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Wisconsin Natural Resources magazine

Wisconsin Natural Resources magazine

Genetics is a controlling factor in survival rate and size of musky. © Ed Murphy
Genetics is a controlling factor in survival rate and size of musky. © Ed Murphy

August 2006

Keeping the fight in the king of fishes

Natural strains and careful matchmaking invigorate the genetic lineage of stocked muskellunge.

Lisa Gaumnitz

The fish
The detective
The men and women in the middle
Revealing the code
Head-to-head competition

Call it CSI: Hayward.

Using the same kind of cutting-edge technology common on the current crop of TV forensics shows, Wisconsin fish managers, hatchery staff and geneticists are unraveling the musky's genetic lineage and launching a comprehensive examination of the state's musky propagation practices.

They hope to determine if Wisconsin harbors distinct musky strains in different waters or if a century of fish stocking has erased genetic boundaries and turned Wisconsin fish into slow-growing "mutts" as some anglers contend.

Fisheries crews now follow precise genetic guidelines when collecting eggs and sperm from parent fish (or "brood stock") to foster a strong, vigorous, diverse bloodline in ensuing generations of stocked musky and to conserve the genetic makeup of muskies that naturally evolved in our lakes and rivers.

As a component of that review, biologists set up side-by-side tests to compare how musky strains produced in Wisconsin hatcheries stack up against a Minnesota strain. The fish are raised under identical conditions and stocked in the same waters at the same time.

"This is a very exciting time for our fisheries program," says Mike Staggs, director of DNR fisheries management. "We're marrying the latest science and forensic techniques in our day-in and day-out hatchery programs to improve the way we manage our brood stocks, and to answer some important questions raised by anglers."

The results, Staggs says, will benefit fish, anglers and the public wallet, given that stocking musky is a pricey proposition.

Muskies fight long odds to reach adult size. Nearly 600,000 musky fry are stocked for every musky that survives to 18 months at a cost of about $800 per fish, according to a 1986 Wisconsin study. The tab drops to about $70 per survivor if fish are stocked as fall fingerlings, or to $27 per survivor when stocked as spring yearlings – the two sizes DNR focuses on.

"We want to be assured that the fish we put in a lake have the best chance to survive and naturally reproduce," Staggs says. "Our aim is to have more lakes where muskies reproduce on their own, providing anglers the best fishing at the best price – free. In those waters where musky aren't native and the fishery must be maintained by stocking, we want to make sure we are putting in the right strains of fish to provide the performance anglers want – steady growth and large size – if the forage base, angler harvest, and other factors are right."

The fish

At the beginning of the 20th century, muskies only inhabited lakes and streams fed from the headwaters of the Chippewa, Flambeau, Black and Wisconsin rivers, with a range covering about 20 counties. In the 1940s, fish managers switched from primarily stocking days-old fry to stocking older, larger fish. By 1970, the musky's range had expanded to include 33 counties.

Today, nearly 90 percent of the state's 794 musky waters are found in northern Wisconsin, reports Steve Avelallemant, a fish biologist stationed in northern Wisconsin for 24 years who is now the region's fisheries supervisor and a member of DNR's musky team.

About three-quarters of these waters currently have self-sustaining musky populations with good, natural reproduction. Most musky waters have been stocked at least periodically over time, mainly with fish spawned from northern waters and raised in state hatcheries in Woodruff and Spooner. Green Bay and the Lake Winnebago system receive a Great Lakes strain of musky raised at the Wild Rose State Fish Hatchery. A total 180 waters are now being stocked regularly.

DNR's stocking program, combined with a phenomenal catch-and-release ethic by anglers and higher minimum size limits, have helped musky populations recover from the low levels in the 1970s following a musky fishing frenzy in the late '50s and '60s; the "musky mania" was sparked by world-record catches in Wisconsin in the 1940s. Now, more than a generation later, anglers in Wisconsin are enjoying some of the highest musky densities and best catch rates anywhere, Avelallemant says. The so-called "fish of 10,000 casts" is now caught in an average of 3,000 casts.

However, some fish managers were concerned that the stocked fish were not surviving as well as expected in some waters, and were not building self-sustaining populations as hoped. In other waters, managers saw growth rates decline as musky numbers increased, causing concern that the fish are outstripping the forage base.

One group of anglers believes one lot of muskies stocked into Lac Courte Oreilles in 1956 has resulted in interbreeding that reduced musky growth. The anglers question the growth potential of the Bone Lake musky strain, originally derived from Lac Courte Oreilles fish, used as brood stock at the Spooner hatchery, and stocked widely throughout the state. The group has called on DNR to stock a musky strain from Leech Lake, Minn. that recently yielded a large number of 50-inch fish when stocked in some Minnesota waters.

