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Water clarity is the strongest predictor of lake sturgeon harvest success on the Winnebago System (Figure 1; Line Graph). Several factors play a role in what the water clarity looks like leading up to the sturgeon spearing season; however, the main factor is ice conditions.
Figure 1. Lake Winnebago average water clarity (grey series; right y-axis) and total annual spear harvest (black series; left y-axis) from 2002-2022 (x-axis). Red dashed lined represents 12-foot clarity threshold.
Shifting ice, snow-covered ice, how early the lake freezes over, and thawing and refreezing events will likely determine whether spearers hang their decoy 2 feet or 12 feet below the surface. Generally, water clarity conditions tend to be favorable in years of early ice, weak winds and enough snow cover to limit light penetration and phytoplankton growth.
History has shown that in years when water clarity is 12 feet or greater, harvest caps tend to be met before the entire 16-day season. Last year was anything but predictable and even though the lake-wide average water clarity was 12 feet, the season continued for the full 16 days. The last time water clarity was that good was in 2015, which is also the last time harvest caps were met before the end of the season.
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During the week of Jan. 24, 2022, the DNR conducted pre-season water clarity readings. To collect readings, a tool called a secchi disk is dropped through a 10-inch ice hole to capture two depth measurements – one when the disk disappears on the way down and another when the disk reappears on the way up. Then, the measurements are averaged to achieve the most accurate reading.
In total, 14 depth readings over the 6 geographic regions of Lake Winnebago were gathered in January. Reading locations were dictated by access and safety of travel conditions (Figure 2; Map).
Figure 2. Map of Lake Winnebago with sampling locations denotated by the yellow stars. Numbers next to individual stars correspond to sampling locations and data in the table below.
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The average water clarity was 10.71 feet at sites deeper than the 12-foot threshold (Table 1). Strong winds prior to freeze-up and patches of open water that held strong into January likely played a role in the decreased average clarity this season. Water appears to be a bit clearer in the northern portion of the lake with fairly uniform visibility across the entire Winnebago system. If stable weather patterns continue leading up to the sturgeon spearing season, spearers could see improved water clarity resulting in a potentially longer Lake Winnebago season again this year.
Table 1. Secchi disk clarity readings from Lake Winnebago. Each row corresponds to the clarity (feet) at the reported lake depth and specified distance off an access point. The bold value at the bottom of the clarity column denotes the average Lake Winnebago water clarity.
Water clarity readings were not conducted on the Upriver Lakes as water clarity has less of an impact on Upriver Lakes harvest numbers. Preliminary reports from fisherman and spearers out scouting on the Upriver Lakes indicate favorable water clarity in several areas again this season.
The DNR may conduct another round of water clarity readings the week before the season opener on Feb. 12 to determine if average clarity has changed or improved.
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