Otters are
long-bodied, semiaquatic members of the weasel family, Mustelidae. This group includes the
SEA OTTER, Enhydra; the river otters, Lutra; the giant otter, Pteronura, of South America;
the African clawless otter, Aonyx; and the small-clawed otters of Asia, Amblonyx, and
Africa, Paronyx, both of which are often classified with the clawless otter.
The river otters, Lutra, comprise 11 or 12 species found on all the continents except
Australia and Antarctica and include the North American otter, L. canadensis, and the
European otter, L. lutra. They have broad snouts, small ears, short legs with fully webbed
feet, and a thick but tapering tail. Their underfur is short and dense, brownish or
grayish in color, and is overlain with darker, coarser guard hairs. Male river otters
reach about 1 m (3 ft) in head and body length, plus a 50-cm (19-in) tail, and stand about
25 cm (10 in) high at the shoulders; they weigh up to about 14 kg (30 lb). Females are
about one-third smaller.
River otters feed on fish, crustaceans, amphibians, turtles, and even birds and small land
mammals.
Northern populations of river otters mate in summer, and the young are not born until 9
1/2 to 12 1/2 months later, usually in late winter or early spring. This prolonged
gestation is due to the delayed implantation, or attachment, of the newly developing
embryo to the wall of the uterus.