River Otter, North American


ORDER: Carnivora

FAMILY: Mustelidae

GENUS: Lutra

SPECIES: canadensis

DESCRIPTION:
Long, slender, sleek body, weighing 12-25 pounds and 3-4.5 feet long. Tail is muscular and flattened and is about 12-20 inches in length and makes up approximately 1/3 of the total body length. It tapers towards the tip and has musk-producing glands at the base. Head is small and round, with small eyes and ears; prominent whiskers. Legs short, but powerful; all four feet webbed. The short dense fur ranges from blond to nearly black on top of the body. Upper lip, chin and stomach are generally paler. Females can be up to 20% smaller than males of the same age.

GEOGRAPHICAL RANGE AND HABITAT:
Historically found in all of the United States and Canada except the tundra and parts of the arid southwestern United States. Populations throughout the central US and Canada have been extirpated. Allied species occur in Mexico and Central and South America. Found in streams, rivers, lakes, estuaries, and salt and freshwater marshes.

DIET:
Carnivorous. Fish and aquatic invertebrates. Less frequently amphibians, birds and their eggs, small mammals, and reptiles. Because otters prey mostly on fish that are slow-moving and most abundant, much of the diet consists of "rough" fish like carp, suckers, catfish, and sculpins.

LIFE CYCLE/SOCIAL STRUCTURE:
Spends two-thirds of the time on land. Can be found in a variety of social groups. Females mate shortly after giving birth to one to four young. Timing of the birth and breeding season is dependent upon the latitude at which the female lives; otters in the southern parts of their range give birth as early as November and in the northernmost parts of their range births don't occur until April or May. North American river otter females experience delayed implantation where, after successful breeding occurs, the fertilized eggs stop developing at the blastocyst stage and float freely in the uterus for many months before implanting in the uterine wall. True gestation is only 68 -74 days, with a total gestation of 302-351 days. The otter pups start their life in a den far from water, since they are unable to swim at birth. They spend most of the first months of their lives nursing, spending more time outside of the den after their eyes open at approximately one month old. Females have to teach their pups how to swim and usually begin by placing them in shallow water and gradually introducing them to deeper water where they will hold them underwater and swim with them so that they are forced to hold their breath. Pups stay with their mother until they are approximately a year old. The otter pups start their life in a burrow in a river bank, usually an abandoned muskrat den. Born blind and helpless, they are nursed by the female for a month. Venturing out of the den, they rough-house and play in the shallow water, where their mother teaches them to swim and hunt.

SPECIAL ADAPTATIONS:
Almost impervious to cold because of an outer coat of coarse guard hairs, plus a dense, thick undercoat that helps to "water-proof" the animal. They have no blubber but have thick skin that contains more subcutaneous fat than terrestrial mammals. They also have glands that produce a lipid squalene that aids in the water repellency of their coat. They seem to enjoy frolicking in ice and snow. Perianal scent glands are used for identification, defense, marking territory, and trail marking. Small ears and nostrils can be tightly closed when in water; they are excellent swimmers and divers. Both diurnal and nocturnal. They do not have clavicles, allowing greater mobility of their forelimbs.

INTERPRETIVE INFORMATION:
Otter droppings are called spraints. King James I of England kept a pack of trained otters to catch fish for his table, even appointing a "Keeper of the King's Otters" to tend them. This is still in practice with fishermen in Bangladesh who train smooth-coated otters (Lutrogale perspicillata) to chase fish into nets and the practice of "otter-fishing" is passed down through families.

OUR ANIMALS:
The river otters can be found in the Wayne and Gladys Valley Children's Zoo.

STATUS IN WILD:
The river otter is native to northern and central California, being found in the delta region of the Sacramento and San Joaquin Rivers where it sometimes dens in thick tules. Populations have steadily been increasing in the Bay Area. In California the river otter is fully protected under law and may not be taken at any time. Listed on the IUCN Red List as Low Risk.

BIBLIOGRAPHY:

  1. Grzimek, Bernhard. 1972. Animal Life Encyclopedia, Vol. 12, Van Nostrand Reinhold Co, New York.
  2. Internet: IUCN Red List.
  3. Leopold, A. Starker, Ralph Gutierrez and Michael Bronson. 1981. North American Game Birds and Mammals. Charles Scribner
  4. MacDonald, David. 1987. Encyclopedia of Mammals, Facts on File, New York.
  5. Nowak, Ronald. 1991. Walker