BIOLOGICAL DATA AND HABITAT REQUIREMENTS
WILDLIFE SPECIES: Lutra canadensis | River Otter 



TIMING OF MAJOR LIFE HISTORY EVENTS : 
Breeding - River otters breed in late winter or early spring; the
breeding season is spread over a period of 3 months or longer [1,4].

Gestation period and litter size - There is much discrepancy in the
literature regarding the length of gestation in the river otter.
Gestation periods of 288 to 375 days have been reported.  The extreme
length of gestation is due to a process called "delayed implantation",
wherein the development of the blastocyst is arrested for a period of
time before it implants into the uterine wall.  Litters are generally
born from November through May.  In northwestern North America, river
otters generally give birth from March through May following an average
delay of 9 months and an actual gestation of about 62 days [6].  Litter
size ranges from one to six, with two to four young most common [4].

Pup development - River otter pups are born helpless.  They begin to
open their eyes by age 21 to 35 days; by 25 to 42 days pups begin
playing.  River otter pups are introduced to water by age 48 days and
may venture out of the den on their own by the age of 59 to 70 days.
Weaning occurs at about 91 days of age [4].

Age at sexual maturity - Female river otters normally become sexually
mature when they are about 2 years old, but may or may not breed at that
time.  Female river otters may not breed every year [6,14].  Although
male river otters also become sexually mature at about 2 years of age,
they may not become successful breeders until they reach 5 to 7 years
[4].

Life span - River otters have lived at least 16 years in captivity [1].

River otters are primarily nocturnal, but may be active in the early
morning and late afternoon in remote areas.  They are active all winter
except during the most severe periods, when they take shelter for a few
days [1].


PREFERRED HABITAT : 
River otters are adapted to a variety of aquatic habitats from marine
environments to high-elevation mountain lakes.  Optimum habitat for
river otters includes slow-moving water with deep pools, abundant
riparian vegetation, and plentiful fish [6].  River otters are generally
most abundant along food-rich coastal areas, such as the lower portions
of streams and rivers and in estuaries, and in areas having extensive
nonpolluted waterways [4].  In Canada, they occur north beyond the tree
line in tundra lakes and streams [1].

Melquist and Hornocker [14] found that in west-central Idaho, river
otters prefer valley habitats to mountain habitats, and prefer
streamassociated habitats to lake, reservoir, and pond habitats.
Mountain lakes and streams were used most often during the fall.  Most
river otters lived entirely in the valleys, and no otters lived solely
in the mountains.  The use of lakes, reservoirs, and ponds was greatest
during the winter.  Mudflats and associated open marshes, swamps, and
backwater sloughs were used most often in summer [14].

River otter habitat is generally limited to open water during the
winter months.  Outflows from lakes are favored habitat at this time.
In late winter, water levels usually drop below ice levels in rivers and
lakes, leaving a layer of air that allows river otters to travel and
hunt under the ice [16].


COVER REQUIREMENTS : 
River otter habitat must provide adequate escape cover, rest sites, and
den sites.  Rather than excavate their own dens, river otters use dens
dug by other animals, or natural shelters.  They commonly use hollow
trunks of large trees, beaver (Castor canadensis) or nutria (Myocastor
coypus) dens, hollow logs, log jams, drift piles, jumbles of loose
rocks, abandoned or unused boathouses, and duck blinds [4].
Occasionally river otters occupy large, bulky, open nests of grasses in
marshes or riverbank thickets [1].  Understory bank cover is also
important to river otters.  In a study of river otter habitat in
northwestern Montana, areas with less than 25 percent understory bank
cover were used significantly less than expected based on availability
[6].  Stream habitats generally provide more adequate escape cover and
shelter and less human disturbance than pond, lake, and reservoir
habitats [16].


