Genetic Studies Of Lake Wissota Muskies Prompt Changes

By Jordan Weeks, Research Editor

Changes in the stocking practices of muskies in Wisconsin’s Lake Wissota are likely following new discoveries by genetic researchers.

This research was part of a comparative study regarding stocking of Leech Lake strain and Wisconsin strain muskies. For the past two years, Wisconsin Department of Natural Resources staff have been collecting tissue samples from muskellunge captured during all fish surveys on Lake Wissota, a 6000-plus-acre impoundment of the Chippewa River near Eau Claire. The research was spearheaded by Wisconsin DNR biologist Joseph Gerbyshak.

Of 156 musky tissue samples analyzed, only four (2.6 percent) were of Leech Lake origin. “This is much lower than expected and likely can be attributed to poor survival,” Gerbyshak said. The four pure Leech Lake strain fish measured 40.0, 37.0, 34.9 and 12.2 inches long.

Genetic samples analyzed by the Molecular Conservation Genetics Laboratory at the University of Wisconsin-Stevens Point also found four of the muskies handled by WDNR biologists were hybrids between the Upper Chippewa River and Leech Lake strains. Since 2005, 30 percent of the muskies stocked in Lake Wissota were of Leech Lake strain, while 70 percent were of Upper Chippewa River lineage. The four hybrids measured 36.2, 15.2, 12.4 and 11.4 inches in length, and their presence confirms natural reproduction by muskellunge in Lake Wissota.

“Based on department policy (Statewide Musky Management Team) and because natural reproduction has now been documented in Lake Wissota, it will no longer be designated as a ‘universal receptor lake’ and stocking of strains other than Upper Chippewa River strain will not be allowed,” Gerbyshak said.

What the WDNR calls “universal receptor lakes” are waters where no natural reproduction of a fish species can be documented, so multiple strains of the species are allowed for stocking. Gerbyshak explained the reason why Leech Lake strain fish will not be permitted for stocking is “their effect on the Lake Wissota musky population is not just limited to the lifespan of the fish. The genetic lineage of the Leech Lake strain may be a part of the population for many, many generations.”

He continued: “This matters because in other populations the progeny of introgression between different genetic strains have reduced the fitness of that population in terms of growth and survival and there can be long term negative consequences for population viability.  “Large scale impacts to the population are not anticipated because the number of hybrids at large is expected to be small, but now that there is documented natural reproduction, there is no reason put the future Lake Wissota musky population at additional risk.”

The largest musky sampled in the genetic study was a 50-inch Chippewa River strain fish thought to be 13 years old.

Gregg Thomas

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