Winter Redux: What Do Fish Do Under the Ice?

This weekend saw temperatures in the 20s, the sun shining and scores of anglers sitting over holes in the ice of Madison lakes. So we thought we’d revisit a post from this time last year – what life is like for the fish in winter.
These guys can't wait for ice-off so they can start sneakin' Photo: Fargo-Moorhead Dive News

These guys can’t wait for ice-off. Photo: Fargo-Moorhead Dive News

[Originally posted Jan. 30, 2015] – While we’ve been spared (so far) by any sort of climate shenanigans like a polar vortex this winter, our lakes have had a nice thick cover of ice on for a month or more. And lots of people ask variations of the question – what’s life like for fishes under the ice?

Well, the short answer is “Not much different than the rest of the year.” They eat and breathe and try to avoid becoming lunch.But there are some interesting elements to winter life, so we asked CFL grad student, Alex Latzka to help explain. (NOTE: Alex is now a post doctoral research at McGill University)

Up on land, while everything from bears to bats to turtles to raccoons is all curled up, cozy and hibernating, fishes have no such luxury. They have to keep moving enough to pass water over their gills and continue to breathe. But, still, Latzka says, everything slows way down.

“Most forage fishes (like bluegill, or other species that serve as prey for bigger fish) have to stay really still and not expend a lot of energy,” Latzka says. “So they are hanging out in structure, or weed beds, where there’s cover and some food.”


Alex Latzka holds up an impressive pike pulled form the ice of an “undisclosed” Madison lake. Dan Oele assists.

Predators, like northern pike, are then hanging out near the weed beds waiting for something to venture out. Still, Latzka says, “They’re not eating a lot.” Cool water fish like pike and bluegill lose weight in winter, since they can’t find enough food to make up for the “metabolic cost,” or calories they’re burning just staying alive.

In fact, according to the book, “Ecology of Teleost Fishes,” by Robert J. Wootton, in some instances, fish like bluegill won’t eat all winter long, relying on fat stores they accumulated in the fall to get by.

Burbot. Image: New York DNR

Burbot. Image: New York DNR

On the opposite end of that spectrum, cold-water species of fishes thrive in these conditions. While a pike looks a little worse for wear in spring, species like burbot come out of the experience fat and happy. We don’t have burbot in Lake Mendota, but we once had lake trout and cisco, other cold water species that loved long winters, since they weren’t confined to their summer hangout in the coldest, deepest parts of the lake.

And that brings us to another winter issue for fish under the ice – oxygen. With the “lid” on the lake, precious little oxygen enters the water column and  fish are left to survive on what got mixed into the lake in the fall. That’s one reason they slow down so much – being all active and burning through their oxygen reserve is a bad idea.

Oxygen is particularly limited at the bottom of the lake, where microbes are decomposing all of the organic matter that settled out during more productive months. Thanks to the overabundance of nutrients driving all of that growth (and algal blooms) during the summer and fall, Lake Mendota has a LOT of organic matter resting on the bottom and those microbes use up a ton of oxygen breaking it down. The end result can be either hypoxic “low-oxygen” or anoxic “no-oxygen” conditions at the bottom of the lake.

These so-called “dead zones” can also form in summer and are a big reason why you don’t see lake trout or cisco in Lake Mendota anymore – those fishes couldn’t survive when the only remaining parts of the lake with cold-water habitat kept running out of  oxygen every summer.


This is as much excitement as this pike (and Alex Latzka and Jereme Gaeta) will have all winter! Photo: A. Hinterthuer

One final thing about life under the ice that Latzka finds fascinating, is that, in winter, a lake’s habitats get a lot less diverse. “In warmer months, the temperature can vary all over the lake,” he says. Water is nice and warm at the surface, still quite cold down deep, and all sorts of temperature in between those two extremes.

Every species can spread out in search of their optimal temperature comfort zone.

But in winter the entire lake is, more or less, the same temperature. Usually 3 or 4 degrees Celsius. And that leads to behavior you won’t see quite so dramatically in summer.

“If you find warm water inlets,” Latzka says, “and let me qualify by saying ‘Be careful walking on ice near warm water inlets!’ But, where you have pulses of warm water, a lot of species of fish are going to want to be in it, because those levels of temperature change, just a couple of degrees, effects how active they’re going to be, how much they can eat and they’ll grow better in those conditions.”

So there you have it – the not-quite-exciting story of life under ice for our fishes. They mostly stay still, hang out in the same spot and, like a lot of us, wait for spring and open water to get back in action.

CFL at the Shedd Aquarium: World Fish Migration Day, May 24th!

Stop by the Shedd on Saturday and get your picutre taken AS our very own Solomon David!

Stop by the Shedd on Saturday and get your picutre taken AS our very own Solomon David!

At the break of dawn this Saturday, May 24th, Center for Limnology researchers and your trusty blogger will hit the road for Chicago’s Shedd Aquarium. Once there, we will help Shedd researchers and volunteers set up a number of activity stations celebrating World Fish Migration Day (WFMD).

