The
North American river otter (
Lontra canadensis), also known as the
northern river otter or the
common otter, is a semiaquatic
mammalMammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
endemic to the
North AmericanNorth American generally refers to an entity, people, group, or attribute of North America, especially of the United States and Canada together.-Culture:*North American English, a collective term used to describe American English and Canadian English...
continentA continent is one of several very large landmasses on Earth. They are generally identified by convention rather than any strict criteria, with seven regions commonly regarded as continents—they are : Asia, Africa, North America, South America, Antarctica, Europe, and Australia.Plate tectonics is...
, found in and along its waterways and coasts. An adult river otter can weigh between 5 and 14 kg (11 and 30 lb). The river otter is protected and insulated by a thick, water-repellent coat of fur.
The river otter, a member of the weasel family, is equally versatile in the water and on land. The otter establishes a
burrowA burrow is a hole or tunnel dug into the ground by an animal to create a space suitable for habitation, temporary refuge, or as a byproduct of locomotion. Burrows provide a form of shelter against predation and exposure to the elements, so the burrowing way of life is quite popular among the...
close to the water's edge in river, lake, swamp, coastal shoreline, tidal flat, or estuary ecosystems. Their dens have many tunnel openings, one of which generally allows the otter to enter and exit the body of water. Female otters give birth in these underground burrows, producing litters of one to six young.
North American river otters, like most predators, prey upon the species that are the most readily accessible.
FishFish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
is a favored food among the otters, but they also consume various amphibians, turtles, and
crayfishCrayfish, crawfish, or crawdads – members of the superfamilies Astacoidea and Parastacoidea – are freshwater crustaceans resembling small lobsters, to which they are related...
. There have been instances of river otters eating small mammals, as well.
The range of the North American river otter has been significantly reduced by habitat loss, beginning with the
European colonization of North AmericaThe start of the European colonization of the Americas is typically dated to 1492. The first Europeans to reach the Americas were the Vikings during the 11th century, who established several colonies in Greenland and one short-lived settlement in present day Newfoundland...
. In some regions, though, their population is controlled to allow the trapping and harvesting of otters for their
peltsFur is a synonym for hair, used more in reference to non-human animals, usually mammals; particularly those with extensives body hair coverage. The term is sometimes used to refer to the body hair of an animal as a complete coat, also known as the "pelage". Fur is also used to refer to animal...
. River otters are very susceptible to environmental pollution, which is a likely factor in the continued decline of their numbers. A number of reintroduction projects have been initiated to help stabilize the reduction in the overall population.
Taxonomy and evolution
The North American river otter was first described by German
naturalistNaturalism commonly refers to the philosophical viewpoint that the natural universe and its natural laws and forces operate in the universe, and that nothing exists beyond the natural universe or, if it does, it does not affect the natural universe that we know...
Johann Christian Daniel von SchreberJohann Christian Daniel von Schreber , often styled I.C.D. von Schreber, was a German naturalist.-Career:He was elected Professor of Materia medica at the University of Erlangen in 1769....
in 1777. The mammal was identified as a species of
otterThe Otters are twelve species of semi-aquatic mammals which feed on fish and shellfish, and also other invertebrates, amphibians, birds and small mammals....
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 river otter was first classified in the genus
LutraLutra is a genus of otters.*Lutra nippon - Japanese otter*Lutra sumatrana - Hairy-nosed otter*Lutra lutra - European otter-Habitat:Lutra are semi-aquatic mammals and therefore need to be well-adapted to both water and land...
:
Lutra was the early European name. The species name was
Lutra canadensis. The species epithet
canadensis means "of Canada".
In a new classification, the species is called
Lontra canadensis, where the genus
LontraLontra is a genus of otters from the American continent.The genus comprises four species:*North American River Otter *Southern River Otter *Neotropical Otter...
includes all the
New WorldThe New World is one of the names used for the Western Hemisphere, specifically America and sometimes Oceania . The term originated in the late 15th century, when America had been recently discovered by European explorers, expanding the geographical horizon of the people of the European middle...
river otters.
Molecular biological techniques have been used to determine when river otter and the giant otter having diverged. These analyses suggest that they diverged in the
MioceneThe Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
epoch 23.03 to 5.33 million years ago (Mya), which is "much earlier" than indicated in the fossil record. Fossils of a giant river 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 earliest known fossil of
Lontra canadensis was found in the US Midwest and is from the
IrvingtonianThe Irvingtonian North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology , typically set from 1,800,000 to 300,000 years BP, a period of . It is usually considered to overlap the Lower Pleistocene and Middle...
stage (the geologic timescale that spans the period 1,800,000 to 300,000 years ago). The oldest fossil record of an Old World river otter comes from the late
PlioceneThe Pliocene Epoch is the period in the geologic timescale that extends from 5.332 million to 2.588 million years before present. It is the second and youngest epoch of the Neogene Period in the Cenozoic Era. The Pliocene follows the Miocene Epoch and is followed by the Pleistocene Epoch...
epoch (3.6 to 1.8 Mya). The
New WorldThe New World is one of the names used for the Western Hemisphere, specifically America and sometimes Oceania . The term originated in the late 15th century, when America had been recently discovered by European explorers, expanding the geographical horizon of the people of the European middle...
river otters originated from the
Old WorldThe Old World consists of those parts of the world known to classical antiquity and the European Middle Ages. It is used in the context of, and contrast with, the "New World" ....
river otters after a migration across the
Bering Land BridgeThe Bering land bridge was a land bridge roughly 1,000 miles wide at its greatest extent, which joined present-day Alaska and eastern Siberia at various times during the Pleistocene ice ages. Like most of Siberia and all of Manchuria, Beringia was not glaciated because snowfall was extremely light...
, which existed off and on between 1.8 million to 10,000 years ago. The otters migrated to North America and southwards again across the
Panamanian Land BridgeThe Isthmus of Panama, also historically known as the Isthmus of Darien, is the narrow strip of land that lies between the Caribbean Sea and the Pacific Ocean, linking North and South America. It contains the country of Panama and the Panama Canal...
, which formed 3 Mya.
