Can the W/E pop rebound

[Lee Borgersen]

Can the walleye population rebound in McDermott Lake if bass and panfish are reduced?

  ... It's a long read but an interesting approach.


 
SPRINGSTEAD - Under a cobalt summer sky, the surface of McDermott Lake reflected a thousand diamonds of light.

The lake's ecosystem produced in abundance, too.

"That's 351 (young-of-the-year)," said Levi Feucht, a UW-Madison student and fisheries intern, holding a tray of inch-long fish.

The yield, captured in about 24 hours in a single fyke net on the western shore of McDermott, was impressive.
But an examination of the species caught was truly jaw-dropping.

In a lake historically dominated by walleyes, 350 of the recently-hatched fish were largemouth bass and one was a yellow perch.

That's right - none was a walleye.

In fact, in more than a month of intensive work on the lake, researchers have found a grand total of zero young-of-the-year walleye.

The 2018 results are not an anomaly. They found none last year, too.

Walleye, a culturally, economically and ecologically important fish, are in trouble across much of its native range in the Badger State as well as Minnesota.

The examples are numerous. Poor recruitment led to a 5-year ban on walleye harvest on the Minocqua chain of lakes in Vilas County. It remains to be seen if the prized fish will bounce back.
A virtual lack of young, naturally-reproduced walleye have been documented for the last decade on Lac Vieux Desert, a large waterbody that straddles the Wisconsin and Michigan border.

And in Minnesota, a worrying decline in walleye numbers has led fisheries managers to institute a third consecutive catch-and-release-only open-water fishing season.

Researchers say the reasons for the walleye decline aren't fully understood and are likely complex.

But recent studies have shown a link between higher water temperatures and reduced production of walleyes, a cool-water fish.

As largemouth bass have increased in northern lakes, it's clear walleye numbers have dipped, too.

And the age-old preference of fishermen to keep walleyes remains high.

Fun to catch and unsurpassed as table fare, walleyes are the most-prized fish that swims in Wisconsin waters, according to angler surveys by the Department of Natural Resources. What's more, the golden-flanked fish are harvested at a rate several times higher than largemouth bass.

It's also known that walleye fry are preyed on by other species. A 1/2-inch-long walleye is a quick dinner for even a 3-inch largemouth or 4-inch bluegill.

With abundant bass and panfish populations in many northern Wisconsin waters, it's arguably never been tougher for recently-hatched walleyes to survive.
But there is much to learn about the dynamics of this predator-prey relationship.

For example, is there a certain density of bass and panfish in a lake that flips the switch from a walleye-dominated to a bass-dominated system?

And, from a management perspective, could it be possible to reduce a bass and panfish population to a level that would allow walleyes to recover via natural reproduction?


The work on McDermott, led by researchers from the University of Wisconsin and UW-Stevens Point and the Wisconsin Department of Natural Resources, is looking at such questions.

In an audacious whole-lake experiment, bass and panfish are being removed.

The goal is to reduce the lake's population of centrarchids (which includes largemouth bass, bluegill, pumkinseed sunfish, black crappie and rock bass) by 80%.

The effects on the lake, and principally the walleye population, will be studied over the next four years.

The universities received a grant for the work from the U.S. Geological Survey.

Holly Embke, a graduate student at the UW Center for Limnology, is leading the field work.

"Interactions between walleye and other fish may be playing a large role in the ability for walleye to maintain self-sustaining populations," Embke said. "This whole-lake experiment will allow us to look at bass and panfish, especially, and any change in walleye recruitment."

The project falls under a principle called "safe operating space," or SOS. The researchers hope to understand conditions needed to maintain self-sustaining walleye populations and inform recreational fisheries management.

On a glorious summer day last week in the North Woods, Embke and four summer interns - Feucht, Matt Chotlos, Abbie Dalton and Keegan Epping - checked traps and nets on McDermott and recorded the catches.

Tiny largemouth bass outnumbered all other fish caught by a wide margin. Small bluegill (2 to 4 inches in length) were second.