"The current controversy asks, 'Do we have fewer big fish than we used to?'" Avelallemant says. "We don't have any problem producing enough muskies. If you want to catch a musky, you should come to Wisconsin because nobody is going to beat our fish densities and catch rates." And he notes that by other measures, Wisconsin isn't producing fewer big fish. Voluntary reporting by Muskies, Inc. members shows the number of 50-inch fish has reached an all-time high.

"Most of the evidence shows it isn't the fish, it's where it is put," he says. Genetics is only one factor determining growth rate and size, and it's rarely the controlling factor. "It's not that simple."

The availability of food, amount of habitat, populations of competing species, mortality from angler and tribal harvest, and mortality from poor handling practices or hooking injuries when fish are released, all affect the growth rate, survival and ultimate size muskies attain.

Still, Avelallemant, Staggs and other members of the department's musky team think the group has raised some important questions at a time when technological advances can help provide answers. So the DNR team has contracted with Brian Sloss, a University of Wisconsin-Stevens Point geneticist, to do some detective work while DNR continues studies of its own to uncover answers.

The agency already has made some adjustments. Beginning in 2001, muskies have been stocked at one of several fixed levels lower than in the past, and stocking has been stopped entirely on other waters. Holding to this stocking strategy for at least a decade will show patterns in the resulting musky populations which will help to better match the amount of stocking to available food, levels of natural reproduction and competition among species. Biologists are also identifying musky habitat and educating people why certain lakeshores should not be developed. A recent study showed muskies reproduce on waters where less than 20 percent of the shoreline is developed, and that musky reproduction starts to drop off significantly once 40 percent of the shoreline is developed.

"I consider [addressing all these factors to be] the next step in the long evolution of our musky management program," Staggs says. "It's time to take the next steps to keep us at the head of the pack."

The detective

Since joining the UW-Stevens Point's Cooperative Fishery Research Unit in 2002, Brian Sloss has helped establish and build its Molecular Conservation Genetics Laboratory in the College of Natural Resources. The facility now has three DNA sequencing machines capable of running genetic tests on more than 500 individuals a day. Ninety-five percent of the lab's work involves fish, but Sloss recently helped DNR untangle the genetic heritage of prairie chickens. (See our February 2006 story, The drummer of love.)

In 2004, DNR hired Sloss to review its stocking strategies and practices. Those strategies assumed musky strains taken for stocking would be best suited to waters within the same river drainages where they naturally evolved.

Brian Sloss, UW-Stevens Point geneticist. © Ed Murphy
Brian Sloss, UW-Stevens Point geneticist.

© Ed Murphy

"I was pleasantly surprised at how well the program was set up," Sloss says. He also appreciated the openness of DNR propagation staff to his review and their willingness to embrace suggested changes.

As a geneticist, Sloss wants to see stocked populations that mimic the diversity found in nature, not in the barnyard, where it's common to mate the biggest bull and the biggest cow to get even bigger calves.

"From a genetic health standpoint, I want a population that has enough genetic diversity to adapt as their environment changes. For example, as waters warm through global climate change or are invaded by exotic species," Sloss says. "Without genetic diversity, they have a higher probability of becoming extinct."

Although DNR's hatchery operations already were very close to what he would recommend, Sloss felt that with a few changes the stocking programs could be made even stronger. He was concerned DNR wasn't collecting eggs and sperm from enough different fish, and that the fish selected as brood stock came from waters that were stocked year after year rather than from waters with naturally reproducing populations. "There was no evidence that any harm had been done," Sloss was quick to say. "But using those populations every year could slowly erode genetic diversity."

So Sloss developed a precise plan by which the two hatcheries would each need to spawn milt and eggs from 70 to 100 fish each year so that within five to seven years, there would be a 95 percent chance of mimicking the genetic strength found in natural populations. Fish would be collected only from naturally reproducing populations, throughout the spawning run, not just at the beginning, and each population would be put on a five-year rotation to avoid harming its reproductive potential. Eggs from each female were to be fertilized by three males.

The men and women in the middle

Starting this spring, Gary Lindenberger and his staff at the Gov. Tommy G. Thompson State Fish Hatchery in Spooner started putting the genetics plan into practice.

Instead of collecting eggs and milt from fish in Bone Lake (a stocked lake), Spooner hatchery staff and fish biologists from the Department of Natural Resources and Lac Courte Oreilles' Conservation Department collected eggs and milt from fish in the Chippewa Flowage (a lake that historically had good natural reproduction).

They exceeded their goal – collecting 30 female fish and successfully mixing their eggs with milt from two to three different males each, ensuring a high degree of genetic diversity among young fish to be reared at Spooner this year.

Hatchery crews from the Art Oehmcke Hatchery in Woodruff also followed Sloss' plan, collecting and fertilizing eggs from the naturally reproducing water of North Twin Lake. They fell just short of their goal, demonstrating some of the challenges in propagating fish.

