North American river otter
North American river otter | |
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A pair at the San Francisco Zoo in 2005 | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Mammalia |
Order: | Carnivora |
Family: | Mustelidae |
Genus: | Lontra |
Species: | L. canadensis
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Binomial name | |
Lontra canadensis (Schreber, 1777)
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Subspecies | |
See text | |
Synonyms | |
Lutra canadensis |
The North American river otter (Lontra canadensis), also known as the northern river otter and river otter, is a
The North American river otter, a member of the subfamily
North American river otters, like most predators, prey upon the most readily accessible species.
The range of the North American river otter has been significantly reduced by
Taxonomy and evolution
The North American river otter was first
In a new classification, the species is called Lontra canadensis, where the genus Lontra includes all the New World river otters.[12]
Subspecies
Listed alphabetically:[17]
- L. c. canadensis (Schreber, 1777) – (eastern Canada, U.S., Newfoundland)
- L. c. kodiacensis (Goldman, 1935) – (Kodiak Island, Alaska)
- L. c. lataxina (Cuvier, 1823) – (U.S.)
- L. c. mira (Goldman, 1935) – (Alaska, British Columbia)
- L. c. pacifica (J. A. Allen, 1898) – (Alaska, Canada, northern U.S., south to central California, northern Nevada, and northeastern Utah)
- L. c. periclyzomae (Elliot, 1905) – (Queen Charlotte Islands, British Columbia)
- L. c. sonora (Rhoads, 1898) – (U.S., Mexico)
Description
The North American river otter has long whiskers that are used to detect prey in dark waters.[18] 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).[19] About one-third of the animal's total length consists of a long, tapered tail.[16] Tail lengths range from 30 to 50 centimetres (12 to 20 in).[19] Large male North American river otters can exceed a weight of 15 kilograms (33 lb).[20] It differs from the Eurasian otter by its longer neck, narrower visage, the smaller space between the ears and its shorter tail.[21]
Its whiskers (
Males and female river otters show different non-sexual physical characteristics,[22] with males typically being larger.[16]
North American river otters can live 21–25 years in captivity,[22][16] or 8–13 years in the wild.[22][16]
Form and function
North American river otters characteristically approach within a few feet of a boat or a person on shore because they're
Most mustelids, including otters, have 36 specialized teeth, including sharp
Behavior
North American river otters only settle in areas that consist of vegetation, rock piles, and sufficient coverage.[26]
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. North American river otters rely upon play to learn survival skills such as fighting and hunting.[25]: 52–54
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.[27] This availability is influenced by the following factors: 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.[28][29]
The diet of the North American river otter can be deduced by analyzing either stool obtained in the field, North American river otters are not scavengers; they avoid consuming
Ecological impacts on prey species
When left unchecked, though, otters can be significant predators under certain circumstances (e.g. in hatcheries or other fish culture facilities). Likewise, the potential predatory impact of otters may be considerable whenever fish are physically confined (most commonly in smaller ponds offering sparse cover or other escape options). To protect fish in these cases, the otters may need to be removed or relocated. Even in larger bodies of water, river otters may take disproportional advantage of any seasonal concentrations of fish when and where only very limited areas of suitable spawning, low-flow, or over-wintering habitat may exist. Even fast-swimming fish like trout slow down in extremely cold water, leaving them vulnerable. As such, careful consideration of any threatened, endangered, or fish species of special interest is warranted prior to reintroduction of otters to a watershed.[25]
Social behavior
A North American River Otter can have a territory as large as 30 square miles (78 square kilometers). However, their usual territory is about 3 to 15 square miles (4.8 to 24 square kilometers). This can change during mating seasons, but that topic is up for debate.[40]
Although North American River Otters are known to be social animals, they can also survive by themselves. Their bodies allow them to avoid predators quite effectively since they can dive, burrow, twist, and turn their bodies for evasive techniques, enabling them to survive independently. North American River Otters famously love to play together, which creates strong social bonds, improves hunting skills, and marks territory. North American River Otters are not aggressively territorial, but frequently scent-mark certain spots to make their presence known. Delayed implantation distinguishes the species from the Eurasian otter, which does not do this.[41][42]
In early spring, expectant mothers begin to look for a den where they can give birth. The female otters do not dig their own dens; instead, they rely on other animals, such as beavers, to provide suitable environments to raise their offspring. When the mothers have established their domains, they give birth to several kits.[19] Litter size can reach five, but usually ranges from one to three.[16] Each otter pup weighs approximately five ounces.[19]
The mothers raise their young without aid from adult males. When the pups are about two months old and their coats grow in, their mother introduces them to the water. North American river otters are natural swimmers and, with parental supervision, they acquire the skills necessary to swim.[19]
The North American river otters may leave the den by eight weeks and are capable of sustaining themselves upon the arrival of fall, but they usually stay with their families, which sometimes include the father, until the following spring. Prior to the arrival of the next litter, the North American river otter yearlings venture out in search of their own home ranges.[43]
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 the Gulf of Mexico. They also inhabit the forested regions of 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.
