Lontra canadensis - North American River Otter

Skull Pictures:      
Dorsal      Posterior mandible
Lateral     Ventral
Mandible    

Physical Description:

The North American river otter’s taxonomic designation is Lontra canadensis, but was recently changed from Lutra canadensis. The river otter is morphologically separated from other mustelids, by its fully webbed feet, short and dark glossy fur, and a long tapered tail. River otters do coexist with sea otters (Enhydra lutris) along costal habitats. A distinct difference exists between these two mustelids. The sea otter’s size is larger (>15kg), has thicker vibrissae, large flipper-like hind feet, and a short less tapered tail (Lariviere, 1998).

The river otter has adapted well to semi aquatic life. The waterproof fur is short and dense (guard hairs average 23.8mm) with a thick layer of fat beneath the skin. A river otter is mostly rich brown in color, ventrally a grayish brown color, and more gray color around the throat, chin and muzzle (Lariviere, 1998). The neck is very muscular with head similar in size and flat on top. Their small eyes are positioned anteriorly, near the top of the head, and have nictitating membranes that cover the eyes while swimming. The river otter has a stocky and elongated body, which is broadest at the hips, with short legs (hind foot length: 110-135 mm), and five fully webbed toes on each foot (Lariviere, 1998; Kurta, 1995). The ears (ear height: 10-25mm) are round, inconspicuous, and close while the animal is submerged. Otters have very long vibrissae used to sense prey. The thick, muscular tail (tail length: 320-500mm) is one-third of the total body length (total length: 900-1,300 mm) and it tapers to a point. The river otter is the second largest mustelid (weight: 5-14kg) living in the Great Lakes Region, with the badger being the largest (Kurta, 1995). Sexual dimorphism is present in river otters with the males being on average 5% larger than the females. Juvenile, yearling, and adult male otters from Idaho, weigh on average 8, 11, and 17% heavier, respectively, than females of the same age (Lariviere, 1998).

Distribution and Habitat:

The North American river otter was once very common throughout the United States and Canada (Lariviere, 1998). The river otter’s distribution has decreased due to the continual increase of urbanization and pollution as noticed by the early 1900’s. The approximate range of otters is between 25o N latitude and 70o N latitude (Hill, 2001). The otter is presently found in the states bordering the Great Lakes, eastern Newfoundland region, Atlantic Ocean, Gulf of Mexico, Pacific coast forested regions in North America, Alaska and the Aleutian Islands, north slope of the Brooks Range, and most of Canada. The river otter is found in all provinces and territories in Canada, except for Prince Edward Island. In recent years there have been reintroductions of otters mainly to the Midwestern United States, so as to expand their distribution (Lariviere, 1998).

The North American river otter has a fairly broad home range, that can be anywhere between 8-78 square km. Within their habitat, otters are dependent on an aquatic lifestyle and live in or near riparian zones. Some vegetation that can be found in riparian communities include cattails (Typha spp.), sedges (Carex spp.), and grasslands. River otters prefer a habitat that has slow moving waters with deep pools, surrounded by vegetation, with a steady supply of fish. Otters are commonly found in larger numbers near coastal areas and lower elevations, of rivers and estuaries. Some important habitat entities needed for otters are denying sites, resting sites, and cover to avoid other top predators. In reference to den sites of river otters, it has been found that they do not dig their own dens. Otters use other animals’ empty dens, or natural shelters such as tall marsh grasses, riverbank thickets, and hollowed out trees (Hill, 2001). The distribution of Lutra canadensis covers all of Wisconsin. The North American river otter has been commonly observed in the Tomahawk River of north central Wisconsin (Beckel-Kratz, 1979). In winter months, they occupy ice-free sections of the river (Beckel, 1982).

Ontogeny and Reproduction:

The mating system associated with the North American river otter is polygyny. The breeding season for otters is typically from December to April. It is possible for female yearlings to reproduce, but more common at the age of 2 years or later (Lariviere, 1998). It is believed that not all females reproduce every year (Hill, 2001). Around 2 years of age, males become sexually mature (Lariviere, 1998). It may take a male 5-7 years of age before he successfully breeds (Hill, 2001). The period of time females are in heat is between 42-46 days and the gestation length is 61-63 days. Female otters delay implantation for 8 months or longer. This means the time period between copulation and parturition can be 10 to 12 months. Female otters typically give birth between the months of February and April, lasting 3 to 8 hours (Lariviere, 1998). Litter sizes may range from 1 to 6 pups, but more common litter sizes range between 2 and 4 (Hill, 2001). At the time of birth, the pups are toothless, fully covered with fur, have well developed claws, facial vibrissae, and blind. The eyes begin to open somewhere between 30-38 days. Playful behavior starts at 5 or 6 weeks old. The mother begins weaning her kin around 12 weeks, but continues providing solid food to about 38 weeks (Lariviere, 1998).

Ecology:

The North American river otters’ aquatic lifestyle shows the need to be close to watershed habitat. Studies in northern Canada showed otters living in riparian habitat. River otters are found in bog lakes with banked shores and lakes with beaver (Castor canadensis) lodges. River otters coexist with beavers and records show both using the same lodge, at the same time, during three different occasions. Otters do not prefer gradually sloping shorelines of sand or gravel. Otters in Idaho prefer staying in valleys over mountains. The preference of valley streams comes before valley lakes, reservoirs, and ponds. Densities of river otters in Florida are highest in swamp forest, intermediate in salt marshes, and lowest in freshwater marshes (Lariviere, 1998).

