North American River Otter

 

Common Name: North American River Otter
Class: Mammalia
Order: Carnivora
Family: Mustelidae
Genus: Lutra
Species: Lutra canadensis

photo M Noonan

 


Taxonomy/Description

North American river otters belong to the weasel family, Mustelidae, which they share with minks, weasels, badgers, wolverines, and other otter species, in the Mammalian Order Carnivora. Its scientific name is Lontra canadensis, which means "otter belonging to Canada", although this otter species range includes much more of North America than Canada.

photo M Noonan

The North American river otter is considered a medium to large sized otter, with adults ranging in length from 3 to 5 feet and weighing between 10 and 30 pounds. The fur on their backs is generally dark brown, and their undersides vary from light brown to gray. Some individuals may have a silver or white throat patch. They are very quick animals, both on land and in the water. North American river otters are capable of swimming at speeds of seven miles per hour, and can reach 18 miles per hour at a full run. The life expectancy for this species in the wild is only about ten years, but with the steady food supply and protection that zoos afford, captive individuals can live to be twenty years old. 

Habitat/Diet

The North American river otter is quite possibly the most numerous otter species in the world. Their range extends through most of North America from Alaska and northern Canada down to southern Florida. These animals inhabit a variety of diverse environments, from saltwater estuaries to freshwater lakes, rivers, marshes and streams. The bulk of these animal’s diets consist of slow-swimming fish and small crustaceans, but they are also very opportunistic hunters. North American river otters will eat frogs, turtles, snakes, insects, small mammals and birds whenever this type of prey is readily available.

Behavior/Reproduction

North American river otters very vocal, and the animals use a variety of calls to communicate. The calls may range from high-pitched chirps, whistles and twitters, to low grunting chuckles and buzzes.  This species is highly inquisitive and playful. They have been observed using muddy riverbanks and snow drifts as slides, rushing down on their bellies and slipping into the water. The skills they build during their frequent play sessions later serves them well when they need to make quick escapes from predators such as wolves or coyotes.  Other “play” behaviors help these animals find food. For example, North American river otters have been observed swimming in circles to create a small whirlpool. The suction created by the whirlpool pulls hiding fish up from the bottom of a river or stream.

Reproduction in North American River Otters is highly seasonal.  Females are in estrus for approximately 1 month per year, and males start sperm production and have increased testosterone levels for approximately 3 months per year.  Additionally, there is some evidence that seasonality is related to geographic location in that those in more southern latitudes start estrus and testosterone increases much earlier in the year than those in northern latitudes.  This geographic influence also extends to parturition, where females with give birth at earlier times in more southern latitudes.

The North American River Otter is one of only two known otter species to have delayed implantation (the other is the Sea Otter).  Fertilized eggs will remain in diapause for 7-10 months before implanting - usually during late winter/early spring months.  Once the embryos implant the gestation period is fairly consistent at 68-73days.  The total resulting duration of pregnancy (from date of last observed breeding to parturition) is thus 302-351 days. 

Females do not usually excavate dens; instead, they prefer to use abandoned dens of other animals or naturally existing shelters. The typical litter is 2-3 kits, but there may be as many as six kits in a single litter. The kits are only about 4.5 ounces at birth, and they cannot swim until their dense undercoats grow in at about two months of age. When they are learning to swim, the kits sometimes climb onto their mother’s back. Young will leave their mother when they are about one year old, and they will reach maturity between two and three years of age.

photo M Noonan

Conservation

Fossils of the North American river otter have been dated back to the Pleistocene period. They were well established throughout their range, as they have few natural predators. Native Americans hunted them for their warm, dense fur, but the number of animals taken was not high enough to impact the size of their populations. The real trouble for these animals began with the arrival of the Europeans in the Americas. Extensive hunting drastically reduced their numbers in the wild, and North American river otters vanished from some states entirely. There are a number of examples of Native American folklore involving the otter. Several origin myths place the otter as one of the animals sent down to the bottom of the water to find earth, upon which all the seeds of life are then planted. The otter is also frequently portrayed as carefree, comical, or lazy. Sometimes, even as a rather obnoxious character. In a Shoshone myth, Otter mocks Beaver for working too hard. Beaver’s wounded pride causes him to prove that he can slide farther than Otter. Beaver slides down a mountain on his tail, to which a laughing Otter replies, “The slide was perfect, but look what you have done to your tail!”

While North American river otters are not endangered, their populations are still threatened by humans. It is still legal to trap river otters in 38 states, and anywhere from 20,000 to 30,000 individuals are killed each year for their pelts. Apart from the fur trade, the two largest threats to these animals are habitat destruction and water pollution. Despite the wide variety of habitats in which the North American river otter can be found, they are particularly shy animals and will try to avoid human contact in the wild. As human populations develop areas in which wild otters live, the animals are forced into smaller and smaller territories. They are also incredibly sensitive to pollutants, and otter populations have suffered declines around human settlements and agricultural areas.

As the otters began to disappear from their historical ranges, steps were taken to help slow the rate of decline. Several states in which the otters were entirely wiped out now have budding populations thanks to reintroduction programs. In the 1980’s, the North American river otter was rare or extinct in 26 states. Today, that number has been reduced to fifteen. Zoos and wildlife rehabilitation centers all across the country are partnering in breed and release programs to help further the recovery of these energetic animals.

 

CAC is a program of the Institute for the Study of Human-Animal Relations at Canisius College in Buffalo, NY.