Subspecies
Listed alphabetically
- L. c. canadensis (Schreber, 1777) – (Eastern Canada, USA, Newfoundland)
- L. c. enudris – (Northern South America, throughout the Amazon Basin and rivers of eastern Brazil, Argentina, Trinidad)
- L. c. evexa (Goldman, 1935) – (British Columbia, western slope of Rocky Mountains)
- L. c. kodiacensis (Goldman, 1935) – (Kodiak Islands, Alaska)
- L. c. lataxina (Cuvier, 1823) – (USA)
- L. c. mira (Goldman, 1935) – (Alaska, British Columbia
- L. c. pacifica (J. A. Allen, 1898) – (Alaska, Canada, northern USA, south to central California, northern Nevada, and northeastern Utah)
- L. c. periclyzomae (Elliot, 1905) – (British Columbia)
- L. c. preblei (Goldman, 1935) – (Alberta, Saskatchewan, Manitoba)
- L. c. sonora (Rhoads, 1898) – (USA, Mexico)
Physical characteristics
The North American river otter is a stocky animal of 5 to 14 kg (11–31 lb), with short legs, a muscular neck no smaller than the head, and an elongated body that is broadest at the hips. An average adult male weighs about 11.3 kg (25 lbs) against the female's average of 8.3 kg (19 lbs). Its body length ranges from 0.66 m (26 in) to 1.07 m (42 in). About one-third of the animal's total length consists of a long, tapered tail. Tail length ranges from 30 to 50 cm (11.75 to 19.75 in). Large male North American river otters can exceed a weight of 15 kg (33 lbs). It differs from the
European otterThe European Otter , also known as the Eurasian otter, Eurasian river otter, common otter and Old World otter, is a European and Asian member of the Lutrinae or otter subfamily, and is typical of freshwater otters....
by its longer neck, narrower visage, the smaller space between the ears and its shorter tail.
A broad muzzle is found on the river otter's flat head, and the ears are round and inconspicuous. The
rhinariumThe rhinarium is the moist, naked surface around the nostrils of the nose in most mammals. In actual scientific usage it is typically called a "wet snout" or "wet nose" from its moist and shiny appearance...
is bare, with an obtuse, triangular projection. Eyes of the animal are small and placed
anteriorlyStandard anatomical terms of location are designations employed in science that deal with the anatomy of animals to avoid ambiguities that might otherwise arise. They are not language-specific, and thus require no translation...
. A short, broad
rostrumThe anterior end of the corpus callosum is named the genu, and is bent downward and backward in front of the septum pellucidum; diminishing rapidly in thickness, it is prolonged backward under the name of the rostrum, and is connected below with the lamina terminalis, which stretches from the...
for exhaling and a long, broad cranium define the relatively flat skull. The river otter's nostrils and ears close during submersion, inhibiting water from entering these regions. Its
vibrissaeVibrissae , or whiskers, are specialized hairs usually employed for tactile sensation. The term may also refer to the thick hairs found inside human nostrils, but these have no sensorial function and only operate as an airborne particulate barrier...
, or whiskers, are long and thick, enhancing sensory perception underwater and on land.
The fur of the species is short (guard hairs average 23.8 mm), with a density of about 57,800 hairs/cm
2 in the midback section. The pelage has a high luster and varies from light brown to black. The throat, chin, and lips are grayer than the rest of the body. Fur of senescent river otters may become white-tipped, and rare albinos may occur.
Sexual dimorphismSexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...
exists among the river otters. Males are, on average, 5% larger than females. In Idaho, juvenile, yearling, and adult males averaged 8, 11, and 17% heavier, respectively, than females of the same age. A clinical reduction in size may exist from north to south along the Pacific coast, but not from east to west.
North American river otters usually live 21 years of age in captivity, but they can reach 25 years of age. However, they normally live about 8 to 9 years in the wild, but are capable of living up to 13 years of age.
Form and function
The river otter is physically well-equipped for aquatic life. The ears are short, the neck is the same diameter as the head, the legs are short and powerful, the toes are fully webbed, and the tail (one-third of body length) is tapered. These qualities give the river otter a streamlined profile in water, but reduce agility on land. The smell and hearing abilities of the river otter are acute. The otter has a delicate sense of touch in the paws in addition to great dexterity.
The
lungThe lung is the essential respiration organ in many air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located near the backbone on either side of the heart...
s of the river otter are triangular in outline, with the apex directed
craniallyStandard anatomical terms of location are designations employed in science that deal with the anatomy of animals to avoid ambiguities that might otherwise arise. They are not language-specific, and thus require no translation...
. The right lung is larger than the left, and has four lobes compared with two for the left. Reduced lobulation of the lungs are presumed to be an adaption to aquatic life. In addition, the length of the
tracheaIn tetrapod anatomy the trachea, or windpipe, is a tube that connects the pharynx or larynx to the lungs, allowing the passage of air. It is lined with pseudostratified ciliated columnar epithelium cells with goblet cells that produce mucus...
of the river otter is intermediate between that of
terrestrialTerrestrial animals are animals that live predominantly or entirely on land , as compared with aquatic animals, which live predominantly or entirely in the water , or amphibians, which rely on a combination of aquatic and terrestrial habitats...
carnivoreA carnivore meaning 'meat eater' is an organism that derives its energy and nutrient requirements from a diet consisting mainly or exclusively of animal tissue, whether through predation or scavenging...
s and marine mammals. The mean tracheal length of the river otter is 15.3 cm, or 23.2% of the body length. A shorter trachea may improve air exchange and increase lung ventilation in diving mammals.
Most mustelids, including otters, have specialized teeth, including sharp
caninesIn mammalian oral anatomy, the canine teeth, also called cuspids, dogteeth, fangs, or eye teeth, are relatively long, pointed teeth...
and
carnassialCarnassials are large teeth found in many carnivorous mammals, used for shearing flesh and bone in a scissor- or shear-like way. In the Carnivora, the carnassials are the modified last upper premolar and the first molar, but in the prehistoric creodonts, the carnassials were further back in the...
s that inflict lethal bites to prey. Also, river otters have large
molarsMolars are the rearmost and most complicated kind of tooth in most mammals. In many mammals they grind food; hence the Latin name mola, "millstone"....
used for degenerating hard objects, such as the shells of molluscs. An adult river otter has a total of 36 teeth. Additional
premolarThe premolar teeth or bicuspids are transitional teeth located between the canine and molar teeth. In humans, there are two premolars per quadrant, making eight premolars total in the mouth. They have at least two cusps. Premolars can be considered as a 'transitional tooth' during chewing, or...
s may be present. The
dental formulaDentition pertains to the development of teeth and their arrangement in the mouth. In particular, the characteristic arrangement, kind, and number of teeth in a given species at a given age...
of an adult river otter is:
Behavior
The river otter is active year-round, and is most active at night and during
crepuscularCrepuscular animals are those that are active primarily during twilight, that is during dawn and dusk. The word is derived from the Latin word crepusculum, meaning "twilight." Crepuscular is, thus, in contrast with diurnal and nocturnal behavior. Crepuscular animals may also be active on a bright...
hours. The otter becomes much more nocturnal in the spring, summer, and fall seasons and it becomes more diurnal during winter. The otters may
emigrateEmigrate is a heavy metal band based in New York, led by Richard Z. Kruspe, the lead guitarist of the German band Rammstein.-History:Kruspe started the band in 2005, when Rammstein decided to take a year off from touring and recording...
as a result of food shortages or environmental conditions, but they do not migrate annually.
