continent found in and along its waterways and coasts. An adult river otter can weigh between 5.0 and 14 kg (11.0 and 30.9 lb). The river otter is protected and insulated by a thick, water-repellent coat of fur.
close to the water's edge in river, lake, swamp, coastal shoreline, tidal flat, or estuary ecosystems. The den typically has many tunnel openings, one of which generally allows the otter to enter and exit the body of water. 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 most readily accessible species.
Instances of river otters eating small mammals, such as mice and squirrels, and occasionally birds have been reported as well.
The range of the North American river otter has been significantly reduced by habitat loss, beginning with the
European otter by its longer neck, narrower visage, the smaller space between the ears and its shorter tail.
[17]
A broad muzzle is found on the river otter's flat head, and the ears are round and inconspicuous. The
vibrissae (whiskers) are long and thick, enhancing sensory perception underwater and on land.
[11]
The fur of the species is short (guard hairs average 23.8 mm (0.94 in)), with a density of about 57,800 hairs/cm2 (373,000 hairs/in2 ) in the midback section. The
senescent river otters may become white-tipped, and rare albinos may occur.
[11]
Sexual dimorphism exists among the river otters.[18] 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.[11]
North American river otters live an average of 21 years of age in captivity,[18] but they can reach 25 years of age.[11] However, they normally live about 8 to 9 years in the wild,[18] but are capable of living up to 13 years of age.[11]
Form and function
The river otter's sensitive whiskers allow it to detect prey in murky water. Note the inconspicuous ears.
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.[11] River otters characteristically approach within a few feet of a boat or a person on shore because they're near-sighted, a consequence of vision adapted for underwater sight. River otters have transparent nictitating membranes to protect their eyes while swimming.[6] [19] [20]
The right
marine mammals. The mean tracheal length of the river otter is 15.3 cm (6.0 in), or 23.2% of the body length. A shorter trachea may improve air exchange and increase lung ventilation in diving mammals.
[11]
Most mustelids, including otters, have specialized teeth, including sharp
is 3.1.4.1 3.1.3.2 .
North American River Otter at the River dart
Behavior
River otters are active year-round, and are most active at night and during
nocturnal in the spring, summer, and fall seasons, and more
diurnal during winter. They may
migrate as a result of food shortages or environmental conditions, but they do not migrate annually.
[11] River otters only settle in areas that consist of vegetation, rock piles, and sufficient coverage
[22] .
Movement
River 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. It must remain in motion to maintain its position at the surface.[11]
Sliding across ice is an efficient means of travel. Note the long, tapered tail.
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. Rear leg paddling enables continuous sliding where gravity is an insufficient or an opposing force.[23] During winter, the river otters heavily use openings in the ice, and may excavate passages in beaver dams for accessing open water.[11]
Tracks in the snow
North American river otters are highly mobile and have the capacity of traveling up to 42 km (26 mi) in one day. Daily movements of yearling males and females in Idaho averaged 4.7 and 2.4 km (2.9 and 1.5 mi) in spring, 5.1 and 4.0 km (3.2 and 2.5 mi) in summer, and 5.0 and 3.3 km (3.1 and 2.1 mi) in autumn, respectively. Daily movements of family groups averaged 4.7, 4.4, and 2.4 km (2.9, 2.7, and 1.5 mi) in spring, summer, and winter, respectively. Both males and family groups travel drastically less during winter.[11]
Playing
River otters are renowned for their sense of play. Otter play mostly consists of wrestling with conspecifics. Chasing is also a common game. River otters rely upon play to learn survival skills such as fighting and hunting. However, playful behavior was found in only 6% of 294 observations in a study in Idaho, and was limited mostly to immature otters.[11]
Hunting
Raft of L. c. pacifica surfacing to eat fish
Prey is 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 (6.8 mph), dive to depths nearing 20 m (22 yd), and travel up to 400 m (440 yd) 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.
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 its food habits and prey choices.[24] 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.[25] [26]
The diet of the river otter can be deduced by analyzing either scat obtained in the field,[27] or gut contents removed from trapped otters.[28]
Fish are the primary component of the river otter's diet throughout the year.
River otters are not scavengers; they avoid consuming
American beaver have been found in otter scat in some regions, although most otter dietary studies in areas where otters and beaver are sympatric do not show them to be regular predators of beavers (despite the claims of fur-trappers that otters frequently hunt beavers) and perhaps only young beaver kits may be attacked.
[34] [36]
Otters do not dramatically reduce prey populations in the wild, generally speaking. When a copious supply of food dwindles or other prey becomes available, otters either transfer to a new location or convert their dietary choices to the most adequate prey.[21] When left unchecked, though, otter depredations 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 fish 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, they 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.[21]
There are reports of photographs of retrieving otters that were used by hunters near Butte, Nebraska.[citation needed ]
Social behavior
Aurora, IL
.
The North American river otter is more social than most mustelids. In all habitats, their basic social group is the family, consisting of an adult female and her progeny. Adult males also commonly establish enduring social groupings, some documented to comprise as many as 17 individuals. In coastal areas, males may remain gregarious even during the estrous period of females. Family groups may include helpers, which can be made up of unrelated adults, yearlings, or juveniles.[11]
Male otters disperse from such family groups more often than females. When females leave, they tend to move much further away (60–90 km or 37–56 mi) than males (up to 30 km or 19 mi), which tend to move shorter distances. Male river otters do not seem to be territorial, and newly dispersing males may join established male groups.[37]
On occasion, groups of unrelated juveniles are observed. River otters living in groups hunt and travel together, use the same dens, resting sites, and
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.
