California Nature

Learn about California's beautiful and unique nature.

California River Otters
A California river otter catching his dinnerThere are two types of otter found in California nature, the northern river otter and the sea otter. The river otter (Lutra canadensis) is a long, elongated water-loving animal. The sea otter (Enhydra lutris) is a marine mammal native to the coasts of the northern and eastern North Pacific Ocean. You can find complete information on the sea otter here.

The river otter is native to northern and central California, being found in the delta region of the Sacramento and San Joaquin Rivers, where it sometimes dens in thick tules. In California the river otter is fully protected under law and may not be taken at any time.

Of all our native wildlife, river otters are usually among the most difficult to observe. Over most of the U.S., otters are trapped and persecuted by man, so they are typically very wary of humans. The river otter, a member of the weasel family, is equally versatile in the water and on land. Northern river otters hunt during the night and prey upon the species that are the most readily accessible. Fishes are a favored food among the otters, but they also consume various amphibians, turtles, and crayfish. There have been instances of river otters eating small mammals as well.

Otters inhabit rivers, streams, lakes, ponds, marshes and inland waterways. These social animals may make their home in a hollow log or abandoned beaver lodge; however, they usually dig a hole into the bank of a stream or lake. This hole leads to a leaf-lined den. They may dig their own burrow, or remodel the burrow of a beaver.

Northern River otters have a long, slender, sleek body, weighing approximately 20 pounds and are about two and a half feet long. The otter head is small and round, with small eyes and ears and prominent whiskers. All four otter feet are webbed, and the legs are short but powerful. An otter's tail is long and slightly tapered toward the tip with musk-producing glands underneath. The short dense fur is dark brown, while the chin and stomach are reddish yellow, tinged with gray. Females are a third smaller than males. River otters are among the most playful of animals. A lone river otter often amuses itself by rolling about, sliding, diving, or "body surfing" along on a rapid current. In family groups, otters take turns sliding and will frolic together in the water. A river otter makes the most of a snow slide by running to get speed, then leaping onto the snow or ice with its forelegs folded close to its body for a streamlined toboggan ride.

river otters spend time on both land and in the watersOtters mate year-round, with activity peaking in late spring and early summer. The gestation period is about 2 months In late spring, expectant mothers begin to look for a den where they can give birth to the yearlings they will soon have. The female otters do not dig their own dens; instead, they rely on other animals, like beavers, to provide suitable environments to raise their offspring. When the mothers have established their domain, they give birth to several kits. Litter size can reach five, but usually ranges from one to three. Each otter pup weighs approximately five ounces. At birth, the river otters are fully furred, blind, and toothless. They stay with their mother for about a year while she teaches them to find and catch food for themselves. Otters reach sexual maturity in about 2 years.

river otters spend time on both land and in the waters Northern River Otters are almost impervious to cold because of an outer coat of coarse guard hairs, plus a dense, thick undercoat that helps to “water-proof” the animal. River otters have no blubber; it’s the fur that keeps them warm. They seem to enjoy frolicking in ice and snow. Perianal scent glands are used for identification, defense, marking territory, and trail marking. River otter have small ears and nostrils that can be tightly closed when in water; they are excellent swimmers and divers. During a dive, the river otter's pulse slows to a tenth of the normal rate of 170 beats a minute, thereby conserving oxygen.

These social animals may make their home in a hollow log or abandoned beaver lodge; however, they usually dig a hole into the bank of a stream or lake. This hole leads to a leaf-lined den. They may dig their own burrow, or remodel the burrow of a beaver. North American river otters usually live to 21 years of age in captivity, but they can reach 25 years of age. However, they normally live about 8 to 9 years in the wild, but are capable of living up to 13 years of age. The otter has few natural predators when in water. Aquatic predators include the Alligator, American Crocodile, and Killer Whale. On land or ice, the river otter is considerably more vulnerable.

Currently in the San Francisco Bay region, river otter populations are stable and unevenly distributed with relatively high numbers in the Delta and Suisun, and lower numbers in the Napa marshes and along the Contra Costa shoreline of the Carquinez Strait. Few studies of river otter density and abundance are reported in California. Instates or countries with snow, locating tracks are the recommended survey technique and the timing of the sample therefore depends on snowfall, but this is not appropriate for the San Francisco Bay region.

Terrestrial predators include: the Bobcat, Mountain Lion, Coyote, Domestic Dog, Gray Wolf, Red Fox, and Black Bear. Most river otter mortality is caused by human-related factors such as trapping, illegal shooting, road kills, and accidental captures in fish nets or set lines. Accidental deaths of river otters may be the result of ice flows or shifting rocks. Starvation may occur due to excessive tooth damage.

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