Movement
Otters swim by quadrupedal paddling, forelimb paddling, alternate hind-limb paddling, simultaneous hind-limb paddling, or body and tail dorsoventral undulation. The tail, which is stout and larger in surface area than the limbs, is used for stability while swimming and for short bursts of rapid propulsion. While swimming at the surface, the dorsal portion of the river otter's head, including nostrils, ears, and eyes, is exposed above water. The river otter must remain in motion to maintain its position at the surface.
On land, the river otter can walk, run, bound, or slide. Foot falls during walking and running follow the sequence of left limb, right limb, right limb, left limb. During walking, the limbs are moved in a plane parallel to the long axis of the body. Bounding is the result of simultaneous lifting of the limbs off the ground. As the front feet make contact with the ground, the back feet are lifted and land where the front paws first contacted the ground, producing a pattern of tracks in pairs typical of most mustelids. Sliding occurs mostly on even surfaces of snow or ice, but can also occur on grassy slopes and muddy banks. Sliding across snow and ice is a rapid and efficient means of travel, and otters traveling over mountain passes, between drainages, or descending from mountain lakes often slide continuously for several hundred meters. During winter, the river otters heavily use openings in the ice, and may excavate passages in beaver dams for accessing open water.
North American river otters are highly mobile and have the capacity of traveling up to 42 km in one day. Daily movements of yearling males and females in Idaho, averaged, respectively, 4.7 and 2.4 km in spring, 5.1 and 4.0 km in summer, and 5.0 and 3.3 km in autumn. Daily movements of family groups averaged 4.7, 4.4, and 2.4 km in spring, summer, and winter, respectively. Both males and family groups travel drastically less during winter.
Playing
River otters are renowned for their sense of play. Otter play mostly consists of wrestling with conspecifics. Chasing is also a common game. Playful behavior was found in only 6% of 294 observations in a study in Idaho, and was limited mostly to immature otters.
Hunting
Prey are captured with a quick lunge from ambush or, more rarely, after a sustained chase. River otters can remain underwater for nearly 4 minutes, swim at speeds approaching 11 km/h, dive to depths nearing 20 meters, and travel up to 400 meters while underwater. Several river otters may even cooperate while fishing. Small fish are eaten at the surface, but larger ones are taken to the shore to be consumed. Live fish are typically eaten from the head.
River otters dry themselves and uphold the insulative quality of their fur by frequent rubbing and rolling on grass, bare ground, and logs.
The river otter can be trained by humans to catch and retrieve fish,
duckDuck is the common name for a large number of species in the Anatidae family of birds, which also includes swans and geese. The ducks are divided among several subfamilies in the Anatidae family; they do not represent a monophyletic group but a form taxon, since swans and geese are not considered...
s (Anatidae), and
pheasantPheasants refer to some members of the Phasianinae subfamily of Phasianidae in the order Galliformes.Pheasants are characterised by strong sexual dimorphism, males being highly ornate with bright colours and adornments such as wattles and long tails. Males are usually larger than females and have...
s (
Phasianus colchicus) from land or water. Otter-fishing originated and has longest been practiced in Asia. China, Malaya, and India were the countries to make the most use of the otter. Among these countries, the Chinese seem to have been the first people to domesticate the otter and use it to catch fishes. A highly active predator, the river otter has adapted to hunting in water, and eats aquatic and semiaquatic animals. The vulnerability and seasonal availability of prey animals mainly governs the food habits and prey choices of the river otter. 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.
The diet of the river otter can be deduced by analyzing either scat obtained in the field, or gut contents removed from trapped otters.
Fishes are the primary component of the river otter's diet throughout the year. Every study done on the food habits of the 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 river otter scats collected during each season. Fish remnants were found present in 91.9% of the scat samples. Moreover, a western Oregon study revealed fish remains were present in 80% of 103 digestive tracts that had been examined. Crustaceans (crayfish), where regionally available, are the second most important prey for otters. Crustaceans may even be consumed more than fishes. 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. However, river otters, as foragers, will immediately take advantage of other prey when readily obtainable. Other prey consumed by river otters includes fruits, reptiles and amphibians, birds, aquatic insects, small mammals, and mollusks.
River otters are not scavengers; they avoid consuming
carrionCarrion refers to the carcass of a dead animal. Carrion is an important food source for large carnivores and omnivores in most ecosystems. Examples of carrion-eaters include vultures, hawks, eagles, hyenas, Virginia Opossum, Tasmanian Devils, coyotes, Komodo dragons, and burying beetles...
.
Otters do not dramatically reduce prey populations in the wild, generally speaking. When a copious supply of food dwindles or other prey become available, otters either transfer to a new location or convert their dietary choices to the most adequate prey. When left unchecked, though, otter depradations can be quite significant under certain circumstances (e.g. in hatcheries or other fish culture facilities). Likewise, the potential predatory impact of otters may be considerable whenever fishes are physically confined (most commonly in smaller ponds offering sparse cover or other escape options). Resolution of such conflicts will usually require removal and/or relocation of nuisance otters. Even in larger bodies of water, 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 such fast-swimming species as trout become lethargic in extremely cold water, with a commensurate increase in their vulnerability to predation. As such, careful consideration of any threatened, endangered, or fish species of special interest is warranted prior to reintroduction of otters to a watershed. Although other prey species are of temporary significance to the river otter, the deciding factor whether the river otter can establish itself as a permanent resident of one location is the year-round availability of fish.
There are reports of photographs of retrieving otters that were used by hunters near Butte, Nebraska.
Social structure
The North American river otter is more social than most mustelids. In all habitats, the basic river otter social group is the family, consisting of an adult female and her progeny. Adult males also commonly establish enduring social groupings that have been documented to comprise as many as 17 individuals. In coastal areas, males may remain gregarious even during the
estrous periodThe estrous cycle comprises the recurring physiologic changes that are induced by reproductive hormones in most mammalian placental females. Estrous cycles start after puberty in sexually mature females and are interrupted by anestrous phases or pregnancies...
of females. Family groups may include helpers, which can be made up of unrelated adults, yearlings, or juveniles.
Male otters disperse from such family groups more often than females. When females leave, they tend to move much further away (60–90 km) than males (up to 30 km), which tend to move shorter distances. Male river otters do not seem to be territorial, and newly dispersing males may join established male groups.
On occasion, groups of unrelated juveniles are observed. River otters living in groups hunt and travel together, use the same dens, resting sites, and latrines, and perform allogrooming. In freshwater systems, groups occur most often in autumn and during early winter. From mid-winter through the breeding season, adult females move and den alone. River otters are not territorial, but individual otters of different groups portray mutual avoidance. Home ranges of males are larger than those of females, and both sexes exhibit intra- and intersexual overlap of their domains.
