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SPOONER — Researchers are wrapping up the first year of a four-year walleye study on 24 northern lakes that they hope will ultimately identify which lakes are best suited for stocking and which are best left to natural reproduction in terms of providing fishing opportunities.
In coming weeks, the researchers expect to finish sampling young walleyes to determine which were propagated in hatcheries and which were naturally reproduced.
"This study will give us an overall idea of how well our walleye stocking program is contributing to the fishery on this type of lake," says Marty Jennings, a Department of Natural Resources northern lakes ecologist who is leading the study. "We can look at individual cases among the 24 lakes and use this information to direct stocking to where it’s more successful and steer away from those lakes where it’s not successful. The idea ultimately is to maximize the effectiveness of the program."
To provide fishing opportunities, the department has for many years stocked walleye fry and fingerlings in lakes. Recent research has suggested that not all lakes are the same when it comes to fish production, and that stocking a lake isn’t always the best way to manage the lake. DNR fisheries biologists will not stock lakes with healthy, naturally reproducing populations for a variety of reasons. Key concerns are that stocked fish compete with the natural populations for food, and that if stocked fish spawn with the naturally reproduced fish, the offspring may not be as well adapted to survive in that particular waterbody.
The study began earlier this year on 24 lakes in nine counties across northern Wisconsin. The lakes were selected with input from DNR fish managers and Great Lakes Indian Fish and Wildlife Commission fisheries staff. All study lakes are thought to have walleye populations that include naturally-reproduced fish and hatchery-raised fish.
Early this summer, researchers stocked 12 of the 24 lakes with walleye propagated at DNR hatcheries this spring. Stocked walleye have a permanent mark that allows them to be distinguished from naturally occurring fish (see sidebar).
During recent weeks, researchers have been collecting young walleye and sampling the fish to check for the mark to determine the percent of young fish that came from the hatchery, and those that were the result of natural reproduction.
"We’ve been collecting some young walleye this fall to see how the stocked ones have survived and what percentage of the young fish were naturally reproduced," says Jeff Kampa, a DNR fish research technician who works in Spooner. The researchers use those samples to estimate the population of young walleye in the entire lake.
Next year, researchers will stock the other 12 lakes, and then will alternate stocking the two sets of lakes in the remaining two years of the study. They’ll survey all 24 lakes all four years, however.
This experimental design, Jennings says, allows the researchers to compare "year class strength," the proportion of fish born in that year that survived to fall -- between years in which the lakes were stocked and years when they weren’t stocked. "And by repeating this over four years, we’ll be able to account for regional climate factors – like a drought, or extremely wet weather -- that might make for stronger classes or weaker classes in one year over another," he says. Researchers can also compare year class strength in the same year between stocked and non-stocked lakes.
In addition to helping identify which lakes are the best candidates for stocking, the study may offer other clues that will help fisheries managers and hatchery staff fine-tune their stocking programs.
For instance, another walleye stocking study in southern Wisconsin on Lake Kegonsa in Dane County has suggested that some stocking is warranted in that lake --25 percent of the fish sampled in the fall had been naturally reproduced, while 75 percent was hatchery reared -- but that stocking larger fish was more successful.
"In our first two years, we learned that stocking fry in April did not do the trick down there – we sampled 100 fish in the fall and only 1 percent of them were stocked fish ," says Mike Vogelsang, the fish manager who conducted the Lake Kegonsa research. "When we stocked 2-inch fingerlings later in the year, in June and sampled 100 fish in the fall, 75 percent of them were stocked fish. It pointed out that stocking the larger fingerling was the way to go rather than fry."
Vogelsang said that the study he conducted, and the northern walleye study, "will give us the ability to manage more on a lake-by-lake basis (as far as stocking goes) and put the hatchery product where it will do the best job."
FOR MORE INFORMATION: Marty Jennings (715) 635-4160; Jeff Kampa, (715) 635-4166; Mike Vogelsang (608) 273-5946
Uploaded: 10/9/1999
Uploaded: 10/9/1999