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Overview

Brief Summary

Biology

The Asian short-clawed otter is a sociable animal, living in loose family groups of about 12 individuals (2). Within each group is an adult monogamous pair, with both parents contributing to the raising of their offspring (5). The female gives birth to up to two litters each year (2), each containing up to six young but often just containing one or two. The young are born after a gestation period of 60 to 64 days (2), into a nest of grass that the female has built two weeks prior (5). The young otters do not open their eyes until 40 days old. At nine weeks of age they take their first swim and, shortly after, they eat solid food (2). The diet of the Asian short-clawed otter consists primarily of crabs, other crustaceans, molluscs, frogs (2), fish, snakes and insects (6). With their sensitive and dexterous front paws, they dig around in the mud or under stones to find their prey (2). With their large back teeth, the Asian short-clawed otter can crush the shells of crabs and molluscs, or they have been known to leave these creatures out in the sun once they have been dug up, where the heat causes the shells to open up (5). In areas of rice fields, the Asian short-clawed otter may serve a valuable function to farmers as it preys on the crabs found in the paddies (6). When not searching for food, this playful otter may be found along the grassy or sandy banks of rivers, resting or grooming (5). It interacts with other members of the family group using a vocabulary of at least 12 calls (2), including greeting, mating and alarm calls (5). In Malaysia at night, their chirps are often heard as they move through rice fields (6).
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Description

This charismatic mammal, equally at home in the water and on land, is the smallest of the world's otters (4). As well as its size, the Asian short-clawed otter can be distinguished from other otters by its small claws (5), after which it is named. These tiny claws, which do not protrude beyond the ends of the fingers (2), enhance the manual dexterity of this otter as it handles prey (5). The Asian short-clawed otter typically has brown fur with a paler underside, although cream-coloured individuals have also been known (5) (6). The edges of the upper lip, chin, throat, sides of neck and face are generally greyish-white (5). Like other otters, the Asian short-clawed otter has a small head, short legs and flattened tail, creating a streamlined silhouette that can move easily through the water (5) (7).
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Distribution

Aonyx cinerea is found in coastal regions from southern India to the Malay Peninsula and southern China.

Biogeographic Regions: oriental (Native ); indian ocean

  • Nowak, R. 1999. Walker's Mammals of the World, Volume 1. Baltimore and London: The Johns Hopkin University Press.
  • Timmis, W. 1971. Observations on breeding the Oriental short-clawed otter, *Amblonyx cinerea*, at Chester Zoo. International Zoo Yearbook, 11: 109-111.
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Range

The Asian short-clawed otter has a large distribution, ranging from north-western and southern India, through southern China and the Malay Peninsula, to Sumatra, Java, Borneo and the Riau Archipelago (Indonesia), and Palawan Island in the Philippines (2).
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Physical Description

Morphology

Aonyx cinerea weigh 2.7 to 5.4 kg, have a combined head and body length of 406 to 635 mm, and a tail length of 246 to 304 mm. They have dark, greyish-brown fur over most of their body, and a lighter cream coloration on their face and neck. Their claws are extremely reduced, and rarely extend past the digit. The paws are only partially webbed, which allows for more dexterity than otters with full webbing.

Range mass: 2.7 to 5.4 kg.

Range length: 406 to 635 mm.

Other Physical Features: endothermic ; homoiothermic; bilateral symmetry

Sexual Dimorphism: sexes alike

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Ecology

Habitat

Aonyx cinerea individuals are commonly seen in the shallows of freshwater streams and rivers as well as coastal regions. There is often dense foliage nearby, which they use as defensive cover, and which restricts behavioral studies in the wild. Nesting burrows are dug into the muddy banks where they live. They have also been seen numerous times in rice paddies.

