The oriental small-clawed otter (Aonyx cinerea), also known as 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, the Philippines, Thailand and Vietnam.^[1] This otter is distinctive for its forepaws, as the claws do not extend above the fleshy end pads of its toes and fingers. These attributes give it a high degree of manual dexterity in using 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 and previous offspring helping 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

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

Morphology

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), about 30 cm (12 in) of which is comprised by the tail. Weight can range from 1 to 5.4 kg (2.2-11.9 lbs).^[6] Their body shape is typically slender, streamlined and serpentine, and its flexibility allows grooming of almost all their fur. Dark, grayish-brown fur covers most of the dorsal surface with a lighter cream coloration on the ventral surface, especially on their 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. Their ears are small and rounded, and a valve-like structure enables closure when swimming underwater. Nose pads are dusky or pinkish in color. They have vibrissae (whiskers) on their muzzle. The vibrissae 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. Thus, they have only partially webbed paws, which distinguishes them from all other otters. 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 in their paws instead of with their mouth. Their small, blunt, peg-like claws are extremely reduced and rarely extend past the digit.

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

This species could be found distributed in coastal regions from southern India to South China, Southeast Asia, Sumatra, Java, and Palawan. It is known from all regions of Sabah and Sarawak, Brunei, and central Kalimantan. It could be found in almost all other parts of Borneo.

Habitat

They commonly could be found in freshwater wetland systems such as freshwater swamps, meandering rivers, mangroves and tidal pools. They also dominated irrigated rice fields and wandering in area between patches of reeds and river debris where many crab species (Brachyura) were more likely to be found. They dislike bare and open areas that do not offer any shelter. Thus, they prefer pond areas and rice fields more than the rivers. However, in the riverine systems they would only chose the area with low vegetation. Their nesting burrows dug into the muddy banks where they live. This species spend most of their time on land unlike any other otters.

Reproduction

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. Their 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 are fully weaned at 14 weeks, and will only open their eyes after 40 days. In the next 40 days, the young can 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.

Behavior

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

They are diurnal animals (active during daytime), found in remote areas, free of human disturbances. They continually groom their fur to maintain its insulating qualities. They dry themselves by rolling on the ground or rubbing against logs or vegetation. The Asian small-clawed otter is an excellent swimmer; it swims by moving its 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 other individuals. Generally, they sleep and rest on land either above ground or in the 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 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

This species to communicates using vocalizations, scent markings and sign heaps. This otter has at least 12 different types of vocalizations. Scent, though, is the most important sense for communication, especially for marking territorial boundaries. Their tails have scent glands they use to deposit their musky scent on their 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, their communication also occurs with chemical and tactile cues, such as social grooming, hormonal changes and posturing.

Diet and eating habits

Oriental Small-clawed otter feed mainly on invertebrates such as crab and other crustaceans, molluscs and amphibians. This is proved from the evident of the last two upper teeth (pm4 and m3) which are larger in size for crushing the exoskeleton 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, snakes and frogs too. Apart from crabs, the major prey items for them are the mudskipper (Gobioidei). Only the relatively rare dietary component of rodents, snails and snakehead fish (Clarius spp.) showed no significant difference among seasons. 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 mouth. Their incomplete webbing gives them a great deal of manual dexterity. They dig in sands and mud for shellfish such as clams and mussels and crabs as well. To get at the meat they crush the shell manually or let heat from the sun open the shells. Therefore, there teeth are broad and robust very suitable for crushing shells.

Economic importances

They 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.

Conservation

Small-clawed otter in Disney's Animal Kingdom

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 2000 square meters (21'528 square feet) and has two rivers, four ponds, and over a dozen tunnels. Only one pair of otters is living on the exhibit, but shares it with Indian rhinoceroses and muntjacs.

References

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Further reading

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