Despite the below average spring temperatures up to this point, our fisheries management team in Oshkosh has been busy in the field conducting stock assessments for yellow perch and walleye, with sturgeon work just around the corner. The ice went out on the Wolf River between April 5-6, and on April 7 our crew headed out on the Wolf River in search of pre-spawn walleye for the first time. We didn’t have much luck capturing fish as the water temperatures were still hovering around 34 degrees in the river channel and in the spawning marshes. Fish weren’t in the spawning marshes yet. The weather over the next week didn’t help much either, with wintery mixes and a great deal of rain. We finally were back out sampling again on April 12. Much to our surprise, and despite water temperatures of 34 degrees, we observed walleye spawning and captured ripe females in our samples. For reference, peak walleye spawning normally takes place at 44-46 degrees. 34 degrees is well below average. As the following week progressed, spawning activity increased even without much of an increase in water temperature. The peak spawn on the Wolf River took place between April 20-22. Water temperatures during this time were 38-40 degrees , but the walleye spawned anyway.
Our crews were very successful over the 10-day tagging period, handling a grand total of 10,244 walleye! We inserted yellow anchor tags into 9,991 new fish -5,132 males, 4,752 females, and 1 immature on the Wolf River and 57 males, 48 females, and 1 immature on the upper Fox River- and had 253 recaptured fish that were tagged in previous years. We tagged almost twice as many females this year, compared to tagging dating back to 1993! In fact, previous to this year, tagging 1,500 females was a pretty good year. The large number of females this year is due mostly to the recruitment of the 2008-year class to the adult female population. We saw a large increase in abundance of male walleye last year as a result of this same year class, with most male recruitment occurring at age 4. Now we are seeing full recruitment of this year class to the adult female population at age 5.
Some have expressed concerns about the low number of males in the river this year. Indeed we are seeing a lower male to female ratio in the adult population this year than past years, but still tagged more than 5,000 males. We are not concerned that there is a low number of males, but rather surprised that we are seeing this many females. Male walleye can spawn with numerous females, so there should be no problem with females finding males to fertilize their eggs during spawning. We observed more large 24+” walleye than we can remember in recent years, suggesting a healthy, balanced fishery. The graph below shows the size distribution of the fish that we were able to capture this spring during our stock assessments. I have also attached a photo of one of the largest females that we have ever handled on the Winnebago System (photo by Rachel Foster). This is a “trophy” fish that we captured up by HWY CCC, just downstream from Shawano, on April 21, 2013. The fish measured 29.6 inches and weighed 12.92 pounds!
I have also been receiving numerous calls and emails from people wanting to know “when are the sturgeon going to spawn?” As most of you probably know, we are a little behind schedule with fish spawning this spring due to the cool temperatures. Past data indicate that peak spawning takes place between April 15 – May 1). I don’t know definitively when fish will start to spawn, but given the forecasted warmer temperatures, it likely will be sooner than later. In fact, I am optimistic that sturgeon will start to spawn sometime late this weekend or early next week. Given the delay in normal spawning time frames and forecasted temperatures in the 60’s and 70’s, this may be a short, intense spawning run. If you have it on your bucket list to see the sturgeon spawn on the Wolf River, I recommend coming out as soon as you hear of fish spawning to witness this amazing event!
Ryan P. Koenigs
Upper Fox - Wolf Fisheries Work Unit
Wisconsin Department of Natural Resources
phone: (920)303-5450e-mail: Ryan.email@example.com