River Otter (Lontra canadensis)
The river otter has been navigating waterways in North America for quite some time, and the Greater Yellowstone Ecosystem (GYE) is home to the playful little fish eaters. These semi-aquatic mammals are pretty well adapted to water for being half land-dwellers: their eyes are near-sighted for underwater vision, their ears have water-tight flaps, their fur is water repellent and insulated, and they can stay underwater for 2 minutes. Otters eat whatever they can find living in the water when they hunt at night, but they especially love fish. In GYE lakes, otters prefer to eat cutthroat trout, and in rivers or streams they eat longnose suckers when cutthroat trout are not available. Since the introduction of lake trout to the GYE about 25 years ago, these native cutthroat trout populations that river otters depend on have been declining. This is problematic for otter populations because otters do not eat lake trout, so competition between invasive lake trout and cutthroat trout is resulting in their food becoming more limited.
River otters are quite social mammals that are tightly wound into the ecosystem. They live in burrows close to water with an opening above ground, but in winter the only available opening is into the water. They are inherently stealthy because they have both land and water predators, including humans who trapped them for their fur. Otters grow up to 30 pounds and just over 2 ft long, so their size helps them defend their large dens. The male otter typically does not help with raising pups. It’s often just the mom that raises the litter of 6 or less pups in underground dens, making sure they are ready to swim at just two months old. Otters tend to live in social groups; some groups are all related individuals, some are all unrelated males, and some are couples. They play games with each other, catch and release fish for sport, and talk to each other with whistles, chirps, chuckles, and growls—would you believe that they are considered shy? Even though they are active all year round, it is super lucky if you get to see them in many GYE waterways and lakes—common otter hangouts are Oxbow Bend and the Yellowstone River.
Written by Celia Karim
PC: Brian Gratwicke on Flickr. https://flic.kr/p/cXuY8j