Aonyx cinerea is found in coastal regions from southern India to the Malay Peninsula and southern China.
Biogeographic Regions: oriental (Native ); indian ocean
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
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
Habitat and Ecology
In west Java, its presence is positively correlated with slow flowing and stagnant broad rivers and smaller streams, depicting a distinct decline in preference from slow to deep-water bodies. On the other hand, they also use shallow fast-flowing mountain creeks narrower than 5 m, particularly when the course of the streams includes natural pools. In rice fields, they chose slow-flowing irrigation channels narrower than 2 m and with a varied, moderate or low vegetation structure. Like smooth-coated otter the Asian small-clawed otter dislike bare and open areas that do not offer any shelter (Melisch et al. 1996). It prefers pond areas and rice fields than the rivers, whereas it uses mangroves and lakes in proportion to their availability (Melisch et al. 1996). In riverine systems it prefers moderate and low vegetation structure, though their presence was also observed from banks with poor vegetation cover. Neither in ponds nor in rice field areas did they show preference for any of the vegetation structure categories, though poor nor bare structural conditions were the least favoured both in riverine and pond areas and along the rice fields.
The small-clawed otter is adapted to feed on invertebrates as evident from the last two upper teeth (pm4 and m3) which are larger in size for crushing the exoskeleton of crabs and other hard shelled prey. The small clawed otter feeds mainly on crabs, snails and other molluscs, insects and small fish such as gouramis and catfish (Pocock 1941, Wayre 1978). They supplement their diet with rodents, snakes and amphibians too.
During a study in Malaysia, Foster-Turly (1992) examined 328 scats and found that around 80.8% of the scats consisted of crabs, 77.8% fish, 12.5% insects and 4.0% snails. This is the first study in which quantitative information on the diet of wild small-clawed otter was made. This study revealed that though the small-clawed otter is adapted for an invertebrate diet it substantiates its diet with large quantity of fish. Apart from crabs, the major prey item for small-clawed otter was the mudskipper (Gobioidei). This was recorded in the 48% of the scats. The other important prey was Trichogaster spp. and Anabantidae fish, which were represented in 27.4% scats. As evident from the scats the major fish prey were Trichogaster spp 20.7%, Anabis testudineus 5.2%, Clarius spp 2.4% and Channa striatus 1.5%. Apart from these the small-clawed otter in Malaysia also fed on snakes, frogs and insects. Foster-Turly (1992) also examined the diet composition at four different times of the year coinciding with different water levels in the rice fields and concluded that the diet of the small-clawed otter was significantly different at different times of the year. Only the relatively rare dietary components of rodents, snails and snakehead fish (Clarius spp.) showed no significant difference among seasons. Crabs were always the most prevalent food items, but the frequency of occurrence in scats varied from 70.4% to 93.2%. Similarly, though the mudskippers were the second most important food items, they were consumed in significantly different amounts in different seasons from a low of 27.3% to 63.6%. The amount of Trichogaster, Anabis and the Anbantidae also varied considerably. This difference in the use of these prey are most likely due to difference in the life cycle and availability of these prey at different times of the year.
Preliminary analysis of the small-clawed otter spraints from west Java showed their preference for crabs in both natural and man-made habitats (Melisch et al. 1996). In 87% of all collected spraints, crabs formed the dominant prey. Remaining part of the spraints consisted of fish bones and scales, ribs and vertebrae, unidentified mammalian hair, shrimps, insects and snake scales.In the Huay Kha Khaeng, Thailand almost 90% of the spraints of small-clawed otter contained remains of crabs Potamon smithianus, whereas 5% scats contained each of Fish and Amphibians. Apart from this, in few scats evidences of rodents and other arthropods were also found. Kruuk et al. (1994) estimated the preference for various size classes of crabs eaten by small-clawed otter. Of the 92 scats, 14 scats had crabs size 10-14 cm, 42 scats had 15-19 cm, 26 had 20-24 cm, 12 had 25-29 cm, 4 had 30-34 and 1 had 40-44 cm. The size distribution of crabs taken by small-clawed otter was similar to what was available, and there was not much evidence for selection of specific size. In west Java a preliminary estimate of preferred size confirmed an average of 3-4 cm carapace width (Melisch et al. 1996).
