| Asian small-clawed otter | |
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| AtMelbourne Zoo, Australia | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Carnivora |
| Suborder: | Caniformia |
| Family: | Mustelidae |
| Subfamily: | Lutrinae |
| Genus: | Aonyx |
| Species: | A. cinereus |
| Binomial name | |
| Aonyx cinereus (Illiger, 1815) | |
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| Asian small-clawed otter native range (in green) | |
| Synonyms | |
Amblonyx cinereus | |
TheAsian small-clawed otter (Aonyx cinereus), also calledoriental small-clawed otter andsmall-clawed otter, is anotter species native toSouth andSoutheast Asia. It has shortclaws that do not extend beyond the pads of its webbed digits. With a total body length of 730 to 960 mm (28.6 to 37.6 in), and a maximum weight of 3.5 kg (7.7 lb), it is the smallest otter species.
The Asian small-clawed otter lives in riverine habitats,freshwater wetlands andmangroveswamps. It feeds onmolluscs,crabs and other smallaquatic animals. It lives in pairs, but also has been observed in family groups with up to 12 individuals.It is listed asVulnerable on theIUCN Red List, and is threatened byhabitat loss,pollution, and in some areas also byhunting.
Lutra cinerea was thescientific name proposed byJohann Karl Wilhelm Illiger in 1815 for an otter collected inBatavia.[2] In the 19th and 20th centuries, severalzoological specimens were described:
Results of a mitochondrialcytochrome B analysis published in 1998 indicated that it should be subordinated to the genusAonyx.[7] Results of a molecular study published in 2008 showed that the Asian small-clawed otter is asister taxon ofLutrogale, lending support to retaining the genusAmblonyx or expandingAonyx to make itmonophyletic. Theygenetically diverged about1.5 million years ago.[8]
The Asian small-clawed otter groups with theAfrican clawless otter (Aonyx capensis) and thesmooth-coated otter (Lutrogale perspicillata) into asister clade with the genusLutra.Hybridisation of Asian small-clawed otter females with smooth-coated otter males occurred inSingapore. The resulting offspring and their descendants bred back into the smooth-coated otter population, but maintained the genes of their small-clawed otter ancestors; a population of at least 60 hybrid otters are present in Singapore as of 2016.[9]
The Asian small-clawed otter has deep brownfur with some rufous tinge on the back, but paler below. Its underfur is lighter near the base. The sides of the neck and head are brown, but its cheeks, upperlip, chin, throat and sides of the neck are whitish.[10]Its skull is short, and the nakedrhinarium rounded above. The muzzle has long coarsevibrissae on either side. Its eyes are located toward the front of the head. The small ears are oval-shaped with an inconspicuoustragus andantitragus. Itspaws are narrow with short digits that are webbed to the last joint. There are short hairs on the lower sides of the interdigital webs. The four-lobed plantar pads are longer than wide. Theclaws are short, almost erect, and in some individuals even absent.[11]Females have fourmammary glands.[12]
The Asian small-clawed otter is the smallest otter species in Asia. In head-to-body length, it ranges from 470 to 610 mm (18.4 to 24 in) with a 260 to 350 mm (10.2 to 13.6 in) longtail. The tapering tail is thick and muscular, especially at the base, and more than half the length of the body. Hind feet are 97 to 102 mm (3.8 to 4 in) long. Length of skull ranges from 3.3 to 3.7 in (84 to 94 mm). It does not have upper premolars and only fourcheek teeth above.[13]Adult captive otters range in weight from 2.7 to 3.5 kg (6.0 to 7.7 lb).[14]
The Asian small-clawed otter's native range comprises parts of India to Southeast Asia including the islands ofSumatra, Java,Borneo andPalawan. It lives in freshwaterwetlands such asswamps, meandering rivers, irrigated rice fields as well asestuaries, coastallagoons andtidal pools. It occurs in West Bengal, Assam andArunachal Pradesh, and in coastal regions ofOdisha. InKarnataka,Nilgiri andPalni hills inTamil Nadu, it lives in shallow mountain creeks up to an elevation of 2,000 m (6,600 ft).[1]InWest Java, it inhabits areas along slow-flowing irrigation channels, pond areas and rice fields surrounded by vegetation that offers shelter. It also occurs inmangrove forests.[15]In February 2025, the Asian small-clawed otter was photographed inDadeldhura District in far-westernNepal.[16]
In the 1980s, a few Asian small-clawed otters escaped from captivity inEngland and established a population in the wild.[17][18] It was likely driven out by the recovery of the nativeEurasian otter.[19]
