Giant otter
Giant otter Ma Late Pleistocene – Holocene
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Cuiabá River, Mato Grosso do Sul, Brazil | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Mammalia |
Order: | Carnivora |
Family: | Mustelidae |
Genus: | Pteronura Gray, 1837 |
Species: | P. brasiliensis
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Binomial name | |
Pteronura brasiliensis (Gmelin, 1788)
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Giant otter range |
The giant otter or giant river otter
The giant otter ranges across north-central South America; it lives mostly in and along the
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
Name
The giant otter has a handful of other names. In Brazil it is known as ariranha, from the
Taxonomy and evolution
The otters form the subfamily
The earliest fossil evidence of the giant river otter dates to the
Physical characteristics
The giant otter 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 ft 11 in and 5 ft 7 in) in length from head to tail and females between 1 and 1.5 m (3 ft 3+1⁄2 in and 4 ft 11 in). The animal's well-muscled tail can add a further 70 cm (28 in) to the total body length.[23][24] Early reports of skins and living animals suggested exceptionally large males of up to 2.4 m (7 ft 10+1⁄2 in); 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.[25] The giant otter has the shortest fur of all otter species; it is typically chocolate brown, but may be reddish or
Giant otter muzzles are short and sloping and give the head a ball-shaped appearance.
At the time of Carter and Rosas's writing, vision had not been directly studied, but field observations show the animal primarily hunts by sight; above water, it is able to recognize observers at great distances. 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
The species possesses 2n = 38 chromosomes.[33]
Biology and behaviour
The giant otter is large, gregarious, and diurnal. Early travelers' 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.[34] Concern over this endangered species has since generated a body of research.
Vocalizations
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.[35] 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 nonhostile intent between groups, although evidence is limited. Newborn pups squeak to elicit attention, while older young whine and wail when they begin to participate in group activities.[36] An analysis published in 2014 cataloged 22 distinct types of vocalization in adults and 11 in neonates.[37] Each family of otters was shown to have its own unique audio signature.[38]
Social structure
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.[14] (Larger figures may reflect two or three family groups temporarily feeding together.)[39]
Group members share roles, structured around the dominant breeding pair. The species is territorial, with groups marking their ranges with
Aggression within the species ("intraspecific" conflict) has been documented. 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.[41] One fight was directly observed in the Brazilian Pantanal in which three animals violently engaged a single individual near a range boundary.[40] In another instance in Brazil, a carcass was found with clear indications of violent assault by other otters, including bites to the snout and genitals, an attack pattern similar to that exhibited by captive animals.[44] While not rare among large predators in general, intraspecific aggression is uncommon among otter species; Ribas and Mourão suggest a correlation to the animal's sociability, which is also rare among other otters.[40] A capacity for aggressive behavior should not be overstated with the giant otter. Researchers emphasize that even between groups, conflict avoidance is generally adopted.[45][46] Within groups, the animals are extremely peaceful and cooperative. Group hierarchies are not rigid and the animals easily share roles.[47]
Reproduction and life cycle
Giant otters build dens, which are holes dug into riverbanks, usually with multiple entrances and multiple chambers inside. They give birth within these dens during the dry season. In Cantão State Park, otters dig their reproductive dens on the shores of oxbow lakes starting around July, when waters are already quite low. They give birth between August and September, and the young pups emerge for the first time in October and November, which are the months of lowest water when fish concentrations in the dwindling lakes and channels are at their peak. This makes it easier for the adults to catch enough fish for the growing young, and for the pups to learn how to catch fish. The entire group, including nonreproductive adults, which are usually older siblings to that year's pups, collaborates to catch enough fish for the young.[48]
