Crescent Lake
Eagle River
The Northwoods
Rhinelander Area
St. Germain

Due to climate change, fish are treading in dangerous waters

Story By Morgan Johnson
Local News Published 10/13/2020 5:40PM, Last Updated 10/13/2020 6:00PM
Rhinelander, WI - Walleye are a cold-water species of fish, likewise, they thrive in colder water temperatures.

That's one reason why the walleye population is going down in Northwoods' lakes.

Fisheries expert Frank Pratt of Wisconsin's Green Fire says the consequences not only bring the populations to an extreme low, but possibly cause extinction.

"Climate change is definitely restructuring our fisheries; there's no doubt about it," Pratt said. "And if you're looking at cold-water and cool-water species, everything from brook trout all the way up to walleye, you're definitely looking at a declining situation, possibly even an extinction situation."

But Pratt added there are several contributing factors to the declining fish population.

"There are lots of complex factors that are interacting, and for some species in some lakes we really don't understand exactly how," Pratt said.

However Pratt explained that some fish could even benefit from the water temperatures changing.

"It depends on the lake type and the species in the existing fish community-- those effects are not the same. Some fish are being benefited, some fish it's not very good for," Pratt said.

Species such as sunfish and bluegill are warm-water fish.

Another negative effect of climate change on fish is the fact that the summer season is extending.

"The growing season is getting so long and the summer is getting so long that we're approaching situations in September where there's not water of adequate temperature, and high enough oxygen," Pratt said.

In habitats like streams and rivers, the brook and brown trout are treading dangerous waters too.

So much so, that things like water levels can determine whether or not a group of fish make it through another season.

"In a worst case scenario is brook trout are going to disappear and our stream will be totally extinct," Pratt said. A total of about 85 percent of the brook trout streams would disappear."

On the other side, the brown trout can adapt to the warmer water easily.
"With brown trout it's a little bit better because they are a little bit more tolerant of warmer water," Pratt said. "But in both cases it's very clear that we are going to be losing trout streams before the end of the century due to climate change."
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