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  The Mammals of Texas - Online Edition

River Otter
Order Carnivora : Family Mustelidae : Lutra canadensis (Schreber)

River Otter (Lutra canadensis).  Photo by John L. Tveten.Description. A large, dark brown "weasel" with long, slender body; long, thick, tapering tail; webbed feet; head broad and flat; neck very short; body streamlined; legs short, adapted for life in the water; five toes on each foot, soles more or less hairy; pelage short and dense; upperparts rich, glossy, dark brown, grayish on lips and cheeks; underparts paler, tinged with grayish. Dental formula: I 3/3, C 1/1, Pm 4/3, M 1/2 X 2 = 36. External measurements average: total length, 1,168 mm; tail, 457 mm; hind foot, 124 mm. Weight, 6-7 kg, occasionally as much as 10 kg.

Species distribution mapDistribution in Texas. Presently known only from eastern one-fourth of state in major watersheds; probably extirpated from the Panhandle, north-central, and southern Texas.

Habits. River otters are largely aquatic and frequent lakes and the larger streams. In the Gulf Coast region, marshes, bayous, and brackish inlets afford suitable range. They are expert swimmers and divers and can remain underwater for several minutes if necessary. They are not bound to water, however, and when occasion demands they do not hesitate to travel overland from one body of water to another. Their movements on land appear awkward. The long body is arched and supported by four short legs and reminds one somewhat of a "measuring" worm.

The slides and apparent playfulness of otters are well-known. The slide, situated on some steep clayey bank, seems to be used chiefly for "recreational" purposes. The otters play "follow the leader" in tobogganing, with front legs folded back, from the top of the slide into the water below.

Otters are notorious wanderers in their chosen habitat and an animal may range over several kilometers of a waterway. For this reason they are never abundant in any locality. They are ordinarily shy, unobtrusive creatures that are seldom seen even though they are active throughout the year.

The den varies with the locality and availability of sites. Most otters locate their dens in excavations close to water under tree roots, rock piles, logs, or thickets. The hollow bases of cypress trees and tupelo gums are especially popular. Occasionally, they will take over beaver lodges or muskrat dens for their own use after killing the occupants. A typical den consists of a hole leading into a bank, with the entrance below water level. Otters may occupy two dens, one as a temporary resting den and the other as a permanent nesting den.

Otters are not specific in their food habits. Their main diet consists of fish, crustaceans, mollusks, amphibians, reptiles, invertebrates, birds, and mammals. One of their choicest morsels is crayfish, and where they are abundant, an otter will consume a tremendous number annually. The fish they eat are primarily rough fish.

Virtually nothing is known about their reproduction in Texas. They probably breed in fall, but males do not generally mate until they are four years of age, and females rarely breed before two years. Males typically engage in fierce combat during the mating season, and they are believed to be solitary except when accompanying estrous females. Estrous lasts 40-45 days, and the female is receptive to the male at about six-day intervals. Mating usually occurs in the water. Delayed implantation results in the gestation period extending to as much as 270 days. Litter size varies from one to five, with two about average. Females may mate again as soon as 20 days following birth, which means that otters may remain continuously pregnant once they reach sexual maturity.

Newborns are about 275 mm in total length and weigh about 130 g. They are fully furred, but the eyes are closed and none of the teeth are erupted. Their eyes open at 22-35 days, and they are weaned at 18 weeks. The adult waterproof pelage appears after about 3 months.

Photo credit: John L. Tveten.