Oriental Small-clawed Otter: Wikis

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Oriental small-clawed otter[1]
Conservation status
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Carnivora
Family: Mustelidae
Genus: Aonyx
Species: A. cinerea
Binomial name
Aonyx cinerea
(Illiger, 1815)
Synonyms

Amblonyx cinereus
Aonyx cinereus
Amblonyx cinerea

The Oriental Small-clawed Otter (Aonyx cinerea), also known as 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, 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]

Contents

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.[3] Another synonym for the Oriental small-clawed otter is Aonyx cinereus.[4]

Morphology

Oriental Small-clawed Otters are the smallest species of all otters in the world, having a head-to-tail length of around 94 cm and weigh of 2.7 to 5.4 kg. 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 total body length. The tail is thick at the base, muscular, flexible, and taper 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, South-east Asia, Sumatra, Java, and Palawan. It is known from all regions of Sabah and Sarawak, Brunei, and in Central of 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

The Oriental Small-clawed otter form monogamous pairs for life. The estrous cycle in the female is 28 days with 3 days period of estrus. The mated pairs can have two litters of 1 to 6 young per year. Their gestation period is about 60 days. The newborn 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 3 to 4 hours for 10 to 15 minutes at a time. They are fully weaned at 14 weeks. The newborn 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. All the young otter 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. Life span of this species is around 11 years to 16 years.

Behaviour

They are diurnal animals. They are very active during daytime in remote areas which are free of human disturbance. They continually groom their fur to maintain their insulating qualities. They spend most of their time grooming and usually could be seen on land grooming and drying their fur. They dry themselves by rolling on the ground or rubbing against logs or vegetation. They are excellent swimmers too. 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 undulates the entire body including their tail up and down while their hind feet steer. They can dive under water for about 6 to 8 minutes. They produce small amounts of feces which are well-known as spraint by otter researchers. The spraints are one of important way for communication among the otters. Other otter could indicate the presence of other individual based on the olfactory and visual of the spraints. Generally, they sleep and resting on land either above ground or in the dens. They often sleep in areas with moderate disturbance. Oriental Small-clawed Otters are most 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

There are few ways for this species to communicate such as vocalizations, scent markings and sign heaps. They often produce sounds and communicate vocally. This species has at least 12 different types of vocalization. Meanwhile, scent is the most important sense for communication especially for marking territorial boundaries. Their tail has scent glands where they deposit their musky scent on their spraint. The spraint is deposited either in tree trunks, boulders, trails and pool edges. Finally, they also have signed heaps which is visual indicator of an otter’s presence. The sign heaps is small mounds of sand, gravel, grass or mud scraped up by the otters. Besides that, 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 importance for humans

They consume small crabs which are considered as agricultural pests. However, they may uproot plants in the paddy fields. Thus, they benefit as pest population controller for the farmer.

Ecosystem roles

They influence the population of shellfish and crustaceans in their living area.

Conservation status

They are seriously threatened by rapid habitat destruction, hunting and pollution. Their population trend is decreasing. Nevertheless, they are protected species. They are managed under Species Survival Program. In this program, they were used as a model for the management of other otter species while not endangered themselves. Meanwhile, Seaworld breeds this species to preserve in zoo as well as in aquarium and also as a part of AZA’s Species Survival Plan (SSP).

References

  1. ^ a b c Wozencraft, W. C. (16 November 2005). Wilson, D. E., and Reeder, D. M. (eds). ed. Mammal Species of the World (3rd edition ed.). Johns Hopkins University Press. ISBN 0-801-88221-4. http://www.bucknell.edu/msw3/browse.asp?id=14001085.  
  2. ^ a b Hussain SA & de Silva PK (2008). Aonyx cinerea. In: IUCN 2008. IUCN Red List of Threatened Species. Downloaded on 06 May 2008.
  3. ^ Koepfli, K.-P. & Wayne, R.K. 1998. Phylogenetic relationships of otters (Carnivora: Mustelidae) based on mitochondrial cytochrome B sequences. J. Zool. 246, 401-416.
  4. ^ IUCN Otter Specialist Group: Aonyx cinereus (Illiger, 1815), the Asian Small-Clawed Otter.

Further reading

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

External links

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