While floating one of Montana’s rivers this summer, you may run into a whiskered, playful fellow floater — an otter. In fact, a group of otters is called a raft.
The northern river otter is native to the state and can be found in streams in the western three-quarters of Montana. They like to eat fish and crayfish, so they have very sharp teeth. They prefer clearer water and so are often seen as a sign of a healthy river or lake.
There are actually 13 different species of otters in the world. The largest is the giant otter of South America, which can grow to almost 6 feet long and weigh up to 90 pounds. Otters are members of the weasel family, which becomes obvious when they run in that slinky, weasel-like lope.
Montana’s otters are much smaller. The biggest can measure close to 4 feet long, about half of which is just their tail. A big Montana otter will weigh only 20 pounds.
What’s cool to me about these water mammals is their hair. The outer hair is waterproof. Under that they have very fine hairs that trap air to provide warmth and allow them to float easily. According to one source, they may have as many as 250,000 to a million hairs per square inch.
Although during the summer otters will become more nocturnal, meaning they are out only at night, I have seen otters in the Missouri River near Townsend in the fall and in Yellowstone National Park at Trout Lake in the spring.
Otters may appear friendly and playful, but they can also be very aggressive if they feel threatened or worry that their babies — called pups — may be in danger. Some people floating on inner tubes have been bitten by otters.
— Brett French, Billings Gazette