Otter

About the otter

Otters are carnivorous mammals in the subfamily Lutrinae, a branch of the Mustelidae family that also includes weasels, badgers, mink, and wolverines. There are 14 extant otter species, and every one of them is semiaquatic, living in either freshwater or marine environments. The word "otter" traces back to the Old English "otor" or "oter," which shares a Proto-Indo-European root with the English word "water" — an origin that fits an animal built almost entirely around living in it.

Otters have long, slim bodies and relatively short limbs, with powerful webbed feet for swimming and, in nearly every species except the sea otter, a long, muscular tail. Adult size varies considerably across the group, from 0.6 to 1.8 m (2.0 to 5.9 ft) in length and 1 to 45 kg (2.2 to 99.2 lb) in weight; the Asian small-clawed otter is the smallest species, while the giant otter and sea otter are the largest. Sharp claws tip most species' feet, and a coat of soft, insulated underfur, protected by an outer layer of long guard hairs, traps a layer of air that keeps an otter dry, warm, and somewhat buoyant underwater. That insulation matters: several otter species live in cold water and run high metabolic rates to stay warm, with Eurasian otters needing to eat 15% of their body weight daily and sea otters needing 20 to 25%, depending on water temperature.

The first otter genus, Mionictis, evolved in the early Miocene from badgers that had adapted to a semiaquatic life, and today's otters remain closely related to the weasel-like Mustelinae subfamily, sharing the same elongated body shape suited to moving through water.

Behavior and diet

Otters are active hunters, chasing prey through the water or searching along the beds of rivers, lakes, or the sea. River-dwelling species generally live beside water but enter it mainly to hunt or travel, spending much of their time on land so their fur doesn't become waterlogged; sea otters are the exception, living in the ocean for most of their lives. Most species hunt for three to five hours a day, though nursing mothers may hunt for up to eight. In water as warm as 10°C (50°F), an otter needs to catch about 100 g (3.5 oz) of fish per hour just to survive. Otters are also notably playful, building waterslides and sliding into the water for what appears to be sheer enjoyment, and finding and playing with small stones; sea otters take stone use further, using them as tools to crack open shellfish balanced on their bellies, a skill young otters have to learn. Social structure varies by species — some are largely solitary, while others live in groups that can grow fairly large.

Fish is the staple food for most otters, often supplemented by frogs, crayfish, and crabs; some species specialize in opening shellfish, while others take small mammals or birds when available. Because otters depend so heavily on their prey base, they are especially vulnerable to any decline in it. Sea otters focus on clams, sea urchins, and other shelled animals.

Reproductively, otters have a gestation period of about 60 to 86 days. A newborn pup is raised by the female, the male, and older offspring together; females reach sexual maturity around two years old, males around three. The den, called a "holt," is typically built under tree roots or within a rocky cairn and lined with moss and grass. A pup can leave the den after a month and swim after two, staying with its family for roughly a year before setting out on its own. Otters can live up to 16 years.

Range and habitat

Otters as a group aren't tied to one country or region — with 14 living species, they occur in freshwater and marine habitats worldwide. All are semiaquatic, occupying both freshwater habitats — rivers and lakes — and marine coastal waters, with river-dwelling species generally staying close to water but spending significant time on land, and sea otters living almost entirely in the ocean.

Conservation status

Otters have no single conservation status, because the IUCN Red List assesses each of the 14 species separately. The North American river otter is Least Concern, while the Asian small-clawed otter is Vulnerable. Otters also have a long history of pressure from people: otters have been hunted for their pelts since at least the 1700s, using darts, arrows, nets, and snares before traps and guns took over, and pelts have been worn as clothing across many cultures, from Chinese royal robes to hats, belts, and mittens made from otter fur elsewhere. Organized otter hunts using dogs, especially the otterhound, once killed over a thousand otters in England and Wales in a five-year span in the late 1950s and early 1960s. More recently, the wildlife trade monitoring network Traffic has reported that otters are at serious risk across Southeast Asia and have disappeared from parts of their former range there, driven by hunting to supply demand for skins.

Otters aren't only hunted, either — in southern Bangladesh, fishermen have bred smooth-coated otters for generations to herd fish into their nets, a traditional practice still used today in the Narail district.