Common MisIdentifications of the North American River Otter

When people hear that I am interested in otters, one of the responses I get is "I saw an otter in my neighborhood pond!" They then go on to describe a critter that is very clearly a beaver. Well, clearly if you know what you're looking for... another common response (on the West coast), is "I saw a sea otter running along _____ (insert near-water road, like Chuckanut) Drive!". These can be tricky critters to distinguish from each other if you don't know the signs, but happily, there are several fairly easy ways to tell a beaver from a river otter from a sea otter.


First, a little background info

This is a North American River Otter

North American River Otters are semiaquatic (lives both on land and in water) mammals found in and near waters across North America. They eat primarily fish and shellfish, generally live in holts (like dens) in the ground in or very near river banks, and are noted for their intelligence, agility, and playfulness. It's not uncommon to see a river otter swimming in the ocean, but you will never see one building a dam!

This is a Beaver

Beavers are also semi-aquatic mammals (to be specific, they're rodents) that live in rivers, lakes, and streams across North America. They eat leaves, shoots, and bark of trees and water plants. They build dams, and live in lodges (see below). Beavers are strong, slow swimmers, and do not move at high speeds on land.

This is a Sea Otter

But this is how you usually see them

Sea Otters are marine mammals. They live off the Western coast of North America (from southern California to British Columbia and Alaska) and off the coast of Japan. They eat fish and shellfish, and go through most of their lives without leaving the ocean. You will almost certainly not see a healthy wild one on land. If you ever do, it will not be further inland than the beach. (And if you think you have seen one inland off the beach, it's a river otter. Really. Even if you just watched it crawl out of the ocean. Because river otters do that ; )


The differences

Between a river otter and a beaver:

• Body shape: River otters have long, slender bodies, with conical rudder-like tails. Beavers are short, stocky, and have very distinctively flattened, leathery tails.
• How they swim: River otters are fast, agile swimmers, well suited to catching fish. Their movement patterns are often a little erratic, but when they are swimming at the water's surface they look like this:
 
Beavers are slow, powerful swimmers. They can move large branches and entire small trees through the water. Beavers do dive, but swim most often at the water's surface like this:

• How they move on land: North American River Otters usually run or bound on land. They do also walk (though not if they can help it ;) and, when the opportunity arises, slide. Their movements on land tend to be a little erratic, as they are in the water. 
 


Beavers tend to walk or shamble on land. They are not the fastest or most graceful critters on land, but they do move with determination to get where they are going.

 
• Behavior: River otters will live in rivers, lakes, streams, and any other body of water that is relatively undisturbed by humans. They can also be found fishing in the ocean, provided there is a source of fresh water nearby in which they can wash off. They are very playful, and will turn most activities into a game, whether they are by themselves or with a group (social and hunting groups are usually 2-4 otters). Otters are very sensitive to pollution and certain types of human activities, so they tend to stay far away from areas that are densely inhabited by people. Beavers tend to live in lakes, ponds, or creeks (large drainage ditches are also popular). They don't care much about proximity to people, and are often found building dams and lodges in places that are highly inconvenient for city planners. They prefer to build their lodges in slow moving or still water, and will create slow moving water if it is not readily available, which brings us to dams. There are a couple of reasons that beavers build dams: Dams cause bodies of water to flood, creating ponds and wetlands. Beavers move much better in water than they do on land, so flooding makes it easier and safer (because other critters can't get to them) for them to get to food trees, and to get to and move "lumber" trees. The water surrounding the lodge also protects it from most predators. 

Between a river otter and a sea otter:

• Body shape: River otters and sea otters are similar in length, but the sea otter weighs about 2 1/2 times as much as the river otter. As you can probably guess from this, the sea otter is much stockier than the river otter. Both otters have the distinctive torpedo shape, but the sea otter is a much thicker torpedo! Its forelimbs are shorter than those of the river otters, and its back feet more closely resemble the flippers of a seal or sea lion.
• Coloration: Sea otters are a dark, grey brown and cream color. Mature sea otters have cream colored heads and chests. River otters tend to be a more chocolatey brown, and have a cream colored patch that runs from the throat all the way down the belly.
• Swimming above water: At the surface, river otters generally swim facing forward, with their heads and sometimes upper backs the only part of them visible above water. Sea otters do not tend to swim from one place to another at the water's surface, though they do spend a lot of time there. Since sea otters are marine organisms, they are more specifically adapted for life in the water than are other otter species. At the water's surface, sea otters float on their backs with their heads, tummies, and feet sticking out of the water (just like the classic sea otter photos!).
• Swimming underwater: Sea otters use their tails and their "flippers" to push them through the water with an undulating motion. They don't use their front feet to swim, or most of the time even to steer. If you've ever been snorkeling, it's a lot like swimming in flippers.

.......And you saw how river otters swim in the section above. They swim with a similar undulating motion to the sea otters, but they are more prone to sudden changes in direction and must use their front feet to steer.

• How they move on land: For all intents and purposes, wild sea otters don't! On the occasion of very bad storms, or at zoos, sea otters are a little awkward on land:

(okay, a lot awkward on land ;) ). Sea otters are very much adapted to life in the water, and as there are tradeoffs with everything, they are not so good at the whole land thing. Again, if you see an otter crawling out of the ocean and heading up the beach into the woods, it's not a sea otter!


If you encounter a critter and you're not sure what it is, tell us about it below and we'll see if we can help you identify it!

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!