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Sturgeon Spawning Update from Ron Bruch on May 13, 2011

May 13, 2011

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

“The 2011 Wolf River sturgeon spawning run looks like it finally may be in the books. Last night there were still a fair number of sturgeon on the Shawano camera, along with a new fish guest star – gizzard shad. Attached is a recorded video snippet from the camera courtesy of the Wolf River cam folks that shows adult gizzard moving up river to spawn along side the remaining lake sturgeon: These are adult (probably 2 or 3 year old) gizzard shad. Most of the shad people see are less than 8-10 inches, but they can get quite large (up to 18 inches or longer) as adults. We have had good hatches of shad the last few years which increases the chances of getting good numbers of these large 2-3 year old adults in the system. They are making their spawning run. They spawn optimally at water temps in the low 60’s or higher, but can start spawning at temps in the 50s. The river is now at about 60 degrees after the warm weather this week.

This morning you can see a sturgeon now and then on the Shawano cam, but the field of view is pretty much completely filled by carp, the next fish in line to begin its spawning activity (and occasionally a smallmouth bass, sucker, and a gizzard shad) The carp also undoubtedly are foraging on the sturgeon eggs which were laid at the Shawano spawning site. As I mentioned in an earlier e-mail this may not be bad as egg predators keeping the rocks clean likely helps promote good water flow and incubation conditions for the lake sturgeon eggs down in the interstitial spaces in the rocks. Male lake sturgeon will also consume large quantities of the sturgeon eggs they only hours earlier helped fertilize.

Back to gizzard shad – the shad are a very important part of the lake sturgeon success story on the Winnebago System over the last 20 years. We are not sure if shad are native to the Winnebago System or not. We have capture records of shad within the Winnebago System going back more than 50 years, but they were never very abundant until the late 1980s and early 1990s. A series of dry hot summers and warm winters in the mid to late 1980s was followed by an explosion of gizzard shad in the Winnebago System as well as throughout the Great Lakes region. Most of our important fish predators especially walleye and northern pike made shad a large part of their diet which increased growth rates, promoted earlier maturation, and overall brought the walleye fishery back from the low point it was at in the early 1990s following year class failures for most of the 1980s. The presence of shad made the fishing more difficult on the Winnebago System for walleye and northern pike in years when the shad hatch was large. Alternatively, in the years when the shad hatch was low, fishing was fantastic all summer for walleye and all winter for northern pike.

Shad – sturgeon connection: Gizzard shad experience a winter die off each year, especially here in Wisconsin which is at the northern edge of the species’ range. The dead and dying shad are perfect fodder for foraging lake sturgeon in the winter in the Winnebago lakes. During the winter sturgeon spearing season in years of high shad hatches we will often see lake sturgeon at our registration stations that have 2 or more gallons of dead shad in their foreguts. Based on our studies we estimate that sturgeon now get 37% of the carbon they assimilate from eating gizzard shad (49% comes from lake fly larvae, 14% primarily from other aquatic insects that live on the bottom). So although shad may make fat walleye and northern pike less susceptible to bite on your bait in some years, they are critical to sustaining the condition and abundance of lake sturgeon in the Winnebago System, and are part of the reason we currently see the healthy sturgeon and the abundance of trophy size sturgeon in the Winnebago system.

I’ll be sending a final wrap up with all of the numbers from this year’s Winnebago lake sturgeon spawning assessment as soon as we get the numbers entered and crunched.

Have a great weekend.

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

One Comment leave one →
  1. September 12, 2011 9:41 am

    Loved you report.

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