FOOD HABITS : 
The typical diet of river otters consists primarily of fish, but also
includes crustaceans (primarily crayfish), amphibians, insects, birds,
mammals, and plants [4,5,13].  Although a wide variety of fish species
are eaten by river otters, some species of fish are more vulnerable to
river otter predation.  Slow-swimming fish species are generally
selected by river otters more often than fast-swimming fishes.  Also
important are fish species that are abundant and found in large schools
[4].  Fishes often eaten by river otters include suckers (Catostomus
spp.), redhorses (Moxostoma spp.), carp (Cyprinus spp.), chubs
(Semotilus spp.), daces (Phinichthys spp.), shiners (Notropis spp.),
squawfish (Ptychocheilus spp.), bullheads and catfish (Ictalurus spp.),
sunfish (Lepomis spp.), darters (Etheostoma spp.), and perch (Perca
spp.).  Crayfish (Cambarus spp., Pacifasticus spp., and others) also
comprise a major portion of the river otter's diet [1,4].

Waterfowl and rails comprise an important part of the river otter diet
in the Pacific Coast states and in many other regions.  Freshwater
mussels (Anodonta californiensia), freshwater periwinkles (Oxytrema
silicula), and unidentified clams and snails have been reported in the
river otter's diet but are not important food items [4].  River otters
may kill young beavers found alone in a lodge [1].


PREDATORS : 
Although essentially safe from predators while in water, river otters
are considerably more vulnerable when they travel overland between
lakes, ponds, and steams [14].  Bobcats (Felis rufus), dogs (Canis
familiaris), coyotes (C. lutrans), foxes, gray wolves (C. lupus), and
American alligators (Alligator mississippiensis) have all been reported
to kill river otters [4,14,15].  In addition, it is likely that other
predators, including cougars (F. concolor), black bears (Ursus
americanus), American crocodiles (Crocodylus acutus), and some large
raptors, also kill river otters on occasion.  No predator has been shown
to have a serious impact on river otter populations, and most predation
is probably directed toward young river otters [4].


MANAGEMENT CONSIDERATIONS : 
River otters have often been blamed for serious depredation of game
fish, particularly trout.  Food habit studies, however, have all
indicated that the bulk of the river otter diet consists of nongame fish
species.  In many circumstances, river otters are beneficial to game
fish populations because they remove nongame fish that would otherwise
compete with game fish for food [4].  River otters, however, may
occasionally cause severe depredation in fish hatcheries [1,4].
     
River otters have been extirpated or reduced in many areas due to human
encroachment, habitat destruction, and overharvest [8].  River otters
are relatively abundant in major nonpolluted river systems and in the
lakes and tributaries that feed them.  They are scarce, however, in
heavily settled areas, particularly if the waterways are polluted.  In
Maryland, no river otters occur in waters altered by acidic mine
drainages.  The disappearance of river otters from West Virginia and
parts of Tennessee and Kentucky has been attributed to increased acidity
of ground water due to mining operations [4].  Little research has been
done in evaluating the range of water quality that otters will tolerate
[4]

The most readily apparent human impact on river otters results from
trappers harvesting otters for their fur.  The river otter has been an
economically important furbearing species since Europeans first arrived
in North America [4].  Habitat destruction has also resulted in a
decline in river otter populations.  Some causes of river otter habitat
destruction include the development of waterways for economic or
recreational purposes, destruction of riparian habitat for homesites or
farmland, and a decline in water quality because of increased siltation
and/or pesticide residues in runoff [4,6,16].  Pesticide residues
including mercury, DDT and its metabolites, and Mirex have been reported
in river otter tissues [4].

Roads and railroad tracks that parallel or cross streams are probably
responsible for a considerable number of river otter deaths each year.
This is an important consideration in mountainous states where roads are
constructed along stream courses [14].

Several researchers have associated good river otter habitat with the
activities of beavers.  River otter population dynamics may be
influenced not only by beaver trapping but also by wide fluctuations in
beaver numbers and subsequent habitat changes.  In the western United
States, with its widely separated waterways and large variations in
flow, beaver-created habitat may be critical to river otter denning and
foraging [6].

A variety of internal parasites affect river otters.  Of these, two
roundworms (Stronguloides lutrae and Gnathostoma miyazakii) may cause
serious pathological damage.  River otters are also susceptible to
canine distemper, jaundice, hepatitis, and feline panleucopenia [4].
     
In recent years several states have transplanted river otters in an
attempt to establish or reestablish breeding populations [17].


REFERENCES : 
NO-ENTRY

Related categories for Wildlife Species: Lutra canadensis | River Otter