One way to remember three river critters that reside in and near the Tahoe Basin — mink, otter, and beaver —is to think of them in terms of size: small, medium, and large.
Minks, the smallest of the group, weigh a mere 2 to 4 pounds. The river otter weighs in at 10 to 30 pounds, and the largest of the trio, the beaver, comes in at a hefty 34 to 50 pounds. As otters and beavers are closer in size than their smaller river mate, the mink, one distinguishing difference between the two lies in the shapes of their heads. Otter heads, cat-like with long whiskers, are much pointier than the beaver’s blockhead.
For the mink and otter, water is home and home is food. Salmon, trout, whatever humans choose to stock or whatever a lake or river naturally holds, is fair game.
Last fall at Webber Lake, I watched five North American river otters, Lontra canadensis, dive and resurface with big catches in their mouths. The otters poke their heads above the water to breathe, sometimes raising their necks high above the surface as if participating in a water polo match. Once above the water, the otters engaged in a crunch fest. Even from the shore I could hear the crackle of fish bones being crushed. Within minutes, they again dove, resurfaced, crunched, and dove yet again, repeating the process until one would swim away, the others following close behind.
While otters swim in rivers, they also swim in salt water. How does one tell the difference between the two? Sea otters float on their backs; river otters don’t. Sea otters are rarely seen on the shore; river otters are often seen on the shore as well as in water.
An interesting tidbit I learned from a UC Davis professor is about an otter’s tendency to design a “latrine site.” Perhaps design is too strong a word; they have bathrooms. At these sites, feces mixed with fish scales or any other leftover inedible items are found along stream and riverbanks. These latrines, in a way, are sites of communication. An otter will roll around on a pile of feces to detect if good food is available or if bad food with a parasite is nearby. From feces, an otter also can determine another otter’s sex. Is a possible mate looming nearby?
A friend of mine who lives on the Truckee River near Olympic Valley was fortunate to observe a family of four otters last summer. Concerning latrine sites, she mentioned their scat as the biggest sign of their presence. “I’d see otter poop all over the rocks, sometimes with crawdad claws in their scat,” she told me. She recounted the playfulness of the otters as she watched them roll around each other and climb rocks, then slide down into the river. “It was like watching a bunch of kids on a water slide going up and down, up and down. I watched them swim in the rapids, too. Who needs a kayak when you can ride the waves on your own?”
Aside from fishing in a lake, otters will sometimes work as a team in a river. When they herd salmon toward shallower water, fishing becomes an easier task. While otters do love their fish, they eat other fare too, such as snakes, insects, birds, turtles, even small mammals, much like their carnivorous counterpart, the American mink or Neovison vison.
A mink that resides along the Truckee River has been observed by another friend who also lives along the banks. She’s been observing this one mink for seven years, or so she’s guessing it’s the same one. “I read that minks only live in the wild for three years, so I’m not sure,” she noted. She once witnessed two baby otters following the mama mink everywhere she’d go. Another time, she saw the babies swimming with her. Only in the early morning hours has my friend observed this ferret-like mammal.
“With binoculars, I watch the entrance of her den, a well-hidden cave under alder bushes, 2 feet from the river,” she explained. “I’ve never seen mink in winter, only in spring and summer. I would describe the mom as playful when she jumps in and out of the water, like she’s doing a little dance. I’ve watched her fish, too, a quick dip in and out of the water, surfacing with a tiny fish in her mouth.”
One would think with all this talk of fishing that beavers would be closely aligned with their otter and mink comrades. After all, they’re all river runners. But the North American beaver, Castor Canadensis, is actually an herbivore. It pursues leaves, roots, twigs, willows, and aspen bark instead of trout and salmon. Despite not being fishers, they do swim underwater like river otters and are able to hold their breath for up to 15 minutes. River otters can stay under for up to eight minutes.
Beavers’ ears and nose flaps close while being submerged; their eyes are protected with a transparent goggle-like inner eyelid. Both otters and beavers use their large, webbed feet (rear feet for beaver) like paddles, much like ducks. Minks have partially webbed feet. One observable distinct difference between the otter and beaver is swimming form. An otter swims with its head and neck above the water while its body trails beneath the surface. A beaver’s head and back are visible along the surface, as if its body is skimming the top of the water.
While we tend to think of these creatures as staying close to water, some young male otters are known to have traveled for miles on land to get to a water source just so they can fish. Beavers, too, sometimes travel on a sort of walkabout. Even the smallest body of water, say a pond, is a welcoming site for a beaver to build a lodge. Beaver lodges only need enough water around them to protect their underwater entrances, and they only need to be deep enough not to freeze solid in the winter so their residents can access their food. On Tahoe’s smaller creeks, the dams are usually only a foot or 2 deep. I’ve often wondered how beavers eat and sleep in such an aquatic environment. The answer? Busy beavers build above-water platforms within their lodges.
All three of these river critters, each with a lifespan of up to 10 years, can be seen in the Truckee/Tahoe area, but sightings are rare. Yet, they’re here — otter families fishing, mother minks pushing their kits to swim, and beavers felling trees to build their homes.
Sources: Alana Chin, UC Davis scientist, The River Otter Ecology Project, Sherry Guzzi, Sierra Wildlife Coalition, Denise Upton, Animal Care Director at Lake Tahoe Wildlife Care
The River Otter Ecology Project, based in Forest Knolls, California, encourages citizens to report otter sightings. If an otter is spotted, take a photo (if possible), even if it’s not
a good one, and fill out the sighting form on the website. The group’s mission — to engage the public in supporting conservation and restoration by linking river otter recovery to watershed health — makes otter recordings an important part of the operation. Otters have been spotted at Alder Creek; Jackson, Serene, and Webber lakes; the Truckee, Yuba, and Feather rivers, among other areas.