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Woods, water & worse/Jim Junttila

Going out on a limn again

October 22, 2010
By Jim Junttila

"It's happening," Tom Rozich reported exclusively to WW&W from the Copper Island Beach Club where he keeps a pretty close eye on the Portage. "The lake's turning over even as we speak."

The water went from green to brown to blue and back as the Keweenaw Waterway rolled over, the surface boiling with hundreds of schooling fish, all jumping, splishing and splashing, enjoying their Fall turnover ride.

You've heard of apple and blueberry turnovers, or turning over a new leaf, but a lotta people, even Yoopers, know very little about lakes turning over. I was one of them until retired MDNRE fisheries biologist turned bartender Rozich 'splained it to me.

Turns out our inland lakes are turning over pretty much on schedule. Last week, the water temperature was still 53 in Copper Harbor and inland lakes, but has since cooled down to the 40s.

Going out on a limn is a pretty decent play on words in that limn means to describe something in words or "paint a picture." Limnology is the scientific study of lakes and their physical and biological features. You've got your money's worth already and this column still has a long way to go.

"You never know when it's gonna happen and you don't see it coming like a tidal wave or tsunami," said WW&W limnology correspondent Sue Nammi. "Whether you call it turn over or roll over, it's more like a small tide or seiche."

"It has been known to create a bait ball that rolls through the water accumulating minnows as it goes," she continued. "As you can imagine, it excites predator fish to the max and triggers a feeding frenzy where they herd the ball ever tighter, packing in as many minnows as possible, then savagely dive into it from all sides with their mouths wide open. It's pretty carnal stuff and a lotta baitfish bite the big one being bitten by bigger ones. It's a fish-on-fish world out there, almost biblical in its horror; As you eat, so shall you be eaten?"

So how does all this eating and being eaten affect fishing? Once things have settled down after turn over, fishing improves. For those who lived to tell about the bait ball barrage, baitfish activity is stimulated, and the mixing and movement of nutrients and plankton set fish to feeding big time, many in shallower water. Fish feel the need to pig out and bulk up for winter under the ice, making for some pretty hot cold weather fishing action with fish so big they leave a hole in the water when you pull them out.

"Unlike most compounds, water is less dense (lighter) as a solid than as a liquid; a good thing otherwise we would have flat fish," Rozich continued. "Water is most dense (heaviest) at 4 degrees Celsius or 39 degrees Fahrenheit, lightest in its solid ice form, and continues to get less dense (lighter) at temperatures above 40 degrees."

During the summer, the warmest, lightest water is at the surface of the lake and is resistant to mixing, like oil floating on toppa water, one being much lighter than the other. As the weather cools, so does the surface water, reducing the difference in density between the top and bottom layers. Eventually, the surface temperature reaches 39 degrees Fahrenheit and that water begins to "sink", being the heaviest. With the entire lake about the same temperature at this point in time, winds mix things up and the lake is said to "turn or roll over." This same phenomenon occurs in the spring; Mother Nature's way of replenishing the oxygen supply to the deepest parts.

During winter, the warmest water in ice-covered lakes is on the bottom. Veteran ice fishermen know this and generally fish on or near the bottom, especially during first ice. Later in the winter, fish move up and suspend, due to lower oxygen levels near the bottom.

While most lakes in Michigan turn over and mix twice a year, others mix only once; still others mix repeatedly. Shallow lakes 20 feet deep or less mix many times a year. During the summer months, they are about the same temperature from top to bottom, on windy days they are "mixed" by the wind.

In other outdoor news, Fall is fading fast. Autumn Equinox has stripped down to her bare branches leaving precious little to the imagination, so you can actually see a partridge or deer in the woods now. Roadkill counts are mounting, the rich golden tamarack are losing their shimmer and needles, and the Lombardi poplar and willow, the last to change color, are tinted with yellow. If you think the moon looked full last night, take a look tonight.

Jim can be reached 24/7/365 at jjunttila@chartermi.net.

 
 

 

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