Study tries to pin down effects of stocking on trout genetics
Written by Appleton Post-Crescent   
Sunday, 26 February 2006 09:34

All brook trout are not alike. That's the basis for Brian Sloss' study of brook trout in southwestern Wisconsin streams. Sloss, assistant unit leader for the U.S. Geological Service Wisconsin Cooperative Fishery Research Program at the University of Wisconsin-Stevens Point, is studying the genetic impact of Wisconsin's wild trout stocking efforts.

For many decades, the Wisconsin Department of Natural Resources — as did fishery agencies in other states — held adult trout in hatcheries year-round to furnish a supply of eggs and sperm necessary to raise future trout for stocking.

The result, fisheries experts have come to believe, was the raising and release of trout better adapted for surviving in hatcheries than in the wild.

In recent years, the DNR has embarked on a program that emphasizes taking eggs and sperm from wild stream trout, hatching those eggs and releasing the fry and fingerlings in other streams where stocking is needed. The donor trout are released back into their home streams.

Those efforts, for the most part, have been successful in providing more survivor-savvy brook trout, Sloss said, but a question has been raised as to whether the trout potential in streams from which wild eggs have been taken were harmed in the process.

"We may be pulling over half the adult fish from some creeks, which may be both a genetic and environmental problem," he said.

He said it's possible the process could affect the population in the stream providing donor trout by reducing the variety of spawning pairings "resulting in a loss of health in the source population."

So far, he said, "we haven't seen any evidence of harm, but we're still early in the study."

Of equal importance, Sloss said, is maintaining the integrity of Wisconsin's native brook trout. When the idea of stocking trout took hold in the early 1900s, trout were often stocked indiscriminately.

"From a genetic standpoint, we have a history of stocking fish from all over the country," Sloss said. "We stocked a lot of trout from New Hampshire in our streams. For a long time, if some state had extra fish and we could obtain them, we'd stock them.

"Everybody thought 'a fish is a fish,' but genetic evidence has shown that's not exactly true."

Backed by an $85,722 grant from the DNR, Sloss is overseeing the work of Mike Hughes, a UWSP graduate student from Oshkosh, in taking genetic samples from trout in up to 20 streams in southwestern Wisconsin.

"We're trying to find out what a typical Wisconsin brook trout looks like in that area, to find out whether New Hampshire fish have polluted our gene pool," Sloss said.

The hilly coulee country in the southwestern counties was not affected by the last glacial period and thus should have the oldest strain of native Wisconsin brook trout.

"There's a very good possibility some of those streams have been polluted with New Hampshire fish," Sloss said. "I believe one of the brook trout strains Wisconsin still uses to stock in streams or lakes where there is no chance of natural reproduction is a New Hampshire strain."

Even if New Hampshire fish were stocked in some of the naturally reproducing trout streams, "there's a good possibility they didn't reproduce and, if they did, they didn't have an effect on the integrity of the native population," he said.

Ultimately, the DNR's goal is to create "genetic management zones" and use only wild trout from a specific zone to provide spawning ingredients for stocking within that zone, Sloss said. Fish would be stocked only in waters that can't maintain a self-sustaining population.

The idea is to retain genetic traits that, for example, brook trout from northeastern counties developed to flourish in that forested region. Trout from the state's sand country might share a different genetic makeup.

The concept isn't perfect. Questions are bound to arise when it comes to the best genetics for a stream that straddles or approaches a management zone border. But the DNR's insistence on stocking wild trout is paying off in the southwestern counties, Sloss said.

"Anglers seem to be happy," he said. "The fishery seems to be better, and the better fish you put out there, the better chance you have of establishing a reproductive population."

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