Aonyx

Diversity

The genus Aonyx is composed of three species grouped together by the common name “clawless otters.” These species can be found in Africa and Southeast Asia nearly anywhere there is a source of freshwater. The genus is semi-aquatic and hunts in bodies of water for crabs, fish, and molluscs. Weight is variable across species and ranges from less than 3.5 kg up to 34 kg. All species in Aonyx have reduced or no claws on the front feet, which is how the genus was named. Two species are near-threatened and one species is vulnerable on the IUCN Red List.

Geographic Range

Aonyx occurs natively throughout most of Africa, beginning as far north as Senegal and Ethiopia and continuing south until South Africa. Aonyx can also be found in large parts of Southeast Asia and parts of India. It has been recently introduced to the wild in England after escaping from captivity. Aonyx is limited by an upper elevation of 3000 meters and a lower depth of 10 meters.

• Biogeographic Regions
• palearctic palearctic
  • introduced introduced
• oriental oriental
  • native native
• ethiopian ethiopian
  • native native

Habitat

Aonyx is semi-aquatic and can be found in most aquatic habitats within its range. Most populations occur in freshwater environments, but some populations can occur along the sea coast as long as freshwater is available nearby. Aquatic habitats are used for hunting and can be natural or man-made, and irrigated rice fields are used by populations occurring in Southeast Asia. Terrestrial habitats include forests, grasslands, and wetlands. Additionally, the presence of nearby freshwater for drinking and relatively shallow bodies of water for hunting are necessary.

• Habitat Regions
• terrestrial terrestrial
• freshwater freshwater

• Terrestrial Biomes
• savanna or grassland savanna or grassland
• forest forest
• rainforest rainforest

• Aquatic Biomes
• lakes and ponds
• rivers and streams

• Wetlands
• swamp swamp

Systematic and Taxonomic History

The genus Aonyx is a monophyletic grouping, though species and lower level classifications are not fully agreed upon. Aonyx currently includes three species of otter: Aonyx capensis , Aonyx cinereus , and Aonyx congicus . Synonyms for the genus name are Amblonyx , Anahyster , Leptonyx , Micraonyx , and Paraonyx . A. cinereus has been considered to be in a separate Amblonyx genus. The specific epithet for A. cinereus was previously ‘cinerea.’ However, ‘Aonyx’ is a masculine genus name, so the species name was modified to be masculine as well. A. congicus has also been previously placed in its own genus Paraonyx . A. congicus has also been thought of as a subspecies of A. capensis , and this continues to be debated. Those who consider them different species split them based upon tooth size and skin differences.

Physical Description

Aonyx varies greatly in size with the smallest individuals being less than 3.5 kg and the largest up to 34 kg. Individuals have a small head, a large neck relative to the head, short legs, and a dorsoventrally flattened tail. Pelage is overall a dark brown. Some areas of the face, neck, and upper torso may have white or greyish pelage. Vibrissae are white as well. All species have reduced or no claws in addition to partial or no webbing. Typically, front feet lack these features compared to the hind feet. Males have a baculum and females have four abdominal mammae.

• Other Physical Features
• endothermic endothermic
• bilateral symmetry bilateral symmetry

Reproduction

Little is known about reproduction in Aonyx . In one species ( A. cinereus ), individuals are monogamous with both parents contributing to raising offspring. Older siblings may help raise offspring in both captive and wild populations.

• Mating System
• monogamous monogamous
• cooperative breeder cooperative breeder

Not much information is readily available regarding reproductive behavior in Aonyx , especially in the wild. In captivity, females go into estrus every 28-30 days. Estrus lasts from 1 to 13 days, and gestation lasts for about 63 days. Births have been reported year round. Litter sizes range from 1 to seven pups per litter. Some pairs may produce 2 litters per year. Females in captivity build grass nests 2 weeks before birth. At birth, young have grey pelage, no teeth, and eyes are closed. Eyes remain closed for 16-35 days, after which cubs will venture outside of dens. Weaning occurs at 45-60 days of age. Young are independent and sexually mature after 1 year. The youngest individual to reproduce was 13 months old, and the oldest was 15 years old. Both individuals were in zoos located in the United States.

• Key Reproductive Features
• iteroparous iteroparous
• year-round breeding year-round breeding
• gonochoric/gonochoristic/dioecious (sexes separate)
• sexual sexual
• viviparous viviparous

Information regarding parental investment is limited due to lack of research on wild populations. In captivity, males spend more time maintaining a nest while the females spend more time grooming and training the young.

• Parental Investment
• female parental care female parental care

Lifespan/Longevity

In captivity, individuals can live for up to 15 years.

