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Aonyxclawless otters

By Katie Badwey

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. (Jacques, et al., 2021a; Jacques, et al., 2021b; Larivière, 2001a; Larivière, 2001b; Larivière, 2003; Wright, et al., 2021)

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. (Jacques, et al., 2021a; Jacques, et al., 2021b; Larivière, 2001a; Larivière, 2001b; Wright, et al., 2021)

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. (Jacques, et al., 2021a; Jacques, et al., 2021b; Larivière, 2001a; Larivière, 2001b; Wright, et al., 2021)

  • Aquatic Biomes
  • lakes and ponds
  • rivers and streams

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 capensis congica. 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. (Jacques, et al., 2021a; Larivière, 2001a; Larivière, 2001b; Larivière, 2003; Wilson and Reeder, 2005)

  • Synonyms
    • Amblonyx
    • Anahyster
    • Leptonyx
    • Micraonyx
    • Paraonyx

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. (Larivière, 2001a; Larivière, 2001b; Larivière, 2003)

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. (Larivière, 2003)

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. (Jacques, et al., 2021a; Larivière, 2001a; Wright, et al., 2021)

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. (Larivière, 2003)

Lifespan/Longevity

In captivity, individuals can live for up to 15 years. (Larivière, 2001a; Larivière, 2003; Wright, et al., 2021)

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. (Jacques, et al., 2021a; Jacques, et al., 2021b; Larivière, 2001a; Larivière, 2001b; Larivière, 2003; Wright, et al., 2021)

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. (Larivière, 2001a; Larivière, 2001b; Larivière, 2003)

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. (Larivière, 2001a; Larivière, 2001b; Larivière, 2003; Wright, et al., 2021)

  • Primary Diet
  • 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. (Larivière, 2001a; Larivière, 2001b)

  • Known Predators
    • Crocodilus spp.
    • Python spp.
    • Haliaetus vocifer

Ecosystem Roles

Aonyx is a host for some parasitic trematode and nematode species. (Larivière, 2001a; Larivière, 2001b; Larivière, 2003)

Commensal/Parasitic Species
  • Microfilaria aonycis
  • Baschkirovitrema incrassatum
  • Clinostomum pyriforme
  • Prudhoella rhodesiensis
  • Cloeoascaris spinicollis
  • Gnathostoma vietnamicum

Economic Importance for Humans: Positive

Aonyx is commonly hunted for fur and pelts, and is occasionally hunted for meat. (Jacques, et al., 2021a; Larivière, 2001a; Wright, et al., 2021)

  • Positive Impacts
  • 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. (Larivière, 2001a; Larivière, 2001b)

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. (Jacques, et al., 2021a; Jacques, et al., 2021b; Larivière, 2001a; Larivière, 2001b; Wright, et al., 2021)

  • IUCN Red List [Link]
    Not Evaluated

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.” (Larivière, 2001b; Larivière, 2003)

Contributors

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

Glossary

Ethiopian

living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

World Map

Palearctic

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

World Map

acoustic

uses sound to communicate

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

cooperative breeder

helpers provide assistance in raising young that are not their own

crepuscular

active at dawn and dusk

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

female parental care

parental care is carried out by females

food

A substance that provides both nutrients and energy to a living thing.

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

freshwater

mainly lives in water that is not salty.

introduced

referring to animal species that have been transported to and established populations in regions outside of their natural range, usually through human action.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

monogamous

Having one mate at a time.

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

oriental

found in the oriental region of the world. In other words, India and southeast Asia.

World Map

rainforest

rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

scent marks

communicates by producing scents from special gland(s) and placing them on a surface whether others can smell or taste them

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

swamp

a wetland area that may be permanently or intermittently covered in water, often dominated by woody vegetation.

tactile

uses touch to communicate

terrestrial

Living on the ground.

tropical savanna and grassland

A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.

savanna

A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.

temperate grassland

A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

year-round breeding

breeding takes place throughout the year

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.

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