15 Fascinating Facts About Otters

Charismatic otters are the largest members of the weasel family. Unlike other weasels, otters are semi-aquatic. Their sleek bodies range in size from 2 to 5.9 feet. Thirteen otter species slide down riverbanks, juggle rocks, and float on their backs in watersheds on five continents. The only places without endemic otters are Australia and Antarctica.

All otter species appear on the IUCN Red List of Threatened Species, and only one is listed as "least concern." Learn 15 more facts about these fascinating mammals.

1. They Aren't All Sea Otters

River otters are frequently mistaken for sea otters. River otters live primarily in freshwater, though they do swim and hunt in seawater. They have visible ears, swim belly down, use webbed feet to paddle, and move swiftly on land and water.

Sea otters live exclusively in the ocean along coastlines. They move clumsily on land, paddle with their hind feet and tail, and are significantly bigger than most river otters, with some males weighing as much as 100 pounds. A male river otter, by comparison, would not exceed 30 pounds.

2. Some Hold Hands While Sleeping

Sea otters, particularly mothers and pups, sometimes hold hands while floating on their backs. Hand-holding keeps the otters from drifting away from each other and their food source while they sleep. They also sleep wrapped in long strands of kelp like a blanket. The kelp acts like an anchor and prevents them from floating out to the open ocean. When a pup is small, the mother will hold it on her belly to keep it from floating away.

3. They Are in Trouble

Of the 13 species of otter, IUCN lists five as endangered, five as near-threatened, and two as vulnerable. Only the North American river otter is a species of least concern.

Numerous threats to otters exist and primarily include pollution, habitat destruction, overfishing, and poaching. They can also be harmed by entanglement with ghost nets and other rogue fishing gear. Oceana reports, "It is thought that oil spills pose the greatest threat due to the proximity of sea otters to major tanker routes and their susceptibility to hypothermia if their fur comes into contact with oil."

A cat parasite called toxoplasmosis also poses a threat to these creatures. Found in cat feces, it enters waterways through runoff and flushable cat litter.

4. They Have Many Names

Baby otters usually are called pups. They can also be called kits or kittens. Female otters are sows, and males are boars.

Otter groups are called a family, bevy, lodge, or a romp. The latter is the most common term for a group of otters on land. A group of otters in the water is most often called a raft.

5. Giant River Otters Live Up to Their Name

The giant otter is an endangered species found in South America, primarily along the Amazon river and the Pantanal. It is the longest of the otter species. Giant otters grow to as long as 6 feet and weigh as much as 75 pounds. They eat 9 pounds of food each day.

Poaching for their velvet-like fur caused significant population declines. Threats also include habitat degradation, pesticides, and pollution from mining. Experts estimate that fewer than 8,000 exist.

6. Hairy-Nosed Otters Are a Lazarus Species

Hairy-nosed otters are an endangered species found in Asia. They were considered extinct until 1998 when a scientist in Thailand found small populations. This rediscovery, after presumed extinction, makes them a Lazarus species.

The biggest threats to hairy-nosed otters are poaching and habitat loss from wildfires, dam construction, and clearing swamp forests for oil palm plantations and fish farms. These otters seem to love peat swamp forests, especially those with Melaleuca, the swamp tea-tree. Unfortunately the number of tea-trees is diminishing.

7. Some Species Lack Claws

Most otters have sharp claws at the end of each toe, which helps them to grab prey. However, there are three species of otter that have blunt claws or none at all. They are the Asian small-clawed otter, African clawless otter, and Congo clawless otter. These otters also have less webbing between their digits. This combination allows them to have greater nimbleness when foraging. They use their front paws with a dexterity that nearly rivals humans.

8. They Have Noteworthy Poop

River otters perform "scat dances" by stomping their hind feet and lifting their tail. They then leave droppings called spraints, which refer to a single bowel evacuation and that researchers describe as smelling like violets.

Otters have a communal latrine area. There they exchange information via chemical cues in feces. Otters also excrete something called anal jelly that contains secretions from anal glands and shed intestinal linings.

9. Sea Otters Have the World's Thickest Fur

Sea otters don't just have the densest fur of all otters—they have the densest fur of all animals. Otters have as many as 2.6 million hairs per square inch. That makes it about a thousand times more dense than human hair. That thick coat is needed because otters are the only marine mammal without a blubber layer for insulation. They rely on all that fur to trap a layer of air against the surface of their skin, and their fur is perfectly designed to do so because it's dense and spiky. The barbs on each hair strand hold in place the air bubbles that the otters blow into their pelts while grooming—which they can spend up to five hours doing each day.

This air has the sometimes undesirable side effect of making them highly buoyant. Occasionally an otter must grab on to a rock or some kelp to remain submerged while swimming.

10. They All Eat a Lot

Hefty appetites aren't unique to giant otters: All otters eat 20-33% of their body weight each day. They spend around five hours each day foraging. They tuck prey into pockets of loose skin under their arms and use rocks as tools to open shellfish. Otters' big appetites protect kelp forests by eating sea urchins. Without sea otters, the urchin population booms and destroys the kelp forest habitat.

11. They Are a Keystone Species

The presence of a healthy otter population indicates a healthy watershed. Otter disappearance is evidence of pollutants, habitat fragmentation, or loss of prey due to habitat destruction. Prey shortages are very damaging due to high caloric needs. Otters may emigrate to find food in that case. Being at the top of the food chain causes pollutants to become concentrated in their bodies, leading to illness and death.

12. Mothers Have a Lot of Work

Sea otters cannot swim at all for their first month, despite being born in the open sea. Clean fluffy fur keeps them warm and traps air, which allows them to float. Mothers groom pups and blow air into the clean coat to create buoyancy. She wraps the pup with kelp to anchor it while she hunts.

Mothers spend up to 14 hours per day foraging to support a pup's intense nutrition needs. This high demand leaves otter mothers depleted, and many die from minor illnesses. They do it all on their own, with no help from the fathers. They provide full-time care for their babies for six to eight months, until the babies can survive independently.

13. They Take Over Other Animal's Homes

Otters sometimes take up residence in abandoned beaver lodges or muskrat dens. Some even move in while beavers are still present.

They also take over the riverbank dens of foxes, badgers, and rabbits. Resting spots, called hovers or couches, are usually little more than a bed of reeds. Otter "holts" are small underground dens where otters escape danger, take shelter, or raise their young. These usually show evidence of regular use in the form of tracks, smell, spraints (feces), and general wear-and-tear. These holts can be found along riverbanks, among tree roots, under branches, brush, or boulders.

14. They Are Speedy Swimmers

Otters reach swim speeds of up to 7 miles per hour. This pace is three times faster than the average human swimmer. Otters can hold their breath for 3-4 minutes, closing their nostrils and ears to keep out water. Powerful tails propel them through the water. River otters have webbing between their toes to aid them as well.

15. Their Play Surprised Researchers

Few animals play as adults, and otters are one of them. Researchers found that playful sliding on a riverbank was not just efficient locomotion, but play. Rock juggling doesn't improve hunting skills or efficient extraction of meat from shells. Instead, researchers learned, they are more likely to juggle rocks when hungry or bored. Young and old otters most often juggle rocks. Playfulness does disappear, though, when food is scarce. This suggests that the otters must first satisfy their nutritional needs before engaging in playful behaviors.