Behavior

Individuals are not migratory and are mostly solitary. Unrelated groups may forage together, and family groups may travel together. Species in Aonyx are either nocturnal or crepuscular. Hunting is in the water, and most other activities, such as resting and grooming, occur on land. Grooming is typically by rolling or rubbing against an object. Play behavior in young is common. This can involve play-fighting, romping, sliding, or manipulating inanimate objects.

• Key Behaviors
• nocturnal nocturnal
• crepuscular crepuscular
• motile motile
• solitary solitary

Communication and Perception

Aonyx has vibrissae used to detect movement of prey. Prey is also detected with the forefeet via touch. Anal glands that may be used for scent-marking can be present. Individuals have diverse vocal repertoires with different vocalizations observed in captivity.

• Communication Channels
• acoustic acoustic
• chemical chemical

• Other Communication Modes
• scent marks scent marks

• Perception Channels
• tactile tactile
• chemical chemical

Food Habits

Crabs are the main prey item for Aonyx as cheek teeth are modified for crushing exoskeletons. Fish and molluscs are also commonly eaten. Individuals will opportunistically consume a variety of items including snakes, lizards, amphibians, and insects. Prey is typically consumed upon capture. In captivity, food may be stored in sleeping boxes for later. Hunting occurs in shallow waters usually no deeper than 1.5 meters.

• Primary Diet
• carnivore carnivore
  • eats non-insect arthropods

Predation

Most mortality is inflicted by humans with various traps, poisoned bait, or fish nets. Predators for African populations include crocodiles, leopards, pythons, and large raptors.

Ecosystem Roles

Aonyx is a host for some parasitic trematode and nematode species.

Economic Importance for Humans: Positive

Aonyx is commonly hunted for fur and pelts, and is occasionally hunted for meat.

• Positive Impacts
• food food
• body parts are source of valuable material

Economic Importance for Humans: Negative

Aonyx is seen as a pest by many. Fishermen view them as competitors for fish and as damaging fisheries. Individuals may also be captured in fishing nets or traps accidentally. Rarely in winter, Aonyx may prey on domestic waterfowl.

Conservation Status

Aonyx species are protected in many parts of their range. Two species are listed as near-threatened and one as vulnerable on the IUCN Red List. Primary threats are habitat loss and degradation from human activities such as deforestation, pollution, and changing land use patterns. Poaching by humans and over-exploitation of prey items are also concerns.

Other Comments

The origin of ‘Aonyx’ is from Greek ‘a’ meaning “without” and ‘onyx’ meaning “claw” or “nail.” The synonym ‘Amblonyx’ is from Greek ‘ambl’ meaning “blunt” and ‘onyx’ meaning “claw” or “nail.”

Additional Links

Encyclopedia of Life

Contributors

Katie Badwey (author), Colorado State University, Tanya Dewey (editor), University of Michigan-Ann Arbor.

References

Jacques, H., J. Reed-Smith, L. Davenport, M. Somers. 2021. "Congo Clawless Otter" (On-line). IUCN Red List. Accessed October 20, 2021 at https://www.iucnredlist.org/species/1794/164576337 .

Jacques, H., J. Reed-Smith, M. Somers. 2021. "African Clawless Otter" (On-line). IUCN Red List. Accessed October 20, 2021 at https://www.iucnredlist.org/species/1793/164575819 .

Larivière, S. 2003. Amblonyx cinereus. Mammalian Species , 720: 1-5. Accessed November 01, 2021 at https://academic.oup.com/mspecies/article/doi/10.1644/0.720.1/2600498 .

Larivière, S. 2001. Aonyx capensis. Mammalian Species , 671: 1-6. Accessed October 20, 2021 at https://doi.org/10.1644/1545-1410(2001)671%3C0001:AC%3E2.0.CO;2 .

Larivière, S. 2001. Aonyx congicus. Mammalian Species , 650: 1-3. Accessed October 20, 2021 at https://doi.org/10.1644/1545-1410(2001)650%3C0001:AC%3E2.0.CO;2 .

Wilson, D., D. Reeder. 2005. Mammal Species of the World . Baltimore: John Hopkins University Press. Accessed October 20, 2021 at https://www.departments.bucknell.edu/biology/resources/msw3/browse.asp?s=y&id=14001077 .

Wright, L., P. de Silva, B. Chan, I. Reza Lubis, S. Basak. 2021. "Asian Small-clawed Otter" (On-line). IUCN Red List. Accessed October 20, 2021 at https://www.iucnredlist.org/species/44166/164580923 .