Habitat Regions: tropical ; saltwater or marine ; freshwater

Aquatic Biomes: rivers and streams; coastal

Other Habitat Features: riparian

  • Hoogerwerf, A. 1970. Udjung Kulon. Leiden: E. J. Brill.
  • Mason, C., S. Macdonald. 1986. Otters: ecology and conservation. Cambridge University Press.
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A truly amphibious animal, the Asian short-clawed otter can be found in, and around, rivers, creeks, estuaries, coastal waters (2), mangroves and rice fields (6), often close to human activity (5). It prefers areas of shallow water, where there is both abundant food and sufficient vegetation (4), and can be found from sea level up to 2,000 metres (5).
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Trophic Strategy

Unlike most otters, A. cinerea individuals use their forepaws to locate and capture items, rather than their mouth. Their incomplete webbing gives them a great deal of manual dexterity. They dig in sand and mud at the shoreline for various types of shellfish (clams and mussels) and crabs. To get at the meat they can either crush the shell manually or let heat from the sun open the shells. Their teeth are broad and robust, well-suited for crushing shells.

Animal Foods: amphibians; fish; terrestrial non-insect arthropods; mollusks

Primary Diet: carnivore (Eats non-insect arthropods, Molluscivore )

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Associations

The role of A. cinereus in the ecosystem is not well understood. They impact the populations of shellfish and crustaceans in their area.

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Predation on A. cinereus has not been described but it is likely that they are taken by large, primarily aquatic predators, such as crocodiles and snakes. Their amazing agility in the water may help them to avoid predation.

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Known prey organisms

Amblonyx cinereus preys on:
non-insect arthropods
Actinopterygii
Mollusca
Arthropoda
Amphibia

This list may not be complete but is based on published studies.
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Life History and Behavior

Behavior

Twelve different vocalizations have been identified in this species, not counting simple alarm vocalizations. Communication also occurs with visual, chemical, and tactile cues such as social grooming, hormonal changes, and posturing.

Communication Channels: visual ; tactile ; acoustic ; chemical

Perception Channels: visual ; tactile ; acoustic ; chemical

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Life Expectancy

A captive specimen of A. cinereus lived about 16 years.

Range lifespan

Status: captivity:
16 (high) years.

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Lifespan, longevity, and ageing

Maximum longevity: 23 years (captivity) Observations: One wild born female was about 23 years old when she died in captivity (Richard Weigl 2005).
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Reproduction

Asian clawless otters form monogamous pairs for life.

Mating System: monogamous

The estrous cycle is 28 days with a 3 day period of estrus. Mated pairs can have two litters of 1 to 6 young (usually 1 or 2) per year. Gestation is approximately 60 days, and newborn young are relatively undeveloped. At birth, they weigh around 50 g and have closed eyes. Eyes open at around 40 days, and pups can be seen outside the den after ten weeks. Young begin eating solid food after 80 days, and start swimming after three months.

Breeding interval: Aonyx cinerea may produce two litters annually.

Breeding season: Mating may occur throughout the year.

Average number of offspring: 2.

Average gestation period: 60 days.

Average weaning age: 80 days.

Key Reproductive Features: iteroparous ; year-round breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; viviparous

Males assist with nest building before birth and food procurement after parturition.

Parental Investment: male parental care ; female parental care

  • Lancaster, W. 1975. Exhibiting and breeding the asian small-clawed otter at Adelaide Zoo. International Zoo Yearbook, 15: 63-65.
  • Leslie, G. 1970. Observations on Oriental short-clawed otter at Aberdeen Zoo. International Zoo Yearbook, 10: 79-81.
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Molecular Biology and Genetics

Molecular Biology

Statistics of barcoding coverage: Aonyx cinerea

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 0
Specimens with Barcodes: 6
Species With Barcodes: 1
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Conservation

Conservation Status

Clawless otters are managed under the Species Survival Program. While not endangered themselves, they are being used as a model for the management of other otter species.