Communication
Communication among North American river otters is accomplished mainly by olfactory and
auditoryHearing is the ability to perceive sound by detecting vibrations through an organ such as the ear. It is one of the traditional five senses...
signals. Scent marking is imperative for intergroup communication. The river otter scent-marks with feces, urine, and possibly anal sac secretions.
MuskMusk is a class of aromatic substances commonly used as base notes in perfumery. They include glandular secretions from animals such as the musk deer, numerous plants emitting similar fragrances, and artificial substances with similar odors. Musk was a name originally given to a substance with a...
from the scent glands may also be secreted when otters are frightened or angry.
The river otters can produce a snarling growl or hissing bark when bothered, and a shrill whistle when in pain. When at play or traveling, they sometimes give off a low purring grunt. The alarm call, given by an otter when shocked or distressed by potential danger, is an explosive snort, made by expelling air through the nostrils. River otters also may use a birdlike chirp for communication over longer distances, but the most common sound heard among a group of otters is low-frequency chuckling.
Reproduction and life cycle
North American river otters are polygynous. Females usually do not reproduce until two years of age, although yearlings produce offspring on occasion. Males are sexually mature at two years of age. The number of corpora lutea increases directly with age.
River otters typically breed from December to April. Copulation among river otters lasts from 16–73 minutes and may occur in water or on land. During the breeding, the male grabs the female by the neck with his teeth. Copulation is vigorous, and is interrupted by periods of rest. Females may caterwaul during or shortly after mating. Females are in heat for 42–46 days, and true
gestationGestation is the carrying of an embryo or fetus inside a female viviparous animal. Mammals during pregnancy can have one or more gestations at the same time ....
lasts 61–63 days. Because the otters delay implantation for at least eight months, the interval between copulation and parturition can reach 10–12 months. Delayed implantation is a trait that distinguishes the species from the European otter, which lacks this feature. Young are born between February and April, and parturition lasts three to eight hours.
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, like beavers, to provide suitable environments to raise their offspring. When the mothers have established their domain, they give birth to several kits. Litter size can reach five, but usually ranges from one to three. Each otter pup weighs approximately five ounces. At birth, the river otters are fully furred, blind, and toothless. The claws are well-formed and facial vibrissae (about 5 mm long) are present. The kits open their eyes after 30–38 days. The newborns start playing at five to six weeks, and begin consuming solid food at 9–10 weeks. Weaning occurs at 12 weeks, and females provide solid food for their progeny until 37–38 weeks have transpired. The maximum weight and length of both sexes are attained at three to four years of age.
The mothers raise their young without aid from adult males. When the pups are about two months old, their mother introduces them to the water. Otters are natural swimmers and, with parental supervision, they acquire the skills necessary to swim.
The 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 otter yearlings venture out in search of their own home ranges.
Geographic range
The Northern American river otter is found throughout North America, inhabiting inland waterways and coastal areas in Canada, the
Pacific NorthwestThe Pacific Northwest is a region in northwestern North America, bounded by the Pacific Ocean to the west and, loosely, by the Rocky Mountains on the east. Definitions of the region vary and there is no commonly agreed upon boundary, even among Pacific Northwesterners. A common concept of the...
, the
Atlantic statesThe East Coast of the United States, also known as the Eastern Seaboard, refers to the easternmost coastal states in the United States, which touch the Atlantic Ocean and stretch up to Canada. The term includes the U.S...
, and the
Gulf of MexicoThe Gulf of Mexico is a partially landlocked ocean basin largely surrounded by the North American continent and the island of Cuba. It is bounded on the northeast, north and northwest by the Gulf Coast of the United States, on the southwest and south by Mexico, and on the southeast by Cuba. In...
. River otters also currently inhabit coastal regions throughout the United States and Canada. North American river otters also inhabit the forested regions of the
Pacific coastA country's Pacific coast is the part of its coast bordering the Pacific Ocean.-The Americas:Countries on the western side of the Americas have a Pacific coast as their western border.* Geography of Canada* Geography of Chile* Geography of Colombia...
in North America. The species is also present throughout Alaska, including the
Aleutian Islands, and the north slope of the
Brooks RangeThe Brooks Range is a mountain range in far northern North America. It stretches from west to east across northern Alaska and into Canada's Yukon Territory, a total distance of about 1100 km . The mountains top out at over 2,700 m . The range is believed to be approximately 126 million years old...
.
However, urbanization and pollution instigated reductions in range area. They are now absent or rare in Arizona, Hawaii, Indiana, Kansas, Kentucky, Nebraska, New Mexico, North Dakota, Ohio, Oklahoma, South Dakota, Tennessee, and West Virginia. Reintroduction projects have expanded their distribution in recent years, especially in the
Midwestern United StatesThe Midwestern United States is one of the four U.S. geographic regions defined by the United States Census Bureau, providing an official definition of the American Midwest....
. In 2010, the Colorado Department of Wildlife reported the species, reintroduced in the 1980s, was "thriving" and recommended its protection status be reconsidered. In Canada, North American river otters occupy all provinces and territories, except for
Prince Edward IslandPrince Edward Island is a Canadian province consisting of an island of the same name, as well as other islands. The maritime province is the smallest in the nation in both land area and population...
.
Historical records indicate river otters were once populous throughout most major drainages in the continental United States and Canada prior to European settlement. North America’s largest otter populations were found in areas with an abundance and diversity of aquatic habitats, such as coastal marshes, the
Great LakesThe Great Lakes are a collection of freshwater lakes located in northeastern North America, on the Canada – United States border. Consisting of Lakes Superior, Michigan, Huron, Erie, and Ontario, they form the largest group of freshwater lakes on Earth by total surface, coming in second by volume...
region, and glaciated areas of
New EnglandNew England is a region in the northeastern corner of the United States consisting of the six states of Maine, New Hampshire, Vermont, Massachusetts, Rhode Island, and Connecticut...
