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The Wisconsin hatchery system is producing walleyes with a sex ratio heavily skewed in favor of females, according to the Department of Natural Resources.
The unexpected discovery has launched an investigation into the possible reason or reasons.
Evidence of a potential issue was observed in spring 2019 field sampling of adult walleyes raised at state hatcheries and stocked in lakes, said Lori Tate, DNR fisheries management section chief.
The fish, planted years earlier as extended growth fingerlings as part of the Wisconsin Walleye Initiative, were about 75% female in some lakes, according to reports from DNR crews.
That led to an analysis of fingerlings at the state's two primary walleye hatcheries, Art Oehmcke in Woodruff and Governor Thompson in Spooner.
Histological testing at the facilities in 2020 showed 70 to 80% of the young walleyes were females, Tate said.
Surveys of naturally reproduced walleye generally show sex ratios closer to a 50:50 or slightly more males, according to the DNR.
There is no evidence at this time to suggest skewed sex ratios exist in other hatchery-reared species, according to the agency.
If the fish are stocked only to supply a "put-and-take" fishery, the sex wouldn't be an issue. In fact, females might be preferred because they tend to grow faster than males.
However, if the stocking goal is to
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help increase natural reproduction, then a more balanced sex ratio of planted fish would be desired.
Walleye stocks have been dropping for more than a decade across the Upper Midwest, prompting reductions in bag limits. The cause is fairly well known: a decline in recruitment, or survival of young fish.
The problem has persisted even in waters such as the Minocqua Chain where sport and tribal harvest has been prohibited for multiple years.
No solution has emerged, however. Most research points to changing climatological and ecological conditions that are unfavorable to walleyes.
The Wisconsin Walleye Initiative began in 2013 and was championed by former Gov. Scott Walker and the Legislature. It included state funding of $8.2 million for infrastructure improvements at hatcheries and $1.3 million each year for annual operating costs.
The program has dramatically increased production of extended growth (typically 6 to 8 inches in length) walleyes for stocking in fall. Prior to the initiative the state stocked about 60,000 to 120,000; it has ranged from 714,222 to 881,997 over the last seven years.
Fish survive better when stocked at larger sizes. It's not yet known whether fish produced through the program have helped increase natural reproduction on lakes where it is lagging. Due to the coronavirus pandemic, no biological samples were gathered from the field in 2020, Tate said.
The DNR announced Wednesday it would work with partners, including at the University of Wisconsin-Stevens Point, to look into the skewed sex ratio of the hatchery-reared walleyes. The investigation will include additional histological sex determination testing, a comprehensive review of hatchery practices and an examination of additional survey and past stocking data, said Dave Giehtbrock, DNR fish culture section chief.
More work will also be done in 2021 to assess the sex ratios of naturally reproduced walleye as well as the gender of extended growth walleyes at additional hatcheries, including those outside the state system.
Giehtbrock said factors such as water temperature, hormones, behavior of fry and water chemistry will be evaluated as part of the investigation.
"We don't have a clear picture of how widespread this issue might be," Giehtbrock said. "We expect to know much more by the end of the year."
Walleye lakes of concern meeting: The DNR will hold a virtual meeting from 6:30 to 8:30 p.m. Wednesday on a proposed walleye rehabilitation plan for four northern Wisconsin lakes with declining walleye populations.
The lakes are Clear and Katherine in Oneida County and Anvil and Laura in Vilas County.
The goal of the plan is to restore natural walleye reproduction and recruitment in the lakes. The proposal was developed in a partnership between the DNR, Lac du Flambeau Ojibwe Band and Great Lakes Fish and Wildlife Commission.
The public can join the meeting by Zoom or by calling 1-929-205-6099 and using meeting ID 851 3948 5837.
Deer advisory council meetings: The 2021 County Deer Advisory Council (CDAC) planning meetings will take place virtually March 22 to April 1 to discuss the upcoming deer seasons.
The CDACs in each county help develop local recommendations for antlerless harvest goals, antlerless tag availability and season options.
The councils develop their recommendations using two meetings separated by a public input period.
Beginning this week, the councils will meet virtually via Zoom to develop preliminary recommendations on harvest quotas and season structure options. All council meetings are open to the public. The public may also view presentations from DNR wildlife biologists on the agency's website. Anyone wishing to provide feedback will be asked to do so using the online public input form available on the DNR website from April 12-25.
A second round of meetings will take place in May, during which council members will review public comments and make final recommendations for the 2021 deer season.
The DNR will review the final CDAC recommendations following the May meetings and provide CDAC and department recommendations to the Natural Resources Board for approval in June. For more information, visit dnr.wi.gov.