What is WFMD, you ask? Well, it’s a one-day global initiative featuring 270 events around the globe all in the name of raising awareness about the importance of migratory fish to ecosystems and economies around the world.

The WFMD website has a great interactive map showing where each event will be held.

World Fish Migration Day Event Map

Our own event at the Shedd will feature a “fish safari” for kids, where they’ll grab a passport and search for five different migratory fish from around the globe within the Shedd’s tanks. We’ll also have life-sized cut-outs where kids can pose as a scientist holding a migratory fish and a science poster session where researchers will discuss their work.

CFL post doc, Steph Januchowski-Hartley loves her work - and it loves her.

CFL post doc, Steph Januchowski-Hartley loves her work – and it loves her.

In our own neck of the woods, pike, suckers, sturgeon and more head upstream to spawn each year. But barriers like road culverts and dams can stand in the way. WFMD is hoping to underscore the importance of open rivers for migratory fish and teach people about some of the amazing journeys our finned-friends make for their own survival.

Researchers here at the CFL, especially students and scientists working with our faculty member, Pete McIntyre, are hard at work on things like mapping barriers for Great Lakes migratory fish and tracking and tagging migratory pike.

If you’re in Chicago this weekend, come on out and say hello!

Fish Fry Day Video: Walleye on the Run

While our post doctoral researcher, Solomon David, prefers more primitive fishes, like the northern pike he was recently catching, tagging and studying during their annual spring migration run, he also stumbled across (okay, waded into) a more modern fish migration. Enjoy this great underwater footage of walleye on the run. And Happy Fish Fry Day!


Fish Fry Day: Fish Q? There’s an App for That

The WIsconsin Fish mobile ID app, your starting point for becoming an expert in local fishes. Photo: A. Hinterthuer

The Wisconsin Fish mobile ID app, your starting point for becoming an expert in local fishes. Photo: A. Hinterthuer

Happy Fish Fry Day! Restaurants around Wisconsin are warming up the deep fryers for our weekly feast and we’re putting fish on the menu here at the blog. Today’s special is an all-you-can-eat buffet of ichthyological goodness, thanks to an awesome new (and free) app for your smartphone, “Wisconsin Fish”

From trophy muskies to the multitude of minnows and every fish in between, “Wisconsin Fish,” has got you covered. A collaboration of the University of Wisconsin Sea Grant Institute, the Wisconsin Department of Natural Resources and yours truly, UW-Madison’s Center for Limnology, Wisconsin Fish is both an online tool and a mobile app that will help you learn about and identify any fish you pull out of our waters.

In our humble opinion, is a “must have” app. Here’s how it works: Continue reading

Fish Fry Day Goes Primitive

Happy Fish Fry Day, Folks!

It’s the day when we (sometimes!) feature fish on the blog and any restaurant worth its salt features fish on the menu here in Wisconsin. Today we’re just going to pass along a cool site called “Primitive Fishes.”

It’s a blog kept by UW-Madison Center for Limnology postdoc, Solomon David (a member of the McIntyre lab). Unfortunately it’s about all we see of Solomon, because he’s conducting his post doctoral appointment at Chicago’s illustrious Shedd Aquarium, where he’s working on conservation of Great Lakes migratory fishes.

Some of his work on northern pike was recently featured in National Geographic. You may remember the pike migration story from a grad student we do see in the office, Dan Oele.

Anyway, here’s to the fish that have been plying our waters long before we came upon the scene. Happy Fish Fry Day!

Fish Fry Day: Northern Pike

Well, it’s that time of the week again. The day in Wisconsin offers up its fabulous fish fry dinners and the day here at the blog where we celebrate some of our favorite fishes. If you missed the first installment of “Fish Fry Day,” you can learn more about that beautiful panfish, the pumpkinseed, by reading this blog post. Today, though, we’re featuring a fish with a bigger, well, bite. Ladies and gentlemen – the northern pike.

CFL grad student, Zack Lawson pulled this impressive pike out of Lake Mendota this winter right outside Hasler Lab's doors. Photo: Dane Oele

CFL grad student, Zack Lawson pulled this impressive pike out of Lake Mendota this winter right outside the doors of Hasler Lab. Photo: Dane Oele

This time last year, the blog was up in Green Bay with CFL grad student, Dan Oele, trying to catch some of these beautiful and popular sport fish on their annual spring spawning runs. Thanks to crazy warm weather in March, though, most pike had already headed back out to the bay before we arrived. Luckily, we did find one slow-moving specimen. Continue reading

Tracking Northern Pike in Green Bay

CFL grad student, Dan Oele, is trying to see if pike return to their “birthplace” to spawn or if any ol’ tributary will do. Thanks to funding from the Great Lakes Restoration Initiative, Oele is out in Green Bay working on an answer. Watch (or read) below:

GREEN BAY — It’s the second day of April and Dan Oele is cruising the tributaries of Green Bay on the hunt for northern pike. Continue reading