North American river otter
The North American river otter, also known as the northern river otter and river otter, is a semiaquatic mammal that is endemic to the North American continent throughout most of Canada and along the coasts of the United States and its inland waterways. An adult North American river otter can weigh between. The river otter is protected and insulated by a thick, water-repellent coat of fur.
The North American river otter, a member of the subfamily Lutrinae in the weasel family, is equally versatile in the water and on land. It establishes a burrow close to the water's edge in river, lake, swamp, coastal shoreline, tidal flat, or estuary ecosystems. The den typically has many tunnel openings, one of which generally allows the otter to enter and exit the body of water. Females give birth in these burrows, producing litters of one to six young.
North American river otters, like most predators, prey upon the most readily accessible species. Fish is a favored food among the otters, but they also consume various amphibians, freshwater clams, mussels, snails, small turtles, and crayfish. The most common fish consumed are perch, suckers, and catfish. Occasional reports also show the river otter eating other small animals, such as mice, squirrels, birds, and even dogs that they have attacked and drowned.
The range of the North American river otter has been significantly reduced by habitat loss, beginning with the European colonization of the Americas. In some regions, though, their population is controlled to allow the trapping and harvesting of otters for their fur. North American river otters are very susceptible to the effects of environmental pollution, which is a likely factor in the continued decline of their numbers. A number of reintroduction projects have been initiated to help halt the reduction in their overall population.
Taxonomy and evolution
The North American river otter was first described by German naturalist Johann Christian Daniel von Schreber in 1777. The mammal was identified as a species of otter and has a variety of common names, including North American river otter, northern river otter, common otter, and simply river otter. Other documented common names are American otter, Canada otter, Canadian otter, fish otter, land otter, nearctic river otter, and Prince of Wales otter. The North American river otter was first classified in the genus Lutra, which was the early European name, and the specific epithet canadensis means "of Canada".In a new classification, the species is called Lontra canadensis, where the genus Lontra includes all the New World river otters.
Molecular biological techniques have been used to determine when the river otter and the giant otter of South America diverged. These analyses suggest they diverged in the Miocene epoch 23.03 to 5.33 million years ago, which is "much earlier" than indicated in the fossil record. Fossils of a giant otter dating back 3.5 Mya have been found in the US Midwest; however, fossils of the modern river otter did not appear in North America until about 1.9 Mya. The New World river otters originated from the Old World river otters following a migration across the Bering Land Bridge, which existed off and on between 1.8 million and 10,000 years ago. The otters migrated to North America and southwards again across the Panamanian Land Bridge, which formed 3 Mya.
Subspecies
Listed alphabetically:- L. c. canadensis –
- L. c. kodiacensis –
- L. c. lataxina –
- L. c. mira –
- L. c. pacifica –
- L. c. periclyzomae –
- L. c. sonora –
Description
Males and female river otters show different nonsexual physical characteristics, with males typically being larger.
North American river otters can live 21–25 years in captivity, or 8–13 years in the wild.
Form and function
North American river otters characteristically approach within a few meters of a boat or a person on shore due to their near-sightedness, a consequence of vision adapted for underwater sight. These otters have a transparent inner eyelid to protect their eyes while swimming.Otters, like most mustelids, have 36 specialized teeth, including sharp canines and carnassials that inflict lethal bites to prey. Also, North American river otters have large molars used for crushing hard objects, such as the shells of molluscs. Additional premolars may be present. The dental formula is.