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
Mothers give birth to furred and blind cubs in an underground den near the river shore and fishing sites.[51] Males actively participate in rearing cubs and family cohesion is strong;[52] older, juvenile siblings also participate in rearing, although in the weeks immediately after birth, they may temporarily leave the group.[49] Pups open their eyes in their fourth week, begin walking in their fifth, and are able to swim confidently between 12 and 14 weeks old.[5] They are weaned by nine months and begin hunting successfully soon after.[49] The animal reaches sexual maturity at about two years of age and both male and female pups leave the group permanently after two to three years.[49][50] They then search for new territory to begin a family of their own.[53]
Studies of giant otters in captivity have given indications about the environment necessary to both maintain a physically and behaviorally healthy population and allow successful cub-rearing. These include providing at least the minimum recommended land-to-water area ratio, and that all enclosure land surfaces (both artificial and natural) are nearly entirely covered with the recommended substrate conditions (e.g. tree-bark mulch and soft pebble-free sand/soil). Ensuring that the animals have sufficient privacy from human disturbances (visual and acoustic, from zoo staff or visitors) at parturition and during cub-rearing is also essential, but not sufficient. Insufficient land area proportions and unsuitable substrate conditions in zoos have historically been the primary cause of high cub mortality and physical and behavioral health problems among giant otters. For example, stress to the parents during cub-rearing due to inappropriate enclosure conditions has been the primary reason for cub neglect, abuse and infanticide.[53][54][55]
In the wild, it has been suggested, although not systematically confirmed, that tourists cause similar stresses: disrupted lactation and denning, reduced hunting, and habitat abandonment are all risks.[53] This sensitivity is matched by a strong protectiveness towards the young. All group members may aggressively charge intruders, including boats with humans in them.[56]
The longest documented giant otter lifespan in the wild is eight years. In captivity, this may increase to 17, with an unconfirmed record of 19. The animal is susceptible to a variety of diseases, including
Hunting and diet
The giant otter is an
The species can hunt singly, in pairs, and in groups, relying on sharp eyesight to locate prey.
Ecology
Habitat
The species is amphibious, although primarily terrestrial.[64] It occurs in freshwater rivers and streams, which generally flood seasonally. Other water habitats include freshwater springs and permanent freshwater lakes.[2] Four specific vegetation types occur on one important creek in Suriname: riverbank high forest, floodable mixed marsh and high swamp forest, floodable low marsh forest, and grass islands and floating meadows within open areas of the creek itself.[64] Duplaix identified 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 clear, black waters with rocky or sandy bottoms over silty, saline, and white waters.[65]
Giant otters use areas beside rivers for building dens, campsites, and latrines.[66] They clear significant amounts of vegetation while building their campsites. One report suggests maximum areas 28 m (92 ft) long and 15 m (49 ft) wide, well-marked by scent glands, urine, and feces to signal territory.[19] Carter and Rosas found average areas a third this size. Giant otters adopt communal latrines beside campsites, and dig dens with a handful of entrances, 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.[67] Giant otters may adopt preferred locations perennially, often on high ground. These can become quite extensive, including "backdoor" exits into forests and swamps, away from the water.[64] Otters do not visit or mark every site daily, but usually patrol all of them, often by a pair of otters in the morning.[68]
Research generally takes place in the dry season and an understanding of the species' overall habitat use remains partial. An analysis of dry season range size for three otter groups in Ecuador found areas between 0.45 and 2.79 square kilometres (0.17 and 1.08 sq mi). Utreras
In 2021, conservationists at Fundación Rewilding spotted a wild giant otter swimming in the
Predation and competition
Adult giant otters living in family groups have no known serious natural
Even if without direct predation, the giant otter must still compete with other predators for food resources. Duplaix documented interaction with the Neotropical otter.
