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Friday, February 3rd, 2023

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Wisconsin Lake Profile – Mississippi River/Pool 8, La Crosse County

Fish biologists try to puzzle out Pool 8 walleye, sauger status

 

DNR Report

 

The Mississippi River’s Pool 8 offers a very diverse fishery, among other outdoor opportunities, along its 23.3 miles that stretch from Lock and Dam 8 near Genoa upstream to Lock and Dam 7 near Dresbach, Minnesota. Pool 8 includes portions of the Upper Mississippi River National Wildlife and Fish Refuge, the south end of French Island, and the city of La Crosse. Visitors access Pool 8 from nearly 40 public and private boat landings.

 

A Wisconsin DNR fisheries team out of La Crosse ran a fall 2019 walleye/sauger survey on Pool 8. David Heath, DNR fish biologist out of La Crosse, drafted the report.

 

The crew didn’t have a lot of success in finding young-of-the-year walleyes or saugers, but Heath said high water elevations in 2019 may have affected the catch.

 

“For 10 of the last 12 years, Mississippi River YOY abundance estimates (saugers and walleyes) were below the long-term average. We could find no long-term trend (1983-2019) in walleye or sauger abundances despite recent declines,” wrote Heath, noting also that sauger abundance declined during the past 22 years.

 

Wisconsin and Minnesota Mississippi River fish teams pay a lot of attention to walleyes and saugers because of their popularity with anglers.

 

“Although angling success is generally good, it can vary based on population fluctuations. Some of these fluctuations can be attributed to spawning success and early life stage survival.”

 

High water temperatures, discharge and surface water elevations can influence fish catch rates during surveys. In Pool 8, water temps in the fall of 2019 were below average while the current was moving at 69,189 cubic feet per second above average, so trying to find YOY walleyes and saugers at an average depth of 7.2 feet wasn’t easy.

 

“Pool 8 walleyes have shown high annual variability in recruitment,” wrote Heath. “Average walleye CPH (catch per hour) has varied from 2.9 fish to 596.7. In 2019, walleye YOY CPH averaged 3.41.”

 

In 2019, CPH was lower than the long-term average of 113.7, calculated from pooled data. Since 2008, 11 of the last 12 years have been below the long-term average.

 

“This nearly consecutive number of below average years is unprecedented since these surveys began in 1983. The most we’ve measured is seven low years from 1988 through 1996. Shoreline catch for 2019 YOY walleye averaged 3.25 fish per mile.”

 

Recent abundance patterns in Pool 8 were also apparent in the two other pools sampled for YOY walleyes. During 10 of the past 12 years, walleye abundance was below the average in all three pools combined (pools 5, 8 and 10).

 

Pool 8 2019 YOY walleyes’ average total length was lower (0.4 inches) than the long-term mean, although the sample size was small. Total length of 2019 YOY walleyes ranged from 6.3 to 7.8 inches. Over the past 37 years, walleye average annual lengths have varied from 6.6 to 8.2 inches and the 2019 mean was the 33rd lowest among all years.

 

“We could find no biologically important trend in YOY walleye lengths over all years” wrote Heath.

 

The long-term (1983-2019) average sauger CPH, calculated from pooled data, was 78.20. Prior to 2019, it varied from 1.8 to 400.1.

 

“In 2019, we caught no YOY saugers and the CPH was 0.0, well below the long-term average. Like walleyes, YOY sauger abundance, as measured by our samples, was below average for 11 of the last 12 years. Shoreline catch for YOY sauger averaged 0.0 fish per mile,” he wrote.

 

Despite the below average annual abundance estimates observed since 2008, there was no statistically significant long-term CPH trend observed from 1983-2019. A declining trend in saugers from 1998 through 2019 was influenced by 11 recent below average recruitment years preceded by mostly average or above average years. The years 2008-2019 were significantly lower than 1996-2007 and 1983-1995. Heath said these data suggest a decline in YOY sauger abundance since about 2008.

 

Over the past 37 years, sauger average annual lengths have varied from 6.0 to 7.3 inches. For YOY fish there was a significantly declining trend in lengths over all years.

 

“The magnitude of this trend appears to be biologically unimportant,” he wrote.

 

Recent abundance patterns observed in Pool 8 were also apparent in the two other pools sampled for YOY saugers. Like Pool 8, YOY sauger catch rates in combined pools were below average in 10 of the past 12 years.

 

“We have not seen this many consecutive years of below average abundance estimates since initiating these surveys in 1980. In addition, there was a significant decline in sauger abundance from 1998 through 2019 of 91 percent,” wrote Heath.

Pool 8

Nearest town La Crosse

Surface area 20,180 acres

Max. depth Varies

Water clarity turbid

 

Fish species present:

Black crappies, bluegills, pumpkinseeds, rock bass, yellow perch, white suckers, shovelnose sturgeon, smallmouth  bass, largemouth bass, northern pike, walleyes, and muskies.

 

For information:

DNR regional fisheries office (608) 785-9000, the DNR web site http://www.dnr.state.wi.us/org/water/fhp/fish, or call Bob’s Bait & Tackle, (608) 782-5552.

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