Distribution and habitat
The North American river otter is found throughout North America, inhabiting inland waterways and coastal areas in Canada, the Pacific Northwest, the Atlantic states, and states on the Gulf of Mexico. They also inhabit the forested regions near the Pacific coast in North America. The species is also present throughout Alaska, including the Aleutian Islands, and the north slope of the Brooks Range.Urbanization and pollution, though, have resulted in a reduction in the otters' range in the United States. They are now absent or rare in Arizona, Kansas, Nebraska, New Mexico, North Dakota, Ohio, Oklahoma, South Dakota, and Tennessee. Reintroduction projects have expanded their distribution in recent years, such as in West Virginia, and especially in the Midwestern United States. Since their reintroduction to Kentucky in the early 1990s, the otters have recovered to the point that a trapping season was implemented in 2006, and the species is now found in all of the state's major waterways. In 2010, the Colorado Department of Wildlife reported the river otter, reintroduced to the state in the 1980s, was "thriving" and recommended its protection status be reconsidered. In late 2012, a river otter nicknamed Sutro Sam took up residence around the former site of the Sutro Baths in San Francisco, the first river otter sighting in that city since the 1950s. North American river otters occupy all Canadian provinces and territories, except until recently, Prince Edward Island. Otters have recently begun re-establishing themselves on Prince Edward Island. In Minnesota, otter populations have rebounded due to reintroduction efforts in the 1980s, improvements in water quality, habitat restoration, and harvest regulation. While river otters are most common in northern Minnesota, they can be seen in urban areas including the Twin Cities.
Historical records indicate North American river otters were once populous throughout most major drainages in the continental United States and Canada prior to European settlement. North America's largest populations were found in areas with an abundance and diversity of aquatic habitats, such as coastal marshes, the Great Lakes region, and glaciated areas of New England. In addition, riverine habitats in interior regions supported smaller otter populations. The North American river otter existed on all parts of the Pacific Coast, including the seashore and inland streams and lakes. In Mexico, North American river otters lived in the Rio Grande and Colorado River Deltas.
Although commonly called a "river otter", the North American river otter is found in a wide variety of aquatic habitats, both freshwater and coastal marine, including lakes, rivers, inland wetlands, coastal shorelines, marshes, and estuaries. It can tolerate a great range of temperature and elevations. Aquatic life ties them almost exclusively to permanent watersheds. Their main requirements are a steady food supply and easy access to a body of water, but they are sensitive to pollution and disappear from tainted areas.
Like other otters, the North American river otter lives in a holt, or den, constructed in the burrows of other animals, or in natural hollows, such as under a log or in riverbanks. An entrance, which may be under water or above ground, leads to a nest chamber lined with leaves, grass, moss, bark, and hair.
Behavior
North American river otters only settle in areas that consist of vegetation, rock piles, and sufficient coverage.Playing
North American river otters are renowned for their sense of play. Otter play mostly consists of wrestling with conspecifics. Chasing is also a common game. They rely upon play to learn survival skills such as fighting and hunting.Hunting
A highly active predator, the North American river otter has adapted to hunting in water and eats aquatic and semiaquatic animals. The vulnerability and seasonal availability of prey animals mainly governs its food habits and prey choices. This availability is influenced by detectability and mobility of the prey, habitat availability for the various prey species, environmental factors, such as water depth and temperature, and seasonal changes in prey supply and distribution in correspondence with otter foraging habitat.The diet of the North American river otter can be deduced by analyzing either stool obtained in the field, or gut contents removed from trapped otters. Fish are the primary component of the North American river otter's diet throughout the year. Every study done on the food habits of the North American river otter has identified varying fish species as being the primary component of its diet. For instance, an Alberta, Canada, study involved the collection and analysis of 1,191 samples of North American river otter scat collected during each season. Fish remnants were found in 91.9% of the samples. Moreover, a western Oregon study revealed fish remains were present in 80% of the 103 digestive tracts examined. Crustaceans, where regionally available, are the second-most important prey for otters. Crustaceans may even be consumed more than fish. For example, a study conducted in a central California marshland indicated crayfish formed nearly 100% of the river otter's diet at certain times of the year. As foragers, though, they immediately take advantage of other prey when readily obtainable. Other prey consumed by North American river otters includes fruits, aquatic plants, reptiles, amphibians, birds, aquatic insects, small mammals, and mollusks.
North American river otters are not scavengers; they avoid consuming carrion. They do not generally handle prey of a large size relative to themselves, but occasionally they have been observed ambushing and killing adult common snapping turtles while the large turtles are hibernating. Remains of the much larger North American beaver have been found in North American river otter scat in some regions, although most otter dietary studies in areas where otters and beaver live near each other do not show them to be regular predators of beavers and perhaps only young beaver kits may be attacked.