An otter refers to a semiaquatic carnivorous mammal of the subfamily Lutrinae under Mustelidae, a family that also includes weasels, badgers, minks, stoats, wolverines, and others. There are currently 13 living otter species found on every continent except Australia and Antarctica. Most otters inhabit freshwater like rivers, lakes, and wetlands, while only marine and sea otters are found in saltwater.
These animals are characterized by slender bodies, strong necks, short legs, and long, flattened tails. Typically, these mammals have webbed feet that equip them for life in water. A layer of long guard hair covers their bodies, providing insulation and buoyancy.
Otters are known for their playful nature, with some species, like sea otters, forming large social groups of up to 2,000 individuals. Their diet consists of fish, crabs, mussels, crayfish, frogs, and turtles, making them key predators in aquatic ecosystems. By feeding on marine invertebrates, they help maintain the ecological balance of their habitats.
On average, otters measure between 2 and 5.9 ft (0.6 to 1.8 m) in body length and weigh around 2.2 to 99 lb (1 to 45 kg). The largest species, the giant otter, reaches around 6 ft in length and generally weighs as much as 71 lb (32 kg). In contrast, the smallest species, the Asian small-clawed otter, measures around 28.6 to 37.6 in (730 to 960 mm), weighing a maximum of 7.7 lb (3.5 kg).
Adult sea otters are the heaviest of all species, weighing between 30 and 100 lb (14 and 45 kg).
Otters have a slender body, a strong neck, and short legs, along with a long, flattened, and muscular tail that helps them to propel easily in water. Very unusual for a mammal, otters possess powerful webbed feet, an adaptation for their semi-aquatic lifestyle. Most species possess sharp claws on their feet.
Their bodies are covered in a soft, insulated underfur layered with long guard hairs. Their fur varies in shades of brown, with the underside being lighter than the upper part of the body.
The term otter stems from the Old English word otor or oter, which traces back to the Proto-Indo-European word wódr̥ (also the origin of the English term water).
13 living species of otters are currently grouped under 7 extant genera.
Here is the list of the extinct genera:
Otters are found on every continent except Antarctica and Australia. Out of the 13 species, only the sea otter and marine otter inhabit the Pacific Ocean and thrive in saltwater environments, while all others live in freshwater habitats such as rivers, lakes, and wetlands.
Most species generally prefer living beside the water source, though river otters spend most of their time on the land and venture into the waters only to travel or hunt. In contrast, sea otters live in the ocean for most of their lives.
Freshwater otters typically feed on fish (their primary prey), crabs, mussels, crayfish, frogs, and turtles. They also eat small mammals, such as muskrats, and aquatic birds, such as coots and gulls.
These animals typically live between 10 and 16 years, though they have been found to survive for almost 20 years in captivity.
Depending on the species, the breeding season of these animals varies. For instance, sea otters are year-round breeders, while North American, spotted-necked, smooth, and marine otters breed primarily in winter and spring. The Eurasian otters of England also breed throughout the year. Most river otters and marine otters are monogamous and mate for life, whereas sea otter males may breed with more than one female in a single breeding season.
These animals typically mate aggressively, with the males (called dogs or boars) grasping the females (called bitches or sows) with their forelimbs and biting onto their noses to hold on. The pair then spins in the water until mating is complete, after which the males release the females from their grasp. While mating, the females often get fatally injured with deep cuts and gouges and may also drown and die.
As females prepare to give birth, they build dens or holts under tree roots or rocks, lining them with moss and grass to create a safe space for their offspring. After a gestation period of about 60 to 86 days, they give birth to around 1 to 6 pups (also called cubs) in a single litter. These pups are nursed by the females, as well as by the males and older offspring.
Around one month after birth, otter pups are ready to leave the holt, and by the following month, they begin swimming. They remain with their family for about a year before becoming independent. Female pups reach sexual maturity at around two years old, while males take about three years to mature.
As semi-aquatic animals, they have both terrestrial and aquatic predators.
Almost all otter species are vulnerable to extinction due to factors like illegal fur trade, habitat destruction, and increased pollution. The accumulation of heavy metals and contaminants, like lead, mercury, and PCBs, in their internal tissues also leads to the mortality of otters.
Here is the IUCN Red List of the extant otter species:
| Species | IUCN Category |
|---|---|
| Smooth-coated otter, Asian small-clawed otter | Vulnerable (VU) |
| Marine otter, giant otter, sea otter, hairy-nosed otter, Southern river otter | Endangered (EN) |
| Congo clawless otter, African clawless otter, Neotropical otter, spotted-necked otter, Eurasian otter | Near Threatened (NT) |
Otters have distinct feces, known as spraints, which can resemble the smell of freshly cut hay or, in some cases, decomposing fish.
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