UW SYSTEM

Warmer springs, variable ice-out dates are hurting walleye spawning

John Myers — Fri, 01 Mar 2024 13:00:00 GMT

MADISON — Walleyes, the favorite game species in many Midwest lakes and Minnesota’s official state fish, are struggling to spawn successfully due to warming springs and highly variable ice-out dates, creating more bust years and fewer boom years for many walleye populations.

That was the finding of a University of Wisconsin study published this week in the journal Limnology and Oceanography Letters.

The problem stems from walleye being creatures of habits that developed over millennia and which can’t keep up with changing climatic conditions, especially increasingly earlier and variable ice-out dates.

The timing of walleye spawning has historically been tied to the thawing of frozen lakes each spring, said Martha Barta, a researcher at the University of Wisconsin-Madison and lead author of the study.

Within a few days of ice-out, walleyes begin laying and fertilizing eggs. That timing, in a normal year, sets tiny walleye fry up for success once they hatch. But Barta said the study found that “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.”

“We’ve known for several years that many walleye populations are not doing well. Now, this adds the phenology piece where we found that either a very early ice-out or very late ice-out in the spring, we didn't see good walleye classes in the fall,’’ Zach Feiner, a co-author of the study and a fisheries biologist for both the University of Wisconsin-Madison and the Wisconsin Department of Natural Resources, told the News Tribune. "The more the ice-out varied from a normal year, the worse the walleye class was that year."

How much variability is occurring? In 2012, many Northland lakes had their earliest ice-out date ever. In 2013, many of the same lakes saw their latest ice-out dates on record. And while ice-out dates have always shifted by a week or so early or late, the variability now is running four to six weeks from year to year, all while the long-term trend is earlier.

Barta and her team used data from walleye surveys from state natural resource departments and the Great Lakes Indian Fish and Wildlife Commission, as well as spring harvest counts from several Ojibwe tribal resource agencies, to track the fate of walleye populations on 194 lakes across Minnesota, Wisconsin and Michigan.

The researchers also had fall fish survey data from 122 of the lakes that showed how many walleye from that year were still around.

...we’re not seeing many or any boom years for a lot of walleye populations.

That data revealed “mismatches” in almost every lake. While the study found walleyes were slightly shifting their spawn earlier, the ice-off dates on Midwestern lakes were shifting at a rate three times faster than walleye spawning dates.

And that has the system mixed up.

“In an average ice-off year, you have this nice progression of events,” Feiner noted. “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.”

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

The problem with the increasing number of early and late ice-outs, Feiner said, is that the “progression of events is totally out of sync.” In an early ice-off year, for example, phytoplankton bloom early and begin to die back as zooplankton get going, which means there’s less food for zooplankton and their numbers are so low that “when the fish hatch, there aren’t enough zooplankton around and (newly hatched) walleye don’t have enough food to survive.”

There’s a similar dynamic in late ice-off years. This mix-up impacts the survival of newly hatched walleye through their first spring and summer of life, called recruitment. Losing one year of spawning success isn’t doomsday for overall walleye populations if the next year’s spawning success is good. But the increasing variability of spring thaws is “increasing the frequency of bust years, and we’re not seeing many or any boom years for a lot of walleye populations,” Feiner said.

While this is obviously bad news for walleye and the people who depend on them, the study underscores the need to identify and protect lakes that can offer refuge in bad years.

There is a need now to “find places where, through management of things we can control — like land use, fish harvest and invasive species — we can buffer or boost their resiliency to be able to handle stuff we can’t control — like climate change,” Feiner says. If fisheries managers can identify lakes where walleye populations are doing relatively well, they can at least try to keep conditions optimal so that the fish can take advantage during the increasingly rare years when ice-off and their spring spawn do line up.

Scientists involved in the study say they hope to move on to determine the impact of changing climate on spawning by several other species, including other spring spawners like perch, bass and muskie, but also fall spawning fish like lake trout that depend on ice for their eggs to over-winter.

]]>

Volunteers needed across Minnesota, Wisconsin to search for invasive species

John Myers — Mon, 07 Aug 2023 15:00:00 GMT

DULUTH — Volunteers are needed across Minnesota and Wisconsin to fan out across each state on Aug. 19 and search for aquatic invasive species in lakes and rivers.

In Wisconsin it’s called invasive species “Snapshot Day.” Minnesota has been holding “Starry Trek” since 2017, named after starry stonewort, a highly invasive algae that is spreading statewide.

In Minnesota, the Minnesota Aquatic Invasive Species Research Center & University of Minnesota Extension are heading the Starry Trek effort. In Wisconsin, the Water Action Volunteers citizen stream monitoring program is an ongoing partnership between the University of Wisconsin–Madison Extension and the Department of Natural Resources. Starry Trek training sites are located across the state and will be hosted by local agencies, organizations and individuals to search nearby locations. Participants will meet at a local training site and will be assigned sites to search upon arrival.

