River otter are highly skilled swimmers. Rough fish make up a substantial portion of an otter's diet, though game fish of medium size are occasionally caught and eaten. Great travelers, otter circuits may cover 60 or more miles and take weeks to complete. This species enjoys play, and otters commonly play either alone or with others of their kind. Powerful and streamlined furbearers, otters are recognized as one of the more intelligent species.
Otters have long, slender bodies with relatively short legs. The neck is long and muscular, as is the tapered tail. Otter fur is considered a short-haired fur. Guard hair lengths are about 1 inch with underfur lengths of about 3/4 inch. Coloration is brown, with chocolate colors common in southern states and darker colors common in northern states. Otters from all areas are lighter in color on cheeks, throats, and bellies.
Males are larger than females. Adult males may measure 48 inches in length and weigh up to 25 pounds. Adult females are usually 4-6 inches shorter and seldom weigh more than 19 pounds.
There are five toes on each foot. A web of skin connects the toes on each foot. Claws are strong and nonretractable. Otters have 36 teeth, including four long, sharp canine teeth. Valves are present in an otter's nose and ears and close automatically as the otter submerges.
A pair of anal musk glands are present on both males and females. This musk can be released when the otter is frightened, but it is not as offensive as the musk of other members of the mustelid, or weasel, family.
Breeding occurs over most of the otter range during March and April, only a few days after the litter is born. Males leave after breeding to find other females, but may return six to eight weeks later to join the family.
Delayed implantation occurs, and this varies a great deal. Implantation of the fertilized eggs may take seven to 10 months before the free-floating eggs attach themselves to the uterus walls to complete the 60- to 65-day gestation. Litter sizes average two or three. Most otter do not mate until they are 2 years old.
Abandoned beaver dens are often selected by the female otter for the natal dens. At times, an otter will use a dry land den near the water to raise the litter. All young must be taught to swim.
Except for the raising of the litter, otters seem to be constantly on the move from place to place. They do not seem to defend their territories from other otters, and the overlapping of regular territories do occur often.
The availability of food, as well as the season, determines how far the individual otter ranges. During summer months when food is easily available, otters may stay within a 20-square-mile area. During winter conditions, the same otters may circulate over 60 or more square miles. Circuit times vary, as well, and an otter may complete a summertime circuit in a week as compared to wintertime travels taking three or four weeks.
Otters commonly travel by swimming and loping along shorelines, but they do not hesitate to take off overland to reach a distant steam or pond. These overland trails may be very distinct when otter populations are high.
Otters certainly enjoy sliding on mud or snow. Under favorable conditions, they might bound three or four times and then slide for yards before continuing to bound and slide some more. Mudslides down steep banks into the water are commonly used in many northern areas as the otters take turns climbing the bank to slide down into the water headfirst.
Length: 48 inches
Weight: up to 25 pounds
Litter size: 2-3
Life span: up to 15 years
Otters have a high metabolic rate, and food passes through the entire digestive system in about an hour. Small fish are eaten whole. Often, an otter will eat a fish while floating in the water on its back, holding the fish much like a person eating corn on the cob. After eating, otters commonly vomit up an abundance of fish scales and bones. This prevents a large number of valueless scales from passing through the entire digestive system.
The elongated body, webbed feet, and powerful tapered tail allow otters to be very quick in the water, and they can swim at least 1/2 mile while submerged. When an otter chooses to swim quickly, it undulates its entire body up and down in a ship-like fashion with its front legs held tightly to the body.
Commonly eaten foods include many types of minnows, sunfish, suckers, perch, and scultins in western habitats. Also eaten are crayfish (claws not eaten), water snakes, frogs, and aquatic insects. Muskrats are eaten when available, as are mice.
Otters are not known to store food. Although an otter does not kill more food than it will eat, the high rate of metabolism keeps the furbearer hungry much of the time.
Young otters will often stay with their mothers throughout their first winter season. Oftentimes, the young will follow the mother in a single-file fashion, both on land and in the water.
Excellent populations have always existed in the northeastern, southeastern, and northwestern states. Due to reintroductions, otters are increasing in all states.
Although otters can and do eat trout, they usually help a trout stream by helping to contain populations of rough fish. When fish are so abundant as to become stunted, predation certainly allows more food for the remaining fish. Although otters sometimes kill muskrats and ducks, the numbers are so small as to be insignificant. Otters can devastate fish farms. This is most apt to happen during the spring when a family of otter may be denned for two or three months.
Adult otters are rarely killed by other predators. Lynx and wolves can kill them, and juvenile otters may also be vulnerable to predation by bobcats and coyotes.
Otters are relatively free of parasites due to infrequent use of dens, constant traveling habits, and little contact with other otters that are not family members. However, they are vulnerable to poisons, which often show up in fish. Fish killed by acid rain may poison otter, and lethal amounts of DDT, PCBs, and mercury have been found in otters.
A significant habitat loss has occurred over much of otters' historic range. Farming practices in many areas allow muddy and silty water with each rainfall, which discourages fish production and interferes with an otter's ability to locate food by sight.
Otters are considered to be old at 15 years.