The project started in 2017 with baseline work on McDermott as well as nearby Sandy Beach Lake, a reference lake.

McDermott had an adult walleye abundance of less than 1 per acre, very low for a lake that at one time featured a naturally-sustaining walleye population, and lots of bass and panfish.

"So many small bluegill we haven't been able to estimate the number yet," Embke said.

This year the meat of the project - removal of bass and panfish - has begun.

The researchers deploy more than a dozen clover traps and fyke nets around McDermott and check them daily. At least once a week fish are caught and removed by electrofishing, too.

All fish removed are donated to wildlife rehabilitation centers in Wisconsin.

McDermott, an 82-acre gem of a lake about 15 miles northeast of Park Falls, was selected because it historically had a good, naturally-reproducing walleye population but recently had changed to a bass-panfish dominated system.

In addition, the project was supported by local residents.

"I'm hoping it will help the walleyes," said Gail Spranger, 65, who has lived on the lake for 21 years and has run a cabin rental there since 1993. "Most of our guests come here to fish."

Spranger said a couple decades ago she and her family would catch walleyes and nice-sized perch on the lake.

"The walleyes weren't overly abundant, but we did catch them," Spranger said. "And we never caught a bass. Now, it's so rare to hear about anyone catching a walleye or a nice-sized perch."

The lake remains open to public fishing, with unchanged regulations, during the project.

The most recent DNR fish assessment on McDermott was conducted in 2012. It found adequate spawning habitat for walleye, but had the "characteristics of a fishery in which walleye have lost their predatory dominance to an increasingly abundant largemouth bass population."

And the average bluegill captured was about 4 inches long. The high capture rate and small size structure of bluegill observed by DNR crews was indicative of an "overabundant population," according to the report.

The DNR has continued moderate walleye stocking in the lake, including 420 large fingerling walleye (6 to 8 inches in length) in 2013 and 409 in 2015.

The rest of the fish community includes muskellunge, northern pike, white sucker, brown bullhead, yellow perch, spot-tail shiner, Johnny darter and a handful of other small species.

Impressively, McDermott has no invasive animal or plant species.

As water temperatures have warmed into the 70s in much of the lake, plant growth is substantial. So much underwater habitat, so much room for small panfish to hide.

The prospect of removing even half of the bass and panfish from the lake is daunting.

A glance over the side of a boat last week revealed the movements of small fish, most likely hatched this year.

"It's a good time to be a piscivore," Embke said.

The abundant fish population benefits the walleyes that remain in McDermott, too. On one recent electrofishing outing, the researchers pumped the stomach of an adult walleye as part of their diet analysis. The fish was packed with young-of-the-year largemouth bass, Embke said.

However, the lake's walleyes are dwarfed in number by bass and panfish. And as the work has shown, no young-of-the-year walleyes have been documented in McDermott.

Embke and the crew remain energized by the opportunities and challenges of the project. It's the largest effort ever undertaken to study the effects of bass and panfish removal on a walleye population, Embke said.

So far this year, the researchers have removed about 50,000 largemouth and panfish, Embke said.

And importantly, most of those caught and removed have been young-of-the-year, Embke said, potentially helping to limit the 2018 year classes of bass and panfish and creating more "space" for walleyes.

Regardless of the removal success, many bass and panfish will remain in the lake.

The lowered bass and panfish populations are likely to benefit the fishery no matter what the research finds, said Mike Vogelsang, DNR district fisheries supervisor in Woodruff.

"They'll either have a better walleye fishery or a better bass and panfish fishery," Vogelsang said. "The lake is dominated by stunted fish now."

The project is scheduled to continue through 2022.

Solutions to the walleye decline may be as elusive as a 32-inch "gravel lizard," But research, like keeping a line in the water, is the only hope.

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[delcecchi]

It would be interesting to know the trends in amount of vegetation and water fertility in recent years.   Eutrophication would tend to favor bass over walleye.