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Sturgeon Spawning Update from Ron Bruch for May 4, 2011

May 5, 2011

This update has been posted with permission from Ron Bruch and the Wisconsin DNR:

“Very productive day dipnetting and tagging lake sturgeon below the Shawano Dam yesterday Wednesday May 4. With two crews working we captured and tagged 340 sturgeon including 72 females. In addition we completed egg collections for the Menominee Tribe, and for our DNR restoration projects on the Milwaukee, Kewaunee, and upper Fox Rivers. Spawning activity was good but not as heavy as we normally see at this stage of the run at the Shawano site. I suspect the cold water (still 8 degrees F or so below optimum) is drawing out the run and causing the pulses of females to begin ovulating at a slower than normal pace. Remember, female lake sturgeon appear to be on their own individual ovulation clock with some beginning at lower temperatures, most in the middle temps, and some at higher temps. The big difference this year is that the middle group is being drawn into the run over a protracted period of time as our water temperatures just don’t seem to want to warm up. Yesterday morning our temps were 45.1 degrees F (7.3 C), and despite sunshine all day and very warm weather, temps at the end of the day only rose to 47.8 F (8.8 C). Normally at this stage of the run we would be seeing water temps at 58 F (14.4 C). Eventually the water will warm up into the 50s and at that point I expect we will see a few sturgeon spawning again – although this year that may be towards the end of May. Females of course can only lay their eggs once – after a female begins ovulating she has to finish no matter what the water temps do. If she has not experienced her individual ovulation point she will wait until that happens even if it is a month after most of the other females have already laid their eggs. Males on the other hand will spawn at every opportunity – 1st run, 2nd run, 3rd run……even if these runs are weeks apart. Males will also spawn at multiple sites and even in multiple rivers within our system in the same year.

We will be back at it again today. We still have not captured the elusive 200 pound fish, although we have seen some in this battleship size class, but have not been able to get our nets on them. Maybe today. The biggest fish we have seen to this point have been in the 150-170 pound class. Also we continue to see large males – absolute brutes when we are attempting to measure and tag them – had one yesterday that was just under 75 inches. People often ask “How old can lake sturgeon get?” We really don’t know the answer to this question yet, but should in the next 40 to 50 years. High exploitation in the mid to late 1900s prevented our fish from living to a ripe old age. Since the implementation of our modern sturgeon management program in the 1970s, and our harvest cap management system in the 1990s, our fish now have the opportunity to experience high survival rates (over 95% at age 1 and older), and to show us their real “stuff” in regards to longevity and size. We now have fish over 100 years old, females over 200 pounds and males over 100 pounds. I fully expect that in 40 to 50 years we could see some females over 300 pounds and at ages of 150+ years. Many of us probably won’t be around to see this, but our children and grandchildren will be able to see what these fish are really capable of.

As far as this year’s spawning assessment work goes – we probably won’t be at this too much longer. The end of our 2011 sturgeon assessment is in sight- could be home by the weekend.

Till tomorrow.

Ronald M. Bruch, PhD
Upper Fox-Wolf Fisheries Work Unit Supervisor, Wisconsin Department of Natural Resources”

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