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Warming Temperatures Could Mean Changes for Door County Fishing

The springtime sucker run means a lot to rainbow trout, caddisflies and some local anglers. But as temperatures continue to change, so could the timing.

“We found that the run has gotten earlier by a week or two over the last half century,” said Evan Childress, a doctoral student at the Center for Limnology at the University of Wisconsin – Madison.

Childress is working with Peter McIntyre, a professor at the Center for Limnology, to study changes in fish migrations and what those changes mean for stream ecosystems.

Suckers know to leave the Great Lakes and head upstream when the temperature and flow of a stream is just right. Certain lake levels and temperatures are preferable to spawning suckers, while different conditions attract other species of fish.

Dean Gordon, owner of Hooked Up Sport Fishing Charters in Sturgeon Bay, said suckers usually come upstream in April after the first warm rain. Nature tends to orchestrate these fish runs in a predictable manner: first northern pike, then rainbow trout and steelhead, then suckers.

But Childress said future runs might not be so easy to foresee, and could leave these fish up a creek with new company.

“With all of these species responding they’re likely to respond in slightly different ways, so the interactions between the species could change,” Childress said.

Gordon said he’s not concerned about changes in timing to fish runs because interactions between the fish have so far been fine, and most Door County fishing is for sport fish like pike and trout, not suckers.

Those interactions, like patterns of habitat and predation (some fish eat other species’ eggs, young or adults) are Childress’s main concerns with potential changes to migration.

While it’s a good sign that suckers are so far responding to changing stream temperatures, changing water levels could be a bigger problem.

“When they use temperature as the cue, it may not be a good predictor of water level anymore,” Childress said. “When there’s low snowpack, like this year or what we expect going forward, the water levels are going to be dropping a lot quicker. They’re going to need to spawn very early to have successful spawning years.”

Childress suspects there will be fewer successful spawning years in the future, which could spell trouble for Door County anglers.

“If populations of suckers decline, you’re eliminating a food source for trout that depend on this in early spring as a source of energy,” Childress said. “I think that it’s going to decrease the productivity of the Door County systems.”

To get predictions of future climate, Childress and McIntyre use models done by John Walker and Randy Hunt, research hydrologists at the Wisconsin Water Science Center.

“We’re building a watershed model of the Lake Michigan basin,” Walker said. “That model will be capable of predicting flows of every stream that flows into the lake.”

Walker and Hunt are working on a model that will consider more regional climate patterns, like lake effect snow, to predict stream flow, groundwater recharge, lake levels and soil moisture levels.

Childress presented his research to a crowd at Crossroads at Big Creek in Sturgeon Bay on June 13.

He chose to study Door County because the local streams’ natural processes are more intact than places with high levels of runoff and sedimentation from development and agriculture.

Childress and McIntyre surveyed many local streams but focused on Lily Bay Creek, Hibbard Creek and Hines Creek.

Childress has now turned his attention to learning how important the sucker run is to the development of trout, a popular sport fish. Trout eat a lot of sucker eggs, but Childress wants to know just how valuable that food source is.