|
PORTAGE, WI - For decades, anglers have fished waters below the Wisconsin Dells Dam and in downstream Lake Wisconsin during a special autumn season for Wisconsin River sturgeon.
What if those sturgeon are not year-round residents of the Lake Wisconsin area after all?
Just where do they come from? Where do they spend the seasons? The in-between years? Where do they spawn? Why?
Might a multiple-residency status affect future fishing regulations?
These questions may be answered by a new study undertaken by the Department of Natural Resources.
"Little is known about the sturgeon population in the Lower Wisconsin River," explained Michael Rennicke, a DNR fisheries technician at Poynette.
"We surgically implanted radio-transmitters in 16 adult sturgeon last fall, hoping to follow those fish for six years if funding allows. We need to know more about them because sturgeon are a species of concern and it's very easy to over-exploit them."
Rennicke is involved in a lake sturgeon
management project on the lower river under the direction of Tim Larson, DNR fisheries biologist.
Sturgeon are a slow-growing, long-lived species. Females begin spawning about the time they reach 50 inches and 24-26 years of age, after which they spawn every four-six years. Males mature around 20 years of age and while some spawn every year, most spawn every other year, Rennicke said.
Angler-caught sturgeon typically weigh 30-70 pounds but can reach weights exceeding 100 pounds.
Wisconsin has the largest inland sturgeon population in the nation. The best-known segment resides in the Lake Winnebago system, where a unique and highly regulated winter spear fishing harvest of sturgeon is allowed.
A restricted fall fishing season for sturgeon is permitted on several designated waters within the state, with the Lower Wisconsin River below the Wisconsin Dells Dam (including Lake Wisconsin) drawing some of the heaviest angling pressure.
Regulations governing sturgeon harvest are based on a minimum length limit designed to allow females to spawn at least once and to hold the angler catch to below five percent of the adult population, Rennicke explained. The rules have been juggled -- particularly in recent years -- as biologists attempt to reach a balance point where the fishery is protected and anglers are still allowed a limited harvest.
The estimated sturgeon population larger than 50 inches dropped from 287 in 2005 to 171 in 2007.
During that time, a 50-inch minimum in 2005 resulted in an angler exploitation rate of 26 percent, a 70-inch minimum in 2006 produced a one percent exploitation rate and the 60-inch minimum in 2007 found the desired five percent rate.
However, even at the five percent rate, Rennicke fears female sturgeon could be over-harvested. Females typically live longer than males and therefore reach the 60-inch mark more frequently, thus putting them in anglers' bags more often.
There is evidence at least some sturgeon spend time in the Mississippi River and make the journey up the Wisconsin River to the Lake Wisconsin and Dells Dam area in late summer to spend the winter in deep holes.
Some may make the journey in anticipation of spring spawning, others are winter migrants and a few could be year-round residents of the Wisconsin River.
"We tagged 142 sturgeon in 2005," Rennicke said. "Of those, we saw 29 in 2006 and 22 in 2007. Four of those sturgeon were seen all three years.
"If females are coming up to spawn every four years, why are we seeing some of these fish year after year?"
The Wisconsin River is believed to have contained sturgeon as far north as Wausau during the early 20th century. Those fish disappeared as dams were constructed and sturgeon populations became isolated. Did dams prevent sturgeon from migrating to previous spawning and wintering areas, thus slowly eradicating their numbers?
The Dells Dam is the first dam upstream from the Mississippi River. Can sturgeon introduced into waters above the Dells establish new spawning and survival patterns that don't require a lengthy migration?
Questions keep coming. Not all the answers will be forthcoming, but insights are expected as data from the radio-tagged sturgeon are accumulated and reviewed.
"The findings should be interesting," Larson said. |
