Facts About River Otters
River otters (Lutra canadensis, have long, streamlined bodies,
short legs, webbed toes, and long, tapered tails that are all adaptations for
their mostly aquatic lives. Their short thick fur is a rich brown above, and
lighter, with a silvery sheen, below. Adult male river otters average 4 feet in
length, including the tail, and weigh 20 to 28 pounds. Female adults are
somewhat smaller than males.
Although seldom seen, river otters are relatively common throughout Washington in ponds, lakes, rivers, sloughs, estuaries, bays, and in open waters along the coast. In colder locations, otters frequent areas that remain ice-free in winter rapids, the outflows of lakes, and waterfalls. River otters avoid polluted waterways, but will seek out a concentrated food source upstream in urban areas.
River otters are sometimes mistaken for their much larger seagoing cousin, the sea otter. However, male sea otters measure 6 feet in length and weigh 80 pounds. Sea otters are acclimated to salt water, and come to shore only for occasional rest periods and to give birth. In comparison, river otters can be found in fresh, brackish, or salt water, and can travel overland for considerable distances.
Facts about Washington River Otters
Food and Feeding Habits
Although seldom seen, river otters are relatively common throughout Washington in ponds, lakes, rivers, sloughs, estuaries, bays, and in open waters along the coast. In colder locations, otters frequent areas that remain ice-free in winter rapids, the outflows of lakes, and waterfalls. River otters avoid polluted waterways, but will seek out a concentrated food source upstream in urban areas.
River otters are sometimes mistaken for their much larger seagoing cousin, the sea otter. However, male sea otters measure 6 feet in length and weigh 80 pounds. Sea otters are acclimated to salt water, and come to shore only for occasional rest periods and to give birth. In comparison, river otters can be found in fresh, brackish, or salt water, and can travel overland for considerable distances.
Facts about Washington River Otters
Food and Feeding Habits
- River otters are opportunists,
eating a wide variety of food items, but mostly fish. River otters usually feed
on 4- to 6-inch long, slowly moving fish species, such as carp, mud minnows,
stickle backs, and suckers. However, otters actively seek out spawning salmon
and will travel far to take advantage of a salmon run.
- River otters can smell
concentrations of fish in upstream ponds that drain into small, slow moving
creeks, and will follow the smell to its origin, even in urban areas.
- River otters also eat freshwater
mussels, crabs, crayfish, amphibians, large aquatic beetles, birds (primarily
injured or molting ducks and geese), bird eggs, fish eggs, and small mammals
(muskrats, mice, young beavers).
- In late winter, water levels usually
drop below ice levels in frozen rivers and lakes, leaving a layer of air that
allows river otters to travel and hunt under the ice.
- River otters digest and metabolize
food so quickly that food passes through their intestines within an hour.
Den Sites
- River otters use dens for giving
birth and for shelter from weather extremes. Birthing dens are lined with small
sticks, shredded vegetation, and other available material.
- Den sites include hollow logs, log
jams, piles of driftwood or boulders, and abandoned lodges and bank dens made
by nutria or beaver.
- Dens are well hidden; those located
at the water’s edge will have an entry far enough below the surface to prevent
it from being seen and/or frozen shut.
- River otters also den under
boathouses, duck blinds, and other human structures up to ½ mile away from
water.
Reproduction and Family Structure
- River otters have what is called
delayed implantation; the fertilized egg does not attach to the uterine wall
for a period of time after breeding. Thus, gestation ranges from 285 to 375
days.
- Two to four pups are born March
through May.
- Young otters begin playing at four
weeks of age and learn to swim at about seven weeks of age. When eight to ten
weeks of age, the pups begin exploring beyond their den and are introduced to
solid food.
- In late fall, the pups leave to
establish their own territories. During this time, wandering youngsters are
seen far from water, traveling on land between lakes, ponds, and from one
stream drainage to another.
- The basic social group for river
otters is a female and her offspring. (Before and after breeding, male otters
usually lead solitary lives.)
Mortality and Longevity
- Essentially safe from predators
while in water, river otters are more vulnerable when they travel on land.
Predators take mostly young river otters and include coyotes, bobcats, domestic
dogs, cougars, and bears.
Humans trap river otters to control fish predation in private ponds and commercial fish hatcheries and to prevent damage to private property. The most significant impacts on river otter populations include reduced water quality from chemical pollution and soil erosion, and stream-bank habitat alteration by developments.
This information was provided by the Washington State Department of Fish and Wildlife, Russell Link, and Michael Holmquist
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