. In addition, riverine habitats in interior regions supported smaller, but practical, otter populations. The otter existed on all parts of the Pacific coast, including the seashore and inlands streams and lakes. However, large populations never occurred in areas of
Southern CaliforniaSouthern California is a megaregion, or megapolitan area, in the southern area of the U.S. state of California. Large urban areas include Greater Los Angeles and Greater San Diego. The urban area stretches along the coast from Ventura through the Southland and Inland Empire to San Diego...
such as the
chaparral and oak woodlandsThe California chaparral and woodlands is a terrestrial ecoregion of lower northern, central, and southern California and northwestern Baja California , located on the west coast of North America...
and
Mojave DesertThe Mojave Desert occupies a significant portion of southeastern California and smaller parts of central California, southern Nevada, southwestern Utah and northwestern Arizona, in the United States...
seasonal waterway regions, or in the
xeric shrublandDeserts and xeric shrublands is a biome characterized by, relating to, or requiring only a small amount of moisture.-Definition and occurrence:...
regions in New Mexico, Texas, Nevada, and Colorado. In Mexico, the otters lived in the
Rio GrandeThe Rio Grande is a river that flows from southwestern Colorado in the United States to the Gulf of Mexico. Along the way it forms part of the Mexico – United States border. Its length varies as its course changes...
and
Colorado River DeltaThe Colorado River Delta is the region where the Colorado River flows into the Gulf of California . The delta is part of a larger geologic region called the Salton Trough. Historically, the interaction of the river’s flow and the ocean’s tide created a dynamic environment, supporting freshwater,...
s.
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 and marshes, and estuaries. It can tolerate a great range of temperature and elevations. A river otter's 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.
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. Den sites include burrows dug by woodchucks (
Marmota monax),
red foxThe red fox is the largest of the true foxes, as well as being the most geographically spread member of the Carnivora, being distributed across the entire northern hemisphere from the Arctic Circle to North Africa, Central America, and the steppes of Asia...
es (
Vulpes vulpes), nutria (
Myocastor coypus), or
beaverThe beaver is a primarily nocturnal, large, semi-aquatic rodent. Castor includes two extant species, North American Beaver and Eurasian Beaver . Beavers are known for building dams, canals, and lodges . They are the second-largest rodent in the world...
s, or beaver and
muskratThe muskrat , the only species in genus Ondatra, is a medium-sized semi-aquatic rodent native to North America, and introduced in parts of Europe, Asia, and South America. The muskrat is found in wetlands and is a very successful animal over a wide range of climates and habitats...
(
Ondatra zibethicus) lodges. River otters also may use hollow trees or logs, undercut banks, rock formations, backwater sloughs, and flood debris. The use of den and resting sites is chiefly opportunistic, although locations that provide protection and seclusion are preferred.
Population localization
Aquatic life ties North American river otters almost exclusively to permanent watersheds. The river otters favor
bogA bog, quagmire or mire is a wetland that accumulates acidic peat, a deposit of dead plant material—often mosses or, in Arctic climates, lichens....
lakes with banked shores containing semiaquatic mammal burrows and lakes with beaver lodges. The otters avoid water bodies with gradually sloping shorelines of sand or gravel. In Maine, use of watersheds by river otters is negatively associated with the proportion of mixed hardwood-softwood stands in forested areas adjacent to waterways. However, it is positively associated with the number of beaver flowages, watershed length, and average shoreline diversity. In Idaho, river otters prefer valley habitats over mountainous terrain, and they select valley streams over valley lakes, reservoirs, and ponds.
Log jamA log jam is an accumulation of Large Woody Debris that can span an entire stream or river channel.-Effects on stream/river geomorphology:...
s are heavily used by river otters when present. In Florida, inhabitation of North American river otters is lowest in freshwater marshes, intermediate in salt marshes, and highest in swamp forests. During the dry season, they will recede from the marshland and move to permanent ponds, where water is available and food is in greater supply. In Idaho and Massachusetts, ecological elements preferred for latrine sites include large conifers, points of land, beaver bank dens and lodges,
isthmusAn isthmus is a narrow strip of land connecting two larger land areas usually with waterforms on either side.Canals are often built through isthmuses where they may be particularly advantageous to create a shortcut for marine transportation...
es, mouths of permanent streams, or any object that protrudes from the water.
River otters often reside in beaver ponds, but encounters between otters and beavers may not be hostile. In Idaho, otters and beavers were recorded in the same beaver lodge simultaneously on three separate occasions. The otters may compete with the
American minkThe American mink is a semi-aquatic species of Mustelid native to North America, though human intervention has expanded its range to many parts of Europe and South America. Because of this, it is classed as Least Concern by the IUCN. Since the extinction of the sea mink, the American mink is the...
(
Mustela vison) for resources. In Alaska, the two species living in marine environments indicate niche separation through resource partitioning, probably related to the swimming abilities of these mustelids.
Fish
River otters consume an extensive assortment of fish species ranging in size from two to 50 centimeters (0.8 to 19.5 inches) that impart sufficient caloric intake for a minute amount of energy expenditure. River otters generally feed on prey that is in larger supply and easier to catch. As a result, slow-swimming fishes are consumed more often than
game fishGame fish are fish pursued for sport by recreational anglers. They can be freshwater or marine fish. Game fish can be eaten after being caught, though increasingly anglers practise catch and release to improve fish populations. Some game fish are also targeted commercially, particularly...
es when both are equally available. Slow-moving species include
suckersCatostomidae is the sucker family of the order Cypriniformes. There are 80 species in this family of freshwater fishes. Catostomidae are found in North America, east central China, and eastern Siberia...
(Catostomidae);
sunfishesThe sunfishes are a family of freshwater ray-finned fish belonging to the order Perciformes. The type genus is Centrarchus . The family's 27 species includes many fishes familiar to North Americans, including the rock bass, largemouth bass, bluegill, pumpkinseed, and crappies...
and
bassBass is a name shared by many different species of popular gamefish. The term encompasses both freshwater and marine species. All belong to the large order Perciformes, or perch-like fishes, and in fact the word bass comes from Middle English bars, meaning "perch."-Types of basses:*The temperate...
(Centrarchidae); and
dacesThe family Cyprinidae, from the Ancient Greek kyprînos , consists of the carps, the true minnows, and their relatives . Commonly called the carp family or the minnow family, its members are also known as cyprinids...
,
carpCarp are various species of oily freshwater fish of the family Cyprinidae, a very large group of fish native to Europe and Asia. The cypriniformes are traditionally grouped with the Characiformes, Siluriformes and Gymnotiformes to create the superorder Ostariophysi, since these groups have certain...
, and
shinersThe family Cyprinidae, from the Ancient Greek kyprînos , consists of the carps, the true minnows, and their relatives . Commonly called the carp family or the minnow family, its members are also known as cyprinids...
(Cyprinidae). For instance, Catostomidae are the primary dietary component of river otters in Colorado's Upper Colorado River Basin. Likewise, the
common carpThe Common carp is a widespread freshwater fish of eutrophic waters in lakes and large rivers in Europe and Asia. The wild populations are considered vulnerable to extinction, but the species has also been domesticated and introduced into environments worldwide, and is often considered an invasive...
