The playful North American river otter is equally at home in the water and on land. It makes its home in a burrow near the water’s edge, and can thrive in river, lake, swamp, or estuary ecosystems. Otter abodes feature numerous tunnels—one of which usually allows them to come and go from the water.
These otters swim by propelling themselves with their powerful tails and flexing their long bodies. They also have webbed feet, water repellent fur to keep them dry and warm, and nostrils and ears that close in the water. They remain active in winter, using ice holes to surface and breathe. They can hold their breath underwater for some eight minutes.
On land, river otters can bound and run quite well, if not quite as effectively as they swim. They love to playfully slide down snow-covered, icy, or muddy hills—often ending with a splash in the water. Otter families of mother and children can be seen enjoying such fun, which also teaches survival skills.
Otters breed February or March and have 3-4 pups per litter. Males do not help raise young otters. Females retreat to their underground dens to deliver litters of one to six young. When the young are only about two months old, they get an advanced swimming lesson—their mother pushes them into the water. Otters are natural swimmers and, with parental supervision, they soon get the hang of it. Otters measure about 3-4 feet long with a 12-18 inch tail.
Preventing Conflicts with Otters
River otters are often blamed for preying on wild game fish, particularly trout. Nevertheless, studies indicate that the bulk of the river otter’s diet consists of non-game fish species. However, river otters—particularly families containing young pups in spring—occasionally cause severe problems in fish hatcheries and private ponds. Otters also den under houses, decks, and other structures near water, and the smell of their droppings and discarded food remains can be unpleasant.
To prevent conflicts or remedy existing problems
Eliminate access to feeding sites and other areas. Because river otters have heavy bodies and aren’t jumpers, a 4-foot high fence constructed with 3-inch mesh wire can keep them out of an enclosed area, such as where fish or aquaculture activities are concentrated. Because river otters are strong, fences should be sturdy and extend 6 inches below the surface to prevent otters from pushing under the fence. Alternatively, include a wire apron on the animal side of the fence to prevent otters from entering from underneath.
River otters are resourceful and will thoroughly investigate fence lines to find a way into a food source. They are known to use abandoned animal burrows as routes under fences. So, inspect fences regularly to make sure river otters have not dug or pushed their way under or worked their way over them.
Provide fish with hiding places. Give fish safe places to hide by constructing sturdy hiding places on the bottom of ponds using cinder blocks, ceramic drain tile, wire baskets made from leftover galvanized fencing, or upside-down plastic crates held in place with heavy rocks. In larger ponds, attach a group of cut conifer trees to a heavy anchor on the bottom of the pond. Eliminate access to convenient denning sites. Close potential entries under porches, houses, sheds, and other structures with ¼-inch mesh welded-wire (hardware cloth), boards, or other sturdy material. Aluminum flashing, or aluminum or stainless-steel hardware cloth is recommended in saltwater areas since galvanized materials quickly corrode.
Eliminate noxious odors. Commercial odor-eliminators can be used to remove the smell of otter droppings and other debris under structures. Such products are available through hospital supply houses, drugstores, pet stores, and from the Internet using the keywords “Pest Control Supplies.” If the smell is really bad, the beams and other areas under the structure may have to be cleaned with a bleach solution (1½ cups of household bleach in 1 gallon of water). Be very careful of fumes.
River Otter in or Under Buildings
Occasionally a river otter will find a suitable den site in or under a building. Otters normally occupy a den site for only two or three consecutive nights. However, during the mating and nesting season, females are attracted to warm, dry, dark, easily defended areas, and will remain longer if the setting remains favorable. You may choose to let otters occupy an area, such as under an outbuilding, if they don’t pose a problem. Should you choose to remove the animals, a wildlife control company can be hired (call the hotline to find one near you), or you can complete the process yourself using the steps below.
1. Seal all openings except the main entrance used by otters. Use sturdy wire mesh (1/4-inch hardware cloth or similar materials) to screen vents near ground level in houses and other structures. Tightly seal holes in foundations or under porches to prevent otters from entering.
2. To determine entry points, you can use “tracking patches” of a fine layer of sand, flour, or dust placed at suspected entrances. Wadded up newspaper lightly stuffed into the entry hole also works great. Otters will push the paper out of the way when exiting.
3. After dark, when the otter has left seeking food they will leave tracks at the den entrance. Inspect the powder or the dislodged newspaper for exiting otter tracks.
4. Once a otter has left the building, immediately seal the entrance with a hardware cloth “one-way door”. (You will not want to permanently exclude at this point, not being sure of the number of otters present.) The one-way door can be made from 1/4 -inch hardware cloth that is attached over the opening, and hinged at the top and left loose on the other 3 sides. It should be larger than the opening so that it cannot swing inward. The otter will push it open to leave, but cannot re-enter.
5. Put a layer of flour on the inside and outside of the door after the one-way door has been installed for two to three nights. Any footprints in the flour should be outside the door with none inside. This means the otter is out. If you have any doubt, then smooth out the dirt on both sides of the door with your hand or a tool, reapply the flour and observe. Once a couple of days have gone by with no footprints, the skunk is probably gone. Another way to check is to open the door and shove a few pieces of wadded up newspaper into the otter’s entrance. If the paper stays in place for two to three nights, then the otter is gone.
Important Note: Be sure all animals are out before sealing up the entrance. Pay close attention and use extra caution if trying this option March through May when babies may be in the den. If you find babies in the den, please call the Wildlife Hotline @ 1-855-WILD-HELP for further instruction.
To try and drive an otter away, consider harassing the animal. Lighting up the den site with battery operated flashing lights and adding a portable radio can cause a otter to seek a more suitable habitat.