Giant Otter

Giant Otter

Conservation status

Endangered [1]

Scientific classification

Kingdom: Animalia Phylum: Chordata Class: Mammalia Order: Carnivora Family: Mustelidae Subfamily: Lutrinae Genus: Pteronura Species: P. brasiliensis

Binomial name

Pteronura brasiliensis (Gmelin, 1788)

The Giant Otter (Pteronura brasiliensis) is an amphibious mammal. About as long as an adult human being, the Giant Otter is the largest member of the mustelidae, or weasel family, a successful group of mammalian predators. Native to South America, the Giant Otter 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.

Contents [hide] 1 Taxonomy and evolution 2 Biology and behaviour 2.1 Physical characteristics 2.2 Social structure 2.3 Reproduction and lifecycle 2.4 Hunting and diet 3 Ecology 3.1 Habitat 3.2 Distribution and conservation status 4 Notes 5 References 6 External links

Taxonomy and evolution

The otters form the Lutrinae subfamily within the mustelids, and the Giant Otter is their largest member. It is the only member of its genus, Pteronura. The Giant Otter shares the South American continent with three of the four members of the Lontra otters: the Neotropical River Otter, the Southern River Otter, and the Marine Otter.[3] Gene sequencing research on the mustelids from 2005 suggests the Giant Otter lineage diverged between between 10.6 and 7 million years ago; the corresponding phylogenetic tree places the Lontra divergence first amongst otter genera, and Pteronura second, although divergence dates overlap.[4]

Biology and behaviour

The Giant Otter is large, gregarious, and diurnal (active through the day). 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.[5] Concern over this endangered species has since generated a significant corpus of research.

Physical characteristics

The Giant Otter is the largest species of its biological family, and is clearly distinguished from other otters by morphological and behavioural characteristics. Males are between 1.5 and 1.8 meters (4.9–5.9 ft) in length and females between 1.5 and 1.7 m (4.9–5.6 ft). Early reports of skins and living animals suggested exceptionally large male lengths of up to 2.4 m (7.9 ft); heavy hunting likely reduced such massive specimens. Weights are between 26 and 32 kilograms (57–70 pounds) for males and 22 and 26 kg (48–57 lb) for females.[6]
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.[6] The fur is extremely dense, so much so that water cannot penetrate to the skin.[7] Guard hairs trap water and keep the inner fur dry; the guard hairs are approximately 8 millimeters (one third of an inch) in length, about twice as long the inner fur.[8] Its velvety feel makes the animal highly sought after by fur traders and has contributed to its decline.[9] Unique white or cream fur colors the throat and under the chin, allowing individuals to be indentified from birth.[6]
Otter muzzles are short and give the head a globular appearance;[5] the ears are small and rounded.[7] The nose (or rhinarium) is completely covered in fur, with only the two slit-like nostrils visible. As of Carter and Rosas' writing, vision had not been directly studied, although in other otter species it is generally normal or slightly myopic, both on land and in water.[6] Hearing and sense of smell are believed to be excellent.[5] 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 and nose while underwater.[10]
It has a lifespan of 12 years in their natural habitat, and 21 years in captivity.

Social structure

The Giant Otter is a highly social animal and lives in extended family groups. Group sizes are anywhere from two to twenty members but likely average between three and eight.[11] (The largest figure may reflect two or three family groups temporarily feeding together.[12]) 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.[13] At least one case of a change in alpha relationship has been reported, with a new male taking over the role of a previous animal; the mechanics of the transition were not determined.[14] Duplaix suggests a division between residents, who are established within groups and territories, and nomadic and solitary transients; the categories do not seem rigid, and both may be a normal part of the Giant Otter life cycle.[5] One tentative theory for the development of sociality in Mustelids is that locally abundant but unpredictably dispersed prey causes groups to form.
Aggression within the species ("intraspecific" conflict) has been documented amongst Giant Otters. Defence against intruding animals appears to be cooperative: while adult males typically lead in aggressive encounters, cases of alpha females guarding groups has been reported. One fight was directly observed in the Brazilian Pantanal in which three animals violently engaged with a single individual near a range boundary. In another instance in Brazil, a carcass was found with clear indications of violent assault from other otters, including bites to the snout and genitals, an attack pattern similar to that found in captive animals. While not rare amongst large predators in general, intraspecific aggression is uncommon amongst otter species; Ribas and Mourão suggest a correlation to the animal's sociability, which is also rare in other otters.

 Reproduction and lifecycle

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. Males actively participate in rearing cubs and family cohesion is strong. The Giant Otter 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 Giant Otter is the only species of mustelid that is monogamous.

Hunting and diet

The Giant Otter is an apex predator and its population status reflects the overall health of riverine ecosystems. It feeds mainly on fish, including characins (such as piranha), catfish, and perch; if fish are unavailable it will also take crabs, snakes, and even small caimans and 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.

Ecology

Habitat

An amphibious species, the Giant Otter is found in freshwater rivers and streams, which are generally seasonally flooded. Areas adjacent to rivers are used for the construction dens, campsites, and latrines. Other habitats include marshes and bogs, freshwater springs, and permanent freshwater lakes. Duplaix identifies two critical factors in habitat selection: food abundance, which appears to positively correlate to shallow water, and low sloping banks with good cover and easy access to preferred water types. The Giant Otter seems to choose black waters with rocky or sandy bottoms over silty, saline, and white waters.
Research is generally carried on in the dry season and an understanding of the species' habitat use remains partial. Dry season range size analysis of three otter groups in Ecuador found areas between 0.45 km and 2.79 km². Habitat requirements and availability were presumed to be dramatically different in the rainy season: range sizes of 1.98 to as much as 19.55 km² were estimated for the groups. Other researchers suggest approximately 7 km² and note a strong inverse correlation between sociality and home range size; the highly social Giant Otter has smaller home range sizes than would be expected for a species of its mass.

Distribution and conservation status

The Giant Otter once ranged across the entire South American continent. While still present in a number of north-central countries, Giant Otter populations are under considerable stress. Considered "vulnerable" for years, the IUCN listed the species as "endangered" in 1999. It lists Bolivia, Brazil, Colombia, Ecuador, French Guiana, Guyana, Paraguay, Peru, Suriname, and Venezuela as current range countries.Although not listed in Argentina, investigation there has shown thinly distributed population remnants.
Poaching has long been a problem: in the 1980s, pelt prices were as high as $250 on the European market. The threat has been excerbated by the otters' relative fearlessness and tendency to approach human beings. More recently, habitat destruction and degradation has become the principal threat and a further reduction of 50% is expected in Giant Otter numbers within twenty years of 2004, about three generation lengths. Other threats to the Giant Otter include conflict with fishermen, unsustainable mahogany logging,and the concentrations of mercury in its diet of fish; mercury is a by-product of gold mining in parts of the Giant Otter range.
Total population numbers are difficult to estimate. Research in 1988 suggested 1000 to 3000 individuals remain, although this may have been an underestimate. One conservation group suggests 2000 to 5000 otters. Populations in Bolivia were once widespread but became a "black spot" 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 in southern Brazil, although decreased hunting pressure in the critical Pantanal may have led to recolonization; a rough estimate suggests 1000 animals in the region.As of 1997, only Suriname, French Guiana, and Guyana showed strong population numbers, according to Carter and Rosas in 1997. In the last of these, interviews and surveys show relatively widespread populations.Seven years earlier, the IUCN's Otter Specialist Group reported that Columbia was still a stronghold for the species.