[11]
Communication
Communication among North American river otters is accomplished mainly by
anal sac secretions.
Musk from the scent glands may also be secreted when otters are frightened or angry.
[11]
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 low, purring grunts. The alarm call, given 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.[11]
Reproduction and life cycle
North American river otters are
corpora lutea increases directly with age.
[11]
River otters typically breed from December to April.
parturition can reach 10–12 months.
[11] Delayed implantation distinguishes the species from the European otter, which lacks this feature.
[39] Young are born between February and April,
[1] and parturition lasts three to eight hours.
[11]
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.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.
[11]
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. Otters are natural swimmers and, with parental supervision, they acquire the skills necessary to swim.[15]
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.[40]
Geographic range
The species inhabits coastal areas, such as marshland. 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 . 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 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, Hawaii, Kansas, 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 States . Since their reintroduction to Kentucky in the early 90s, they have recovered to the point that a trapping season was started in 2006, and the species is now found in all major waterways.[41] In 2010, the Colorado Department of Wildlife reported the species, reintroduced in the 1980s, was "thriving" and recommended its protection status be reconsidered.[42] 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.[43] In Canada, North American river otters occupy all provinces and territories, except for Prince Edward Island .[1]
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
Habitat
A river otter in the San Anselmo Creek . 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. 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.[18]
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.nutria (
Myocastor coypus ), or
beaver and muskrat 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.
[11]
River otter swimming in San Francisco Bay stop to sun themselves on rocks at Richmond, CA Marina
Population localization
Aquatic life ties North American river otters almost exclusively to permanent watersheds.[11] The river otters favor bog 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 jams are heavily used 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, isthmuses , mouths of permanent streams, or any object that protrudes from the water.[1]
River otters often reside in beaver ponds. Encounters between otters and beavers are not necessarily 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 mink (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.[11]
Fish
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.pike (Esocidae), are not a significant component of their diets.
[26] [28] They are less likely to be prey for the North American river otters since they are fast-swimming and can find good escape cover.
[26] However, river otters will prey on trout, pike,
walleye (
Sander vitreus vitreus ),
salmon (
Oncorhynchus spp.), and other game fish during
spawning .
[29]
Adult river otters are capable of consuming 1 to 1.5 kilograms (2.2 to 3.3 lb) of fish per day.[32] 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).[24] Otters are known to take larger fish on land to eat, whereas smaller fish are consumed in the water.[32]
Northern river otter eating a white sucker (catostomus commersonii ) at the Seedskadee National Wildlife Refuge (Wyoming)
Crustaceans
Otters may prefer to feed on
Pacifasticus, and others) more than fish where they are locally and seasonally plentiful.
[25] In Georgia, crayfish accounted for two-thirds of the prey in the summer diet, and their remnants were present in 98% of the summer
spraint . In the winter, crayfish made up one-third of the otter's diet.
[46] A study conducted on North American river otters in a southwestern Arkansas swamp identified a correlation between crayfish consumption, fish consumption, and water levels.
[47]
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.[47] 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.[25]
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.
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.[47]
Birds
Although they consume birds, river otters do not feed on bird eggs.[24]
Insects
adult beetles).
[30] [45] 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.
[27] [29]
Mammals
Mammals are rarely consumed by river otters, and are not a major dietary component.
Records of otters preying upon beavers (Castor canadensis ) vary; it has been reported in the southern boreal forest of Manitoba.[49] Trappers in Alberta, Canada commonly assert otters are major predators of beavers.[30] A 1994 river otter study reported findings of beaver remains in 27 of 1,191 scats analyzed.[30] However, many other studies did not report any findings of beaver remains in the scat sampled.[47] [50]
Threats
The otter has few natural predators when in water. Aquatic predators include the
mountain lion (
Felis concolor ),
black bear (
Ursus americanus ) and (in young or small otters)
red fox (
Vulpes vulpes ) .
[33] 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.
[11]
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 others. 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 Island .[1]
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.[1] 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.[11]
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 and pose long-term threats if the enforcement of water quality standards is not upheld.
sucking lice(
Latagophthirus rauschi ), and
fleas (
Oropsylla arctomys ).
[1]
River otters are hunted and trapped for their valuable fur.
Conservation status
Lontra canadensis is listed in Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora. They have been virtually eliminated through many parts of their range, especially around heavily populated areas in the midwestern and eastern United States.[51] Appendix II lists species that are not necessarily threatened with extinction currently, but may become so unless trade is closely controlled.[52]
The North American river otter is considered a species of
least concern according to the
IUCN Red List , 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.
[1]
interleukin-6 immunoreactive protein, but decrease body mass. Home ranges of river otters increase in size on oiled areas compared to unoiled areas, and individual otters also modify their habitat use. Declines in the
richness and
diversity of prey species may explain these changes.
[11]
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^ a b Boyle, Steve (2006). "North American River Otter (Lontra canadensis ): a technical conservation assessment" (PDF) . USDA Forest Service, Rocky Mountain Region. Retrieved 2009-01-14 .
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Further reading
Hans Kruuk (2006). Otters: ecology, behaviour and conservation . Oxford: Oxford University Press. . Recent monograph on otters in general, with many references to the river otter.
External links