Northern River Otter

The North American River Otter, Lontra canadensis, also known as the Northern River Otter, is a North American member of the Mustelidae, or weasel, family. It is a common animal in North American waterways, but its population has significantly dropped ever since Europeans came to colonize the Americas.²

Taxonomy

The North American river otter is a species of otter. It is a member of the genus Lontra, which is comprised of New World otters. It was previously included, with the other members of Lontra, in the genus Lutra, but was placed in a newly-created genus when it was determined that the New World otters are more closely related to the genera Lutrogale and Pteronura than to the other species in Lutra.

Description

The Northern Otter has a streamlined, muscular body with short legs, webbed toes, and a long muscular tail. The North American river otter’s body length is somewhere between 0.66m (26") to 1.07m (42"), and its tail length is between 0.30m (12") to 0.46m (18"). A river otter’s tail makes up 30 to 40% of the total length of its body. It can weigh between 3 kg and 14 kg (6 and 31 pounds). The river otter has a round, small head, short, powerful legs, and long whiskers. The vibrissae are long and thick, as they are essential for sensory perception. The otter also has nostrils and ears that close while underwater. The fur is dark brown on the posterior (dorsal) side and is a lighter shade on the anterior (ventral) side. Also, the fur is dense and water repellent, serving as an effective insulator for the animal on land and in water. Otters remain active during the winter season, using ice holes to breathe at the surface of the water. They can hold their breath for up to eight minutes.³

Otters display sexual dimorphism, as the male otter is typically larger than the female in all physical aspects. ⁴

Geographic range

North American river otters once existed throughout Canada and the United States, except for areas of southern California, New Mexico, and Texas, as well as the Mohave desert regions of Nevada and Colorado. In Mexico, the otters live in the delta areas of the Rio Grande and Colorado rivers. These otters are now rare or locally extinct throughout much of the eastern, central, and southern United States. ⁵

Habitat

Although commonly called a "river otter", the name can be misleading, as it inhabits marine as well as freshwater environments, and the freshwater environments include standing bodies of water such as lakes. Some populations permanently reside in marine shoreline habitats, and are often mistaken for sea otters. River otters can be distinguished from sea otters by the former's narrower faces and differences in behavior: Sea otters always eat floating on their backs in the water, whereas river otters bring their prey ashore to eat.^{citation needed}

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 and marshes, and estuaries. It can tolerate a great range of temperature and elevations; its main requirements are a steady food supply and easy access to a body of water. However, the North American river otter is sensitive to pollution, and will disappear from polluted areas. ⁶

Like other otters, the North American river otter lives in a holt, or den. The den is 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.⁷

Diet

The North American river otter is a carnivore. It mainly eats fish, but also insects, frogs, crustaceans and sometimes small mammals. On occasion some larger river otters will attack and kill water birds such as ducks, geese, and even herons. During their formative years, the fur on the underbelly of the otter acts as a filter as the otter swims, trapping small food items for later consumption. The North American river otter is capable of swimming in circles, which creates a whirlpool-like motion that brings fish from the bottom of the water up to the top. It is generally nocturnal or crepuscular, but is diurnal, active during the day, where undisturbed by human activity. It uses musk and urine to mark the land bordering its territory. This type of behavior is called sprainting.

Reproduction

In early spring, expectant mothers begins to look for a den for their pups. The female otters do not dig their own den. Instead, they rely on other animals, like beavers, to provide suitable environment to raise their offspring. Once they have settled in, they give birth to several tiny pups. One to six pups can be produced, but a normal litter size is two to four pups. Each baby weighs approximately five ounces. The pups are helpless at birth and incapable of surviving on their own. Their eyes are closed and they are covered with a light coat of fur. After three or four weeks, the pups open their eyes, and their social behavior begins to develop, which is marked by playing. Males do not aid the mother to raise young otters. When the pups are about two months old, their mother subjects them to the water. Otters are natural swimmers and, with parental supervision, they acquire the skills necessary to swim.⁸ and the otters may leave the den by eight to ten weeks of age. The pups fully weaned by ten weeks. The young otters are finally capable of fending for 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 otter yearlings venture out in search of their own home ranges.

Breeding season comes right after the females give birth. It usually lasts about three months. As soon as they are bred, female otters go through a process known as delayed implantation. Instead of going into gestation right away, the embryos remain dormant in the mother’s uterus for about nine months. The actual gestation period lasts about two months.⁹

Threats

Threats to otter populations in North America vary among regions. 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, otters were prevalant among aquatic habitats throughout most of the continent.¹⁰ Unregulated trapping, loss or degradation of aquatic habitats through filling of wetlands, and development of coal, oil, gas, tanning, timber, and other industries, resulted in extirpations, or declines, in otter populations in many areas.¹¹ Nilsson (1980) reviewed the status of otters in the United States and determined that populations were extirpated in 11 states and had experienced drastic lapses in 9 other states. The most severe population declines occurred in interior regions where fewer aquatic habitats supported smaller fewer otter populations. Although the distribution of otters became reduced in some regions of southern Canada, the only province-wide extirpation occurred on Prince Edward Island.¹²

During the 1970’s, improvements in natural resource management techniques emerged along with raised concerns about otter population declines in North America.¹³ Consequently, many wildlife management agencies developed strategies to restore or enhance otter populations, including the use of reintroduction projects.¹⁴ Since 1976 over 4,000 otters have been reintroduced among 21 states. Also, 29 states and all Canadian provinces except Prince Edward Island have viable populations that sustain annual harvests. Annual harvest numbers of Northern river otters are similar for Canada and the United States¹⁵, with most pelts being used in the garment industry.¹⁶ In the late 1970s, annual harvest in North America reached ca. 50,000 pelts, for a value of U.S. $3 million.¹⁷ Otters are incidentally harvested by traps set for beavers¹⁸, and therefore management plans should consider both species simultaneously.¹⁹ While current harvest strategies do not pose a threat to maintaining otter populations, harvest may limit expansion of otter populations in some areas. ²⁰

