The Asian small-clawed otter (Aonyx cinereus), also known as the oriental small-clawed otter and the small-clawed otter, is an otter species native to South and Southeast Asia. It has short claws 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 5 kg (11 lb),[citation needed] it is the smallest otter species in the world.
The Asian small-clawed otter lives in riverine habitats, freshwater wetlands and mangroveswamps. It feeds on molluscs, crabs and other small aquatic animals. It lives in pairs, but was also observed in family groups with up to 12 individuals.
Lutra concolor proposed by Constantine Samuel Rafinesque in 1832 was a uniform coloured otter from Assam. Rafinesque also proposed Amblonyx as name for a subgenus for otters with short, obtuse claws.[3]
Amblonyx cinerea nirnai proposed by Reginald Innes Pocock in 1940 was a dark brown small-clawed otter from Virajpet in South India.[6]
Phylogeny
Results of a mitochondrial cytochrome B analysis published in 1998 indicated that it should be subordinated to the genus Aonyx.[7] Results of a molecular study published in 2008 showed that the Asian small-clawed otter is a sister taxon of Lutrogale, lending support to retaining the genus Amblonyx or expanding Aonyx to make it monophyletic. They genetically diverged about 1.5 million years ago.[8]
The Asian small-clawed otter groups with the African clawless otter (Aonyx capensis) and the smooth-coated otter (Lutrogale perspicillata) into a sister clade with the genus Lutra. Hybridisation of Asian small-clawed otter females with smooth-coated otter males occurred in Singapore. 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]
Characteristics
Closeup of a small-clawed otter's mouth
The Asian small-clawed otter has deep brown fur 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 naked rhinarium rounded above. The muzzle has long coarse vibrissae on either side. Its eyes are located toward the front of the head. The small ears are oval-shaped with an inconspicuous tragus and antitragus. Its paws 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. The claws are short, almost erect, and in some individuals even absent.[11]
Females have four mammary 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) long tail. 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 four cheek teeth above.[13]
Adult captive otters range in weight from 2.7 to 3.5 kg (6.0 to 7.7 lb).[14]
Distribution and habitat
The Asian small-clawed otter's native range comprises parts of India to Southeast Asia including the islands of Sumatra, Java, Borneo and Palawan. It lives in freshwater wetlands such as swamps, meandering rivers, irrigated rice fields as well as estuaries, coastal lagoons and tidal pools. It occurs in West Bengal, Assam and Arunachal Pradesh, and in coastal regions of Odisha. In Karnataka, Nilgiri and Palni hills in Tamil Nadu, it lives in shallow mountain creeks up to an elevation of 2,000 m (6,600 ft).[1]
In West Java, it inhabits areas along slow-flowing irrigation channels, pond areas and rice fields surrounded by vegetation that offers shelter. It also occurs in mangroves.[15]
In the 1980s, a few Asian small-clawed otters escaped from captivity in England and established a population in the wild.[16][17]
Behaviour and ecology
Family group of Asian small-clawed otters
The Asian small-clawed otter is mostly active after dark.[18][19]
It lives in groups of up to 15 individuals.[19] In the Bangladesh Sundarbans, 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.[20]
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.[21]
When swimming on the surface, otters row with the forelimbs and paddle with the hind limbs.[22] 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 their spraint at latrine 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 with territorial marking displays. They use grassy or sandy banks for resting, sun bathing and grooming. In marshes, they use mostly islands.[19]
The Asian small-clawed otter feeds mainly on crabs, mudskippers and Trichogaster fish. Its diet varies seasonally. When and where available, it also catches snakes, frogs, insects, rats and ricefield fish like catfish, Anabas testudineus and Channa striata.[19]
The size of crabs found in spraints in Huai Kha Khaeng Wildlife Sanctuary ranged in carapace width from 10 to 44 cm (3.9 to 17.3 in).[23]
Captive Asian small-clawed otters were observed to leave shellfish 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]
Reproduction
Information about the Asian small-clawed otter's mating and breeding behaviour has been studied in captive environments. Captive pairs are monogamous. The estrous cycle of females lasts 28 to 30 days with estrus lasting between one and 13 days. Usually, mating takes place in the water.[24]Gestation lasts 62 to 86 days. Interval between births is at least eight months.[25]
About two weeks before parturition, 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 a litter. Pups are born with closed eyes, which open in the fifth week.[24]
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.[26] 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.[24]
Threats
The Asian small-clawed otter is threatened by poaching for its fur, loss and destruction 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 through pesticides.[1]
It is the most sought after otter species for the illegal pet 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.[27]
Between December 2015 and October 2018, 49 Asian small-clawed otters were confiscated from wildlife traffickers in Thailand, Vietnam and Japan; 35 of them were bound for sale in Japan.[28]
Conservation
Asian small-clawed otter swimming with Indian rhinoceros at Zoo Basel
The Asian small-clawed otter was listed on CITES Appendix II and is protected in almost all range countries prohibiting its killing.[1] Since August 2019, it is included in CITES Appendix I, thus strengthening its protection in regards to international trade.[29]
Asian small-clawed otters with osteoporosis display resorption of hyperactive bone and cartilage by osteoclasts in many bone sites, which causes pockmarks on all the bones.[33]
^Rafinesque, C. S. (1832). "Description of a New Otter, Lutra concolor, from Assam in India". Atlantic journal, and friend of knowledge in eight numbers : containing about 160 original articles and tracts on natural and historical sciences, the description of about 150 new plants, and 100 new animals or fossils ; many vocabularies of languages, historical and geological facts. Philadelphia. p. 62. ISBN9780665414664.