The Asian small-clawed otter is mostly active after dark.[20][21]It lives in groups of up to 15 individuals.[21] In the BangladeshSundarbans, 53 individuals were recorded in 351 km (218 mi) of water courses in 13 locations between November 2014 and March 2015. Group size ranged from one to 12 individuals.[22]Group members communicate using 12 or more distinct calls, and utter a variety of yelps and whimpers.[12] When disturbed, they scream to rally the help of others.[23]
When swimming on the surface, otters row with the forelimbs and paddle with the hind limbs.[24] When diving under water, they undulate their bodies and tails. Captive otters swim at speeds of 0.7–1.2 m/s (2.3–3.9 ft/s).[14]
Observations of wild Asian small-clawed otters revealed that they smear theirspraint atlatrine sites, using their hind feet and tails. Large groups smeared more than groups of three or fewer animals. The frequency of latrines with smeared scats varied in different locations, indicating a preference for certain sites. Spraint smearing most likely facilitates social ties among group members and is associated withterritorial marking displays. They use grassy or sandy banks for resting, sun bathing and grooming. In marshes, they use mostly islands.[21]
The Asian small-clawed otter feeds mainly oncrabs,mudskippers andTrichogaster fish. Its diet varies seasonally. When and where available, it also catches snakes, frogs, insects, rats and ricefield fish likecatfish,Anabas testudineus andChanna striata.[21]The size of crabs found in spraints inHuai Kha Khaeng Wildlife Sanctuary ranged incarapace width from 10 to 44 cm (3.9 to 17.3 in).[25]Captive Asian small-clawed otters were observed to leaveshellfish in the sun so the heat causes them to open, making it possible for them to eat them without having to crush the shells.[12]
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Information about the Asian small-clawed otter'smating and breeding behaviour has been studied in captive environments. Captive pairs aremonogamous. Theestrous cycle of females lasts 28 to 30 days withestrus lasting between one and 13 days. Usually, mating takes place in the water.[26]Gestation lasts 62 to 86 days. Interval between births is at least eight months.[27]About two weeks beforeparturition, both female and male engage in building a nest. They collect grass, hay or straw and carry this material into the breeding chamber. Between one and seven pups are born in alitter. Pups are born with closed eyes, which open in the fifth week.[26]Newborn pups weigh between 45.6 and 62.5 g (1.61 and 2.20 oz) and reach a weight of 410–988 g (14.5–34.9 oz) after 60 days.[28] They start exploring the environs of the breeding den at the age of ten weeks. At about three months, they enter and paddle in shallow water under the guidance of the mother. They become independent at the age of four to five months.[26]
The Asian small-clawed otter is threatened bypoaching for its fur, loss anddestruction of habitats such as hill streams, peat swamp forests and mangroves for aquaculture projects. Threats in India include deforestation, conversion of natural habitat for tea and coffee plantations, overfishing of rivers and water pollution throughpesticides.[1]
It is the most sought after otter species for the illegalpet trade in Asia. At least 711 Asian small-clawed otters were offered for sale through online websites by 280 traders in Indonesia, Thailand, Malaysia and Vietnam between 2016 and 2017.[29]Between December 2015 and October 2018, 49 Asian small-clawed otters were confiscated from wildlife traffickers in Thailand, Vietnam andJapan; 35 of them were bound for sale in Japan.[30]
The Asian small-clawed otter was listed onCITES Appendix II and is protected in almost all range countries prohibiting its killing.[1] Since August 2019, it is included inCITES Appendix I, thus strengthening its protection in regards to international trade.[31]
TheAssociation of Zoos and Aquariums established aSpecies Survival Plan for the Asian small-clawed otter in 1983 to encourage research on captive breeding.[32][33]
In Europe,Zoo Basel keeps Asian small-clawed otters together withIndian rhinoceros.[34] In Tallinn Zoo, Asian small-clawed otters share an enclosure with a binturong.[35]
Asian small-clawed otters withosteoporosis display resorption of hyperactive bone and cartilage byosteoclasts in many bone sites, which causes pockmarks on all the bones.[36]
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