Sustaining a fishery or fighting natural change?
Largemouth bass populations are slowly replacing walleye in some northwestern Wisconsin waters. As biologists determine the causes, can and should they take steps to restore walleyes as the dominant fish in these waters?
Call it the case of the missing walleye. Ol'marble eyes, anglers' No. 1 target and the ultimate shore lunch, is disappearing from some lakes in northwestern Wisconsin.
Adult walleye populations are dropping in these lakes and natural reproduction is sputtering. The stocking of small fingerling walleye, successful in the past, is netting next to nothing.
Frustration is setting-in in some communities where walleye has long been king of the creel and a top tourism draw that feed the local economy.
"The number one complaint I hear from anglers locally is, "We want our walleye back," says Heath Benike, DNR fisheries biologist for Polk and Barron counties since 2003.
"We've tried increasing our walleye stocking rates and adding more walleye spawning habitat, and that did not help increase walleye survival or solve the existing problem."
Right now, the leading suspects are:
Popular sentiment and some fish biologists finger largemouth bass as the leading suspect, but there's no smoking gun, says Steve Avelallemant, a DNR fisheries biologist in northern Wisconsin for the last 25 years and top fisheries supervisor in the region.
"There is no clear cause-and-effect relationship between the increase in bass and decline of walleye in waters where this relationship has been observed," he says. "It's likely that many factors contributed."
Studies are underway in Wisconsin and in Minnesota, where they're seeing similar trends in some waters, to help solve this walleye "whodunit." Wisconsin is trying to "flip" target waters back to walleye dominance while also learning something about what contributes to their decline and which, if any, management approaches work best.
The Department of Natural Resources wants to test these ideas on 21 target lakes by removing bass size limits, stocking larger walleye, and protecting all walleye under 18 inches in order to more rapidly rebuild these fisheries, hoping the combination of tactics will work.
"We don't know if there are enough anglers out there who are willing to help by harvesting limits of largemouth bass, but we should be making it as easy as possible for anglers to do so," Benike says.
"If we can't get the harvest we need, at least I can say we tried to do our best to correct the situation on a select group of lakes, which is important to our local anglers and lake organizations."
Other biologists are concerned that removing size limits will only sacrifice the 10- to 14-inch bass now providing good fishing action for many anglers in those lakes with no guarantee that it will improve the walleye fishery.
Largemouth bass are found in all three drainage basins in Wisconsin – Lake Michigan, Mississippi River and Lake Superior. George Becker, author of the seminal work, Fishes of Wisconsin, and other fish experts have suggested that bucketmouths are here, especially in northern counties, because they were introduced to new waters.
Walleye got a helping hand as well. Originally confined to Wisconsin's larger lakes and waterways, extensive stocking of walleye fry and fingerlings over the last century spread the species widely across the state. Now, however, bass and walleye are on opposite trajectories in some waters.
Big Butternut and Ward lakes in Polk County are classic examples of how some northwestern Wisconsin waters have flipped from waters dominated by walleye to a sport fishery dominated by largemouth bass, Benike says.
Walleye were introduced into Ward Lake, a 92-acre seepage lake east of Luck, Wis., in 1934. Stocking stopped in 1954 because abundant natural reproduction was sustaining the fishery, he says. Twenty years ago, DNR electrofishing survey crews caught walleyes here at a rate of 160 per hour and largemouth bass at rates of less than 20 fish per hour. By 2000, the catch rate for walleye decreased to 13 fish per hour while largemouth bass abundance increased to 133 fish per hour. Walleye natural reproduction is now absent, and stocking of small walleye fingerlings in 2003 and 2005 failed. Angler harvest isn't up significantly and tribal spearing has never occurred on Ward Lake.
Big Butternut Lake similarly saw walleye densities drop, from a high of about 4.7 fish per acre in 1990 to one fish per acre in 2003, as largemouth densities have steadily increased during this same time period, Benike says.
He thinks the 14-inch bass size limit is a major reason largemouth bass have become more abundant on local waters.
