What you should know about fish and their habitat during winter
Fish fly south for the winter.
Where do fish go in the winter?
As winter closes in, fish need to find safety in a warm, well-oxygenated area of the lake.
Due to fall turnover, more dissolved oxygen is available at the bottom of the lake, which still retains some warmth, even as ice forms on the surface. The hypolimnion averages a chilly 35 degrees Fahrenheit in the winter, and although cold water retains oxygen better than warm water does, oxygen levels do change under the ice. Fish rely on the fall turnover, underwater plants and sunlight to regulate dissolved oxygen levels in the winter.
At a bare minimum, fish need at least 2.0 mg/L of oxygen in the water in order to survive.
Fall turnover is a natural phenomenon that allows the lake to mix in a wind-powered cycle. During this cycle, the dissolved oxygen from the top layer of the lake moves to the bottom of the lake until ice forms across the surface. After the lake freezes, the only new dissolved oxygen is produced by underwater plants, so it has to be used sparingly.
Fish conserve oxygen use by entering into a state called “torpor.”
What is torpor?
Torpor is a very “chill” state of living.
When in torpor, fish compensate for limited dissolved oxygen and food by shutting down much of their metabolism. Their heartbeat, breathing and muscular activity slow significantly, making them lethargic. While fish use small amounts of dissolved oxygen as they lazily rest in the cold water, bacteria use dissolved oxygen to decompose plant material produced during warmer months. Some plants, like floating-leaf pondweed, die as the temperatures drop. They accumulate on the bottom of the lake with other organic material. Decomposition uses large amounts of the lake’s dissolved oxygen.
If there are too many decomposing plants, then dissolved oxygen could deplete faster than it can be replenished and suffocate the fish. (If you have noticed a fish kill in the spring, it was likely caused by depleted dissolved oxygen during the winter!)
On the other hand, underwater plants (those rooted in the bottom, like curly-leaf pondweed, and those that are free-floating, like some hard-weather algae) can produce oxygen as they photosynthesize. Clear ice is better, because it lets sunlight pass through. Deep snow cover lets very little sunlight through. The whole balance of dissolved oxygen under the ice depends on the snow on top of the ice! Of course, when the snow and ice melts, spring turnover will bring fish large amounts of oxygen once again and plants will have all the sunlight they need.
How does all of this relate to ice fishing?
How to ice fish
Before you fish, check the ice.
There needs to be at least four inches of ice for safe ice fishing, according to the Indiana DNR. If you want to take a vehicle on the ice, like a snowmobile, car or truck, you need between five and ten inches of ice, depending on the size of the vehicle. The best way to check the thickness of the ice is to drill a hole into it.
Use a short pole, but a long line.
Ice fishers don’t need long poles because they don’t cast their lines out, but they do need a long line to reach all the way down to where the fish are hiding.
Use colorful lures.
Fish use very little energy while they are in torpor, so getting their attention can be tricky.
The fish also eat significantly less in the wintertime than they do any other time of the year; zooplankton, phytoplankton and other fish can be hard to find, especially when snow is covering the ice. With all that snow, the bigger fish, who are often visual predators, can have a hard time seeing. This is why many ice fishers prefer colorful lures that more effectively draw a fish’s attention.
Wear a life jacket and take a buddy.
The life jacket will provide extra warmth and keep you afloat in case of an emergency. Using the buddy system will ensure that someone is there to help you if you fall through the ice.
The lakes are filled with native plants, fish and wildlife that all help to keep the lake healthy. Take a look at what good lake ecosystems look like and how to keep them clean!