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There is some
degree of sexual dimorphism in that males are generally larger than females. The
body is slender, with nose and whiskers prominent. The tail measures as much as
31-46 cm (12 – 18 inches). It is thick nearest the body, tapering towards the
tip. River otters have short legs and webbed feet, with 5 toes on each foot.
Eyes are located near the top of the skull, allowing otters to view above the
water’s surface while swimming. Another adaptation to the otter’s aquatic
lifestyle is the presence of a nictitating membrane which coves the eyes while
swimming. Additionally, the nose and small ears close while the animal is
submerged. Otters are protected from the cold by a thick layer of fat beneath
the skin and dense, oily fur. Body color is generally black to shades of
red-brown on the dorsal surface, and a lighter gray-brown ventrally. The throat
and cheeks tend toward a yellow-gray color.
River otters have an acute sense of touch, aided by
facial whiskers that enable otters to locate prey even in turbid water. Their
sense of smell is also keen; but hearing and sight are somewhat less well
developed.
II. HABITAT AND
DISTRIBUTION
Regional Occurrence:
Historically, river otters ranged over the most of
the United States and Canada, but became rare, or were extirpated during the fur
trading period. Presently, they are distributed from approximately 25°
N latitude in Florida through the Gulf of Mexico, to 70°
N latitude in Alaska; and from eastern Newfoundland west throughout Canada,
Alaska and the Aleutian Islands (Chapman and Feldhamer 1982).
IRL Distribution:
River otters occur throughout the Indian River
Lagoon system.
III. LIFE HISTORY AND POPULATION BIOLOGY
Age, Size, Lifespan:
Captive otters have been documented to live 16
years or more (Banfield 1974). Body size of adults is generally 1 m (3 feet) or
more in length, including the tail. The tail measures as much as 31-46 cm (12
– 18 inches). Adults can weigh from 3-15 kg (7-35 pounds), with males
typically outweighing females.
Abundance:
Chapman and Feldhamer (1982) suggested that otter
populations in many areas are apparently stable and may be slowly increasing.
Large populations of river otter exist in many states throughout the northern
U.S. (including Alaska) and Canada where the river otter is still trapped for
its fur. In Florida, however, river otters are not considered abundant in the
Indian River Lagoon area. Intense pressure from coastal development and
resulting loss of habitat have caused otter populations in this area to decline.
There are apparently several population strongholds including the Merritt Island
National Wildlife Refuge -Canaveral National Seashore complex, as well as other
relatively undeveloped areas (Ehrhart 1995).
Locomotion:
Lontra canadensis actively swims, and
crawls. They are capable of achieving running speeds of 29 km/hr (18 miles/hr),
and have been observed to remain submerged for as long as 8 minutes.
Reproduction:
Breeding occurs in late winter and early spring (Banfield
1974; Chapman and Feldhamer 1982). Females are considered sexually mature at 2
years of age, but do not necessarily breed upon first reaching maturity.
Some evidence suggests that females do not breed every year (Melquist and
Hornocker 1983; Dronkert-Egnew 1991). Males mature at approximately 2 years of
age, but may not successfully breed until they are 5-7 years old (Chapman and
Feldhamer 1982). Copulation occurs in water.
Embryology:
There is much discrepancy in the scientific
literature regarding the length of river otter gestation periods, with reports
ranging from 288 – 375 days (Chapman 1974; Wren 1991). This extreme difference
has been attributed to a process known as delayed implantation, in which young
are born following a period of arrested development. In this process, fertilized
eggs develop to the blastocyst stage, and then remain floating in the uterus for
a variable period of time before implanting into the uterine wall. Litters are
born nearly a year following conception, generally from November to May; though
in the Pacific northwest, pups are delivered from March through May. The actual
gestation period following implantation is estimated to be 60-62 days (Chapman
and Feldhamer 1982; Dronkert-Egnew 1991; Nebraska Game and Parks Commission
2001).
Litter size ranges from 1- 6 pups per litter, with 2-4
being most common (Chapman 1982). Pups open their eyes at 21-35 days. At 25-42
days, they begin to play. Parents introduce pups to water at 48 days, and they
begin to venture outside the den alone at 59-70 days. Pups are fully weaned by
91 days, and will leave parents at approximately 1 year old (Chapman 1982).
IV. PHYSICAL TOLERANCES
Salinity:
River otters are well adapted to various aquatic
environments from marine to fresh water.
Physical Tolerances:
Disease:
L. canadensis is susceptible to a variety of
diseases including roundworm infections, canine distemper, jaundice, hepatitis,
and feline panleucopenia (Chapman 1982).
