North American River Otter: Harbinger of Clean Water & Healthy Habitat

The North American river otter (Lontra canadensis) is one of Minnesota’s most playful, clever creatures. This large, aquatic member of the weasel family inhabits most of North America north of Mexico, including our state’s lakes, ponds and streams. I was alerted to their spirited zest for life by once encountering them shooting through the rushing water of a culvert for the apparent sheer thrill. But the most interesting otter story I’ve heard is that of a rehabilitated otter learning to retrieve ducks by first watching a Labrador retriever! Like some other wildlife populations, otter experienced a dramatic decline, but then a fortunate, amazing recovery due to concerted conservation efforts. As a top carnivore in the aquatic food web, its presence in our aquatic ecosystems is an indicator of clean waters and healthy habitats, and thus highly desired.

Skilled Swimmer

Otter have keen adaptations to life in water include long, flexible, sleek bodies; short powerful legs with webbed feet; a strong, rudder like tail; superb, underwater, near-sighted vision; long sensitive whiskers near their nose to detect vibrations of prey in dim light; and the ability to close their eyes and nostrils to keep water out. They can dive for up to 8 minutes and 60 feet deep. As mammals, they must surface for air, swimming with their heads above water and occasionally rising from the water like a periscope to see farther and watch for predators. If ever paddling through otter territory, you may have detected an otter keeping an eye on you in this way. Their rich brown to black, silky fur is short and dense to repel water and offer warmth against cold water and ice. A silvery color graces underside, throat, and cheeks. Adults can grow up to 5½ feet and 30 pounds, but average 15-19 pounds.

Romp and Roll

A group of otters is appropriately called a ‘romp’. They romp, roll in the grass, wrestle, play with their prey, bump sticks across the water, drop pebbles to the bottom to fetch, and slide down muddy or snowy stream banks on their bellies. These antics likely polish their hunting skills. Their slide marks which alternate with footprints leave a “dot-dash” trail, a telltale sign of their presence. Other otter sign includes their normal tracks (five toes in front and back, 2-4 inch imprints of heel pad and claws, wider than long), their toilets (piles of scat often on high spots along stream banks or trails between water bodies), and wallows of flattened and raked vegetation or dirt which they likely use when grooming.

Otter slide marks with the telltale dot-dash. Photo courtesy John Erb.

 

Family Life

Otter family life begins with mating in late winter/early spring. Males mark their territory, which intersects several females’ territories, by leaving scent from scat and glands. Most females don’t give birth until three years old, while males don’t usually breed successfully until five to seven years old. Like other members of the Mustelidae or weasel family, otters have ‘delayed implantation’. Mating occurs shortly after the birth of a litter, but the fertilized embryos do not implant and begin growing for about more eight months. One to six pups are born 50 days after implantation in late winter/early spring.

The female otter doesn’t dig her own den. She cares for her pups in an existing structure, usually close to water. It may be a natural hollow in a lake or river bank; old beaver lodge or beaver or muskrat bank burrow; a space under roots, a log, or overhang; a dense thicket near water; man-made brush pile; a hollow log; in a higher upland location such as a bluff or cave to protect her pups from floods; or even under a garage or deck. Pups begin expressing their frisky manner at four weeks, then leave the den to swim, explore and catch their own food at seven weeks. The male has little to do with raising them, though he may rejoin the family after they’ve left the den, as otter are fairly social. Pups are weaned at about three months, but stay with their mother until the next spring when she boots them out to search for a new home.

Vivacious Voyager

Individual otters regularly move great distances and use multiple dens. Because they typically follow streams and other small waterways in search of food, their home ranges are large and linear – up to 20-30 miles. They will travel across land too, particularly in snow. Activity occurs year round and any time of day, with peaks from dawn to midmorning and in the evening. Food items are comprised of clams, muskrats, frogs, tadpoles, salamanders, snakes, turtles, a variety of fish like minnows, pumpkin seeds, crappies and bullheads, and especially crayfish. On land, insects, chipmunks, mice, young rabbits, and small birds are fair game. Otters have few predators other than bobcats, coyotes, and wolves when on land, plus human-caused mortality from trapping and vehicle collisions. They may live 10-15 years in the wild, and as long as 25 years in captivity.