Other species that prey upon similar food resources include the caimans and large fish that are themselves
Conservation status
The IUCN listed the giant otter as "endangered" in 1999; it had been considered "
Threats
The animal faces a variety of critical threats. Poaching has long been a problem. Statistics show between 1959 and 1969 Amazonian Brazil alone accounted for 1,000 to 3,000 pelts annually. The species was so thoroughly decimated, the number dropped to just 12 in 1971. The implementation of CITES in 1973 finally brought about significant hunting reductions,[14] although demand did not disappear entirely: in the 1980s, pelt prices were as high as US$250 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.[76] The animal's relatively late sexual maturity and complex social life makes hunting especially disastrous.[14][77][78]
More recently, habitat destruction and degradation have become the principal dangers, and a further reduction of 50% is expected in giant otter numbers within the 25 years after 2020 (about the span of three generations of giant otters).[2] 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. Subadults leaving in search of new territory find it impossible to set up family groups.[79] Specific threats from human industry include unsustainable mahogany logging in parts of the giant otter range,[76] and concentrations of mercury in its diet of fish, a byproduct of gold mining.[80][81]
Other threats to the giant otter include conflict with fishermen, who often view the species as a nuisance (see below). Ecotourism also presents challenges: while it raises money and awareness for the animals, by its nature it also increases human effect on the species, both through associated development and direct disturbances in the field.[79] A number of restrictions on land use and human intrusion are required to properly maintain wild populations. Schenck et al., who undertook extensive fieldwork in Peru in the 1990s, suggest specific "no-go" zones where the species is most frequently observed, offset by observation towers and platforms to allow viewing. Limits on the number of tourists at any one time, fishing prohibitions, and a minimum safe distance of 50 metres (164 ft) are proposed to offer further protection.[82]
Distribution and population
The giant otter has lost as much as 80% of its South American range.[76] 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.[2] Given local extinctions, the species' range has become discontinuous.[14] Total population numbers are difficult to estimate.[2] 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.[39] The species has likely been extirpated from southern Brazil, but in the west of the country, decreased hunting pressure in the critical Pantanal has led to very successful recolonization; an estimate suggests 1,000 or more animals in the region.[76][83]
As of 2020, the IUCN estimates that there may be 4,569 otters living in Brazil.[2] A significant population lives in the wetlands of the central Araguaia River, and in particular within Cantão State Park, which, with its 843 oxbow lakes and extensive flooded forests and marshlands, is one of the best habitat patches for this species in Brazil.[48]
Suriname still has significant forest cover and an extensive system of protected areas, much of which protects the giant otter.
The three Guianas remain the last stronghold of giant otters in South America, with pristine giant otter habitat on some rivers and good giant otter densities overall—still, but for how long? The survival of the giant otter populations in the Guianas is essential to the survival of this endangered species in South America.
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.[86][87] Bolivia designated wetlands larger than the size of Switzerland as a freshwater protected area in 2001; these are also home to the giant otter.[88]
Interactions with indigenous peoples
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 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.[89]
In Suriname, the giant otter is not a traditional prey species for human hunters, which affords some protection.[85] (One researcher has suggested the giant otter is hunted only in desperation due to its horrible taste.)[79] 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.[71] 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 pup seizure may have led groups to be far more wary of human activity.[64]
Local people sometimes take pups for the
The species has also appeared in the folklore of the region. It plays an important role in the mythology of the
The
Notes
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- ^ ISBN 978-0-521-41103-5.
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- ^ "none", Antropológica. 1981–1982, volume 55–58, page 107
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- ^ Duplaix 1980, p. 614
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References
- Carter, S.K.; Rosas, F.C.W. (1998). "Biology and conservation of Giant Otter (Pteronura brasiliensis)" (PDF). Mammal Review. 27 (1): 1–26. . Retrieved 6 November 2007.
- Duplaix, Nicole (1980). "Observations on the ecology and behavior of the giant river otter Pteronura brasiliensis in Suriname" (PDF). Revue d'Écologie (La Terre et la Vie). 34 (4): 495–620. S2CID 140641854.
External links
- Media related to Pteronura brasiliensis at Wikimedia Commons
- ARKive – images and movies of the giant otter (Pteronura brasiliensis)