Fighting wind and persistently cold air and water temperatures, the Department of Natural Resources fisheries team in Windom completed their walleye spawning operation on Lake Sarah, south of Marshall, on April 27.
Area Fisheries Supervisor Ryan Doorenbos and his team have taken eggs annually at Lake Sarah since 2015, only pausing in 2020 at the start of the COVID-19 pandemic. This year’s quota, just over 260 quarts and around 33 million eggs, was slightly exceeded in a little over one week’s time.
“This was the seventh time we did this,” Doorenbos told me, “and by far, this was the most brutal conditions we’ve had since we started. Between the wind and the water and air temperatures, and some precipitation, all in all it was challenging. We even had some days we had to shut down for a day and regroup and put the nets down. We definitely had some inclement weather.”
The challenges of the spring of 2022 were buffered by one new addition to the Windom DNR Fisheries team.
“The most positive thing was that this year’s weather justified our need for a big boat to handle the inclement weather safely for our crew,” Doorenbos explained. “There was never any insecurity for the staff aboard working the nets and picking up the walleye.”
The new boat measures 20 feet in length, is all aluminum welded, and includes high sides on the gunnels, which came in handy when Sarah experienced four-and-a-half foot swells on the downwind side of the lake.
The Windom Fisheries team collects spawning walleye from six nets that have historically produced the best on the 1,200-acre lake. The team separates male and female walleyes, taking eggs when females are ready and ripe and holding females overnight that need time for final hormonal shots that loosen the ovary and let the eggs flow freely.
Males are typically ready and available throughout the spawning run, but are harder to come by and can be spent of semen by late in the run.
Walleye spawning phenology is keyed into a combination of photoperiod (length of daylight tied to calendar date) as well as water temperature, and in some occasions, rapid weather shifts.
In a short assembly line, the team of Windom Fisheries staff and volunteers shuffle fish into a small portable trailer that can offset variable weather and precipitation, strip eggs and mix them with milt.
Roughly two males are used with every large-sized female. The key, Doorenbos said, is to keep females and males dry. Water activates the male’s milt and likewise the female’s eggs to open their micropyles and allow fertilization to happen.
The eggs are open for fertilization for roughly a half-minute. Mixing the eggs and milt quickly, then dashing on some water puts the process of fertilization into motion, and the eggs are gently stirred for two minutes with a fine-bristled paintbrush.
Eventually, a fine bentonite clay is added to keep the eggs from sticking to each other and clumping, which can cause issues with bacterial or fungal infection.
The eggs are transferred to a fine mesh basket or cradle where they will water harden after four hours, in which time the eggs swell and harden and can be safely transported to a hatchery for incubation.
Walleye eggs, and all fish eggs, are temperature dependent as cold water organisms, so once they have enough temperature units for development, typically 18-22 days for walleye, the fish begin hatching.
Despite being a relatively new walleye eggtake site, Lake Sarah is an important location.
“In the 1980s and 1990s, several year classes of non-stocked walleyes were showing up over time,” explained Doorenbos of the Sarah Lake walleye fishery. “Fisheries managers at the time wanted to know what would happen if the DNR just stopped stocking or stretched it out with longer gaps between stocked years. Could natural reproduction take care of itself and create a self-sustaining population? In 1991, Sarah received her last standalone walleye fry stocking.”
The source of some of those stockings in the 1980s, explained Doorenbos, were from fish from the Cannon River near Waterville. In the meantime, genetic evaluation of walleye progressed in leaps and bounds.
Sequencing of DNA short snippets, called microsatellites, assigned Sarah’s fish to a unique and genetically distinct grouping, the Lower Mississippi Strain, amongst several strains found in Minnesota. The Lower Mississippi Strain was and is found in other locations, from natural reproduction of certain populations in lakes and rivers, and from DNR stockings in parts of southern Minnesota.
The thinking for Doorenbos and other fisheries managers was simple when it came to the decision to start taking eggs at Sarah — what if they could create lightning in a bottle again, and create other Lake Sarah’s that were self-sustaining?
“We put fry back into Lake Sarah for the first three years, a common practice with Minnesota DNR eggtakes across the state, but we stopped when we realized that we were contributing fish that weren’t necessary,” Doorenbos said.
Again using the power of genotyping, the Windom Fisheries team takes scale samples from each parent used during their spawning operation at Sarah, which then allows them to compare the genetics against the same young-of-the-year cohort sampled later in the fall with electrofishing. In turn, they can definitively see if their artificially propagated offspring are contributing to the lake’s walleye population.
“Sarah is amazing,” Doorenbos said. “We get anywhere from 200 to 400 young-of-year per hour of time electrofishing. One of the years, through genetic evaluation, we found that 100 of the fish per hour were from our fry putback. But when you know from previous electrofishing survey work in our area in southwestern Minnesota that the threshold to producing a strong year class is anywhere higher than 30 per hour, it’s a judgement call that says its really not necessary. We’re getting off-the-charts good natural reproduction and there’s more than enough recruitment going on in this system.”
To illustrate the point of plenty of walleyes doing their thing, consider this: When Doorenbos’ team shut down their operations last week and reached their quota, they were in the midst of what was their highest volume day of catching ripe walleye.
The lake’s natural spawning run may not have even peaked by the time the eggtake was completed. Past estimates of how many of the lake’s walleye population are captured and processed for statewide stocking quotas has ranged from 20 to 35%, a mere fraction of the many walleye in the lake.
Doorenbos even noted that their Lake Management Plan for Sarah calls for the discontinuation of the eggtake if a negative impact to the walleye population was found.
Eight years in, Sarah’s walleye are still thriving, and other lakes around the state are reaping their own benefits.
Lake Sarah’s eggs have been sent to the Waterville State Fish Hatchery the past eight years, ironically sending the genetics back to where they may have come from. In an experimental trial, equivalent proportions of northern Minnesota walleye strains and Lower Mississippi strain fish have been stocked into a series of lakes in the Upper Cannon River watershed situated around Waterville.
Preliminary results are showing significantly higher survivorship of the Lower Mississippi Strain, fish that were spawned at Lake Sarah.
It could be revolutionary news, considering that much of southern Minnesota has been stocked with admixtures of various strains from across watersheds in northern Minnesota, where large lakes lent themselves to voluminous eggtakes that offered economy of scale in ease of collecting many eggs in a short amount of time.
“We’re taking two strains and comparing them in these southern lakes,” explained Doorenbos. “Ultimately, you want to be stocking a strain of walleye that performs best, so that in theory it creates better fishing for the angler. What we’re finding to date, and it’s still preliminary, is that this Lower Mississippi strain is performing better in these southern lakes.
“This is not a commentary that this strain is way better than northern strains. It’s simply suggesting this strain may be better suited to local waters and have a competitive advantage. We’re building up the pyramid of our understanding. The question we don’t know is why they are doing better. We’re trying to find answers to these questions, and you build upon your understanding over time.”
Scott Mackenthun has been writing about hunting and fishing since 2005. Email him at [email protected].