Monday, December 23, 2013

The ice abides: The otter slides

Last winter for the first time, on one of my walks around the rim of Birch Lake, I saw otter tracks in the snow. I wasn’t certain that’s what I had seen until I did a little research – which also told me I wasn’t rightly interpreting what I had seen.

Along the frozen shore of your lake is a great place to look for otter tracks, especially before the snow gets too deep. Otters (technically river otters, scientific name Lontra canadensis) come out of their winter burrows, usually near water, to forage for food.

The tracks I saw had paw-print trails interrupted by long, slender depressions in the snow. I assumed those depressions were made by the otter’s belly dragging. That wasn’t quite accurate. Actually, according to an article from Wisconsin Natural Resources magazine, otters “conserve energy moving across the snow by taking a few bounds and then sliding on their tummies. From above, these tracks look a bit like Morse code, in a dot, dot, dash pattern.” Otters can travel quite fast, about 15 to 18 miles per hour, faster than most people can run.

So knowing what I do now, I am even a little more inclined to be anthropomorphic about otters and say: Here’s an animal that knows how to enjoy life.


I followed the trail of last winter’s otter until I came to a hole in the ice up against a mucky shoreline interlaced with tree roots, near our lake’s outlet to a creek. I had followed him (or her) home. Go down to your lake soon and see if you can’t find an otter’s trail to follow across the snow. 

Thursday, December 19, 2013

The ice abides: If Thoreau had a Secchi disc

Your lake is probably clearest at the time you’re least likely to be looking down into it – which is now, in winter, the water encased in ice and covered with snow.

Lakes clear up in winter for a variety of reasons. Cold water slows down the growth of algae (phytoplankton). In addition, the snow cover shuts out sunlight so that the algae cannot photosynthesize (make food) and so die back. Also, in essentially a closed vessel, the water is very still – no wave action from wind or boaters means bottom sediments are not stirred up and particles suspended in the water can settle out. There’s no rainfall runoff to wash soil and debris into the lake. Water still enters from springs, but that’s groundwater, essentially clear.

If you’re lucky enough to experience an early winter when the lake freezes solid enough to walk on, and a week or so goes by with no snow, you can enjoy a real spectacle. Even in fairly deep water, you can see all the way to the bottom and make out every detail.

Scenes like this remind me of a favorite passage from Henry David Thoreau’s Walden, telling about the clarity of the author’s beloved pond:

“Once, in the winter, many years ago, when I had been cutting holes through the ice in order to catch pickerel, as I stepped ashore I tossed my axe back on to the ice, but, as if some evil genius had directed it, it slid four or five rods directly into one of the holes, where the water was twenty-five feet deep.

“Out of curiosity, I lay down on the ice and looked through the hole, until I saw the axe a little on one side, standing on its head, with its helve erect and gently swaying to and fro with the pulse of the pond; and there it might have stood erect and swaying till in the course of time the handle rotted off, if I had not disturbed it. Making another hole directly over it with an ice chisel which I had, and cutting down the longest birch which I could find in the neighborhood with my knife, I made a slip-noose, which I attached to its end, and, letting it down carefully, passed it over the knob of the handle, and drew it by a line along the birch, and so pulled the axe out again.”


I wonder what a Secchi disc clarity measurement would have yielded in water that clear. Of course, Walden pond was naturally clear – Thoreau reported seeing the bottom 25 to 30 feet down while canoeing even in mid-summer. Your lake most likely is not that clear; my lake (Birch, near Harshaw, Wis.) certainly isn’t. Still, I long to experience an early December of clear ice. It almost happened this year. A couple of cold, still nights created a smooth skin, but then came snow. Now about a foot of snow lies on the ice; there will be no looking down into clear, cold water this year.

Friday, December 13, 2013

The ice abides: Turtles in winter

On my winter walks on the Birch Lake ice I come upon fallen logs where, in summer, painted turtles line up to sun themselves.

You may have asked, “Where do the turtles go in winter?” And that’s an easy answer, right? To the lake bottom, to hibernate. But then, we know turtles aren’t like fish. They spend a lot of time underwater, it’s true, but they don’t have gills. They need to surface to breathe; we’ve seen their snouts poke up in calm water, then disappear.

