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River Otter

Scientific Name: Lontra canadensis

Description

River otter

The North American river otter is a member of the mustelid or weasel family that can be easily identified by a stout body, short legs, noticeably tapered tail and dense, short, glossy fur. Their streamlined body, fully webbed feet, broad and flattened head and stout, muscular tail, and closeable nostrils and ears all serve to assist in swimming and foraging. Their eyes, ears, and nose are located on the top of the head so they can see, hear, and smell while most of their body remains in the water. Fur color can range from light brown to black, with a lighter, grayish colored chin and throat. Males are generally larger than females, 44 inches and 38 inches total length, respectively. Body weight ranges from 10 - 30 pounds, and is likely dependent on age and dietary limitations.

Distribution and Habitat

Historically, river otter could be found in all watersheds of New York, and declines were attributed to unregulated harvest, habitat destruction, and water pollution. Legal protection was first established in 1936, with a nine-year moratorium on otter harvest. After this lengthy season closure, trapping seasons were reopened with more rigorous restrictions and bag limits. As recent as the early 1990s, the river otter was only found in the eastern half of New York State, while the western regions were devoid of otter except for the occasional individual that happened to be passing through.

New York River Otter Project logoIn the late 1990s, the New York River Otter Project aimed to restore river otter to the watersheds of western New York. Volunteers and DEC staff live-trapped otter primarily in the Adirondacks (DEC Regions 5 and 6), but some otter from the Catskills and Hudson Valley (DEC Regions 3 and 4) were included as well. From 1995 through 2000, 279 river otter were captured in eastern New York and released at 16 different sites across the western part of the state. Some of the release sites in western New York had been devoid of otter populations for longer than many local residents could remember, and the public was very excited about the project and the return of the otter to these watersheds.

Life history studies have shown that otter are dependent upon permanent watersheds, and otter may be found in rivers, lakes ponds, small streams, marshes and other inland wetlands. Suitable habitat will exhibit a high percentage of emergent vegetation, or in the case of natural waterways, expansive riparian corridors. Throughout most of their range, there is a close relationship between beaver and river otter populations, indicated by a positive relationship between annual trapper harvests of the two species.

Food and Feeding

Biomagnification of environmental contaminants in otterRiver otter could be considered somewhat of an aquatic generalist, as they consume almost anything they encounter and can catch. Primarily visual predators, their eyes are shaped in a way that facilitates underwater vision and acuity. In situations where murky water occurs, they are further enabled to forage by 'motion sensitive' whiskers that help them cue in on prey location and movement.

Although fish comprise the majority of their diet, amphibians and crustaceans and other aquatic invertebrates are also taken when available. Opportunistic endeavors may net small mammals and birds (e.g., muskrat and waterfowl), reptiles, and even fruit. Two such examples of opportunistic foraging include the near exclusive consumption of hibernating turtles, wood and snapping turtles within individual territories. These instances have detrimental effects on local populations of turtles, and may in effect extirpate said populations.

Being that river otter are at the top of the food chain, they have a greater chance of being exposed to elevated levels of environmental contaminants such as PCBs, DDT and its associated metabolites, and heavy metals such as cadmium and mercury. This means of exposure is referred to as bio-magnification. As contaminants accumulate in the organic materials and sediments on the bottom of a waterway, they become ingested by aquatic invertebrates such as snails, mussels, and insects. These are in turn consumed by fish, which may then be eaten by larger fish, all of which are consumed by river otter. This accumulating effect results in elevated levels of pollutants in river otter due to the ingestion of contaminated food items. At such high levels, some of these contaminants can have negative impacts on otter ranging from poor survivorship to sterility or infertility.

Reproduction

River otter kitsAdult river otters breed with more than one mate in their lifetime, and the breeding season may span from December to May, depending on geographic location. Females delay implantation of sperm, and this may result in fertilization occurring from 10-12 months after initial copulation. Gestation of embryos lasts from 61-63 days, and young are born in April or May, fully furred yet blind and toothless. Litters usually range from 1-3, but 5 kits may occur. Eyes open after 30-40 days, and solid food is taken after 9-10 weeks. Adult otters will provide food for their offspring for up to 40 weeks. Juvenile dispersal usually occurs between 12 - 13 months of age, and distances of over 100 miles may be traveled before a suitable home range is found. Males and females are reproductively mature in their second year, but occasionally one-year-olds have been found to have given birth.

Behavior

The main social unit is the family, or an adult female and her young. Otter do maintain home ranges, but little in the way of documented territorial disputes exists, as family groups have been noted to avoid one another. One such method of maintaining a home range would be the classic latrine sites, or toilet areas that they will both defecate and urinate at repeatedly. They will choose almost any object or piece of land that protrudes from the water or the bank including large conifers, points of land, beaver lodges or exposed root systems.River otter track patterns

Otters are nocturnal by nature, but they can be seen by day foraging or playing, and daytime activity increases during the winter months. There is no hibernation period, they are active year round. Like all true members of the weasel family, they travel overland in a loping or bounding manner, and prints may vary considerably with terrain, ground surface and stride. Prints are often paired, grouped, or laid out in angled strings. One key feature to look for is the tail drag marks (see track pattern diagram to the right). Due to their large, thick tail, it is often seen scraping over and between print sets, especially in snow. Another feature indicative of otter sign will be their slides (see photo below). They will move along the ground or down a slope on their belly. These slides can be found on flat ground with snow or grass cover, or snowy or muddy slopes into the water. This method of locomotion is used as a means of transport and play.

Ecology

Although the accepted, common name is the river otter, it might be suitable to rename it the swamp or inland wetland otter, due to its strong association with aquatic, emergent vegetation, and their affinity to freshwater wetlands. Beaver ponds are River otter slideoften inhibited with both otter and beaver, and there have been reports of both species inhabiting the same lodges with little in the way of reported, antagonistic encounters. The creation of dams and lodges provide structure for the eventual inhabitation of these wetlands, while the damming of waterways or inland wetlands increases the surface area and depth of open water, thereby creating more habitats suitable for the denning and foraging behavior of otter.

A diversity of structure along occupied water bodies appears to be of considerable importance, not just for foraging opportunities, but in regards to suitable den sites as well. Steep banks, with ample structure above and below the water allow for habitation of winter retreats, and ensure that unrestricted access to both terrestrial and submerged habitat are available. They do not excavate their own dwellings, but rely on beaver and other mammal burrows for their den sites. In rivers, log jams with abundant woody material may be used extensively for denning and latrine sites. During dry seasons, otter will move from their inland wetland habitats to more permanent bodies of water, in order to adapt to drought conditions and for ease in finding food.

Predators, Parasites and Disease

Other than the annual harvest of river otter by trappers for their pelt and the occasional road mortality, there is little in the way of natural predators in New York; however, overland travel makes otter more vulnerable to attack by animals such as bobcat, coyote and domestic dogs.

Like all mustelids, the viscera or internal organs of otter do serve as habitat for a variety of intestinal nematodes, trematodes, acanthocephalans, and cestodes. Externally, ticks, fleas, and lice can be found.

Susceptible to both rabies and distemper, since 1998 there have been 3 documented cases of rabies in New York State otter. Although actual numbers are not available, distemper may play a role in wild otter mortality.


More about River Otter :

  • Watchable Wildlife: River Otter - A description of the appearance, habitat and habits of the North American River otter, the only species of otter that lives in New York State.