North American River Otter
Similar to other predators at the top of the food chain, river otters historically had a large range, covering almost all of the continental United States excluding the arid Southwest. In South Dakota, the river otter is thought to have occurred throughout the state in suitable habitats. As early as the 1900s, the river otter was rare or absent from much of its range, due to unregulated harvest. More recently, efforts to reintroduce this species have been successful in many states and river otters now have a distribution similar to its historical range in this county. Beginning in 1998, the Flandreau Santee Sioux Tribe released 35 river otters on tribal lands along the Big Sioux River in Moody County, South Dakota. As a result, river otters are found along the Big Sioux River in eastern South Dakota. River otters also occur in northeastern South Dakota likely due to expansion of populations from Minnesota and North Dakota.
CONSERVATION AND MANAGEMENT
In South Dakota, the species is listed as state threatened. Current known threats to river otters in South Dakota include incidental trapping, road kills and habitat loss and degradation.
Game, Fish and Parks (GFP) is interested in observations of river otters or their sign. This information is used to monitor otter distribution in the state. If you observe a live river otter or see sign (tracks, scat or slides in snow), record the date, location (Township, Range and Section, GPS coordinates or direction and mileage from the nearest town), general habitat, and behavior and why you think it is an otter. Pictures are helpful. Visit the Tracks and Scat and It kind of looked like... sections of this webpage for more information on how to identify river otters and their sign. Submit your report via phone (605.773.3387), email, or fill out a rare species report card to GFP Natural Heritage Program.
In 2012, GFP developed a South Dakota River Otter Management Plan. The 5-year plan is intended to provide guidance to SDGFP and potential partners for the recovery and sustained management of the river otter in South Dakota.
AVOIDING RIVER OTTERS WHEN TRAPPING BEAVERS
Because river otters often use the same areas as beavers, trapping efforts targeted at beavers may also incidentally capture or kill river otters. GFP developed an informational brochure containing ways to decrease the chance of incidentally capturing a river otter while legally targeting beavers. In addition, the Association of Fish and Wildlife Agencies has developed a series of Best Management Practices (BMPs) for trapping furbearers. The BMP for trapping beavers includes a section on how to avoid capturing river otters.
Because there is no season on river otters, if a river otter is incidentally trapped the animal must be released alive. If the animal is found dead, it must be left undisturbed in the snare or trap and a GFP representative contacted within 12 hours.
RIVER OTTER BASICS
The river otter is an aquatic carnivore adapted to life in the water. The fur is brown with a tan to silvery-white chin and chest. The underfur is thick, soft and oily, and densely interspersed with guard hairs. A river otter’s body is torpedo-shaped with a flattened tail that tapers to a point. Body length is 35 to over 50 inches long with the tail comprising about 35-40% of the total body length. Weight ranges from 7.5 to about 35 pounds. Females are typically smaller than males. River otters have short legs and webbed feet. Eyes sit high on the head and small, rounded ears are set far back to allow a mostly submerged river otter to see and hear.
Tactile and auditory senses are acute in the river otter. Individuals presumably use their long, sensitive whiskers to locate prey in turbid water and while foraging in the dark. The importance of their sense of smell is unknown, but their use of scent marking may indicate the value of this sense.
Photo of a river otter showing silvery white underside, long tail that tapers to a point and short legs.
|Still image of a curious river otter with long whiskers visible.|
River otters can be found in a variety of aquatic environments including rivers, streams, lakes and marshes with abundant riparian vegetation and prey. Good water quality, year-round access to open water and limited disturbance are also important habitat characteristics.
|River otter habitat. North Fork, Whetstone River.||River otter habitat. Marsh near Punished Woman's Lake.|
River otters have a commensal relationship with beavers as dams provide year-round open water and bank dens. Dens and lodges are used by river otters as rest and natal sites. River otters also use fallen trees or logjams for shelter or foraging.
|River otter habitat. Continental Divide, Lake Traverse and Big Stone Lake.||Fallen tree along bank provides habitat for river otter.|
River otters primarily eat fish, in addition to crayfish, frogs, aquatic invertebrates, birds, and small mammals. River otters prey on fish species based on abundance and ease of capture.
|Female river otter and her pup. Photo by Dr. Wayne Melquist, CREX Consulting.|
Female river otters can breed when a year old. Males typically do not become successful breeders until 5-7 years of age. The breeding season begins in late winter and can extend until early spring. River otters have delayed implantation. This means when an egg is fertilized, it remains undeveloped in the uterus. After this delay, the fertilized egg will attach to the uterus and begin growing over a 50-60 day gestation period. Two to 4 young are then born in early spring almost a year after conception. Pups leave the natal den with the female at two months of age and are weaned at three months, but may stay with the adult until she gives birth to her next litter. Males are typically solitary except during breeding. River otters are most active during the evening and early morning. Life expectancy in the wild is 6-7 years with some living close to 20 years.