So, if in summer they need to surface every so often for a breath, how do they survive under the ice for, say, four to five months with no access to the air? It turns out they actually can breathe down there – though not with their lungs, by way of the snout. And they need very little oxygen to make it through the winter, because their metabolism slows to almost nothing. 

At the lake bottom, the winter water temperature hovers around 4 degrees C (39 degrees F). Since turtles are cold-blooded, that becomes their body temperature. They become extremely sluggish; if they crawl or swim at all, it’s very slowly. Their hearts slow down to as low as one beat every ten minutes. They eat very little, if at all.

Yet because their body functions don’t shut down completely, they need oxygen. They get it from the oxygen dissolved in the water. It enters their bodies through the linings in the mouth and throat, and through two small sacs near the anus with very thin skin, laced with numerous tiny blood vessels. They could never survive breathing this way in summer, when their metabolism is high, but in winter, it’s enough. Larry the Bullfrog speaks about living in Wisconsin

So unless we go through a winter of truly epic proportions, there will be enough oxygen in the water for turtles to survive. And next summer we’ll see them again, sunning themselves on those same old fallen logs.

Monday, December 9, 2013

The ice abides: When winter kills

When winter starts this way – snowy and very cold from early December – we know we’re in for a long slog until spring. We may worry about the birds, about deer starving in their yards, and about the fish in our lakes, especially if those lakes are shallow. We’ve all heard of winterkill. Can a lake really freeze clear to the bottom?

Well, not likely. But that doesn’t mean a long, cold winter can’t kill fish. It can, and it does. Only it’s not the ice that kills them – not directly anyway. They die from lack of oxygen, which is to say, from suffocation. The ice seals the lake, cutting off the supply of fresh air. The water’s oxygen level then has only one way to go, and that’s down. The fish themselves, and the decay of organic matter, use up oxygen. If the ice cover remains for too long, there’s so little oxygen left that the fish can’t breathe.

Fish need a certain level of dissolved oxygen in the water – at least 2 parts per million. An oxygen concentration below 1 part per million is lethal to many if it persists. Fish that are the most vulnerable are those in shallow lakes with lots of vegetation and mucky bottoms rich in organic matter.

“Winterkill begins with distressed fish gasping for air at holes in the ice and ends with large numbers of dead fish, which bloat as the water warms in early spring,” says an article on the Michigan Department of Natural Resources website. Of course, some fish tolerate low oxygen better than others. Bass, walleyes and bluegills are fairly tolerant; perch and northern pike are more so. Bullheads can withstand severe oxygen depletion.

“February is usually a critical period and is the best time to check the oxygen content of lakes prone to winterkill,” says the Michigan DNR article. “A good mid-winter thaw about then often recharges the lake’s oxygen supply by means of photosynthesis and melt water. Conversely, a prolonged winter, with continuous snow cover and late ice-out increases the chance of winterkill.”

People on many small lakes protect them against winterkill by pumping in air with motor-driven aerators. It’s effective, though not a permanent solution. The real answer is to reduce the amount of nutrients entering the lake – nutrients that feed an abundance of plants that ultimately die, decompose, and deplete the winter oxygen supply.

Property owners can help by avoiding lawn fertilizers and making sure their septic systems are functioning properly, instead of seeping nutrient-rich water into the lake. Of course, some lakes are just naturally rich in nutrients, and in such cases there isn’t much lake residents can do, short of an extremely costly process of dredging out sediment. Winterkill in such cases is just part of the natural cycle. 

What happens to lakes that go through winterkill? Well, seldom do all the fish die. Enough usually make it through to reproduce. If the lake has an inlet stream, fish may come in that way and repopulate it faster. Nature takes its course; things heal. Some even maintain that a minor or moderate fish kill can be good for a lake: The fish populations are thinned out so there is more food for the survivors, which then prosper and grow.

Still, a winter die-off is not something to look forward to. If you live on a shallow lake, or if you have such a lake as a favorite fishing spot, a long and harsh winter can be a legitimate cause for worry.

Thursday, December 5, 2013

The ice abides: In cold blood

What’s it like to live under the ice? We’ll never know the sensations, because after all, we’re not fish – and we can never relate to their experience because our metabolism is radically different from theirs.

We are warm-blooded; fish (along with frogs, crayfish, turtles and other water creatures) are cold-blooded. Our bodies regulate our temperature; much of the energy we consume as food goes to feed the inner furnace that keeps us at 98.6 (or so) degrees F. Cold-blooded creatures’ temperatures rise and fall with the temperature of their environment, which means right now the fish in your lake are at somewhere around 40 degrees F, just like the water.

