The Giant Otter [Pteronura brasiliensis]

Jan 13, 2019 Features / Columnists, Interesting Creatures in Guyana

---

 

The giant otter or giant river otter (Pteronura brasiliensis) is a South American carnivorous mammal. It is the longest member of the Mustelidae, or weasel family, 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 vocalisations have been documented that indicate alarm, aggression and reassurance.
The giant otter ranges across north-central South America; it lives mostly in and along the Amazon River and in the Pantanal. Reports suggest that it has lost as much as 80 percent of its South American range. While still present in a number of north-central countries, giant otter populations are under considerable stress.
The IUCN lists Bolivia, Brazil, Colombia, Ecuador, French Guiana, Guyana, Paraguay, Peru, Suriname, and Venezuela as current range countries. Given local extinctions, the species’ range has become discontinuous. Total population numbers are difficult to estimate.
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 caiman. It has no serious natural predators other than humans, although it must compete with other species, including the neotropical otter and caiman species, for food resources.
The giant otter has a handful of other names. In Brazil it is known as ariranha, from the Tupí word ari’raña, meaning water jaguar.
The giant otter is large, gregarious, and diurnal. Early travellers’ reports describe noisy groups surrounding explorers’ boats, but little scientific information was available on the species until Duplaix’s groundbreaking work in the late 1970s. Concern over this endangered species has since generated a body of research.
It is clearly distinguished from other otters by morphological and behavioural characteristics.
It has the greatest body length of any species in the mustelid family, although the sea otter may be heavier. Males are between 1.5 and 1.7 m (4.9 and 5.6 ft) in length from head to tail and females between 1 and 1.5 m (3.3 and 4.9 ft). The animal’s well-muscled tail can add a further 70 cm (28 in) to the total body length.
Early reports of skins and living animals suggested exceptionally large males of up to 2.4 m (7.9 ft); intensive hunting likely reduced the occurrence of such massive specimens. Weights are between 26 and 32 kg (57 and 71 lb) for males and 22 and 26 kg (49 and 57 lb) 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. 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 eight millimetres (one-third of an inch) in length, about twice as long as the fur of the inner coat. Unique markings of white or cream fur color the throat and under the chin, allow individuals to be identified from birth. Giant otters use these marks to recognize one another, and upon meeting other otters, they engage in a behavior known as “periscoping”, displaying their throats and upper chests to each other.
Giant otter 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. The giant otter’s 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 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.
The giant otter is a highly social animal and lives in extended family groups. Group sizes are anywhere from two to 20 members, but likely average between three and eight. (Larger figures may reflect two or three family groups temporarily feeding together.) The groups are strongly cohesive: the otters sleep, play, travel, and feed together.
Group members share roles, structured around the dominant breeding pair. The species is territorial, with groups marking their ranges with latrines, gland secretions, and vocalizations. At least one case of a change in alpha relationship has been reported, with a new male taking over the role; the mechanics of the transition were not determined.
Defence against intruding animals appears to be cooperative: while adult males typically lead in aggressive encounters, cases of alpha females guarding groups have been reported.
[Source: Wikipedia]

---

---