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Whitefish return to spawn in few Wisconsin rivers

MARINETTE, Wis. — Lake Michigan whitefish have been spawning in northeastern Wisconsin rivers where they haven’t been seen in more than a century.

The fish’s return has created a welcome mystery for scientists, who aren’t sure why they are migrating from Green Bay into rivers. It could be a sign of improving water quality. Or, the population in Green Bay may have grown enough that young fish are being pushed out of traditional spawning areas.

The fish do not appear to be leaving Lake Michigan to spawn in tributaries of Wisconsin rivers, the Milwaukee Journal Sentinel reported. The migration seems to be coming only from Green Bay.

Whitefish rebounded on Lake Michigan and Green Bay in the 1980s. They were discovered on the Menominee River in 1993, but until this fall had not been seen on other inland waterways.

The fish have now been found on at least four rivers in northeastern Wisconsin, according to the Wisconsin Department of Natural Resources. The most surprising location may be the Fox River in Green Bay, home to the nation’s largest toxic cleanup project.

Many scientists believe the fish’s appearance is a sign of improving water quality.

“It’s a feel-good thing about the ecology of the rivers that they can actually support spawning whitefish,” said Scott Hansen, a fisheries biologist with the DNR.

He was out in a boat Nov. 18 with Solomon David, a postdoctoral research associate at the John G. Shedd Aquarium in Chicago.

The whitefish’s return shows “something has changed,” David said. “We don’t know exactly what, but fish tend to be really good indicators of what is going on in the environment.

“If the habitat stinks, they aren’t going to be there.”

The river migration is even more perplexing because invasive species have eaten all the shrimplike creatures that were the whitefish’s main food source. The fish are now eating such invaders as alewives, gobies and mussels, which is causing them to change as well.

A 7-year-old whitefish in 1985 would have weighed about 5 pounds. Today, a similar fish weighs just 1 pound, according to the DNR.

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