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Update from Ron Bruch on April 23, 2010

April 23, 2010

“Dear Winnebago Lake Sturgeon Enthusiasts,

The lake sturgeon spawning run is pretty much complete for 2010 on the Wolf and upper Fox Rivers, although we still may see a few fish spawning yet in the “2nd” or “3rd” runs. Nearly every year cool or cold weather interrupts the main spawning run which causes some female sturgeon to hold off and spawn sometimes 2 weeks to a month after the main run is over. Each female sturgeon is on her own biological clock for ovulation with some fish spawning at lower temperatures (or at an lower number of thermal units), most spawning at a mid-range (or optimum) temperature or number of thermal units, and a few spawning at higher temperatures or higher number of thermal units. A daily thermal unit is the average water temperature (F) for a day minus 32. By adding the thermal units each day after ice out on the river, we can somewhat predict when sturgeon may begin spawning. Females, once they begin to ovulate, complete spawning within 12 hours or so and move back downstream to the lakes fairly rapidly after they are finished spawning. Males will spawn for days at numerous spawning sites and then will wait in the river for the 2nd and 3rd runs for up to a month if they sense there are still females waiting to ovulate and spawn. We have also seen males that not only spawned at numerous sites in one river, but also spawned in both the upper Fox and Wolf Rivers in the same year.

This spring my outstanding crew, along with the great help of a number of volunteers and especially a large group of students from the University of Wisconsin-Stevens Point Fisheries Society, captured and tagged a record number of adult females during our sturgeon spawning assessment and the second highest number of adult males. We (DNR) have been tagging sturgeon on the Wolf River during their spawning run since 1954.

Females newly tagged – 169
Female recaptures – 26
Females Total – 195

Males newly tagged – 619
Male recaptures – 305
Males Total – 924

We typically capture only adult fish during our spring spawning assessment (which consists of dip netting the fish while they are actively spawning on the rocks at the spawning sites). Our telemetry work though has shown that sub-adult sturgeon undergoing puberty enroute to their first spawn, but not quite there yet, also join the adults on spawning runs, but stay in the river adjacent to the spawning sites, not joining in the action taking place on the rocks. We have seen this phenomena occur with wild sub-adults, and with sub-adults reared in the lab and released into the Upriver Lakes just prior to the final movement of adults up the river in early spring. So – it appears these fish may be “hard-wired” for their run and migrational patterns. We are continuing our telemetry research and other studies to unlock the mysteries of our Winnebago lake sturgeon.

This spring we had a large amount of media coverage of the Wolf River sturgeon spawning run and here are some links to some of that coverage, photo slide shows, and video:

Also this spring we celebrated the 51st year of sturgeon tagging by Dan Folz, Father Sturgeon of the Winnebago lake sturgeon program. Dan has been my mentor for all of my career and I was fortunate to follow him as the sturgeon biologist after he retired in 1990. Here’s to you Dan……..(photo by Pat Durkin)…….

One more last minute link to a Wolf River sturgeon video you may be interested in seeing…………..

AP, “Endangered sturgeon fish flourishing in Wisconsin”

Also – someone e-mailed and asked what was the biggest fish we saw this year………we captured numerous fish in the 150-170 pound class this year, but also saw numerous fish in the 200-240 pound class that we could not get our nets on – these big fish looked like nuclear submarines in the water at Shawano.

I’ll be sending out a report later this summer with a summary of the data we collected this year during the spearing and spawning seasons.

Finally, I want to mention and thank the hundreds of people who donated their time to babysit spawning sturgeon 24 hours a day at the numerous spawning sites as part of our “Sturgeon Guard” program. This program, funded by Sturgeon for Tomorrow, has been in effect since 1977 and has contributed significantly to the success we enjoy today with our Winnebago System lake sturgeon population and fishery.

Till my next report…………………..”

Ronald M. Bruch PhD, Upper Fox-Wolf Fisheries Work Unit Supervisor, Wisconsin DNR

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