North American River Otter - Physical Characteristics

Physical Characteristics

The North American river otter is a stocky animal of 5 to 14 kilograms (11 to 31 lb), with short legs, a muscular neck no smaller than the head, and an elongated body that is broadest at the hips. An average adult male weighs about 11.3 kilograms (25 lb) against the female's average of 8.3 kilograms (18 lb). Its body length ranges from 66 to 107 centimetres (26 to 42 in). About one-third of the animal's total length consists of a long, tapered tail. Tail lengths range from 30 to 50 centimetres (12 to 20 in). Large male North American river otters can exceed a weight of 15 kilograms (33 lb). It differs from the European otter by its longer neck, narrower visage, the smaller space between the ears and its shorter tail.

A broad muzzle is found on the river otter's flat head, and the ears are round and inconspicuous. The rhinarium is bare, with an obtuse, triangular projection. Eyes of the animal are small and placed anteriorly. A short, broad rostrum for exhaling and a long, broad cranium define the relatively flat skull. The river otter's nostrils and ears close during submersion, inhibiting water from entering them. Its vibrissae (whiskers) are long and thick, enhancing sensory perception underwater and on land.

The fur of the species is short (guard hairs average 23.8 mm (0.94 in)), with a density of about 57,800 hairs/cm2 (373,000 hairs/in2) in the midback section. The pelage has a high luster and varies from light brown to black. The throat, chin, and lips are grayer than the rest of the body. Fur of senescent river otters may become white-tipped, and rare albinos may occur.

Sexual dimorphism exists among the river otters. Males are, on average, 5% larger than females. In Idaho, juvenile, yearling, and adult males averaged 8, 11, and 17% heavier, respectively, than females of the same age. A clinical reduction in size may exist from north to south along the Pacific coast, but not from east to west.

North American river otters live an average of 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.