US Federal List: no special status

CITES: no special status

IUCN Red List of Threatened Species: vulnerable

  • Lankard, J. 2001. AZA annual report on conservation and science 1999-2000. Volume I: Conservation programs reports. Silver Springs, MD: American Zoo and Aquarium Association..
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Status

Classified as Vulnerable (VU) on the IUCN Red List (1) and listed on Appendix II of CITES (3).
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Threats

The most significant threat to the Asian short-clawed otter is the destruction of habitat (1). Throughout Asia, deforestation is resulting in the loss of hill streams, peat swamp forests are drained for agriculture, and mangroves are being converted for aquaculture (1) (4). Aquaculture projects are a particular problem, as they bring otters in closer contact with humans who view them as pests. Few areas can afford the fences needed to keep otters from killing the fish or prawn stocks; instead, the otters are killed (6). Further threats to this species include a reduction in their prey as a result of overexploitation by humans, and pollution, which may also affect prey abundance, as well as the otter directly (1) (4). Tea and coffee plantations in India, and other forms of intensive agriculture elsewhere, not only often destroy the otter's natural habitat, but result in the surrounding streams and rivers being polluted by pesticides (1) (4).
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Management

Conservation

Limited conservation measures are in place for the Asian short-clawed otter. There is some national legal protection in place for this species (4), for example, in Malaysia and Singapore, all otters are totally protected (8), but local habitat protection needs to be established (4). In 1983, the American Association of Zoological Parks and Aquariums established a species survival plan to encourage more research on the captive breeding of this species (5). Many zoos in the world keep this species (8), creating the opportunity for scientists to gain further knowledge about this fascinating mammal, which can then be used to assist their conservation in the wild. One of the key organisations involved in the conservation of the Asian short-clawed otter is the IUCN Otter Specialist Group, which has developed a network of biologists across Asia that are conducting field surveys and popularising this species' conservation. Nevertheless, concerted conservation effort—involving policy, research and habitat-based action—is required if the long-term survival of the Asian short-clawed otter is to be assured (1).
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Relevance to Humans and Ecosystems

Benefits

Rice farmers complain about Asian clawless otters uprooting plants in the paddies.

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Aonyx cinerea consume small crabs which are considered agricultural pests.

Positive Impacts: controls pest population

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Wikipedia

Oriental small-clawed otter

The oriental small-clawed otter (Aonyx cinerea), also known as the Asian small-clawed otter, is the smallest otter species in the world,[3] weighing less than 5 kg. It lives in mangrove swamps and freshwater wetlands of Bangladesh, Burma, India, southern China, Taiwan, Laos, Malaysia, Indonesia, Singapore, the Philippines, Thailand, and Vietnam.[1] Its paws are a distinctive feature, its claws not extending beyond the fleshy end pads of its partially webbed fingers and toes. This gives it a high degree of manual dexterity so that it can use its paws to feed on molluscs, crabs and other small aquatic animals.

The oriental small-clawed otter lives in extended family groups with only the alpha pair breeding; offspring from previous years help to raise the young. Due to ongoing habitat loss, pollution, and hunting in some areas, the oriental small-clawed otter is evaluated as vulnerable on the IUCN Red List of Threatened Species.[2]

History[edit]

This species was formerly thought to be the only member of the genus Amblonyx;[1] however, it has recently been confirmed as being a member of the genus Aonyx after mitochondrial DNA analysis.[4] Another synonym for the oriental small-clawed otter is Aonyx cinereus.[5]

Morphology[edit]

Oriental small-clawed otters are the smallest of all otters in the world. The overall length can range from 70 to 100 cm (28–39 in), of which about 30 cm (12 in) is the tail. Weight can range from 1 to 5.4 kg (2.2-11.9 lbs).[6] The body is slender, streamlined and serpentine, and is flexible enough to allow grooming of almost all the body. Dark, grayish-brown fur covers most of the dorsal surface with a lighter cream coloration on the ventral surface, especially on the face and neck. The fur has relatively short hairs less than 2.5 cm in length, and it is fine, dense and velvety. Otters have two types of fur: long, stout guard hairs and a short, fine undercoat.