"Recent studies conducted on Wisconsin lakes suggest that walleye and largemouth bass can have negative interactions," he says. Most recently, DNR fisheries colleague Andy Fayram documented that largemouth bass were the only game fish to become more abundant at the same time managers noted significant declines in walleye populations. Smallmouth bass and other game fish populations show no such tendencies. Fayram also documented that largemouth bass affect the survival of stocked walleye. Several other studies throughout North America have documented poor survival of stocked walleye in lakes with good largemouth bass populations. And UW-Stevens Point fisheries researcher Nancy Nate found higher densities of largemouth bass and northern pike in lakes where walleye populations are maintained by stocking than in lakes where they are sustained by natural reproduction.
Past survey information and current population modeling suggest that smallmouth and largemouth bass were significantly less abundant before 1989 when the first minimum size limit was put in place. Growth rates of bass were somewhat faster then, but high angler harvest resulted in very few large fish. Other bass regulations such as reduced bag limits and the early catch-and-release season did not affect bass harvest as much as implementing the 14-inch minimum size limit.
"It's debatable if this is a cause-and effect relationship or if it is driven by some other factors, however, there is enough evidence to suggest we should do something," Fayram says.
Fayram says his study is one piece of "fairly strong circumstantial evidence that when largemouth bass and walleye interact, the largemouth bass win."
Whether it's strong enough to tip a fishery is another matter.
"I found walleye in bass stomachs (during a study), but bass eat anything," he says. "So if there are walleye in the lake, they'll eat them. Do they eat enough to reduce the walleye population in the long run? That we don't know."
He favors the hypothesis that climate change creates conditions more conducive to bass at the same time anglers are releasing far more bass.
"It looks like climate change is a suspicious character in this whole thing," Fayram says.
UW-Madison climatologists who have analyzed weather data collected in the last 50 years have documented that the annual average temperature has risen by 1.1 degrees Fahrenheit statewide and average precipitation by about 10 percent. Most significantly, there are big differences across the seasons and across geography. For example, temperatures have risen fastest in winter and spring, while summer and fall have actually cooled a bit. Winters in northwestern Wisconsin have warmed by as much as 4.5°F.
Northeastern Minnesota has seen similar climate changes and increases in bass populations. Don Pereira, fisheries research and policy manager for the Minnesota Department of Natural Resources, says that even small temperature increases can benefit bass, which prefer warmer water temperatures.
Warmer temperatures may mean that young-of-the-year fish can feed later in the year so that they are larger, are in better condition heading into winter, and survive in greater numbers.
"The dominant thesis is that longer growing seasons lead to higher survival rates for young fish," he says.
Pereira and colleague Mike McInerny caution that Minnesota has limited long-term data on smallies and largemouth bass, making it difficult to quantify the rate or magnitude of increase in bass populations. McInerny hopes to get a handle on that in coming years. He is in the early stages of looking at first-year growth rates in bass over the last 20 to 30 years.
For now, he is skeptical that bass are preying on walleye to any great degree.
"If bass are preying on young walleye, it has to occur during a relatively short period during the summer because age one and older walleye should be big enough to avoid predation by most bass," he says.
Pereira says Minnesota is putting together a plan to investigate causes and work on this issue.
The drought in northern Wisconsin may be another factor contributing to declining walleye populations. Low water levels on some waters have left walleye spawning substrate high and dry, making spawning success even more tenuous than normal, Avelallemant says. At the same time, the lower lake levels can also spur weed growth in the lake, which favors bass.
Once female walleye deposit their eggs and the eggs are fertilized, neither parent cares for the eggs nor the young fry. Weather can result in year-classes of walleye that can vary considerably from year to year.
Rapidly warming water can cause eggs to hatch early. Prolonged cool weather can delay and impair hatching. A cold snap after the hatch can suppress the production of microcrustaceans that walleye fry eat.
Bass reproductive success also depends a lot on the weather, but their parenting habits would appear to give their eggs and the resulting fry a better shot at making it to their first birthday.
Male bass guard the nest until the eggs hatch and mature into a swarm of fry. They strike at intruding fish but do not eat them– at least until the fry leave the nest upon growing to one inch. Then the bass start feeding again and may eat any young bass they encounter, including their own.
John Lyons, a longtime DNR fisheries researcher and member of the statewide bass management team, believes that the strong catch-and-release ethic that's developed among bass anglers is a potential factor that tipped some lakes toward bass dominance.
"People keeping or not keeping fish has driven a lot of this and may be the single most important factor," he says.
