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River Otters - Lontra Canadensis
People who see otters in saltwater areas, such as the Puget Sound, often think they’ve seen a sea otter when in fact they’ve seen a river otter. Sea otters can be seen along rocky coves at the ocean, but not in inland waters such as Puget Sound. River otters are long and slender, with pointed tails, and never swim on their back, while sea otters are much stockier and spend most of their time floating on their backs. The river otter is almost entirely aquatic, but, unlike the sea otter, it dens on land and sometimes forages along the shore.
Otters hunt primarily at night. Foods include fish (including non-game species such as suckers), crayfish, clams, crabs, amphibians, birds, small land mammals, muskrats, eggs, insects, beavers, snapping turtles, roots, and aquatic plants.
Prey is captured with the mouth. Their long whiskers are used to detect organisms in the substrate and the dark water. Prey is eaten immediately after capture, usually in the water, although larger prey is eaten on land.
Washington: statewide, including salt water of Puget Sound and fresh water rivers and lakes, usually in wooded areas. They do not excavate their own dens but use vacated beaver lodges, hollow logs, log jams, unused boat-houses, etc. They den up to 500 yards from a river or stream.
Otters are very resourceful and opportunistic. They can survive wherever there is a fresh-water stream or river flowing through a riparian habitat and a food source. Otters have large home ranges and are constantly on the move within this range. Males have longer home ranges than females and will overlap two or more females’ home ranges. A researcher in Colorado reported one male’s home range was 38 linear miles.
They prefer to introduce their young to slower currents at first. In fact, otters do not take readily to water. They need to be ‘strongly encouraged’ by mom to enter the water the first time.
Otters are very susceptible to bioaccumulation of contaminants such as mercury, PCBs, DDT, and other pesticides. Otters are occasionally predated by bobcats, lynxes, coyotes, and wolves, as well as great horned owls. They are still trapped for their rich, glossy coat. Otters can live 13 years in the wild.
Sexual maturity is reached after about 2 years in females and 5 years in males. Breeding season begins in the late winter or early spring, immediately after the birth of the litter, and spreads over a period of three months or longer. Copulation occurs in the water.
The length of gestation varies from 9-12 months due to delayed implantation. Initially, otter embryos develop normally, but then the process is suddenly stopped. The fetus does not implant in the wall of its mother’s uterus, but is put on hold. It may be that implantation, and subsequent birth are timed to coincide with periods of high resource availability.
Between 1- 4 young are born in the den, fully furred, with large heads and tapered tails, but they are blind. After 30 days, the young otters’ eyes open, and soon afterward, they are ready to play. They are weaned at 4 months.
Importance & Abundance
River otters are important predators of trash fish. River otters generally do not have adverse affects on humans. River otters are important indicators of healthy aquatic ecosystems for they are sensitive to water pollution.
River otters have been hunted for many years for their attractive and durable fur. In the 1983-84 hunting season, 33,135 otters were taken with an average selling price of $18.71 per pelt. Otters are stll an important source of income for many people in Canada and the Western United States.
River otters are listed in Appendix II of CITES. They have been virtually eliminated through many parts of their range, especially around heavily populated areas in the midwestern and eastern United States.
How to Spot Signs of a River Otter
Otter slides are difficult to recognize, but fairly common around water in wild areas.
The most common sign of otters are the remains of a meal on top of a rock, usually accompanied by scat.
Otters are intelligent mammals that play throughout their lives. Males and females do not associate except during the mating season. Males often breed with several females, probably those whose home ranges overlap with their own. The river otter whistles, snorts, snuffs, and also barks and grunts in alarm.
Coexisting with Otters
Otters sometimes wreak havoc for those trying to rear fish.
Fencing is the long term solution. A fence around the pond that also goes down into the ground is best.
If you trap an otter or two from the pond, then others from the surrounding area will eventually migrate and fill the void. This necessitates more trapping. Fencing is a long term solution. Another solution is to provide more cover for the fish such as aquatic vegetation or artificial cover (old Christmas trees). This gives the fish more cover and makes it harder for the otter to capture their prey.
For more information, visit the Burke Museum website.
Information from “Living with Wildlife” by Russell Link and Burke Museum of Natural History.