The river otter (Lutra canadensis) is the best swimmer of the weasel, or Mustelidae, family. It is at home in streams, rivers, ponds and lakes and is well-adapted for its aquatic lifestyle.
The river otter is a remarkable animal to watch on the move, either in the water or on the shore. Its dense fur coat is prized by trappers. The loss of habitat and over trapping in the 1800s led to a decline in their numbers in Vermont. However, the river otter has made a comeback since.
Suitable habitat for river otters is any wetland that provides adjacent bank vegetation, burrow sites, and a food supply. Otters can be found in streams, rivers, ponds, and lakes. During the winter, they may leave ponds and lakes that freeze over for the open water of rivers and streams.
Burrows may be constructed in the bank or in submerged trees. They will also use the abandoned burrows of other animals including beaver lodges. Factors that are considered in a den site location are food availability, cover, water supply, and human activity. Though otters will commonly "scent" or mark their territories, they generally do not fight in defense of this area.
River otters can be seen at any time of day but are considered to be nocturnal, or most active at night. They are not social. A group may be comprised of a female and her young. Generally, the males live separately except during the breeding season.
They are very intelligent and show a great curiosity and playfulness. Excellent swimmers and divers, a common activity is sliding into the water along riverbanks, seemingly just for pleasure.
In the northeast river otters breed from March to April. After mating, the fertilized egg remains in limbo through a process known as delayed implantation. During this process, all development of the embryo ceases for approximately nine to ten months. After this time, the fertilized egg is implanted into the uterus wall and development of the embryo begins.
After a seven-week gestation period, the young are born in late March to May of the following year. The litter size varies from one to five, with two or three being average. The young are born altricial, (sightless and nearly helpless) and are raised in a leaf or grass lined den of a hollow log or abandoned den near water.
They spend the first couple months of their lives slowly developing and growing. The kits open their eyes after about twenty days. They are generally weaned from their mother's milk at ten to 14 weeks. And by three to four months, they are able to leave the den.
The female otter is responsible for raising the young, teaching them how to swim and hunt, with the male assisting once they are older. At six months of age, the young are mature and independent of their parents. They will reach sexual maturity at the age of two, and females typically have one litter every year.
Regardless of its playful nature, the river otter is still a carnivore that feeds on other animals. Favorite foods include fish, frogs, crayfish, snakes, turtles, amphibians, birds and small mammals.
Unlike some other members of the weasel family, the river otter avoids eating carrion (dead animals). Their preferred food is fish and they will eat trout, bass, and perch. However, the river otter is more likely to take species that are slower swimmers and easier to catch like suckers and bullhead.
The otter uses its sense of sight as its primary means of hunting. Its long, stiff whiskers also aid it in locating and catching fish in murky water. Depending on water depth, the otter will vary its hunting strategy. In shallow water, it commonly walks along and searches for bottom dwelling species under rocks. In deeper water, it searches with its head underwater and, in even deeper water, it will submerge its entire body in search of prey.
The river otter population is monitored closely to regulate hunting and trapping limits. In Vermont, it is protected from over hunting with the season only lasting about five months, from the end of October through the end of March. This time of year is chosen to protect against mothers or newborns being harvested. Another management tool is to protect its preferred habitat. There are some programs in various parts of the otter's range that focus on wetland protection and restoration to maintain current otter populations in these areas.
The river otter has an extensive range covering much of the United States except for the desert regions of the southwest. However, due to loss of habitat, pollution, and excessive harvesting years ago, its numbers have experienced a significant decline.