However, urbanization and pollution instigated reductions in range area.[1] They are now absent or rare in Arizona, Kansas, Nebraska, New Mexico, North Dakota, Ohio, Oklahoma, South Dakota, Tennessee. Reintroduction projects have expanded their distribution in recent years, both in West Virginia,[44] and especially in the Midwestern United States. Since their reintroduction to Kentucky in the early 1990s, they have recovered to the point that a trapping season was started in 2006, and the species is now found in all major waterways.[45] In 2010, the Colorado Department of Wildlife reported the species, reintroduced in the 1980s, was "thriving" and recommended its protection status be reconsidered.[46] 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 in more than half a century.[47] In Canada, North American river otters occupy all provinces and territories, except until recently Prince Edward Island.[1] Otters have recently re-established themselves on Prince Edward Island.[48]
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 North American river otter populations were found in areas with an abundance and diversity of aquatic habitats, such as coastal marshes, the Reproduction and life cycle
Geographic range
Ecology
Habitat
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 North American river otters almost exclusively to permanent watersheds.[16] Their main requirements are a steady food supply and easy access to a body of water. However, it is sensitive to pollution, and will disappear from tainted areas.[22]
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 river banks. An entrance, which may be under water or above ground, leads to a nest chamber lined with leaves, grass, moss, bark, and hair.[22]
Diet
The diet of the North American River otters is extensive and mostly consists of fish, frogs, crayfish, turtles, insects and some small mammals. They are known to hunt in pairs or alone and can hunt on both land and in the water. “The North American river otter (Lontra canadensis) is a predator adapted to hunting in water, feeding on aquatic and semi-aquatic animals. The vulnerability and seasonal availability of prey animals primarily determines the food habits and prey preference of the river otter.”[50]
Fish
North American river otters consume an extensive assortment of fish species ranging in size from 2 to 50 centimeters (0.79 to 19.69 in) that impart sufficient caloric intake for a minute amount of energy expenditure.
Adult North American river otters are capable of consuming 1 to 1.5 kilograms (2.2 to 3.3 lb) of fish per day.[35] A study conducted on captive otters revealed they preferred larger fish, ranging from 15 to 17 centimeters (5.9 to 6.7 in), more than smaller fish, ranging from 8 to 10 centimeters (3.1 to 3.9 in), and they had difficulty catching fish species less than 10 centimeters (3.9 in) or larger than 17 centimeters (6.7 in).[27] Otters are known to take larger fish on land to eat, whereas smaller fish are consumed in the water.[35]
Crustaceans
North American river otters may prefer to feed on
During the winter and spring, when the water levels were higher, North American river otters had a greater tendency to prey upon crayfish (73% of scats had crayfish remains) rather than fish.[54] However, when water levels are lower, crayfish will seek out shelter while fish become more highly concentrated and susceptible to predation. Therefore, fish are more vulnerable to being preyed upon by otters because the crayfish have become more difficult to obtain.[28]
Reptiles and amphibians
Amphibians, where regionally accessible, have been found in the North American river otter's diet during the spring and summer months, as indicated in many of the food habit studies.
Amphibians and reptiles are more obtainable by the North American river otter during the spring and summer as a result of breeding activity, appropriate temperatures, and water supply for the prey.[54]
Birds
Although they consume birds, North American river otters do not feed on bird eggs.[27]
Insects
Mammals
Mammals are rarely consumed by North American river otters, and are not a major dietary component.
Records of North American otters preying upon North American beavers (Castor canadensis) vary; it has been reported in the southern boreal forest of Manitoba.[56] Trappers in Alberta, Canada commonly assert North American river otters are major predators of North American beavers.[33] A 1994 river otter study reported findings of beaver remains in 27 of 1,191 scats analyzed.[33] However, many other studies did not report any findings of North American beaver remains in the scat sampled.[54][57]
Threats
Cases where otters have been ambushed and consumed by grizzly bears (Ursus arctos horribilis) and polar bears (Ursus maritimus) have also been reportedly witnessed near the Arctic region.[58][59][36][60]
Threats to North American river otter populations in North America vary regionally. North American river otter inhabitation is affected by type, distribution, and density of aquatic habitats and characteristics of human activities. Preceding the settlement of North America by Europeans, North American river otters were prevalent among aquatic habitats throughout most of the continent. Trapping, loss or degradation of aquatic habitats through filling of wetlands, and development of coal, oil, gas, tanning, timber, and other industries, resulted in
During the 1970s, improvements in natural resource management techniques emerged, along with increased concerns about North American river otter population declines in North America. Consequently, many wildlife management agencies developed strategies to restore or enhance otter populations, including the use of reintroduction projects. Since 1976, over 4,000 otters have been reintroduced in 21 U.S. states. All Canadian provinces except Prince Edward Island and 29 U.S. states have viable populations that sustain annual harvests. While current harvest strategies do not pose a threat to maintaining otter populations, harvest may limit expansion of otter populations in some areas.[1]
Conservation status
Lontra canadensis is listed in Appendix II of the
The North American river otter is considered a species of
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Further reading
- Kruuk, H. (2006). Otters: ecology, behaviour and conservation. Oxford: Oxford University Press. ISBN 0-19-856586-0. Recent monograph on otters in general, with many references to the river otter.
External links
- Media related to Lontra canadensis at Wikimedia Commons
- Data related to Lontra canadensis at Wikispecies