Over 50 inches of snow already this winter is making it challenging for fish as well as some wildlife in north-central Minnesota.

The biggest potential impact may be on fish populations, particularly largemouth bass.That’s because lakes have been under more than a foot of snow since the beginning of December.

Doug Kingsley, the Park Rapids area fisheries supervisor with the Minnesota Department of Natural Resources (DNR), said heavy snow blocks sunlight. As a result, aquatic plants die and decompose.

“During decomposition, bacteria use up oxygen. It also depends on how long the lake is snow-covered. The way it’s shaping up, it’s probably going to be a bad winter for fish.”

Kingsley said fish in shallow lakes with a mucky bottom and lots of organic matter are more likely to suffer winterkill. “Moran, south of town, Portage, Middle Crooked and some up in the northern part of the county like Hennepin,” he said. “Big lakes, like Long and Mantrap, have a large enough volume of water to buffer the effects of oxygen loss.”

He said later in the winter DNR staff will check lakes with a history of winter kills with a meter that analyzes the parts per million of dissolved oxygen to see what their status is. “If we’re seeing lots of low oxygen measurements then we’ll maybe expand to some of the other shallower lakes,” he said. “If we find problems with low oxygen levels, then we’ll go in the spring and set some nets to evaluate the extent of any winterkill and if we’re finding we’re missing species, then we may restock.”

Kingsley said that largemouth bass are more susceptible to low oxygen levels, while northern pike are a little more tolerant.

“Unfortunately, bullheads are the most tolerant,” he said. “In some cases, they’re the only thing that’s left after a winterkill. Walleye and muskies are usually in bigger lakes so they’re not as much at risk.”

An early spring could help reduce winterkill. “If we get melting that runs off into the water, that adds oxygen and would be helpful,” he said.

Deer are adapting to deep snow

For deer, deep snow makes it more challenging to find food. To conserve energy, they follow existing trails, when possible.

Erik Thorson is Park Rapids DNR wildlife supervisor. He said deer will take the path of least resistance by using trails made by humans. They also tend to “yard up” in an area with conifer cover where the snow depth is less.

With the feeding ban to help prevent the spread of chronic wasting disease in place and much of their food source buried under the snow, deer are browsing on the tips of branches and standing corn.

“In agriculture areas, there is a fair amount of corn that was not harvested this fall,” he said. “Even without human food sources, deer are pretty well adapted to survive severe winter conditions as long as they have good habitat and natural browse within their reach. They also don’t need as much food in the winter because their metabolism changes.”

Thorson said it is the combination of snow and cold that takes a toll on deer populations, and while this winter has had cold snaps, it has not experienced long periods of below zero temperatures.

Impact on birds

Ruffed grouse, who dive into the snow for protection from the cold at night are enjoying a good winter, while more snow on the ground is making it harder for wild turkeys to find food.

“This is a really good winter for ruffed grouse because of the light, fluffy snow they can roost in to stay warm, so they’re not exposed to those cold temperatures like they would be on a branch,” Thorson said. “These are ideal conditions for them. They fly out during the day to feed and then return to their snow roosts where they are well-insulated at night.

It is a different story for turkeys. “Deep snow is more of a problem for them than for deer,” Thorson said. “Turkeys need to get to ground level to get to their food, so usually they winter near farms or where there are bird feeders.”

Most small birds who stay here for the winter have adapted to both snow and cold. During our recent January thaw, lack-capped chickadees have even been heard whistling their “phoebe” pre-breeding song, a sign spring will return to the northwoods.

“January 22 is the average coldest day of the year,” Thorson said. “A lot of bird activity, like breeding calls, is also dependent on the length of the day, so you will hear those more as we move towards spring.”

Winter Severity Index

The DNR website features a map showing the numbers for the Winter Severity Index (WSI) for each region of the state. One point is given for each day of zero degrees Fahrenheit or colder and each day with 15 or more inches of snow on the ground. Higher numbers mean a more challenging winter for deer, with an index of 180 or greater considered severe.

“Most of the state is still under 50 right now, but this could still be a significant winter,” Thorson said. “We’ll have to wait and see how February and March play out.”

WSI numbers are reported by observers around the state and updated weekly on the DNR website.