Family: Mustelidae, Weasels view all from this family
Description A large aquatic mustelid with elongated body and broad, flattened head. Dark brown above (looks black when wet), with paler belly. Throat often silver gray. Ears and eyes small. Prominent, whitish whiskers. Long tail thick at base, gradually tapering to a point. Feet webbed. Male larger than female. L 35–52" (889–1,313 mm); T 11 7/8 –20" (300–507 mm); HF 3 7/8 –5 3/4" (100–146 mm); Wt 11–30 lb (5–13.6 kg).
Similar Species Sea Otter is yellowish or grayish on head and back of neck.
Breeding Mates in early spring, just after birth of litter; implantation delayed; total gestation 8–9 1/2 months. Litter of 1–6 young born blind and fully furred, in March or April.
Habitat Primarily along rivers, ponds, and lakes in wooded areas, but otters will roam far from water.
Range Alaska and most of Canada south to n California and n Utah; in East, from Newfoundland south to Florida; extirpated from most areas of Midwest, but currently being reintroduced into some areas.
Discussion The Northern River Otter is active by day if not disturbed by human activity. Well adapted to its aquatic life, it has a streamlined body, rudder-like tail, and ears and nostrils that are valved to keep out water. The animal swims rapidly both underwater and on the surface, moving like a flexible torpedo, either forward or backward, with astonishing grace and power. To observe its surroundings, it raises its head high and treads water. A river otter can remain submerged for several minutes and can dive to a depth of 55 feet (17 m), swimming as far as 1/4 mile (.4 km) underwater if necessary. Also at ease on land, the river otter will lope along, then slide, and it also runs fairly well. 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 snowslide 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. The Northern River Otter feeds mainly on fish, often caught in a quick broadside snap, but also eats small mammals such as mice, as well as terrestrial and aquatic invertebrates. It may capture fish by pursuit or by digging into the sand and lying in wait. Some anglers suspect the Northern River Otter of depleting game fish stocks, particularly trout. While it will eat game fish, it more often eats the slower-moving suckers, chubs, daces, darters, and catfish, as well as schooling fish such as the bluegill, which are caught more easily. A pair of river otters may work together to drive a school of fish into an inlet, where they can be easily caught. The otter can manipulate items in its forepaws and carries large catches to land to be eaten. It often digs its permanent den in banks, establishing underwater and aboveground entrances. Inside it constructs a nest of sticks, grass, reeds, and leaves. This species rests under roots or overhangs, in hollow logs, burrows of other animals, or beaver lodges, which if heavily used by otters may also contain some nesting materials. The river otter’s vocalizations include a whistle, probably used to communicate over distances, and a shrill, chattering call, emitted during the mating season. Otters chuckle softly to siblings or mates, apparently as a sign of affection, and also chirp, grunt, snort, and growl. The male river otter presumably mates with one or more females that have home ranges within his territory. The female establishes the natal den shortly before giving birth. Weaned at four months, the young disperse in fall or winter before the arrival of the next litter. The male, evicted while the young are small, returns to help care for them when they are half-grown. While sociable most of the year, during the breeding season competing males may battle. The Northern River Otter’s fur is durable, thick, and beautiful, and excessive trapping in the past has greatly diminished the animals in number. More recently, water and air pollution, including mercury fallout, have taken a toll on otter populations. Some river otters, however, may be developing a tolerance to certain toxic substances, and their populations are slowly increasing.
