Reef mapping on Lake Michigan is progressing

Julian’s Reef, this outcrop on the bottom of Lake Michigan off Lake Forest and Highland Park, has been the primary stock for lake trout in Illinois waters since 1981.

Around 2009-11, records of wild Lakers began to proliferate, said William Stacy-Duffy, an aquatic ecologist with the Illinois Natural History Survey at Lake Michigan Biological Station in Zion. In the last decade, Illinois on Lake Michigan has recorded the highest percentage of wild lakers in the entire lake area, which anglers will not find surprising.

Stacy-Duffy led the Lake Michigan Fisheries Seminar at the Whiting Public Library in Indiana last Wednesday on “Lake Trout Sampling and Offshore Reef Mapping”. After a three-year hiatus, these Illinois-Indiana Sea Grant seminars returned and, like many things post-pandemic, were a mix of in-person and online.

I was most interested in reef mapping which I find fascinating with the use of side scan sonar and GoPro cameras. So far, bathymetric maps (mapping of the bottom) are being produced for seven reefs, including in 3D.

Reefs are spawning grounds for Lakers, once Lake Michigan’s premier predator.

“Reefs have big piles of boulders and cobblestones with nooks and crannies,” Stacy-Duffy said. “In these crevices, eggs can be laid and protected, but there is still oxygen flow.”

The reefs are broken bedrock. But an additional feature is the shells of invasive quagga that now cover many areas.

“Dead shells become an important part of the lake bed, filling crevices in the rocks,” he noted.

This could be problematic for eggs reaching the cracks. There are so many shells that currents seem to sweep them into heaps.

Lakers are the most commonly observed. Interestingly, at Gumby Reef, large numbers of whitefish were observed foraging around a pile of mussel shells, and at Wilmette Reef, a large school of large freshwater drumsticks happily followed the camera. Invasive round gobies were also frequently observed.

Reefs charted to date are Gumby, Julian’s, North, Lake Bluff 10 miles, Lake Bluff 18 miles, Waukegan and Wilmette.

For reef maps go to then Places to Fish then Lake Michigan then Fish Habitat.

  • Ben Dickinson, Lake Michigan fisheries biologist for Indiana, said during his update that he would like to receive more winter steelhead heads at the Michigan City DNR office from anglers in Salt Creek and Little Cal.


In a lakewide shift on Lake Michigan, both Illinois and Indiana plan to increase their Chinook stocks over the next year. Indiana will increase theirs by 50,000 to 275,000 and Illinois by 30,000 to 210,000.

Hunting deer in Illinois

I’m excited to see what the weather might have done to harvest the totals for the first batch of firearms stag season. Once these numbers are in, I’ll post them at

wild things

Notable movement of sandhill cranes through the Chicago area on Friday and Saturday, with several reports of whooping cranes. Doug Stotzsenior conservation ecologist at the Field Museum, tweeted that there were at least nine reports totaling 17 whooping cranes in thousands of sandhills.

Not surprisingly, the number at Indiana’s Jasper-Pulaski Fish and Wildlife Area was near an all-time high at 31,975.

Stray cast

Bears season feels like planning a Boundary Waters trip without remembering the days when it rained or the wind howled in your face while paddling across a lake.


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