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"This past summer, bluegills were out in the main channel, but in the winter, these same panfish are current haters," said Ron Benjamin, Wisconsin Department of Natural Resources Mississippi River fisheries team leader in La Crosse.
Winter habitat is just as crucial to a bluegill's survival as spring spawning and summer feeding areas, so fish biologists from Iowa, Minnesota and Wisconsin set out to identify bluegill over-wintering areas and assess their quality.
"The problem is we never had a complete inventory of where over-wintering sites are, so it's hard to document everything when you lose sites like Shady Maple," said Jeff Janvrin, DNR Mississippi River habitat specialist in La Crosse. "We believe we've lost over-wintering areas due to loss of islands, sedimentation and flow into backwater areas."
To set a baseline, fisheries biologists inventoried bluegill over-wintering areas in the Mississippi River and its backwaters from Wabasha, Minn. to Dubuque, Iowa. The survey work was conducted between mid October and late November, 2003. Data is now being studied.
"We gathered knowledge of potential sites in several ways before we actually went in and surveyed the areas," Janvrin said. "We flew over to see where anglers were fishing for panfish. We looked at maps to identify potential areas based on structure and we did interviews at public meetings."
Once nearly 600 potential over-wintering sites were identified, crews set out to assess fish populations, measure water depths, water temperature and dissolved oxygen. By ice-up, biologists had gathered data from 450 Mississippi River sites.
"We did see huge gaps in places along the river where there were no over-wintering areas," Janvrin said. "From Lansing to Dam 9, we only found one over-wintering site."
In general, bluegills move two to three miles to find over-wintering areas. If they don't find suitable locations, they try to over-winter in marginal areas, or they die.
"If bluegills are in a marginal site during a severe winter, they will die," Janvrin said. "On the other hand, we found that some river improvement projects we've worked on are some of the top winter bluegill habitat sites."
An ideal bluegill winter site has little or no current and averages about four feet deep. If these areas connect to a channel, bluegills begin moving toward the channel as oxygenated water is depleted in areas farthest back from the channel. That may explain why bluegill fishing is better at first ice in small backwater areas, but produces few fish later in winter.
"There is some data that suggests bluegills stop feeding when they are stressed, too," Janvrin said.
"If you look at the ways we fish bluegills in summer and winter, we are taking advantage of how these fish feed," Benjamin said. "In summer, we may use a gob of worms, but in winter we use a tiny wax work."
Northern pike, on the other hand, feed almost as much during winter as they do in summer, according to Benjamin.
"Northerns key on forage, and find places to go and eat," Benjamin said. "They often go into backwaters where the bluegills are, but you can't pinpoint where they are going to be. They could be anywhere."
Janvrin said his crews did not uncover any secret fishing holes and almost every location, even over-wintering areas, were as small as five acres.
A few bluegills measured 10 inches long, while many others were 8½ inches, so there are some trophy fish out there for winter anglers.
Water levels, according to Janvrin's surveys, are at historically low levels and could spell trouble for bluegills, depending on winter severity.
"Fish in the upper parts of pools are going to have a hard time with such low water levels," he said.
Jerry Davis, an outdoors writer, can be contacted at (608) 924-1112 or at sivadjam@mhtc.net
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