Climate change threatens walleye reproduction, study says - Madison.com

Climate change threatens walleye reproduction, study says

Humans aren’t the only species questioning the unusual weather patterns.

A study from a UW-Madison researcher published Monday in the journal Limnology and Oceanography Letters contends that walleye, one of Wisconsin’s most sought-after fish and one of its tastiest, are not only struggling to survive in warming waters; their reproduction is also being interfered with and has been “unable to keep up with increasingly early and more variable ice-off dates.”

Lead author Martha Barta, a research intern at the university, said that within a few days of ice-off, walleye begin laying eggs and fertilizing them. That timing, in a normal year, sets baby fish up for success once they hatch. But, according to Barta, “climate change is interrupting the historical pairing between ice-off and walleye spawning and that threatens the persistence of walleye populations across the Upper Midwest.”

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Barta and her team used data from walleye surveys from various state natural resource departments and the Great Lakes Indian Fish and Wildlife Commission, as well as spring harvest counts from several Ojibwe tribal nations, to track the fate of walleye populations on 194 lakes across Minnesota, Wisconsin and Michigan. That data revealed “mismatches in almost every single lake.” While there has been a slight shift to earlier spring spawning dates for walleye, the ice-off dates on Midwestern lakes were shifting at a rate three times faster.
This walleye was caught under a lighted bobber in open water Sunday night on Lake Mendota. Ice-out is well underway on the 9,800-acre lake, which will be off limits to ice fishing for the last days of the game fishing season, which closes Sunday.

“In an average ice-off year, you have this nice progression of events,” said Zach Feiner, a fisheries scientist with both the UW-Madison Center for Limnology and the state Department of Natural Resources. “The ice goes off, you get light and warmer water that creates a bloom of small plant life called phytoplankton and then tiny animals called zooplankton emerge and eat the phytoplankton and, usually, the walleye spawning is timed for them to hatch when zooplankton are around in high abundance and can serve as fish food for the baby walleye.”

Lakes, on average, are thawing earlier, but the number of winters where lakes thaw late is also increasing. What’s being lost are the “nice, normal, average years when lakes thaw right about when they used to,” Feiner said.

Photos: Ed the Diver and his fishing lures

Ed the Diver
Ed Bieber is seen here in 2021 during one of his dives in the Menominee River near his home in Marinette. He uses a kayak to hold what he finds, but at other times will use a boogie board with a plastic bib on top.

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Ed Bieber tries on a pair of sunglasses he retrieved during a river dive near his home in Marinette, Wis. Tuesday, April 25, 2023. JOHN HART, STATE JOURNAL

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Artifacts retrieved during one of Ed Bieber’s river dives are displayed at his home in Marinette, Wis. Tuesday, April 25, 2023. JOHN HART, STATE JOURNAL

Ed the Diver
Ed Bieber sorts through scuba gear at his home in Marinette. He began diving about five years ago with just a mask on his face and tennis shoes on his feet, but is now a certified diver who has amassed a room full of scuba gear.

Ed the Diver
Anglers are good at losing not just fishing lures, as this tangle of rods and reels demonstrates. It sits in a pile in Ed Bieber's backyard in Marinette.

Ed the Diver
Anchors retrieved during river dives by Ed Bieber share space in the yard of his Marinette home. He once found 28 anchors in a single dive.

Ed the Diver
Glass bottles retrieved during river dives by Ed Bieber, right, and Jason Younk fill a table on Bieber's back porch. The round object in the middle is the top of an Evinrude motor found while diving in Oshkosh.

Ed the Diver
Lettering on the travel trailer of Ed Bieber echoes his perspective on river diving.

Ed the Diver
Fishing lures amassed by Ed Bieber, many retrieved from his dives into the Menominee and Fox Rivers, fill the walls of the dining room of his Marinette home. Known as "Ed the Diver," Bieber is making a full-time living off finding, refurbishing and reselling lures.

Ed the Diver
Ed Bieber, right, and Jason Younk sort through a collection of fishing lures they retrieved during a recent dive in Oshkosh. This ball of nearly 200 baits was estimated to be worth about $1,800 new, but once Bieber and Younk clean them up and, in some cases, replace the hooks, they can get $5 per bait.

Ed the Diver
Ed Bieber will likely never buy a pair of sunglasses again. This is just a portion of the eyewear he has found while diving.

Ed the Diver
"The Young Swimmers,” sculpted by James F. Hopfensperger, shares the shoreline of Stephenson Island in the Menominee River near the home of Ed Bieber. The island has been productive for Bieber in his quest for lures since it is a popular spot for walleye anglers.