(
Cyprinus carpio) is a preferred fish species for the otter in other regions of Colorado. Fish species that have frequently been found in the diet of the North American river otter include: Catostomidae, which consists of suckers (
CatostomusCatostomus is a genus of fish belonging to the family Catostomidae, commonly known as suckers.- Species :FishBase lists 27 species:* Catostomus ardens D. S. Jordan & C. H. Gilbert, 1881...
spp.) and redhorses (
Moxostoma spp.); Cyprinidae, made up of carp (
Cyprinus spp.),
chubsSemotilus is the genus of creek chubs, ray-finned fish in the Cyprinidae family. The term "creek chub" is sometimes used for individual species, particularly the Common Creek Chub, S. atromaculatus. The Creek Chub are a species of minnows that can grow from 6 to 10 inches and resemble the...
(
Semotilus spp.), daces (
Rhinichthys spp.), shiners (
Notropis and
Richardsonius spp.), and squawfishes (
Ptychocheilus spp.); and Ictaluridae, which consists of
bullheadsAmeiurus is a genus of catfishes in the family Ictaluridae. It contains the three common types of bullhead catfish found in waters of the United States, the black bullhead , the brown bullhead , and the yellow bullhead , as well as other species, such as the white catfish Ameiurus is a genus of...
and
catfishCatfishes are a diverse group of ray-finned fish. Named for their prominent barbels, which resemble a cat's whiskers, catfish range in size and behavior from the heaviest and longest, the Mekong giant catfish from Southeast Asia and the second longest, the wels catfish of Eurasia, to detritivores...
(
Ictalurus spp.). Other fishes an integral part of the river otter's diet are those that are often plentiful and found in large schools: sunfishes (
Lepomis spp.);
dartersThe fish popularly known as darters are small perch-like fish.They inhabit freshwater streams in North America. They are members of the family percidae and include members of the Ammocrypta, Crystallaria, Etheostoma and Percina genera....
(
Etheostoma spp.); and
perchPerch is a common name for fish of the genus Perca, freshwater gamefish belonging to the family Percidae. The perch, of which there are three species in different geographical areas, lend their name to a large order of vertebrates: the Perciformes, from the Greek perke meaning spotted, and the...
es (
Perca spp.). Bottom-dwelling species, which have the tendency to remain immobile until a predator is very close, are susceptible to river otters. These include mudminnows (
Umbra limi) and
sculpinA Sculpin is a fish that belongs to the order Scorpaeniformes, suborder Cottoidei and superfamily Cottoidea, that contains 11 families, 149 genera, and 756 species...
s (
Cottus spp.). Game fishes, such as
troutTrout is the name for a number of species of freshwater and saltwater fish belonging to the Salmoninae subfamily of the family Salmonidae. Salmon belong to the same family as trout. Most salmon species spend almost all their lives in salt water...
(Salmonidae) and pike (Esocidae), are not a significant component of the river otter's diet. They are less likely to be prey for the North American river otters since they are fast-swimming and can find good escape cover. However, river otters will prey on trout, pike,
walleyeWalleye is a freshwater perciform fish native to most of Canada and to the northern United States. It is a North American close relative of the European pikeperch...
(
Sander vitreus vitreus),
salmonSalmon is the common name for several species of fish in the family Salmonidae. Several other fish in the same family are called trout; the difference is often said to be that salmon migrate and trout are resident, but this distinction does not strictly hold true...
(
Oncorhynchus spp.), and other game fishes during
spawningSpawn refers to the eggs and sperm released or deposited, usually into water, by aquatic animals. As a verb, spawn refers to the process of releasing the eggs and sperm, also called spawning...
.
Adult river otters are capable of consuming 1 to 1.5 kilograms (2 to 3 pounds) of fishes per day. A study conducted on captive otters revealed they preferred larger fishes, ranging from 15 to 17 centimeters (6 to 7 inches), more than smaller fishes, ranging from 3 to 4 inches (8–10 centimeters), and they had difficulty catching fish species less than 10 centimeters (4 inches) or larger than 17 centimeters (7 inches). Otters are known to take larger fishes on land to eat, whereas smaller fishes are consumed in the water.
Crustaceans
Otters may prefer to feed on crustaceans, especially
crayfishCrayfish, crawfish, or crawdads – members of the superfamilies Astacoidea and Parastacoidea – are freshwater crustaceans resembling small lobsters, to which they are related...
(
CambarusCambarus is a large and diverse genus of North American crayfish. The adults range in size from about up to approximately .-Classification:...
,
Pacifasticus, and others) more than fish where they are locally and seasonally plentiful. In Georgia, crayfish accounted for two-thirds of the prey in the summer diet, and their remnants were present in 98% of the summer
spraintSpraint or scat is the dung of the otter.Spraints are typically identified by smell and are known for their distinct aromas, the smell of which has been described as ranging from freshly mown hay to putrefied fish....
. In the winter, crayfish made up one-third of the otter's diet. A study conducted on North American river otters in a southwestern Arkansas swamp identified a correlation between crayfish consumption, fish consumption, and water levels.
During the winter and spring, when the water levels were higher, otters had a greater tendency to prey upon crayfish (73% of scats had crayfish remains) rather than fish. 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.
Reptiles and amphibians
Amphibians, where regionally accessible, have been found in the river otter's diet during the spring and summer months, as indicated in many of the food habit studies. The most common amphibians recognized were
frogFrogs are amphibians in the order Anura , formerly referred to as Salientia . Most frogs are characterized by a short body, webbed digits , protruding eyes and the absence of a tail...
s (
Rana and
Hyla). Specific species of reptiles and amphibians prey include: boreal chorus frogs (
Pseudacris maculata);
Canadian toadThe Canadian Toad is a species of toad that ranges from the prairie regions of central Canada south to parts of United States upper midwest. Its name is derived from the Latin words bufonis, meaning toad, and hemiophrys, meaning eyebrow, which refers to its pronounced cranial crest between and...
s (
Bufo hemiophrys);
wood frogThe Wood Frog has a broad distribution over North America, extending from the southern Appalachians to the boreal forest with several notable disjunct populations including lowland eastern North Carolina...
s (
Rana sylvatica);
bullfrogThe American bullfrog , often simply known as the bullfrog in Canada and the United States, is an aquatic frog, a member of the family Ranidae, or “true frogs”, native to much of North America. This is a frog of larger, permanent water bodies, swamps, ponds, and lakes, where it is usually found...
s (
Rana catesbeiana);
green frogThe Green Frog is a species of frog native to the eastern half of the United States and Canada. There are two subspecies—the Bronze Frog and the Northern Green Frog.-Description:...
s (
Rana clamitans); northwestern salamanders (
Ambystoma gracile);
Pacific giant salamanderPacific giant salamanders are a family of large salamanders.The family includes only a single genus, Dicamptodon. The genus was formerly thought to contain two species, Cope's Giant Salamander on the Olympic Peninsula, Washington, and the Pacific giant salamander Pacific giant salamanders...