V. COMMUNITY ECOLOGY
Trophic Mode:
In the absence of large mammalian predators such as
wolves and bears, river otters are top predators in some of the ecosystems where
they occur, including the Indian River Lagoon. Though often blamed for damaging
or depleting commercial fish stocks, the bulk of the diet consists of slow
moving or schooling non-game fish species (Chapman 1982). Common prey types
include: cyprinids, suckers (Catostomus spp.), chubs (Semotilus
spp.), shiners (Notropis spp.), catfish (Ictalurus spp.), and
perch (Perca spp.) (Banfield 1974; Chapman 1982).
Besides non-game fish, river otters also consume
crustaceans (primarily crayfish), amphibians, insects, small birds and
waterfowl, mammals and plants (Meehan 1974; Chapman 1982; Davis et al. 1992).
Competitors:
River otters practice mutual avoidance behaviors in
order to reduce intraspecific competition. Melquist and Hornocker (1983)
observed otters to practice "personal space dispersion" whereby
individuals defended territories based on their current location, rather than
upon fixed environmental parameters. They postulated that this behavior probably
had the effect of reducing direct competition for resources. Mutual avoidance is
practiced primarily through vocalization and scent marking rather than by direct
confrontation.
Predators:
River otters have few natural predators other
than man; however, young otters are placed at risk for predation from foxes,
bobcats, wolves, coyotes and snapping turtles when they leave water to traverse
land areas.
Habitats:
River otters have somewhat large home ranges of
approximately 8-78 square km. They utilize a wide variety of riparian
communities including cattails (Typha spp), sedges (Carex spp.)
and grasslands (Chabreck 1971; Dronkert-Egnew 1991; Waller 1992).
Lontra canadensis is
well adapted to aquatic habitats from marine to fresh water. Optimum otter
habitat, according to Chapman (1982) is in highly vegetated areas having slow
moving waters with deep pools, and abundant fish. Otters tend to be most
abundant in coastal areas, or in the lower portions of rivers and estuaries. The
total habitat area must provide otters with escape cover, den sites, and resting
sites.
Otters do not dig their own dens; rather, they rely on
those dug by other animals, or on natural shelters such as the hollows of trees,
tall marsh grasses, or riverbank thickets (Banfield 1974; Chapman 1982).
Activity Time:
Lontra canadensis is primarily nocturnal.
However, it is also highly active in the early morning and in late afternoon (Banfield
1974).
VI. SPECIAL STATUS
Special Status:
Lontra canadensis is a top predator in the
Indian River Lagoon system.
Benefit in IRL:
Their aesthetic value aside, river otters may help
reduce direct competition between commercially valuable fish species and other
fishes. Otters have historically been blamed for depleting game fish stocks;
however, they may actually be of benefit to commercial species due to their
preference for slow moving, non-game species of fishes. Through removal of
non-game fishes, commercial species thus enjoy reduced competition for food
(Davis et al. 1992).
Economic Importance:
River otter fur is still highly prized today in the
fur trade and nearly all U.S. states allow the export of otter pelts, subject to
regulation by state wildlife authorities. In some states, river otter
populations are low enough to have gained them threatened or endangered status.
They are thus protected and managed for in these areas. However, in all Canadian
provinces, Alaska, and approximately half of the remaining U.S. states otters
are still trapped seasonally under highly regulated conditions. Perhaps
surprisingly, Louisiana generally has the highest harvest of river otters in the
U.S., with annual totals sometimes exceeding 10,000 animals (Nebraska Game and
Parks Commission 2001). River otter pelts in 2001 were valued at an average of
$48.00 USD (North American Fur Auctions 2001).
VII. REFERENCES
Banfield, A.W.F. 1974. The mammals of Canada.
University of Toronto Press,
Toronto, Canada. 438 pp.
Beckel, A.L. 1990. Foraging success rates of North
American river otters, Lutra
canadensis, hunting alone and hunting in pairs.
Canadian Field-Naturalist.
104(4):586-588.
Ben-David, M., R.T. Bowyer, and J.B. Faro. 1995. Niche
separation by mink
and river otters: coexistence in a marine environment.
Oikos. 75:41-48.
Chabreck, R.H. 1971. Ponds and lakes of the Louisiana
coastal marshes and
their value to fish and wildlife. Proceedings, 25th
annual conference of
Southeastern Association of Game and Fish
Commissioners. pp. 206-215.
Chapman, J.A., and G.A. Feldhamer, eds. 1982. Wild
mammals of North
America. The Johns Hopkins University Press, Baltimore
MD. 1147 pp.
Davis, H.G., R.J. Aulerich, S.J. Bursian, et al. 1992.
Feed consumption and food
transit time in northern river otters (Lutra
canadensis). Journal of Zoo and
Wildlife Medicine. 23(2): 241-244.
Dronkert-Egnew, A.E. 1991. River otter population
status and habitat use in
northwestern Montana. University of Montana, Missoula,
MT. 112 pp. Thesis
Duffy, D.C. 1995. Apparent river otter predation at an
Aleutian tern colony.
