If a river otter is nearby, you can kiss the fish in your privately stocked pond goodbye.
Illustration by Robert Meganck
You could live all your life in Virginia without ever laying eyes on a river otter. It’s not that these beguiling, aquatic-adapted mammals are rare in the Commonwealth; in the eastern parts of the state in particular their numbers are abundant, according to Mike Fies of the Virginia Department of Game and Inland Fisheries. However, says Fies, otters are elusive and often solitary creatures, and “you have to get close to the water to see them.”
You might want to bring your patience, and maybe some night-vision goggles as well. While otters may be active during the daytime, typically they prefer the crepuscular hours of dusk and dawn or the nighttime itself. And while they can get about quite ably on land, it is in the water that they are at their nimble best, though they are not necessarily easy to spot as their dark, streamlined bodies slip below the surface.
The river otter—also known as the northern river otter or the North American river otter—is ideally built for an aquatic Cirque du Soleil, with a long, sinewy body, webbed feet and a powerful tapered tail that is about a third the length of its body. “They are fantastic swimmers, very agile and fast,” says Fies.
Beyond these features, the otter can also close off its nostrils and ears underwater and has a clear “nictating membrane” eyelid to protect its eyes while still allowing it to see—like a pair of swim goggles you never lose. One lung is also larger than the other. Their physiology allows otters to swim as fast as 6-7 miles per hour, to dive deeper than 50 feet underwater and remain there for minutes at a time. They also bear an extremely dense (more than 50,000 hairs per square centimeter), water-repelling, two-layered coat of fur that keeps them warm and dry.
River otters are members of the weasel family, and like their cousins such as the mink, fisher and marten, their “cuteness” factor—with short legs, small heads and compact ears—belies the fact that they are smart, aggressive predators. They need to be: members of the weasel family have fast-burning metabolisms that require them to consume as much as a third or more of their own weight each day in food. For river otters, the preferred diet is fish, though frogs, crayfish, mussels, snakes and even small mammals or birds can also be on the menu.
While fishing enthusiasts sometimes regard otters as competition, Fies notes that on the whole otters prefer slower-moving fish like suckers and carp to faster game species like trout. On occasion, however, says Fies, otters can get into privately stocked ponds or small lakes, with the result akin to giving a small child charge of the cookie jar: “It’s pretty literally like shooting fish in a barrel.”
Although otters can see well underwater, their long snout whiskers, called vibrissae, help them hunt by detecting turbulence caused by the movement of their prey. Perhaps for this reason, otters prefer lakes, swamps or slow-moving rivers where the water is calm. They live close by the water, taking advantage of natural shelters or the abandoned dens of other animals to make their own dens, or “holts,” and they tend to be solitary in habit; if you see a group of otters together, it is likely a mother and her not yet fully independent offspring.
And speaking of those offspring, otters have a reproductive adaptation known as delayed implantation, or embryonic diapause. A phenomenon found in a number of different species, it remains something of a mystery to biologists. Somehow, early-stage blastocysts simply float freely for months in the mother otter’s uterus before finally implanting and developing, so that despite a relatively short embryonic development period of about two months, an otter may not give birth for nearly a year after breeding. A litter is usually one to three pups, and they are born small and helpless; they have to learn from their mothers not only how to hunt but also how to swim.
Because their lives are so closely connected to the water, otters are vulnerable to degraded environmental and water-quality conditions, and their populations in the past have also been affected by over-harvesting for the fur trade. River otters were actually listed as an endangered species in Virginia in the late 1970s when, the Virginia Department of Game and Inland Fisheries notes, “they were virtually extirpated from the western portion of the state.” Conservation and environmental restoration, however, have allowed their numbers to rebound to the point where they are no longer considered endangered, and that’s one in the win column for our Commonwealth’s natural heritage.