The sexual behaviour of small clawed otter has been observed in as young as 18 months old. In captivity, successful breeding has been reported for 2.1 year females and 2.8 year males. The youngest animal to reproduce was a female of 13 months captive born at Bronx Zoo, and the oldest was a 15 years male at the National Zoo, USA (Foster-Turley and Engfer 1988). In the females oestrous cycle has duration of anywhere from 28 to 30 days, with breeding occurring the year round (Lancaster 1975). Some facilities report this cycle extending to "every few months" with older animals. Oestrus lasts from one to thirteen days. Behavioural signs of the onset of oestrus may include increased rubbing and marking.
In captivity mating usually takes place in the water, but has also been observed on land on a few occasions. In most cases the exact gestation period could not be ascertained but it is believed to be around 60-86 days (Lancaster 1975, Sobel 1996). The litter size ranges from 2-7. Life span in captivity is around 11 years (Crandall 1964).
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 )
The role of A. cinereus in the ecosystem is not well understood. They impact the populations of shellfish and crustaceans in their area.
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.
Known prey organisms
This list may not be complete but is based on published studies.
Life History and 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
A captive specimen of A. cinereus lived about 16 years.
Status: captivity: 16 (high) years.
Lifespan, longevity, and ageing
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
Molecular Biology and Genetics
Statistics of barcoding coverage: Aonyx cinerea
Public Records: 0
Specimens with Barcodes: 6
Species With Barcodes: 1
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
IUCN Red List Assessment
Red List Category
Red List Criteria
- 2004Near Threatened
- 1994Insufficiently Known(Groombridge 1994)
- 1990Insufficiently Known(IUCN 1990)
- 1988Insufficiently Known(IUCN Conservation Monitoring Centre 1988)
The next important threats to Asian small-clawed otter are reduction in prey biomass due to over-exploitation, which make its remaining habitats unsustainable. Pollution is probably the single most factors causing decline in the population of many fish species (Dehadrai and Ponniah 1997). Reduction in prey biomass affects otter population, and organochloric and heavy metal contamination interferes with their normal physiology leading to the decline in population. The threats to small-clawed otter is prominent in its western range so much so that since last 60 years its range has been shrunk considerable moving west to east from Himachal Pradesh to Assam (Hussain 2007). Once common in the mangroves of east Calcutta and Sunderbans (Sanyal 1991) now it is believed to be locally extinct. It is likely that the present range boundary at the western limit is Assam and in the Western Ghats of Southern India.
Over the years the Otter Specialist Group has developed a cadre of biologist across Asia to conduct field surveys and has popularize otter conservation by promoting otter as ambassador of the wetlands. However, concerted effort to conserve this species is needed. For the long term survival of the species, policy based action, research on factors affecting its survival, habitat based action on creation and where required expansion of protected areas and communication and awareness building actions are needed.
Relevance to Humans and Ecosystems
Rice farmers complain about Asian clawless otters uprooting plants in the paddies.
Aonyx cinerea consume small crabs which are considered agricultural pests.
Positive Impacts: controls pest population
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, 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. 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.
This species was formerly thought to be the only member of the genus Amblonyx; however, it has recently been confirmed as being a member of the genus Aonyx after mitochondrial DNA analysis. Another synonym for the oriental small-clawed otter is Aonyx cinereus.
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). 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.
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.
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.
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.
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.
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
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.
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.
They are seriously threatened by rapid habitat destruction, hunting and pollution. Their population trend is decreasing despite being a protected species.
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.
|This article includes a list of references, but its sources remain unclear because it has insufficient inline citations. (October 2008)|
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- 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.
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- (German) Zoo-Nachwuchs sorgt für Trubel. Zoo Basel, written 2012-05-15, retrieved 2013-03-15
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