The most common food eaten by North American river otters is fish and this includes suckers (Catostomus spp.), chubs (Semotilu spp.), shiners (Notropis spp.), catfish (Ictalurus spp.), and perch (Perca spp.), (Hill, 2001). Their diet also consists of amphibians (mostly frogs), insects, birds, crustaceans (mainly crayfish), small mammals, mollusks, reptiles and fruit (Hill, 2001; Lariviere, 1998).

Population estimates of North American river otters are done by counting tracks in the snow or even using scent-station surveys. In Oregon, river otters were found to have survival rates of 68% for the first year, 46% between ages 1-2, and 73% between ages of 2-11. River otters live about 13 years of age in their natural environment (Lariviere, 1998).

There are endo and ectoparasites associated with river otters. Some of these endoparasites are cestodes, nematodes, and trematodes. The ectoparasites are ticks, fleas, and sucking lice (Lariviere, 1998). River otters also carry diseases such as canine distemper, jaundice, hepatitis, pneumonia, rabies, and feline panleucopenia (Hill, 2001 and Lariviere, 1998).

The North American river otter is considered to be a top predator. There are few predators that prey on otters in the water and these include alligators (Alligator mississippiensis), American crocodiles (Crocodylus acutus), and killer whales (Orcinus orca). Land predators consist of bobcats (Lynx rufus), cougars (Felis concolor), coyotes (Canis latrans), domestic dogs (Canis familiaris), and wolves (Canis lupus). Humans are the leading cause of death for otters do to trapping, illegal shootings, and road kills. North American river otters are trapped using foothold traps with padded jaws and Hancock traps. The fur of river otters is highly looked upon as a standard to rate other pelts durability, because it is the most durable of Native American furs (Lariviere, 1998).

Behavior:

The North American river otter is active throughout the year and mostly at night. In winter, otters are more diurnal and nocturnal the other three seasons. Due to seasonal changes and food abundance, otters will emigrate. Family groups and males do not move as much during the winter months. The river otter’s ability to slide across surfaces can allow it to travel roughly 42 km per day. River otters are not territorial, but try to avoid individual groups. Males have larger home ranges than females and both have intra and intersexual overlap (Lariviere, 1998).

The North American river otter moves through water with various paddling techniques. The swimming motions are quadrupedal paddling, alternate hind-limb paddling, forelimb paddling, simultaneous hind-limb paddling, or tail dorsoventral undulation. Otters can swim with their heads above the water, which allows the ears, eyes, and nostrils to be as well. The tail is mainly used for quick movements and keeping the otter stable while swimming. Once the otter is on land, it can run, walk, slide, or bound. River otters use the sliding approach when on snow, ice, river banks, and grassy slopes. As otters descend from higher elevations they can efficiently slide for several hundred meters (Lariviere, 1998).

River otters catch their prey by either a quick attack or sometimes after a long chase. Otters may work together to catch fish, so as to improve there success. Fish still alive are usually eaten head first and depending on the size, larger ones may be brought to land. Otters have been recorded staying under water for about 4 minutes, swimming to depths near 20 meters, swimming up to 11km/hr, and traveling up to 400 meters underwater (Lariviere, 1998).

Out of all mustelids, otters are considered the most social. Family social groups, of freshwater otters, include an adult female and her offspring. Sometimes family groups will include unrelated adults, yearlings, or juveniles. Family groups form in autumn, early winter, and mid-winter up to the breeding season (Lariviere, 1998). During breeding season, the river otters copulate anywhere from 16-73 minutes. Mating can occur on land or in the water. Males will bite the neck of females during copulation. The male otters do not help the female raise their offspring (Lariviere, 1998). River otters travel and hunt together, along with using the same resting sites and dens (Beckel, 1990; Lariviere, 1998).

The North American river otter uses olfactory and auditory signals to communicate with one another. Scent markings are made with feces, urine, and anal sac secretions. These markings are essential for inter group communication, so as to identify one another. Scent glands can also secret musk, which is released, when otters are scared or angry. An auditory signal for pain is a shrill whistle and if disturbed will give a growling or hissing bark sound. If danger is near, otters will give a quick snort of air to alarm others. River otters play together by sliding around, swimming, juggling sticks or pebbles, tail chasing, rolling around, wrestling, and playing with objects (Lariviere, 1998).

Literature Cited:

Beckel, A. L.  1990.  Foraging success rates of North American river otters, Lutra Canadensis, hunting alone and hunting in pairs. Canadian Field-Naturalist 104:586-588.

Beckel, A. L.  1982.  Behavior of free-ranging and captive river otters in north central Wisconsin.  Ph.D. Diss., Univ. of Minnesota 198 pp.

Beckel-Kratz, A.  1979.  Preliminary observations on the social behavior of the North American  otter (Lutra canadesis). J. Otter Trust 1977:28-32.

Hill, K.  2001.  Lontra canadensis. Smithsonian Marine Station at Fort Pierce 1-8 pp.

Kurta, A.  1995.  Mammals of the Great Lakes Region. The University of Michigan Press, Ann Arbor, MI. 247-250 pp.

Lariviere, S. and L. R. Walton.  1998.  Mammalian Species Lontra canadensis. American Society of Mammalogists 587:1-8.