Story URL: http://news.medill.northwestern.edu/chicago/news.aspx?id=228757
Story Retrieval Date: 11/27/2014 9:55:26 AM CST

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Mark Kuykendall/MEDILL

Ice fishermen drill through ice 30 inches deep in northern Michigan.


Chill: Great Lakes fish survive below the ice

by Mark Kuykendall
Mar 6, 2014


Fishkill02

Michigan Department of Natural Resources

Fish along the shore of a Michigan lake after a weather-related die-off in 2008

While fish further south shiver, the fish of the Great Lakes seem to be shrugging off this year’s harsh winter.

Despite elevated numbers of cold weather-related fish kills recorded from Missouri to the Gulf of Mexico, fish populations in the Great Lakes have suffered little, if at all, according to Illinois fisheries officials.

“This extended winter will have little effect on the fisheries, especially in those lakes and rivers that have a good maximum depth,” said Dan Stephenson, assistant chief of fisheries at the Illinois Department of Natural Resources. “There will be no damage to the Great Lakes.”

High numbers of fish die-offs in Missouri have attracted media attention and heightened concern among Missourians battling through an unusually frigid winter. Missouri residents have noticed high numbers of dead fish in lakes and ponds throughout the state.

“We are getting dozens of reports of significant winter fish kills from all over the state,” said Missouri Department of Conservation resource scientist Rebecca O’Hearn. She noted that winter fish kills are normal, but the scale of this year’s die-offs are abnormal, even occurring in some of the state’s deeper lakes.

Despite these events, the fish of the Great Lakes are better suited to survive this year’s harsh winter than their southern cousins.

“The roughly 200 fish species found in Illinois are temperate fish with the ability to adapt very well to harsh climates,” said Stephenson.

Even for hardy fish, colder than normal temperatures can pose challenges. Fish use stored fat reserves to survive the winter, so fish that came into the winter too small may have difficulty surviving a long, harsh winter. A lengthy winter could potentially delay spawning, creating a higher population of these young, small fish, ill-prepared for next year’s winter.

In general, though, problems should not be widespread, and effects should be limited to fish populations in more shallow lakes, streams and private ponds, where ice cover and buildup can result in low oxygen levels.

“Some of the more than 90,000 private ponds statewide could have problems,” said Stephenson.

Thick ice cover and deep snow on lakes, streams and rivers can trap fish and block light from reaching aquatic plants. If the plants die, oxygen levels in the water are depleted, threatening fish health and potentially causing die-offs.

“If that goes on for long enough, like it has this year, fish can suffocate,” said O’Hearn.

Fish populations struggling through the harsh winter are not limited to the U. S. As far away as Scandinavia, scientists have noticed the detrimental effects of recent extreme winters on some fish species. In this month’s issue of BioScience, Norwegian University of Science and Technology professor Christer Nilsson presents the results of his research showing that extreme winters make survival difficult for fish, particularly in waterways that have been altered by humans.

"Rivers that have been exploited for hydroelectric power can be especially hard for fish to live in, because the way hydropower is produced…. Cold air is fed downward in the water and forms ice crystals that cover the bottom, making it hard for fish to survive," says Nilsson.

While many Midwesterners can’t wait for spring, one particular group of sportsmen is enjoying one of their best winters in years.

“Ice fishing, as you might expect, has been much better, especially the farther south you go,” said Stephenson.  “In some years, this 400-mile long state doesn't get enough ice for fishing in the southern third. This year, ice on the ponds extends to Cairo.”

It appears that ice fisherman and deep-water lake fish are the only ones counting their blessings this winter.