River otters have five toes on both the front and hind feet and all will typically show in a track. Length and width of a river otter track range from 2.5-3.5". Toe pads are often teardrop-shaped as the claw registers close to the pad. The middle three toes may be grouped close together while the outer two toes extend out slightly producing "1-3-1" spacing.
|Track of a river otter in sand with a quarter for scale. Notice overall size, five tear drop-shaped tow pads and possibly the outline of webbing||Tracks of a river otter in snow with a 6-inch ruler for scale.|
When a river otter is moving fast, the hind feet are placed on top of the tracks of the front feet leaving a bounding track pattern of evenly spaced pairs of tracks. This track pattern will also be at an angle to the direction of travel. When loping or galloping, a 1-2-1 track pattern is created.
|Track pattern of four fast-moving river otter showing a 2x pattern in snow.||Track pattern (1-2-1) of a loping river otter in snow on ice.|
During the winter, river otters will travel in snow by leaping onto their belly and sliding for some distance leaving a trough that is about 10” wide and creating a dot-dot-dash pattern from the two sets of tracks (dot-dot) and the slide (dash). The slide can range from 10 to 20’ long. Keep in mind that the type of substrate (sand, mud, snow, etc.) will influence the overall track size and shape. Tracks in mud are likely to be more distinctive than tracks in dry sand. Webbing doesn’t always show in tracks and a trail drag may be visible in good substrate.
|Track pattern of a river otter sliding on its belly creating a dot-dot-dash pattern from the two sets of tracks (dot-dot) and the slide (dash).||Track pattern of river otter sliding on its belly.|
River otter scat can vary in color but is often dark and deposited in prominent areas near water such as exposed logs or rocks and small islands or peninsulas. Many river otters may use the same latrine site. Fish scales and bones or other prey parts are often visible in scat.
|River otter scat with a quarter for scale. Notice the dark color and visible fish scales||River otter scat deposited on an exposed log.||River otter scat with a ruler for scale. Notice the visible fish scales.|
IT KIND OF LOOKED LIKE
Mink, beaver and muskrat can be mistakenly identified as river otter. Differences in body size and shape as well as the tail will help you differentiate among these aquatic mammals.
American Mink (Neovison vison)
Like the river otter, mink are a carnivorous mustelid with brown fur and a long tail, but they are smaller than river otters. Mink are only 1-2 feet long with a tail that is less than 1/2 the length of the body. They weigh 1.5-3.5 lbs. Mink have distinct white spots on the chin and chest. Mink are adapted to living in the water, but less so than the river otter (e.g. feet are not webbed) and mink are equally adept at living on land. They are often found along the edges of lakes, streams and wetlands and take a variety of prey items including mammals, fish, invertebrates, amphibians and birds.
American Beaver (Castor Canadensis)
Beavers are aquatic rodents with brown fur and large front teeth. Beavers are similar in length to river otters, about 4 feet long, including a 9-12" tail, but are quite stocky and much heavier, weighing 30-60 lbs. The tail is wide, flat and scaly. A swimming beaver with only the head above water looks convincingly similar to a swimming river otter with its head above water. River otters have a commensal relationship with beavers taking advantage of beaver ponds, dens and lodges for food and shelter so seeing both species in the same area is highly likely.
Common Muskrat (Ondatra zibethicus)
Muskrats are stocky, semi-aquatic rodents that look much like a beaver except for their tail and smaller size (26" long and 2-4 lbs.). Their 8-10" tail is narrow, naked and scaly. Primarily an herbivore, muskrats are often found in wetlands with vegetation such as cattails that grow above the surface of the water. Unlike river otters, muskrats are more likely to be active during the day.
For information on track patterns of these and other furbearers view the brochure "Track Identification of Common South Dakota Furbearers."