^Horsfield, T. (1824). "Lutra leptonyx". Zoological researches in Java, and the neighbouring islands. London: Kingsbury, Parbury & Allen. pp. 185–191.
^Gray, J. E. (1843). "The Wargul. Aonyx leptonyx". List of the specimens of Mammalia in the collection of the British Museum. p. 71.
^Blanford, W. T. (1888). "Lutra leptonyx. The clawless Otter". The Fauna of British India, Including Ceylon and Burma. Vol. Mammalia. London: Taylor and Francis. pp. 187–188.
^ abcTimmins, W. H. (1971). "Observations on breeding the oriental short clawed otter Amblonyx cinerea at Chester Zoo". International Zoo Yearbook. 11: 109–111. doi:10.1111/j.1748-1090.1971.tb01868.x.
^Pocock, R. I. (1941). "Genus Amblonyx, Rafinesque". The Fauna of British India including Ceylon and Burma. Vol. Mammalia II. London: Taylor and Francis. pp. 303–317.
^ abBorgwardt, N. & Culik, B. M. (1999). "Asian small-clawed otters (Amblonyx cinerea): resting and swimming metabolic rates". Journal of Comparative Physiology B: Biochemical, Systemic, and Environmental Physiology. 169 (2): 100–106. doi:10.1007/s003600050199. PMID10227184. S2CID22682528.
^Melisch, R.; Kusumawardhani, L.; Asmoro, P. B. & Lubis, I. R. (1996). The otters of west Java – a survey of their distribution and habitat use and a strategy towards a species conservation programme. Bogor, Indonesia: Wetlands International – Indonesia Programme.
^Jefferies, D. J. (1989). "The Asian short-clawed otter Amblonyx cinerea (Illiger) living wild in Britain". Otters (Earsham). 2 (3): 21–25.
^Jefferies, D. J. (1991). "Another record of an Asian short-clawed otter living free in Oxford with notes on its implications". Journal of the Otter Trust. 2 (2): 9–12.
^Aziz, M.A. (2018). "Notes on population status and feeding behaviour of Asian Small-clawed otter (Aonyx cinereus) in the Sundarbans mangrove forest of Bangladesh". IUCN Otter Specialist Group Bulletin. 35 (1): 3–10.
^Sivasothi, N. & Nor, B. H. M. (1994). "A review of otters (Carnivora: Mustelidae: Lutrinae) in Malaysia and Singapore". Hydrobiologia. 285 (1–3): 1–3. doi:10.1007/BF00005663. S2CID44011643.
^Fish, F. E. (1994). "Association of propulsive swimming mode with behaviour in the river otters (Lutra canadensis)". Journal of Mammalogy. 75 (4): 989–997. doi:10.2307/1382481. JSTOR1382481.
^Kruuk, H.; Kanchanasaka, B.; O'Sullivian, S. & Wanghongsa, S. (1994). "Niche separation in three sympatric otters Lutra perspicillata, Lutra lutra and Aonyx cinerea in Huai Kha Khaeng, Thailand". Biological Conservation. 69: 115–210. doi:10.1016/0006-3207(94)90334-4.
^ abcLancaster, W. E. (1975). "Exhibiting and breeding the Asian small-clawed otter at Adelaide Zoo". International Zoo Yearbook. 15: 63–65. doi:10.1111/j.1748-1090.1975.tb01355.x.
^Sobel, G. (1996). Development and validation of noninvasive, fecal steroid monitoring procedures for the Asian small-clawed otter, Aonyx cinerea (Master of Science). Gainesville, Florida: University of Florida.
^Maslanka, M. T. & Crissey, S. D. (1998). "Nutrition and diet". In Lombardi, D. & O’Connor, J. (eds.). Asian small-clawed otter (Aonyx cinerea) husbandary manual. Powell, Ohio: Columbus Zoological Gardens and AZA Asian Small-Clawed Otter SSP. pp. 1–18.
^Foster-Turley, P. & Engfar, S. (1988). "The Species Survival Plan for the Asian small-clawed otter Aonyx cinerea". International Zoo Yearbook. 27: 79–84. doi:10.1111/j.1748-1090.1988.tb03199.x.
^Foster-Turley, P. (1986). "A progress report on the species survival plan for Asian small-clawed otters in United States zoos". Otter Specialist Group Bulletin. 1: 19–21.
