the giant otter, it is more vulnerable to predation and, hence, a lack of conspicuousness is to its advantage. The Neotropical otter is active during twilight and darkness, reducing the likelihood of conflict with the diurnal giant otter. Its smaller prey, different denning habits, and different preferred water types also reduce interaction. Other species that prey upon similar food resources include the caimans and large fish that are also piscivores. Gymnotids, such as the electric eel, and the large Silurid catfish are among aquatic competitors. Two river dolphins, the Tucuxi and Boto, might potentially compete with the giant otter but different spatial use and dietary preferences suggest minimal overlap.
Pteronura brasiliensis was discovered in 1788 by Gmelin. In addition to its common name, giant otter, it has also been called the Guiana flat-tailed otter, winged-tailed otter, and margin-tailed otter.
The giant otter has a handful of other names in English. River wolf (Spanish: Lobo del Río) and water dog (Spanish: Perro del Agua) are used occasionally. The last of these may have been more common in the reports of explorers in the nineteenth and early twentieth centuries. All three names are in use in Spanish and Portuguese, with a number of regional variations. “Giant otter” translates as Nutria Gigante and Lontra Gigante in Spanish and Portuguese, respectively; a fourth name, Ariraí or Ariranha is also in use in South America. Among the Achuar people, they are known as Wankanim, and among the Sanumá as Hadami. The genus name, Pteronura, is derived from the Ancient Greek words pteron (πτερον) ‘feather’ or ‘wing’ and ura (ουρά) ‘tail’, a reference to its distinctive wing-like tail.
Their curious nature, ravenous appetite, affinity for humans, and size are probably the reasons why these aquatic creatures are known as “water dogs”.
The species has also appeared in the folklore of the region. It plays an important role in the mythology of the Achuar people, where giant otters are seen as a form of the Tsunki, or water spirits: they are a sort of “water people” who feed on fish. The Bororo have a legend on the origin of tobacco smoking: those who used the leaf improperly by swallowing it were punished by being transformed into giant otters; the Bororo also associate the giant otter with fish and with fire. A Ticuna legend has it that the giant otter exchanged places with the Jaguar: the story says Jaguar formerly lived in the water and the giant otter came to the land only to eat. The indigenous Kichwa peoples from Amazonian Peru believed in a world of water where Yaku runa reigned as mother of the water and was charged with caring for fish and animals. Giant otters served as Yaku runa’s canoes.
Total population numbers are difficult to estimate. An IUCN study in 2006 suggested 1,000 to 5,000 otters remain. Populations in Bolivia were once widespread but the country became a “black spot” on distribution maps after poaching between the 1940s and 1970s; a relatively healthy but still small population of 350 was estimated in the country in 2002. The species has likely been extirpated from southern Brazil, but in the west of the country decreased hunting pressure in the critical Pantanal may have led to recolonization; an estimate suggests 1,000 animals in the region.
The animal faces a variety of critical threats. Poaching has long been a problem. Statistics show that between 1959 and 1969 Amazonian Brazil alone accounted for 1,000 to 3,000 pelts annually. The species was so thoroughly decimated that the number dropped to just 12 in 1971. The implementation of CITES in 1973 finally brought about significant hunting reductions, although demand did not disappear entirely: in the 1980s, pelt prices were as high as 250USD on the European market. The threat has been exacerbated by the otters’ relative fearlessness and tendency to approach human beings. They are extremely easy to hunt, being active through the day and highly inquisitive. The animal’s relatively late sexual maturity and complex social life makes hunting especially disastrous.
More recently, habitat destruction and degradation has become the principal danger and a further reduction of 50% is expected in giant otter numbers within the 20 years from 2004 (about the span of three generations of Giant Otters). Typically, loggers first move into rainforest, clearing the vegetation along riverbanks. Farmers follow, creating depleted soil and disrupted habitats. As human activity expands, giant otter home ranges become increasingly isolated. Sub-adults leaving in search of new territory find it impossible to set up family groups. Specific threats from human industry include unsustainable mahogany logging in parts of the giant otter range, and concentrations of mercury in its diet of fish, a by-product of gold mining. Water pollution from mining, fossil fuel extraction, and agriculture is a serious danger: concentrations of pesticides and other chemicals are magnified at each step in the food chain, and can poison top predators like the giant otter.
Throughout its range, the giant otter interacts with indigenous groups, who often practice traditional hunting and fishing. A study of five indigenous communities in Colombia suggests that native attitudes toward the animal are a threat: the otters are often viewed as a nuisance that interferes with fishing, and are sometimes killed. Even when told of the importance of the species to ecosystems and the danger of extinction, interviewees showed little interest in continuing to coexist with the species. Schoolchildren, however, had a more positive impression of the animal.
In Suriname, the giant otter is not a traditional prey species for human hunters, which affords some protection. (One researcher has suggested that the giant otter is hunted only in desperation due to its horrible taste.) The animal sometimes drowns in nets set across rivers and machete attacks by fishermen have been noted, according to Duplaix, but “tolerance is the rule” in Suriname. One difference in behavior was seen in the country in 2002: the normally inquisitive giant otters showed “active avoidance behavior with visible panic” when boats appeared. Logging, hunting, and cub seizure may have led groups to be far more wary of human activity.
Local people sometimes take cubs for the exotic pet trade or as pets for themselves, but the animal rapidly grows to become unmanageable. Duplaix relates the story of an Arawak Indian who took two cubs from its parents. While revealing of the affection held for the animal, the seizure was a profound blow to the breeding pair, which went on to lose their territory to competitors. Diane McTurk manages giant otter rehabilitation work with rescued and orphaned giant otter cubs at Karanambu Ranch in Guyana.
Other countries have taken a lead in designating protected areas in South America. In 2004, Peru created one of the largest conservation areas in the world, Alto Purús National Park, with an area similar in size to Belgium. The park harbors many endangered plants and animals, including the giant otter, and holds the world record for mammal diversity. Bolivia designated wetlands larger than the size of Switzerland as a freshwater protected area in 2001; these are also home to the giant otter.
Jacksonville Zoo History:
The rare and endangered giant otter has been here at the Jacksonville Zoo since 2007.