What does that mean in a practical sense? It means the fish are quite sluggish. Their muscle movements rely on complex chemical reactions that proceed rapidly when warm and slowly when cold.

Imagine what it would be like to live in cold water as the warm-blooded mammals we are. Staying warm would be impossible. Even at 70 degrees, water pulls heat out of our bodies dramatically faster than does air at a similar temperature. At 40 degrees water temperature, our bodies simply could not keep up; we would be uncomfortable to say the least and would die soon from hypothermia. Think about the mammals that live in water (like whales) or spend a lot of time in it (seals, sea otters, walruses). Their adaptations tend to include heavy fur, a thick layer of insulating blubber, or both.

Cold-blooded creatures are perfectly fine in cold water. They don’t have to heat themselves, which means they don’t use a lot of energy. They don’t have to eat a great deal in winter because the cold tamps down their metabolism. Ice anglers can see evidence of this in the fish they catch and clean – the stomachs are often full of food. Prey that might digest in a day in summer may take a week in winter.

You may have wondered, if you ice fish, why you catch certain species in winter more so than others. It’s because fish react differently to the cold. Walleye and northern pike eat plenty as ice forms, weeds die back, and prey fish become more exposed. Bass and muskies, on the other hand, don’t move around much and eat just enough to sustain basic functions.

Where do fish go in winter? Some stay relatively near the surface where the water contains more oxygen. Some hunker down in the depths. Bullheads bury themselves in the bottom, not actually hibernating but moving very little.Many fish hang around the same kinds of places they haunted in warmer times – weed beds, brush piles, manmade cribs and other cover. Bluegills, for example, crowd around cover for protection. The flips side is that their presence in turn attracts predators, like northern pike.

Right now, the air temperature over my lake (Birch, near Harshaw, Wis.) hovers in the single digits, and a wind whips over the snow. Talk about wind chill all you want, but being in the water below the ice would feel much colder. This warm-blooded creature is glad to have a heated cabin and a bowl of soup to come to after a walk.


Tuesday, December 3, 2013

The ice abides: What if you break through and fall in?

It’s every winter adventurer’s nightmare: Breaking through the ice on a lake or river and falling into deep, frigid water. It’s obviously an adventure to be avoided, but also to prepare for, just in case the worst should happen.

First, remember that ounce of prevention. If you’re not sure the ice is safe, stay off or, at the very least, stay where you know the water beneath you is shallow, so that if you break through, you can essentially walk out.

If you’re planning to venture out where it’s deep, ideally go with a companion. Go with a survival plan already mapped out in your head. And go with a little equipment, which includes proper clothing. If you are mentally and physically prepared, you will be less inclined to panic and more able to act appropriately.

Contrary to what you may think, winter clothing is not a handicap if you fall through the ice. Heavy clothes will not drag you down. They will trap air inside, helping you float and keep warm. Snowmobile suits are especially good in this regard.

It also helps to take along simple survival tools, in the form of spikes or a pair of screwdrivers. If you fall through, you can use them to gain enough traction to pull yourself back up onto the ice. Last winter my son made me a pair of ice picks, each with a half-inch or so of a nail protruding from a wooden handle. The picks are connected by a string that I can feed through my coat sleeves, so in case of an accident they would be at the ready; I would not have to fish in my pockets for them and would be at no risk of losing them.

As for taking action, here are a few ice accident survival tips from the Minnesota Department of Natural Resources:
  • If you fall in, turn back toward the direction from which you came. Chances are the ice is stronger there.
  • Place your hands and arms on the ice surface and hold yourself up. If your clothes have trapped a lot of water, you may have to lift yourself partly out of the water, such as on your elbows, to let the water drain – lightening the load – before you start forward.
  • This is where the ice picks (or screwdrivers) come in. Reach out, jab them into the ice, and try to pull yourself up. As you do that, kick your feet to provide forward propulsion (think of those kick boards you used in swim lessons).  
  • Once you are on solid ice, lie flat and roll away from the hole. This keeps your weight distributed and may help prevent your breaking through again.
  • As soon as you can, get to a warm, dry, sheltered place.


The lake ice is wonderful, but don’t push your luck. Be careful – and be prepared – when you do go out.