Colonial Waterbirds. 18(1):91-92.
Ehrhart, L. 1995. Mammals of Indian River marshes and
maritime hammocks:
status and threats. Bull. Mar. Sci. 57(1): 280-285.
Halbrook, R.S., J.H. Jenkins, P.B. Bush and N.D.
Seabolt. 1994. Sublethal
concentrations of mercury in river otters: monitoring
environmental
contamination. Archives of Environmental Contamination
and Toxicology.
27:306-310.
Humphrey, S.R. and T.L. Zinn. 1982. Seasonal habitat
use by river otters and
Everglades mink in Florida. Journal of Wildlife
Management. 46(2): 375-381.
Jenkins, J.H. 1983. The status and management of the
river otter (Lutra
canadensis) in North America. Acta Zool. Fennica
174:233-235.
McCall, R. 1995. A novel foraging association between
southern river otters
Lutra longicaudis and great egrets Casmerodius
albus. Bull B.O.C.
116(3): 199-200.
Meehan, W.R. 1974. The forest ecosystem of southeast
Alaska: 4. Wildlife
habitats. U.S. Department of Agriculture, Forest
Service, Pacific Northwest
Forest and Range Experiment Station. Gen. Tech. Rep.
PNW-16. Portland,
OR. 32 pp.
Melquist, W.E. and M.G. Hornocker. 1983. Ecology of
river otters in west
central Idaho. Wildlife Monographs 83:1-60.
Nebraska Game and Parks Commission. 2001. The river
otter. Online wildlife
publication: www.ngpc.state.ne.us/wildlife/otters.html.
Newman, D.G., and C.R. Griffith. 1994. Wetland use by
river otters in
Massachusetts. Journal of Wildlife Management.
58(1):18-23.
North America Fur Auctions. 2001. Online Auction sales
results, September 5
and 6, 2001. Toronto, Ontario, Canada. Online
publication:
www.nafa.ca/sales/results_sept2001.asp.
Reid, D.G., T.E. Code, A.C. Reid, and S.M. Herrero.
1994a. Food habits of the
river otter in a boreal ecosystem. Canadian Journal of
Zoology.
72:1306-1313.
Reid, D.G., T.E. Code, A.C. Reid, and S.M. Herrero.
1994b. Spacing,
movements and habitat selection of the river otter in
boreal Alberta. Canadian
Journal of Zoology. 72:1314-1324.
Rock, K.R., E.S. Rock, R.T. Bowyer and J.B. Faro. 1994.
Degree of
association and use of a helper by coastal river
otters, Lutra canadensis, in
Prince William Sound, Alaska. Canadian
Field-Naturalist. 08(3):367-369.
Serfass, T.L. 1995. Cooperative foraging by north
American river otters, Lutra
canadensis. The Canadian Field-Naturalist. 109:
458-459.
Shirley, M.G., R.G. Linscombe, N.W. Kinler, et al.
1988. Population estimates
of river otters in a Louisiana coastal marshland.
Journal of Wildlife
Management. 52(3):512-515.
St.-Georges, M., S. Nadeau, D. Lambert and R. Decarie.
1995. Winter habitat
use by ptarmigan, snowshoe hares, red foxes, and river
otters in the boreal
forest – tundra transition zone of western Quebec.
Canadian Journal of
Zoology. 73:755-764.
Stenson, G.B., G.A. Badgero, and H.D. Fisher. 1984.
Food habits of the river
otter Lutra canadensis in the marine environment
of British Columbia.
Canadian Journal of Zoology. 62:88-91.
Stoskopf, M.K., L.H. Spelman, P.W. Sumner, et al. 1997.
The impact of water
temperature on core body temperature of north American
river otters (Lutra
canadensis) during simulated oil spill recovery
washing protocols. Journal of
Zoo and Wildlife Medicine. 28(4):407-412.
Tumlison, R. and M. Karnes. 1987. Seasonal changes in
food habits of river
otters in southwestern Arkansas beaver swamps. Mammalia.
51(2):225-231.
Waller, A.J. 1992. Seasonal habitat use of river otters
in northwestern Montana.
University of Montana, Missoula, MT. 75 pp. Thesis.
Wren, C.D. and K.L. Fischer. 1986. Mercury levels in
Ontario mink and otter
relative to food levels and environmental
acidification. Canadian Journal of
Zoology. 64:2854-2859.
Wren, C.D. 1991. Cause-effect linkages between
chemicals and populations of
mink (Mustela vison) and otter (Lutra canadensis)
in the Great Lakes Basin.
Journal of Toxicology and Environmental Health.
33:549-585.
Report by: K. Hill,
Smithsonian Marine Station
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Page last updated: Oct. 17, 2001
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