Oriental small-clawed otters have flattened heads and short, thick necks; eyes are located toward the front of the head. The ears are small and rounded and have a valve-like structure that enables them to be closed when swimming underwater. Nose pads are dusky or pinkish in color. The muzzle has vibrissae (whiskers) on either side. These are sensitive to touch and to underwater vibrations, and are important in detecting the movements of prey.

Similar to other otters, oriental small-clawed otters have relatively short legs, which are used to swim, walk, groom and manipulate prey. Feet are very narrow and only webbed to the last joint — not all the way to the end of the toe and this distinguishes them from all other species of otter. These partially webbed paws give them an excellent sense of touch and coordination, providing them with more dexterity than other otters with full webbing. Unlike other otters, they catch their prey with their paws instead of with their mouth. Their small, blunt, peg-like claws are extremely reduced and rarely extend past the tips of the digits.

The oriental small-clawed otter's tail is long, about one-third of its total body length. The tail is thick at the base, muscular, flexible, and tapers to a point. Subcutaneous and scent glands are located at the base of the tail. The tail is used for propulsion when swimming at high speed, to steer when swimming slowly and for balance when standing upright on hind legs.

Distribution[edit]

This species can be found in coastal regions from southern India to South China, Southeast Asia, Sumatra, Java, and Palawan. It is known from all regions of Sabah, Sarawak, Brunei, central Kalimantan, and most of the rest of Borneo.

Habitat[edit]

Oriental small-clawed otters can be found in freshwater wetland systems such as swamps, meandering rivers, mangroves and tidal pools. They are found in irrigated rice fields and wander between patches of reeds and river debris where many crab species (Brachyura) are likely to be found. They dislike bare and open areas that do not offer any shelter. Thus, they prefer pond areas and rice fields over rivers with bare banks. When in the riverine systems they choose areas with low vegetation and their nesting burrows are dug into the muddy banks. This species spend most of its time on land unlike most other otters.

Reproduction[edit]

Oriental small-clawed otters form monogamous pairs for life. The estrous cycle in the female is 28 days with a three-day period of estrus. The mated pairs can have two litters of one to six young per year and the gestation period is about 60 days. The newborn pups are relatively undeveloped; when they are born, they weigh around 50 g, are toothless, practically immobile and their eyes are still closed. They remain in their birthing dens and spend their first few weeks nursing and sleeping. The pups nurse every three to four hours for 10 to 15 minutes at a time. They open their eyes after 40 days and are fully weaned at 14 weeks. In the next 40 days, the young start to eat solid food and can swim three months later. Young otters will stay with their mother until the next litter is born. The male otter assists the female building the nest before birth and in food procurement after parturition. The life span of this species is around 11 to 16 years.

Behaviour[edit]

Two oriental small-clawed otters sleeping at the National Zoo in Washington, D.C.

Oriental small-clawed otters are crepuscular animals (active during dusk and dawn), found in remote areas, free of human disturbance. However, some have adapted to life near villages. They continually groom their fur to maintain its insulating qualities. They dry themselves by rolling on the ground or rubbing against logs or vegetation. Asian small-clawed otters are excellent swimmers; they swim by moving their hind legs and tail. They ‘dog-paddle’ with all four feet while swimming or floating. When swimming at a high speed, they undulate their entire bodies, including their tails, up and down while their hind feet steer. They can dive under water for about six to eight minutes. They produce small amounts of feces, known as spraint. The spraints are important for communication among the otters; those with different smells and appearance indicate the presence of strangers. Generally, the otters sleep and rest on land either above ground or in their dens. They often sleep in areas with moderate disturbance. Oriental small-clawed otters are mostly social animals. They live in extended family groups of about 12 individuals. They are often seen playing (which can be seen at zoos) and sliding on muddy banks and in the water in regions where they frequently visit or live. They defend their territories by working, scratching and occasionally fighting.

