Northern River Otter (Lutra canadensis)

County List:

Rule:

Forested or Mixed Forested/Nonforested Landscapes

      (Lake or Pond or River or Marsh 1)
   containing:
      Dead Down Woody Debris

Habitat List:

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Literature:

River otters require clean, moderately deep water in the form of streams, ponds, or lakes. A river otter has a penchant for waterways with steep banks, but the surrounding terrestrial vegetation does not greatly influence otter abundance.

A river otter is a fish specialist, concentrating on minnows, carp, suckers, darters, and sticklebacks. It occasionally takes faster prey, such as trout, perch, and sunfish. Crayfish, clams, amphibians, and small mammals add variety to the menu.

Habitat: Borders of streams, lakes, or other wetlands in forested areas.

Special Habitat Requirements: Body of water such as stream, pond, lake, river; suitable den sites.

Habitat Preferences: The river otter's major habitat requirements are substantial amounts of water and abundant aquatic life therein. Michigan surely provides these environmental essentials. There seems little direct relationship between otter populations and the types of bankside (riparian), emergent or submergent aquatic vegetation. Apparently the quantity of plant life is more important that the quality in providing shelter and foraging areas - whether in cold-water environments of the Upper Peninsula or warm-water environments of the southern part of the Lower Peninsula. According to Schofield and J. E. Vogt, high otter populations occur along the watersheds of the Carp, Cedar, Manistique, Menominee, Michigamme, Ontonagon, Presque Isle, Sturgeon, Tahquamenon, Two-hearted and Whitefish rivers in the Upper Peninsula and the Au Gres, Au Sable, Cheboygan, Manistee, Rifle, Tawas, and Thunder Bay rivers in the Lower Peninsula. Most authors emphasize that the otter requires fairly deep water in streams and lakes. In Michigan, however, the animal appears equally at home in rather shallow and plant-filled marshes. In fact, Field noted that winter foods were more abundant for otter in extensive marshland (shallow ponds surrounded by earthen dikes) then along streams in the Upper Peninsula's Seney National Wildlife Refuge. Along streams, otter seem to prefer sites with prominent banks.

Behavior: Otters use dens between tree roots, in hollow stumps, beneath decayed logs, under brush piles, and even within woodchuck burrows. Some of these may be remote from water. In most instances, however, refuges are in bank dens excavated by a muskrat or beaver, or in logjams, beaver lodges or muskrat beds. Apparently, the otter rarely digs a den of its own, but it will enlarge or remodel one usurped from another animal. The otter chooses bank dens with the entrances either well-hidden or underwater, well below the ice line. A nest, padded with wood chips, grasses, leaves, and aquatic vegetation, is located in an enlarged site in the subterranean tunnel, above the high water line. The same den may be used for many years, although the otter may also have several "over-day" resting areas at strategic places in its home range.

Key Components of Habitat: Water quality; permanent surface water, vegetative cover within and adjacent to wetland; structural cover (e.g., logjams, downfall, boulders) to provide cover and foraging sites; den sites.

Management Actions to Enhance or Maintain Habitat Quality: Maintain vegetative cover within and adjacent to wetlands; increase pool:riffle ratio; increase water permanence; encourage establishment or maintenance of beaver populations.

Habitat: As its broad geographical distribution suggests, the river otter is able to adapt to diverse aquatic habitats. Otters are found in both marine and freshwater environments ranging form coastal to high mountainous elevations. Density appears greatest in the least disturbed food-rich coastal regions, including estuaries, the lower portions of streams, and coastal marshes, and inland where lowland marshes and swamps interconnect with meandering streams and small lakes. River otters may be common in the tributaries of major unpolluted drainages with minimal human impact but may be scarce in highly disturbed and polluted areas. Severe winter conditions probably limit densities in northern inland populations.

Melquist and Hornocker found that differences in habitat use by otters resulted primarily from differences in habitat composition. The availability of certain key components (including shelter, food and water) determine the duration and intensity of habitat use.

Riparian vegetation adjacent to lakes, streams, and other wetland areas is a key component of otter habitat. It may attract beavers, which in turn create ponds, bank dens, and lodges that are later used by river otters. Melquist and Hornocker documented the importance of beavers in creating foraging and denning sites for otters, and several states have correlated good river otter habitat with the activities of beavers.

Fallen or partly submerged trees and logjams created during the spring runoff provide shelter and foraging areas for both the river otter and its prey. Cavities among the tree roots, dense shrubs, and tall grass provide escape cover and temporary resting sites. The conditions created by adequate riparian habitat probably increase the likelihood that an area will be used.

In coastal areas, rugged, rocky, indented shorelines associated with short intertidal lengths provided favorable foraging, feeding, and resting sites. However, river otters tend to avoid extensive shorelines that have long intertidal lengths and are devoid of large trees and other riparian vegetation. Otters in coastal southeastern Alaska avoided 5- to 20-year-old clearcut areas.

In the temperate regions of North America where winters are severe (i.e. lakes and streams freeze over and snow accumulates to considerable depths), certain habitats are used only seasonally. In mountainous areas, river otters vacate high elevation streams and lakes during winter and move into valleys.

The availability of temporary dens and resting sites is an important aspect of river otter habitat. River otters select those sites according to availability and convenience, although sheltered sties that provide protection and seclusion are preferred. In Idaho, as many as 88 dens and resting sites were used by one river otter during a 16-month period. Collectively, instrumented otters used 15 different kinds of resting sites 1,283 times. Active and abandoned beaver bank dens accounted for 38% of the sites used by otters. Resting sites such as logjams are naturally attractive to otters because they offer excellent foraging and shelter. Dispersing river otters in Idaho often rested in dense riparian vegetation and snow or ice cavities, probably because the animals were unfamiliar with the location of more suitable resting sites or because none were available.

Suitable river otter habitat must also provide adequate food, as food influences otter habitat use considerably. Instrumented river otters in Idaho remained at a large logjam for as many as 40 consecutive days while feeding on spawning and spent kokanee salmon; the otters left when the spawning run was over. Termed "activity centers" by Melquist and Hornocker because of their high frequency of use, these areas provide adequate shelter, abundant food, and minimal disturbance.