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Otters in the Northwoods

Image by Peter Hoare from Pixabay

This week’s Wildlife Matters was inspired by a Curious North question, which piqued the interest of the Masked Biologist who shares several interesting facts about otters with all of us.

This feature was inspired by a Curious North question from Christy in Hazelhurst who asks “Where do otters live? Do they sleep part of the winter or are they active? Are they strictly fish eaters? Any information about them would be awesome! They are one of my favorite creatures.” Well, Christy, I have about five minutes to try to make you into an otter expert, so here are a few otterly interesting facts.

Historically, we had otters across a good portion of Wisconsin. In the late nineteenth and early twentieth century, otter numbers dwindled; they were given protection as a managed species around 1915. Careful management brought otter numbers back, and today it is not uncommon to see otters in Northwoods lakes and rivers. Our last otter flight survey seemed to indicate that our otter populations are declining slightly in northern Wisconsin, with an estimated statewide population of just over 10,000 otters coming into this winter, slightly but steadily increasing since 2002.

The main reason for taking otters was for its fur. It is considered one of Wisconsin’s sturdiest and best wearing furs. Going back to the early 1800s, before Wisconsin was even a state, an otter pelt at the Green Bay fur depot was worth twice that of a beaver pelt, which means they could be worth up to $5. That was a lot of money back then – probably equivalent to $125 in modern dollars! Today, otter pelts are still fairly valuable; last winter, the average price of an otter pelt paid by fur buyers was $22.84.

Interestingly, our otters here in the Northwoods have played an important role in a reintroduction effort in Colorado. The last native Colorado otter was captured on the Green River in 1906.  After 70 years of no otters in the state, they undertook an ambitious re-stocking program, bringing more than 100 otters from Newfoundland and 8 U.S. states, including Wisconsin. Northwoods otters were transplanted into the Gunnison, Piedra, and Upper Colorado rivers between 1976 and 1984.  According to the Colorado Division of Wildlife, breeding populations of otters have become established, which allowed down-listing from “endangered” to “threatened” in 2003. 

Otters are basically a semi-aquatic mammal. They spend a lot of time swimming in the water, and they have thick, dense, shiny fur that helps them move easily through the water. So, their fur and muscles are developed and adapted for swimming. Otters are one of the mustelids, a group of related animals like weasels, mink, badger, and fisher. These animals have long bodies compared to relatively short legs. Many of them have a kind of lunging gait, which makes their footprint pattern very easy to identify in the snow. In the winter, having long bellies and short legs, otters employ a unique mode of overland travel; they use a combination of lunging hops and belly slides. In heavily-used areas, these slides can be up to 60 feet long. These slides are so large and visible they can serve as indicators of otter numbers in aerial surveys. You have driven over a slide or two before on rural snow-covered roads, I’m certain; you just didn’t realize it.

There is a perception that otters eat prized game fish, especially trout, and for this they are despised by many fishermen. The studies I have seen indicate that they do eat fish, some of which are game fish, but they eat a variety of other aquatic menu items as well. One study from Michigan examined the stomach contents of 95 otters and found the largest amount of material in their stomachs was non-game forage fish and amphibians. All told, about 23% of their diet was game fish. Otters also eat aquatic insects and a good number of crayfish.

Otters dig a burrow into a bank or shore, complete with an underwater entrance. That way they can use it year-round. They can stay submerged for a couple of minutes between breaths, and dive over sixty feet. In the winter, they will find trapped air bubbles in the ice to help them swim from one hole to another. This means you may see otter slides between ice auger holes or aerator holes on some lakes as well. Thanks for the great questions Christy!

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The Masked Biologist is a weekly commentator on WXPR talking about natural resources and wildlife in the Northwoods. He is anonymous so that he can separate his professional life as a biologist from his personal feelings about the natural world.