Communication[edit]

Small-clawed otter in Disney's Animal Kingdom

This species uses vocalizations, scent markings and sign heaps to communicate. It has at least 12 different types of vocalization but scent is the most important sense for communication, especially for marking territorial boundaries. The tails have scent glands which they use to deposit their musky scent on the spraint. The spraint is deposited either in tree trunks or on boulders, trails and pool edges. They also have signed heaps, which are visual indicators of an otter’s presence. A sign heap is a small mound of sand, gravel, grass or mud scraped up by the otter. Besides these methods, they also communicate with chemical and tactile cues, such as social grooming, hormonal changes and posturing.

Diet and eating habits[edit]

An Asian small-clawed otter at the Wellington Zoo in New Zealand playing with a pebble.

Oriental small-clawed otters feed mainly on invertebrates such as crustaceans and molluscs, but are also known to feed on vertebrates, in particular amphibians. The hindmost upper teeth (pm4 and m3) are broad and robust and are specialized for crushing the exoskeletons of crabs and other hard shelled prey. They also feed on insects and small fish such as gouramis and catfish. They supplement their diet with rodents and snakes. Apart from crabs, the major prey items are mudskippers (Gobioidei). There is much seasonable variability in the diet. They hunt food by using their vibrissae to detect movements of prey in the water. They use their forepaws to locate and capture items rather than their mouths. Their incomplete webbing gives them a great deal of manual dexterity. They dig in sand and mud for shellfish such as clams, mussels and crab. To get at the meat they crush the shell manually or let heat from the sun force the shells to open.

Economic importances[edit]

Oriental small-clawed otters consume small crabs which are considered to be agricultural pests, however, they may uproot plants in the paddy fields. They act as pest population controllers for the farmers by influencing the population of shellfish and crustaceans in their environments.

Oriental small-clawed otter swimming with rhino at Zoo Basel

Conservation[edit]

They are seriously threatened by rapid habitat destruction, hunting and pollution. Their population trend is decreasing despite being a protected species.

As part of the Association of Zoos and Aquariums' Species Survival Plan, SeaWorld breeds this species to preserve it in zoos and aquariums.

One of the largest oriental small-clawed otter exhibits is at Zoo Basel. There, the outdoor otter exhibit is about 2,000 square metres (22,000 sq ft) and has two rivers, four ponds, and over a dozen tunnels. Only one family of otters is living in this enclosure and it is shared by Indian rhinoceroses and muntjacs. The otters get along very well with the other animals and are often seen swimming with the rhinos.[7]

References[edit]

  1. ^ a b c Wozencraft, W. C. (2005). "Order Carnivora". In Wilson, D. E.; Reeder, D. M. Mammal Species of the World (3rd ed.). Johns Hopkins University Press. pp. 532–628. ISBN 978-0-8018-8221-0. OCLC 62265494. 
  2. ^ a b Hussain SA & de Silva PK (2008). Aonyx cinerea. In: IUCN 2008. IUCN Red List of Threatened Species. Retrieved 6 May 2008.
  3. ^ Foster-turley, Pat; Susan Engfar (January 1988). "The Species Survival Plan for the Asian small-clawed otter Aonyx cinerea". International Zoo Yearbook 27 (1). doi:10.1111/j.1748-1090.1988.tb03199.x. 
  4. ^ Koepfli, K.-P. & Wayne, R.K. 1998. Phylogenetic relationships of otters (Carnivora: Mustelidae) based on mitochondrial cytochrome B sequences. J. Zool. 246, 401-416.
  5. ^ IUCN Otter Specialist Group: Aonyx cinereus (Illiger, 1815), the Asian Small-Clawed Otter.
  6. ^ [1] (2011).
  7. ^ (German) Zoo-Nachwuchs sorgt für Trubel. Zoo Basel, written 2012-05-15, retrieved 2013-03-15

Further reading[edit]

  • Payne, J., Francis, C.M., and Phillipps, K. 1994. A Field Guide to the Mammals of Borneo. Kota Kinabalu: The Sabah Society.
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