(
Dicamptodon ensatus);
rough-skinned newtThe rough-skinned newt is a North American newt known for its strong poison.- Toxicity :Many newts produce toxins to avoid predation, but the toxins of the genus Taricha are particularly potent...
(
Taricha granulosa); and
garter snakeThe Garter snake is a Colubrid snake genus common across North America, ranging from Alaska and Canada to Central America. It is the single most widely distributed genus of reptile in North America. The garter snake is also the Massachusettsstate reptile.There is no real consensus on the...
s (Thamnophis).
Amphibians and reptiles are more obtainable by the river otter during the spring and summer as a result of breeding activity, appropriate temperatures, and water supply for the prey.
Birds
WaterfowlWaterfowl are certain wildfowl of the order Anseriformes, especially members of the family Anatidae, which includes ducks, geese, and swans....
,
railsThe rails, or Rallidae, are a large cosmopolitan family of small to medium-sized birds. The family exhibits considerable diversity and the family also includes the crakes, coots, and gallinules...
, and some colonial nesting birds are preyed upon by otters in various areas. Susceptibility of these species is greatest during the summer (when waterfowl broods are vulnerable) and autumn. The otters have also been known to catch and consume moulting
American wigeonThe American Wigeon, also American Widgeon or Baldpate, is a species of wigeon in the dabbling duck genus Anas. If this is split up, all wigeons will go into their old genus Mareca again...
(
Mareca americana) and
green-winged tealThe Green-winged Teal is a common and widespread duck that breeds in the northern areas of North America except on the Aleutian Islands. It was considered conspecific with the Common Teal The Green-winged Teal (Anas carolinensis) is a common and widespread duck that breeds in the northern areas of...
(
Anas crecca). Other species of birds found within their diet include:
northern pintailThe Pintail or Northern Pintail is a widely occurring duck which breeds in the northern areas of Europe, Asia and North America. It is strongly migratory and winters south of its breeding range to the equator...
(
Anas acuta);
mallardThe Mallard , or Wild Duck , is a dabbling duck which breeds throughout the temperate and subtropical Americas, Europe, Asia, and North Africa, and has been introduced to New Zealand and Australia....
(
Anas platyrhynchos);
canvasbackThe Canvasback is the largest of the North American diving ducks, that ranges from between long and weighs approximately , with a wingspan of . The canvasback has a distinctive wedge-shaped head and long graceful neck. The adult male has a black bill, a chestnut red head and neck, a black...
(
Aythya valisineria);
ruddy duckThe Ruddy Duck is a small stiff-tailed duck.Their breeding habitat is marshy lakes and ponds throughout much of North America, and in South America in the Andes. They nest in dense marsh vegetation near water. The female builds her nest out of grass, locating it in tall vegetation to hide it from...
(
Oxyura jamaicensis); and the
American cootThe American Coot is a bird of the family Rallidae, inhabiting wetlands and open water bodies. Measuring in length and across the wings, adults have a short thick white bill and white frontal shield, which usually has a reddish-brown spot near the top of the bill between the eyes...
(
Fulica americana).
Although they consume birds, river otters do not feed on bird eggs.
Insects
Aquatic invertebratesAquatic insects live some portion of their life cycle in the water. They feed in the same ways as other insects. Some diving insects, such as predatory diving beetles, can hunt for food underwater where land-living insects cannot compete.-Breathing:...
have been recognized as an integral part of the river otter's diet. Otters consume more aquatic insects in the summer as the invertebrate populations increase and specific life stages heighten their susceptibility. Most aquatic invertebrates preyed upon by the river otter are from the families Odonata (dragonfly nymphs), Plecoptera (stonefly nymphs), and Coleoptera (adult beetles). Invertebrates discovered within scats or digestive tracts could most likely be a secondary food item, first being consumed by the fish that are subsequently preyed upon by the otters.
Mammals
Mammals are rarely consumed by river otters, and are not a major dietary component. Mammals preyed upon by otters are characteristically small or are a type species found in riparian zones. The few occurrences of mammals found in the river otter's diet include: muskrats (
Ondatra zibethicus);
meadow voleThe Meadow Vole , sometimes called the Field Mouse or Meadow Mouse, is a North American vole found across Canada, Alaska and the northern United States. Its range extends further south along the Atlantic coast. One subspecies, the Florida Salt Marsh Vole , is found in Florida, and is classified as...
s (
Microtus pennsylvanicus);
eastern cottontailThe eastern cottontail is a New World cottontail rabbit, a member of the family Leporidae. It is one of the most common rabbit species in North America.-Distribution:...
s (
Sylvilagus floridanus); and
snowshoe hareThe Snowshoe Hare , also called the Varying Hare, or Snowshoe Rabbit, is a species of hare found in North America. It has the name "snowshoe" because of the large size of its hind feet and the marks its tail leaves. The animal's feet prevent it from sinking into the snow when it hops and walks...
s (
Lepus americanus).
There are varying records of otters preying upon beavers (
Castor canadensis). Otter predation on beavers has been reported in the southern boreal forest of Manitoba. Trappers in Alberta, Canada commonly assert that otters are major predators of beavers. A 1994 river otter study reported findings of beaver remains in 27 of 1,191 scats analyzed. However, many other studies did not report any findings of beaver remains in the scat sampled.
Threats
The otter has few natural predators when in water. Aquatic predators include the
alligatorAn alligator is a crocodilian in the genus Alligator of the family Alligatoridae. There are two extant alligator species: the American alligator and the Chinese alligator ....
(
Alligator mississippiensis),
American crocodileThe American crocodile is a species of crocodilian found in the Neotropics. It is the most widespread of the four extant species of crocodiles from the Americas. Populations occur from the Atlantic and Pacific coasts of southern Mexico to South America as far as Peru and Venezuela. It also lives...
(
Crocodylus acutus), and killer whale (
Orcinus orca). On land or ice, the river otter is considerably more vulnerable. Terrestrial predators include: the
bobcatThe bobcat is a North American mammal of the cat family Felidae, appearing during the Irvingtonian stage of around 1.8 million years ago . With twelve recognized subspecies, it ranges from southern Canada to northern Mexico, including most of the continental United States...
(
Lynx rufus), mountain lion (
Felis concolor),
coyoteThe coyote , also known as the American jackal or the prairie wolf, is a species of canine found throughout North and Central America, ranging from Panama in the south, north through Mexico, the United States and Canada...
(
Canis latrans), domestic dog (
Canis lupus familiaris),
gray wolfThe gray wolf , also known as the wolf, is the largest extant wild member of the Canidae family...
(
Canis lupus),
red foxThe red fox is the largest of the true foxes, as well as being the most geographically spread member of the Carnivora, being distributed across the entire northern hemisphere from the Arctic Circle to North Africa, Central America, and the steppes of Asia...