Spawning seasons start at different times on different lakes, so staff need to learn the spawning sites and dates of each lake. The need to collect eggs from throughout a spawning run, instead of just collecting eggs from "peak" spawning times, means more staff collecting more fish and eggs over a longer period of time – all while juggling other duties including incubating the eggs and collecting walleye and sucker eggs.

Changes to the brood stock policy will similarly ripple throughout the production cycle, Lindenberger says. Eggs collected at different times will be incubated so that they hatch at the same time. Transfering fry of the same size into DNR rearing ponds helps cut down on cannibalism and poor survival.

"The brood stock policy is good, and it's necessary to ensure that the genetic diversity we want in our state's musky population will be found in the thousands of fish that our facility stocks each year," Lindenberger says. "With these new changes, it's quite possible, however, that we'll have to modify and adjust our operation once again so that our musky production is consistently successful from year to year."

Revealing the code

While conducting annual fish population estimates this spring, hatchery staff and fish biologists also snipped nickel-sized pieces of fin tissue from muskies sampled in Lac Courte Oreilles, North Twin Lake and 20 other waters across Wisconsin.

Those tissue samples are destined for Sloss' lab, where he and his graduate student, Ed Murphy, will map the fishes' genetic sequences and look for patterns that could indicate if the fish descended from distinct stocks.

Courtesy of Ed Murphy
Ed Murphy prepares samples for DNA sequencing and analysis at
a UW-Stevens Point lab.

Courtesy of Ed Murphy

Over the next couple years, fisheries crews will collect tissue samples from muskies in about 20 to 30 other waters for similar genetic testing. Sloss and his students will test tissue from DNR's archive of fish samples collected over the past decades on Escanaba Lake and Lac Courte Oreilles to help determine if past stocking has changed musky lineage over the years.

"We're hoping to more or less genetically categorize what's out there," Sloss says. "I hope to give the agency a stock map of the state. The advances in technology should allow us to draw the lines pretty clearly."

In addition, he hopes to answer a question the angler group posed: Has stocking over the last 100 years eliminated natural stock boundaries and turned Wisconsin muskies into "mutts" – meaning there's no need to protect purebred strains and no concern in introducing a new strain of fish that some anglers find more desirable?

Head-to-head competition

Minnesota's switch from stocking a proven slow-growing musky strain from Shoepack Lake to the Leech Lake strain seems a good decision for that state and has Wisconsin anglers talking. In this case, genetics was a controlling factor. The Shoepack strain was slower growing and reached a smaller maximum size than the Leech Lake strain.

Anglers report catching higher numbers of 50-inch and longer fish from some waters stocked with the Leech Lake strain. A Minnesota study suggests the Leech Lake fish grew at faster rates in the first five years than Wisconsin hatchery strains.

Wisconsin researchers have developed a controlled experiment to compare performance standards of the two strains head-to-head. "Past comparisons have been anecdotal, or lacked side-by-side measurements in relevant waters," says Martin Jennings, a longtime DNR fisheries researcher.

Starting this spring, Jennings began a long-term study to see how the two fish strains fare when raised at the same hatchery under the same conditions, and then are stocked at the same time into the same lakes. The research design eliminates differences in lake characteristics, whether the fish were stocked in waters with or without established musky populations, and whether angling pressure might contribute to differences in fish growth rates and ultimate size.

Wisconsin waters differ considerably from Minnesota in some of these factors. Leech Lake, for instance, has the same surface acreage as all of Wisconsin's trophy musky waters combined. The Leech Lake strain was introduced into many Minnesota lakes that lacked established musky populations, so the stocked fish were able to exploit the forage base and thrive. Many of Wisconsin's popular musky lakes have considerably higher angling pressure per acre than Minnesota waters.

The Wisconsin study will include seven lakes in the St. Croix River basin, which was not part of the musky's original range but now has musky fisheries established and maintained by stocking. The study will run a minimum of 10 years; in six years' time, Jennings and fellow researchers will start setting nets to sample fish numbers and estimate survival and growth rates.

If the Leech Lake fish or any particular strain of fish discovered through research have much better survival and growth, DNR managers would stock the strain in lakes with no native populations. "If it turns out that some strain really can produce superior fish, why wouldn't we use it in nonreproducing, nonnative waters?" asks Staggs.

But he also cautions the fish may be "super fish" because they are voracious predators, eating and growing at the expense of other fish in the lake. "It's never as simple as it appears to be," he says.

"In the end, I think we'll find that there is no silver bullet, no supersize fish," Staggs says. "I think this is more about making sure Wisconsin lakes can produce musky on their own, that our stocking program is introducing fish that will survive and grow the best in the lakes we have, and that we will have evaluated this issue systematically in a scientific fashion so we aren't arguing about this in 10 to 15 years."

Lisa Gaumnitz is public affairs manager for DNR's water programs.