Participants under age 18 will need to be accompanied by a parent or guardian. All monitoring is done from shore, so no boats are required. It's good to wear shoes that can get wet.

In Minnesota, go to maisrc.umn.edu/starrytrek to get more information and to sign up to participate. In Wisconsin, go to wateractionvolunteers.org/events.

Minnesota youth clubs can contact Megan Weber at mmweber@umn.edu to learn how to participate as a club.

]]>

Blacklegged ticks carry, probably spread chronic wasting disease

John Myers — Thu, 08 Jun 2023 18:38:05 GMT

ST. PAUL — As if they weren’t horrible enough for spreading Lyme and other nasty human diseases, now we can hate blacklegged ticks for carrying chronic wasting disease that kills deer.

Scientists from the University of Minnesota and the University of Wisconsin are studying how blacklegged ticks — formerly called deer ticks — may be harboring and spreading CWD, the always fatal disease that is sweeping through wild and domestic herds of deer, elk, moose and even reindeer across North America and beyond.

The researchers first determined that ticks were capable of carrying an infectious dose of CWD-causing prions. To do this, they had ticks in a lab feed on blood contaminated with brain tissue from a deer infected with CWD. They found that ticks appeared to both ingest CWD prions and excrete them largely unchanged.

There are a lot of options for how tick burdens could be managed if it is indeed proven that ticks are implicated in CWD spread. Pesticides are one thing, but there are actually a great deal of practical solutions that are solely based upon things like land management and grassland restoration.

Then they examined tick and ear tissue samples in the wild from 174 deer that had been bitten by ticks in a CWD-endemic area of Wisconsin. Of those deer, 15 tested positive for CWD. The team determined they could detect prions in the ear tissue of these 15 deer as well as in several of the engorged ticks that fed on them.

Depending on the sample, CWD prions were present in up to 40% of the ticks they looked at. The doses they carried mirrored what the initial lab study had found: Ticks appear to be able to carry around infectious amounts of CWD prions. If a susceptible deer were to consume a tick from an infected animal, for example, through social grooming, it’s possible that the animal may contract the disease.

The study, published May 23 in Nature Scientific Reports, was led by Heather Inzalaco, a scientist at the University of Wisconsin-Madison, with Stuart Lichtenberg of the University of Minnesota College of Veterinary Medicine and the Minnesota Center for Prion Research and Outreach.

Additional research is needed to confirm that deer ticks do indeed transmit CWD prions to animals in the wild and not just carry them. Ultimately, the authors believe this may lead to new ways to control CWD.

“There are a lot of options for how tick burdens could be managed if it is indeed proven that ticks are implicated in CWD spread,” Inzalaco said in a statement announcing the findings. “Pesticides are one thing, but there are actually a great deal of practical solutions that are solely based upon things like land management and grassland restoration.”

Lichtenberg said it's most likely deer would receive CWD from a tick by ingesting the tick rather than by being bitten by a tick.

"We can't count tick bites serving as a vector out entirely, of course, but we think infection by ingestion is far more likely," Lichtenberg told the News Tribune.

Scientists will now see if mice that are fed infected ticks develop CWD prions.

"Once we've proven that the mice can get sick from the ticks, we could then move on to seeing if deer can get sick from eating infected ticks,'' Lichtenberg said. "Due to the fact that prion diseases have really long incubation periods — on the order of years — these experiments are going to take a bit of time to complete."

He remains optimistic about the direction of future research.

“In the long term, prion research approaches that are multidisciplinary will help reduce spread of CWD and mitigate risk of CWD to human health,'' he said, noting that preserving viable wild deer populations is critical for both tribal and sport hunters and for ecological, social and economic stability.

CWD is not caused by a virus or bacteria, but by a naturally occurring misfolded protein called a prion — transmissible, pathogenic agents that alter normal proteins and cause progressive neurodegenerative disorders, including CWD. Scientists understand that indirect transmission — through ingested or inhaled contaminated soil or eating contaminated plants — may play a central role in CWD transmission among cervids.

CWD is fairly common among wild deer in southern Wisconsin, but so far has been sporadic in wild deer in Minnesota, found as far north as the Grand Rapids and Bemidji areas, but mostly surfacing in far southeastern Minnesota.

The 2023 Minnesota Legislature passed strict new regulations this year to limit the movement and management of tame deer on deer farms across the state. Domestic deer and elk infected with CWD and moved between states and between farms in states is considered a likely vector for the disease to spread in wild deer near those infected farms.

]]>