Oil spills present a localized threat to otter populations, especially in coastal areas. Water pollution and other dimunition of aquatic and wetland habitats may moderate distribution of otters and pose long-term threats if thr enforcement of water quality standards is not upheld. Acid drainage from coal mines is a persistent water quality issue in some areas that eliminates otter prey prevents thereby inhibits recolonization or expansion of otter populations. Recently, there has been discussion of the long-term genetic consequences of reintroduction projects on remnant otter populations.²¹ Similarly, many perceived threats to otters such as pollution and habitat alterations have not been rigorously evaluated. The threat of disease to wild otter populations is poorly understood and has received little study.²² Lontra canadensis may be victim of canine distemper²³, rabies²⁴, respiratory tract disease, and urinary infection²⁵. In addition, North American river otters can contract jaundice, hepatitis, feline panleucopenia, and pneumonia²⁶. North American river otters host numerous endoparasites such as nematodes²⁷, cestodes²⁸, trematodes²⁹, the sporozoan Isopora³⁰, and acanthocephalans³¹. Ectoparasites include ticks³², sucking lice Latagophthirus rauschi³³, and the flea Oropsylla arctomys³⁴. ³⁵

Conservation status

North American river otters are trapped for their highly-prized fur. Over-harvest in the 1800s has led to its disappearance from many parts of its historical range. Trapping is still permitted in some areas where otters remain abundant. In other areas, the otter is being restored to places where it may have long since been extirpated, such as the Hudson River. The North American river otter is not a nationally endangered species, but it is endangered in many states and it is listed as threatened by others. Over-hunting, habitat destruction, and inadequate laws protecting the North American river otter are major factors where otters remain threatened. Since the discovery of the Americas, hunters have captured and killed the otters for their pelts. Hunting still continues today, with otter pelts being worth over $100 (USD) each. Over 30,000 otter pelts are sold each year in the United States and Canada. Efforts have been made to bring the otter back from endangerment. Since 1986, the National Park Service has reintroduced over 100 North American River Otters back into the wild. ²

Like its relatives, the weasels, the North American River Otter is a highly active predator.

Care in captivity

The North American River Otter is very playful, with typical behavioral traits including chasing, sliding, swimming, jumping, and wrestling. These characteristics make the otter popular for zoo exhibits. However, otters are not friendly towards humans if raised in captivity. Captive river otters (especially males) can begin to act defensively and become very aggressive toward humans when they reach sexual maturity. Thus, otters do not make good pets. There are times when otters have remained tame through their adult life. However, "tame" is a relative term; even the most human-friendly otter will still bite and scratch, sometimes quite badly. They can be highly curious animals and have been known to follow trout fisherman along the shoreline opposite from the inhabited bank.^{citation needed}

Otters are only suited for professional exhibits or care. Their diet is flexible. Some groups feed their otters a variety of fresh water creatures in addition to live fish, while others live on a diet of processed meats. They need access to fresh water deep enough to swim and play in, and this water will need to be changed regularly or filtered. Some groups add chlorine to the water to reduce bacteria and algae growth, but this may result in skin problems for the otter. Since otters are very active, they are easy to train for medical exams, demonstrations, and behavioral enrichment. Commonly used objects in enrichment processes include ice with food frozen in it, floating balls, and segments of wide pipe.

Notes

^ Serfass (2004). Lontra canadensis. 2007 IUCN Red List of Threatened Species. IUCN 2007. Retrieved on 06 May 2008. Database entry includes justification for why this species is of least concern
^ ^a ^b Linzey, 2002^who?
^ "North American River Otter", National Geographic Society. Retrieved on 17 November 2008.
^ Dewey, Tanya; E. Ellis (2003). "Lontra canadensis", Animal Diversity Web. Retrieved on 17 November 2008.
^ Dewey, Tanya; E. Ellis (2003). "Lontra canadensis", Animal Diversity Web. Retrieved on 17 November 2008.
^ Dewey, T. and E. Ellis. "Lontra canadensis". Retrieved on 2007-05-25.
^ Kim A. Cabrera. "River Otter". Retrieved on 2007-05-25.
^ "North American River Otter", National Geographic Society. Retrieved on 17 November 2008.
^ Orr, Eric. "North American River Otter", Chattooga Conservancy, Inc.. Retrieved on 17 November 2008.
^ Hall 1981
^ Toweill and Tabor 1982, Melquist and Dronkert 1987
^ Polechla 1990
^ Endangered Species Scientific Authority 1978
^ Ralls 1990; Serfass et al. 1993
^ Obbard 1987
^ Toweill and Tabor, 1982
^ Melquist and Dronkert, 1987
^ Toweill and Tabor, 1982
^ Polechla, 1990
^ Lariviere and Walton 1998
^ Serfass et al. 1998
^ Serfass et al. 1995
^ Harris 1968; Park 1971
^ Serfass et al. 1995
^ Hoover et al. 1984; Route and Peterson 1991
^ Harris, 1968
^ Hoberg et al. 1997
^ Greer 1955
^ Hoover et al. 1984
^ Hoover et al. 1984
^ Hoberg et al. 1997; Hoover et al. 1984
^ Eley 1977; Serfass et al. 1992
^ Kim and Emerson 1974
^ Serfass et al. 1992
^ Sefass, T. and P. Polechla. "Lontra canadensis". 2008 IUCN Red List of Threatened Species. Retrieved on 2008-11-15.

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