Friend Feature: North American River Otter

North American River Otters (Lontra canadensis)

Hello, it’s Team SeaDoc member, Mira, marine scientist, diver, and lover of all things ocean, especially Salish Sea creatures! This month’s Creature Feature is the North American river otter. Like their ocean-faring relatives, the sea otters, river otters belong to the mustelid family (weasels, skunks, badgers and more). You might agree, they are some of our most playful and adorable, wild neighbors in the Salish Sea.

Where it all begins

Unlike sea otters, river otters burrow into hillsides near the water to make cozy dens where they sleep and where females have their litters of pups. Females give birth to 1-4 pups after 63 days of embryo development. But that could be more than a year after mating! Otters have the unusual ability to delay embryo implantation in the womb for 8-10 months, perhaps to wait for the easiest pup-rearing conditions.

Otters love to eat

River otters are busy carnivores that you might spot from bay, lake, or stream shorelines, as they hunt for flounders, sole, sculpin, herring, surfperch, gunnels, rockfish, sandlance, salmon, crabs, soft clams, and other invertebrates. They even take down gulls, ducks, and petrels at times to satisfy their voracious appetites.

River otter hiding out between rockweed-covered rocks Photo by Kendrick-Moholt, Salish Sea In-Focus

River otter eating a hairy helmet crab. River otters eat while rightside up, with their heads up whether on land or in the water. Sea otters eat while belly up, floating on their backs. Photo by P. Greene

Sometimes they live under people’s docks or decks and make a smelly mess of things.

One reason for the stink is that, after all that eating, otters have to poop, and when they do, they like to send smell-o-grams. By using the same “latrine sites” regularly, the messages contained in the scents of their urine and scat can be carried on the breezes to their distant neighbors. This works especially well if their latrine sites are on points that stick out into the sea, such as peninsulas or even docks. If you find yourself on a point of land or a dock, you can spot a latrine site by the bits of crab shells and fish bones in stinky piles. What kinds of messages do you think river otters send?  

River otters love to poop on docks to spread their news! Dock users may not like this, but scientists can learn lots from some good scat. Here, Team SeaDoc Wildlife Vet and Chief Scientist, Dr. Joe Gaydos and Oiled Wildlife Care Network Vet, Dr. Lorraine Thompson-Barbosa, collect river otter scat samples from a latrine site on a boat dock to check for signs of diet and health.

You otter know

Though they live close by, be sure to keep your distance. They are a large member of the Mustelid family (like weasels) and there is a nasty temper and needle-sharp teeth behind that cuddly facade. River otters spend time in the sea, so they are often mistaken for sea otters. Here are a few ways to tell them apart:

Well-adapted for a dive

Some outstanding adaptations give them underwater advantages. A thick, flat tail that helps steer like a rudder and webbed toes for paddling like Labrador retrievers.  To keep warm without the benefit of blubber, they instead have water-repellent guard hair and a high metabolic rate; they eat 1/5th of their body weight in fish and invertebrates daily and burn those calories fast! To seal up tight for dives, they have flaps of skin that cover their nostrils and ears, like nose and ear plugs that swimmers use.

They even have specialized eyes. They can squeeze their lenses to allow them to see well underwater, avoiding the need for swim goggles. When they head for the deep, a special dive reflex kicks in; they hold their breath, their heart rate slows, their blood circulates differently, increased myoglobin in their muscles holds onto more oxygen than other animals, and they have a high tolerance for carbon dioxide (CO2), the gas we breathe out after respiration occurs. CO2 build-up from respiration in our bodies is actually what makes us need to gasp for air after holding our breath, because we can’t stand too much in our systems. I often wish I could hold my breath like an otter!

A really cool behavioral adaptation is cooperative foraging. If you ever see a big group of adult river otters, this is not a family, but unrelated males, working together to herd fish and other prey into a tight bundle to more easily snatch up with their sharp teeth.

A group of unrelated male otters hunting cooperatively. Photo by Dan Guertin

Guys day out: fishing trip! Photo by Jim Wester, Waldron Island

In the middle of food chains

North American river otters are built for speed, agility, and staying warm and wary near shorelines full of prey… and predators. Some otters meet their demise in the jaws of coyotes, bobcats, lynx, and wolves on land and occasionally by transient killer whales in the sea.

Once on the brink

Populations of these hearty and versatile mustelids can be found in most of North America north of Mexico and south of the Arctic Ocean. Though nearly decimated throughout much of the eastern United States by the 1900’s from trapping, pollution, and loss of habitat to streets and buildings, the efforts of people who care enough to help restore their habitats are helping otter populations to recover there now.

They are still thriving on the shores of the Salish Sea, and can only continue to do so if people here care enough here to ensure the health of their entire habitat, including their prey, water, places to burrow, and safe places to cross streets. Infectious diseases, such as those spread in rat and cat scat (where does your kitty go?) and getting hit by cars are currently major causes of mortality in and near dense cities here in the Salish Sea, but not in more wild places.

Salish Sea Heroes

Next time you see a North American river otter, stay back and observe what it is doing and maybe even see where it lives on land. Then consider: is this otter’s habitat safe, free of pollution and healthy? If not, what can I do? One thing you can do is to log your sighting on the Woodland Park Zoo’s Otter Spotter website: https://www.zoo.org/otters . This will help track information about the range of North American river otters in the Salish Sea.

Otters and their wild neighbors can always use another Salish Sea Hero!