Oriental Small-clawed Otter (Aonyx cinereus)

Range Description: The Asian small-clawed otter has a large distribution range, extending from India in South Asia east ward through entire Southeast Asia up to Palawan (Philippines) and Taiwan and southern China in the north (Mason and Macdonald 1986, Wozencraft 1993, Hussain 2000). In recent years, in England it has established itself in the wild after escaping from captivity (Jefferies 1990 and 1991). In India it occurs in the Himalayan foothills of Himachal Pradesh (Kulu), West Bengal, Assam and Arunachal Pradesh as well as in southern Indian hill ranges of Coorg (Karnataka), Ashambu, Nilgiri and Palni hills (Tamil Nadu) and some places in Kerala (Pocock 1941, Prater 1971, Hussain 2000).
Countries: Native:
Bangladesh; Bhutan; Brunei Darussalam; Cambodia; China; India (Arunachal Pradesh, Assam, Himachal Pradesh, Karnataka, Kerala, Tamil Nadu, West Bengal); Indonesia; Lao People's Democratic Republic; Malaysia; Myanmar; Nepal; Philippines; Singapore; Taiwan, Province of China; Thailand; Vietnam


In most of their range the Asian small-clawed otter is sympatric with smooth-coated and Eurasian otters. In India, all the three species occur in Western Ghats and in the Northeast India where the species occur in small group of two to four individuals. In Western Ghats they are mostly found along the hill streams. They were once common in the mangroves of east Calcutta and Sunderbans (Sanyal 1991). The Asian small-clawed otters occur in freshwater and peat swamp forests, rice fields, lakes, streams, reservoirs, canals, mangrove and along the coast (Sivasothi and Nor 1994). In Malaysia and Indonesia they occur in coastal wetlands, and along the banks of paddy fields. Comparable data from Java, Myanmar, and India revealed that the Asian small-clawed otters have a high climatic and trophic adaptability in south and Southeast Asian tropics, occurring from coastal wetlands up to mountain streams (Melisch et al., 1996). A reliable population estimate of the Asian small-clawed otter is lacking. As many as 15 individuals were seen in a group in Malaysia (Wayre 1978), four to eight in coastal Sabha (Mason and Macdonald 1986) and two to four in India.
Population Trend: Decreasing

 Habitat and Ecology:

The typical habitats of the Asian small-clawed otter in west Java are wetland systems having pools and stagnant water, including shallow stretches, with depth less than 1 m. These habitats are represented by freshwater swamps, meandering rivers, mangroves and tidal pools. Muller (1839) observed small-clawed otter from slow-flowing lowland streams to submontane streams dominated by rocks and boulders in forested areas. Irrigated rice fields with many crab species (Brachyura) are extensively used by small-clawed otter if proper shelter for them is available. These can act as suitable man made habitats (Melisch et al., 1996). In Thailand, the rapid-flowing upper areas of the Huay Kha Khaeng are dominated by L. lutra, the slowly meandering river near the dam and the dam itself were used by L. perspicillata while the Asian small-clawed otter occurred mostly in the middle sections, but also at the upper reaches. When different otter species occurred in the same site there was evidence of difference in use of the habitats. Signs of the of small-clawed otter were found wandering further away from the river than the two other species, between patches of reeds and river debris where crabs were more likely to be found (Kruuk et al. 1994). 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 gourami 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).
Systems: Terrestrial; Freshwater; Marine

Major Threat(s):

The threat to Small-clawed otter is similar to that of smooth-coated and Eurasian otters. Throughout Asia the potential threat to its continued survival is destruction of its habitats due to changing land use pattern in the form of developmental activities. In many parts of Asia, the habitats have been reduced due to reclamation of peat swamp forests and mangroves, aquaculture activities along the intertidal wetlands and loss of hill streams. In India the primary threats are loss of habitats due to tea and coffee plantations along the hills, in the coastal areas loss of mangroves due to aquaculture and increased human settlements and siltation of smaller hill streams due to deforestation. Increased influx of pesticides into the streams from the plantations reduces the quality of the habitats.  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.

 Conservation Actions:

 Since 1977, the Asian small clawed otter is listed on Appendix II CITES which indicates that the species is not necessarily threatened with extinction, but the trade on its pelt must be controlled in order to avoid utilization incompatible with their survival. However, most range countries are not able to control the clandestine trade leading to extensive poaching. Nevertheless, it is a protected species in almost all the range countries which prohibits its killing. The Asian small-clawed otter is once common in the streams and wetlands of south and south east Asia is now restricted to a few Protected Areas. Creation of networks of Protected Areas, identification of sites as wetland of national and International importance under Ramsar Convention has to some extent halts the degradation of its habitat.  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.