, and
black bearThe American black bear is a medium-sized bear native to North America. It is the continent's smallest and most common bear species. Black bears are omnivores, with their diets varying greatly depending on season and location. They typically live in largely forested areas, but do leave forests in...
(
Ursus americanus). Most river otter mortality is caused by human-related factors, such as trapping, illegal shooting, roadkills, and accidental captures in fish nets or set lines. Accidental deaths may be the result of ice flows or shifting rocks. Starvation may occur due to excessive tooth damage.
Threats to otter populations in North America vary regionally. 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 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 extirpations, or declines, in otter populations in many areas. In 1980, an examination conducted on U.S. river otter populations determined they 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 fewer otter populations. Although the distribution became reduced in some regions of southern Canada, the only province-wide extirpation occurred on
Prince Edward IslandPrince Edward Island is a Canadian province consisting of an island of the same name, as well as other islands. The maritime province is the smallest in the nation in both land area and population...
.
During the 1970s, improvements in natural resource management techniques emerged, along with increased concerns about 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. Annual harvest numbers of northern river otters are similar for Canada and the United States, with most pelts being used in the garment industry. In the late 1970s, annual harvest in North America reached approximately 50,000 pelts, for a value of US$3 million. Otters are inadvertently harvested by traps set for beavers, and therefore management plans should consider both species simultaneously. While current harvest strategies do not pose a threat to maintaining otter populations, harvest may limit expansion of otter populations in some areas. Otter harvests correlate positively with the beaver harvests and with the average beaver pelt price from the preceding year. Fur of the river otter is thick and lustrous and is the most durable of native American furs. River otter pelts are used as the standard for rating the quality of other pelts.
Oil spills present a localized threat to otter populations, especially in coastal areas. Water pollution and other diminution of aquatic and wetland habitats may limit distribution of otters and pose long-term threats if the enforcement of water quality standards is not upheld. Acid drainage from coal mines is a persistent water quality issue in some areas, as it eliminates otter prey. This dilemma prevents, and consequently inhibits, recolonization or growth of otter populations. Recently, there has been discussion of long-term genetic consequences of reintroduction projects on remnant otter populations. Similarly, many perceived threats to otters, such as pollution and habitat alterations, have not been rigorously evaluated. Little study has gone into assessing the threat of disease to wild river otter populations, so it is poorly understood and documented. River otters may be victims of
canine distemperCanine distemper is a viral disease that affects animals in the families Canidae, Mustelidae, Mephitidae, Hyaenidae, Ailuridae, Procyonidae, Pinnipedia, some Viverridae and Felidae...
,
rabiesRabies is a viral disease that causes acute encephalitis in warm-blooded animals. It is zoonotic , most commonly by a bite from an infected animal. For a human, rabies is almost invariably fatal if post-exposure prophylaxis is not administered prior to the onset of severe symptoms...
, respiratory tract disease, and urinary infection. In addition, North American river otters can contract
jaundiceJaundice is a yellowish pigmentation of the skin, the conjunctival membranes over the sclerae , and other mucous membranes caused by hyperbilirubinemia . This hyperbilirubinemia subsequently causes increased levels of bilirubin in the extracellular fluid...
,
hepatitisHepatitis is a medical condition defined by the inflammation of the liver and characterized by the presence of inflammatory cells in the tissue of the organ. The name is from the Greek hepar , the root being hepat- , meaning liver, and suffix -itis, meaning "inflammation"...
, feline panleucopenia, and
pneumoniaPneumonia is an inflammatory condition of the lung—especially affecting the microscopic air sacs —associated with fever, chest symptoms, and a lack of air space on a chest X-ray. Pneumonia is typically caused by an infection but there are a number of other causes...
. They host numerous endoparasites, such as nematodes, cestodes, trematodes, the sporozoan
Isopora, and
acanthocephalaAcanthocephala is a phylum of parasitic worms known as acanthocephales, thorny-headed worms, or spiny-headed worms, characterized by the presence of an evertable proboscis, armed with spines, which it uses to pierce and hold the gut wall of its host...
ns. Ectoparasites include ticks, sucking lice(
Latagophthirus rauschi), and
fleaFlea is the common name for insects of the order Siphonaptera which are wingless insects with mouthparts adapted for piercing skin and sucking blood...
s (
Oropsylla arctomys).
Conservation status
Lontra canadensis is listed in Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). River otters have been virtually eliminated through many parts of their range, especially around heavily populated areas in the midwestern and eastern United States. Appendix II lists species that are not necessarily threatened with extinction currently, but may become so unless trade is closely controlled.
The North American river otter is considered a species of Least Concern according to the IUCN Redlist, as it is not currently declining at a rate sufficient for a threat category. By the early 1900s, river otter populations had declined throughout large portions of their historic range in North America. However, improvements in water quality (through enactment of clean water regulations) and furbearer management techniques have permitted river otters to regain portions of their range in many areas. Reintroduction projects have been particularly valuable in restoring populations in many areas of the United States. However, river otters remain rare or absent in the southwestern United States. Water quality and development inhibit recovery of populations in some areas. The species is widely distributed throughout its range. In many places, the populations have re-established themselves because of conservation initiatives. Reintroduction of river otters may present a problem in that it may contaminate the genetic structure of the native population.
Habitat degradation and pollution are major threats to their conservation; river otters are highly sensitive to pollution and readily accumulate high levels of
mercuryMercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...
,
organochlorideAn organochloride, organochlorine, chlorocarbon, chlorinated hydrocarbon, or chlorinated solvent is an organic compound containing at least one covalently bonded chlorine atom. Their wide structural variety and divergent chemical properties lead to a broad range of applications...
compounds, and other chemical elements. The species is often used as a
bioindicatorBiological indicators are species used to monitor the health of an environment or ecosystem. They are any biological species or group of species whose function, population, or status can be used to determine ecosystem or environmental integrity. An example of such a group are the copepods and other...
because of its position at the top of the food chain in aquatic ecosystems. Environmental disasters, such as oil spills, may increase levels of blood
haptoglobinHaptoglobin is a protein that in humans is encoded by the HP gene. In blood plasma, haptoglobin binds free hemoglobin released from erythrocytes with high affinity and thereby inhibits its oxidative activity. The haptoglobin-hemoglobin complex will then be removed by the reticuloendothelial system...
and interleukin-6 immunoreactive protein, but decrease body mass. Home ranges of river otters increase in size on oiled areas compared to non-oiled areas, and individual otters also modify their habitat use. Declines in the richness and
diversityBiodiversity is the degree of variation of life forms within a given ecosystem, biome, or an entire planet. Biodiversity is a measure of the health of ecosystems. Biodiversity is in part a function of climate. In terrestrial habitats, tropical regions are typically rich whereas polar regions...
of prey species may explain these changes.
External links