Otterly Amazing Recovery

The decline then recovery of our otter population is a shining example of conservation success. As a native species, it was once found statewide. Changes in land use, destruction and degradation of wetlands and habitat along water bodies and water ways, reduced water quality, and unregulated trapping during the late 1800s led to their near disappearance from Minnesota by the early 1900s. Today, otter are again common in northern Minnesota, have expanded into suitable habitat of southern Minnesota, and the population is relatively stable.

Most of the otter population recovery has been ‘natural’, resulting from harvest management and improved habitat and water quality. Wetland restorations and better regulations (e.g., federal Clean Water Act of 1972, Minnesota DNR Public Waters Permit Program, and Minnesota Wetland Conservation Act of 1991) have been instrumental. In the early 1980s, 21 otters were released in the upper Minnesota River basin in west-central Minnesota. The current estimated fall population in Minnesota is about 18,000 otter, probably the highest in the last 40 years.

Harvest Season

As a result of their recovery, otter harvest limits, season lengths, and trapping zones have increased over the years. Prior to 1917, otter were unprotected. They received complete protection from 1917 to 1942, and in 1942, limited harvest began in northern Minnesota. Harvest is now allowed statewide. Trapping season generally runs from late October/early November to early January. This year’s season is October 28 to January 7, with a total limit of four otter per licensed trapper. In the 1986 to 2016 seasons, the lowest registered otter harvest was 777 and the highest 3450. Last year saw 1170 harvested. Population fluctuations are related to trapper effort which is primarily related to fur prices. Pelt prices this year are expected to be $20-30. They have been as high as $87 in 2004. For more detail on trapping regulations, see the Minnesota Hunting and Trapping Regulations handbook (pages 47-56, www.mndnr.gov/hunting).

Close Monitoring

Despite their recovery and greater adaptability than once thought, our otter population still requires close monitoring and efforts to provide healthy habitats due to several factors. They will not inhabit highly degraded habitats and polluted waters, and are prone to population decline and slow recovery. They have low reproductive rates, occur at low densities, have restricted distributions, remain one of the highest sought after pelts in our state, concentrate contaminants in their bodies as a top carnivore, and rivers and wetlands continue to be altered or destroyed. Impacts from oil spills, water acidification from mining operations, siltation in waters, pesticide accumulation in waters and prey, invasive aquatic species and climate change must all be considered.

To help provide close monitoring of our otter population, Minnesota DNR classifies them as a furbearer. Trappers must have small game and trapping licenses, and otter tags; need a trapping education certificate if born after 1989; and each pelt must be registered with DNR. When registered, information is collected on the sex, date, method of take, and harvest location, and the pelt is tagged. Accurate harvest data allows for better population modeling and adjustment of trapping regulations.

Healthy Habitats, Clean Waters

To help provide healthy habitats and clean waters for otter, landowners can protect, enhance and restore streams, rivers, wetlands, ponds and lakes, and adjacent upland buffers. Chemical and pesticide use can be minimized and pollutants kept out of waters. Forest, trail and stream crossing management can minimize erosion and siltation. Large downed logs, brush piles, burrows and other natural structure can be left and encouraged near water to provide dens. And beaver, and their dams and lodges, allowed on the landscape. These actions will also benefit numerous water birds, reptiles, amphibians, and fishes, providing food for otter, greater recreation for us and our fellow forest and outdoor enthusiasts, and clean water for all.

Thank you to John Erb, Minnesota DNR furbearer research biologist, for input and review of this article.

Jodie Provost
Jodie is with the Minnesota Department of Natural Resources Fish & Wildlife – Forest Habitat Team.

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