Otter Species ~> Sea Otter

Sea Otter

Size: From nose to tail, the Sea Otter is 27 to 64 inches long. The tail is 5 to 13 inches long.
Color: The sea otter's body is brown, with a light tan head, cheeks, and throat, and an even lighter belly.
Nose: Aspen leaf shaped. Females have a pink scar on their noses after mating.
Feet: Sea otters have strong, but very small, forepaws. The rear paws are so elongated and webbed that they are like flippers. The claws are semi-retractable.
 Hair: Very thick, silky, and sleek. The guardhairs are 1.3 to 1.4 inches long, and the underhairs are about 0.7 inches long.
Track/Sign: N/A

Food: Clams, mussels sea urchins, crabs, octopi, abalone. They do not tend to eat fish, though they certainly will if the opportunity arises (sea otters aren't the fastest critters ever).
Conservation Status: Endangered


Sea Otters are found primarily on the Pacific coast of North America. Some are also found on the coast of Russia and Japan. They live in and near kelp beds, which they rely on for both food and shelter. Most of their prey organisms feed on kelp or on other organisms that feed on kelp, and the kelp forests are a challenging habitat for large predators like Orcas. Sea Otters also use kelp beds literally as "beds". One of the unique challenges of living in the ocean is that it's always moving. To avoid drifting away from each other and their habitat, they often wrap themselves in kelp, which is sturdily anchored to the sea floor, before taking a nap.

Oil pollution is one of the primary threats to Sea Otters. Sea Otters are very sensitive to pollution. As well as being toxic if ingested, oil makes it impossible for them to keep their fur clean. Air bubbles trapped in their fur keep the otters from ever actually getting wet, allowing them to stay warm without the thick blubber layer that most marine mammals require. The oil forces the air bubbles out of the otters' fur and mats the fur to their bodies, eventually causing oiled otters to die of hypothermia. Fishing nets and the spread of infectious disease are also major threats to Sea Otters.

Sea Otters are also among the increasing number of animals known to use tools. They primarily eat shellfish, which are notoriously difficult to get into. Sea Otters get around this problem by taking a rock from the sea floor (some otters even have a favorite rock that they keep track of!) and using it to open the shellfish. An otter will place a rock on its stomach, and bash a clam or other shellfish on the rock until the shell is broken enough that they can eat the clam out of it. Otters also use rocks to bash abalone off of surfaces they are attached to on the sea floor. It's not surprising that some Sea Otters have favorite rocks, because every day they have to collect and eat enough shellfish to add up to 30% of their body weight. For the average otter, that's about 20 pounds of food per day! That's a lot of clams!

Otter Species ~> North American River Otter

North American River Otter

Oscar, Kewanee, IL. Ph: Chiara DeNeve

Size: From nose to tail, the North American River Otter is 39 to 60 inches long. The tail alone is 12-14 inches long.
Color: This otter is very dark in color. They have a brown to red back, with lighter cheeks and throat (not demarcated though), and an even lighter belly.
Nose: Diamond shaped, the nostrils are in the lower 1/2 and outer 1/4 of the nose.
Feet: The feet are very strong, with strong claws and webbing.
 Hair: Very thick and sleek. The guardhairs are 0.7 to 0.8 inches long, and the underhairs are 8 to 9 mm long.
Track/Sign: North American river otters scent- and scat- mark their territory.


Food: Fish, molluscs, crustaceans, small reptiles, amphibians, birds, insects
Conservation Status: Least Concern


The North American River Otter is doing extremely well in most of the United States. In fact, it is probably the most numerous of all otter species. They can be found almost everywhere that there is water in North America, including coastal areas. The primary threat to these otters is water pollution and habitat degradation. These otters are highly adaptable to different types of habitats, but are very sensitive to pollution and changes in water quality. They don't tend to live in places of human habitation (though there are some exceptions, I have heard of people having trouble with otters trying to den under their decks!).



North American River Otters are extremely playful, turning almost all regular activities into a game. They often create slides into the water in areas that they visit frequently. They are also very social animals. They don't tend to live in groups (except for females with pups), but they do form social and hunting groups with other otters living nearby. North American River Otters often prefer to live alone, but do not do well alone for long periods of time and will seek out the company of other otters.

Fossils of this species date back to the Pleistocene, and archaeological remains of them have been found as far back as 200 BP!


For more information, visit OtterQuest's North Amercian River Otter page!

Basic Otter Anatomy

A generalized overview of the internal and external anatomy of otters:

External Anatomy

* Otters range in size from 65 cm (Asian small clawed otter) to 180 cm (giant otter) long from nose to tail.

* Otter tails are long and strong. The sea otter has, comparatively, the shortest and least muscular tail of all of the otters.

* All species have long, flexible bodies designed for speed and agility, especially under water. River otters can run ~20 mph (likely faster in bursts) and giant otters can swim 9 mph.

* All otters, except sea otters, have anal scent glands at the base of the tail used for scent marking.

* Fur is very dense and usually very silky (composed of guard-hairs and fine under-hairs) and varies through shades of brown, frequently with lighter undersides and/or spots.

* Otters can close their ears and noses underwater.

* Otters have very good hearing.

* Noses are one of the distinguishing features between otter species, some even have hairy noses! Otters have a good olfactory sense (they have a good sense of smell!). They all have vibrissae (whiskers) that are so sensitive they can sense under water vibrations! (this is very helpful in detecting prey)

* Feet are generally webbed with claws. Otters' feet are distinctive and say a lot about where the species live. The soles of all otters' feet are hairless, except for the sea otter whose hind feet are furred.


Internal Anatomy

Internal Anatomy. L. Spelman 1994

* Otters hold their breath to dive for food, escape predators, and, likely, for fun! River otters can hold their breath 6-8 minutes. The longest sea otter dive recorded is 4 minutes 25 seconds (though they can likely hold their breaths a little longer).

* Otters have a higher rate of metabolism than most similarly sized mammals. Water conducts heat much faster than air, so they are constantly working to keep themselves warm. The super-dense fur just isn't enough to do it on its own, so they have to eat a lot!

* Otter's eyes have specialized lenses and corneas that correct their vision for the change in light refraction between air and water environments.

 
Some links to additional anatomical exams and necropsies:

* An interactive cryo-cross-section of a sea otter fetus.

* Step-by-step river otter dissection .

 * A comprehensive "pictorial guide" of sea otter anatomical exams and necropsies from US Fish and Wildlife Service, Region7, Alaska Veterinary Pathology Services, and Alaska Sea Life Center.