The growing popularity of bass fishing tournaments over the last generation, and the catch-and-release practice promoted by those tournaments and by B.A.S.S. (the Bass Anglers Sportsman Society), have taken hold nationally and in Wisconsin.
Anglers reported harvesting only 5.46 percent of the 10 million bass they caught during the 2006-7 license year, according to a random, statewide mail survey. That's an even lower harvest rate than anglers reported for musky, 5.59 percent of the 223,101 caught.
Meanwhile, walleye are still turning up on anglers' plates at a much higher rate. The fish biologists rule out overharvest of walleye as a cause, noting that walleye harvests have not increased significantly in northwestern Wisconsin waters in recent decades and that such a trend would be quickly noticed. Walleye harvests are the most closely monitored harvests in the state under a 1983 federal court ruling that reaffirmed the Chippewa tribes' rights to hunt, fish and gather wild rice on lands they ceded to the federal government in treaties signed in 1837 and 1842.
Lyons says that changing the harvest dynamics raises social issues that DNR's fisheries program and anglers will need to grapple with.
"Some of the questions we need to engage are almost in the category of value judgments," he says. "Some lakes where walleye may be replaced by bass were marginal walleye lakes to begin with," he says. "It may be we're fighting Mother Nature."
"There's also this idea that having lots of small to medium bass is a bad thing. But 11- and 12-inch fish are easier to catch and it's fun. The numbers of big fish aren't getting worse, it's just that now you catch 10 fish and one might be legal instead of in the old days, when you caught two fish and one would be legal."
"Where is the problem? We're complaining about something that's pretty good."
Despite differing takes on what's behind the walleye's demise and whether Wisconsin can actually flip the target lakes back to higher walleye populations, there's some consensus among biologists that largemouth bass preying on young walleye would hamper efforts to restore naturally reproducing walleye populations. And there is consensus that the most effective tool for reducing bass abundance through angling will be to remove minimum length limits, Avelallemant says.
So, with concern mounting among some local biologists that time may be running out for some walleye lakes, the Department of Natural Resources asked anglers at the Spring Fish and Wildlife Rule Hearings April 12th to weigh in on a proposed three-part plan seeking to restore walleye populations on 21 lakes in Barron, Bayfield, Burnett, Polk, Rusk, Sawyer and Washburn counties. All of the lakes have been primarily managed for walleye, and each has had a walleye population sustained by natural reproduction during the past 20 years.
The plan seeks to:
Benike says those managing the study waters also hope that reducing bass abundance will cull some of the small, stunted fish from lakes with overabundant bass and result in fewer but bigger bass. As bass populations on Half Moon Lake in Polk County grew, for example, bass tournaments became more popular on the lake. But now, with small fish abundant, tournament organizers are going elsewhere, Benike says.
David Butler, who's fished Half Moon Lake for the past 30 years, favors efforts to bring back the walleye. "I fish for walleye all the time, but catch nothing but largemouth bass. I didn't catch a walleye all year in 2009. The few large walleyes I have caught have been in deep water in the area of 30 feet where most people don't bother to fish."
The lake's protection and rehabilitation district recently voted to spend $5,000 to buy walleye fingerlings.
Stephen Hjort, Conservation Director of the Wisconsin Bass Federation, said his organization doesn't back regulation changes on those waters and feels that in the past the Department of Natural Resources has been pressured by some legislators, resort owners and lake associations to remove bass length limits.
"I feel that with the current scientific observations relating to climate change in our region, we need to study these issues and not change regulations that have improved black bass populations for the benefit of the general public over the last 30 years. The Wisconsin Bass Federation is in favor of good science playing the leading role in regulation change, not politically motivated agendas, anecdotal evidence or wishful thinking."
Benike says that one of the keys to helping the walleye recovery plan work is helping bass anglers understand that DNR fisheries biologists aren't trying to get rid of all the bass on all lakes, but only reduce bass populations on the 21 study lakes that have historically been managed for walleye.
"There are about 346 named lakes in my management area in Barron and Polk counties," Benike says. "We are going to leave things alone on 98 percent of the lakes but try something different on these two percent to see if we can learn something to better understand and manage the fishery that anglers prefer and desire."
Fayram, Lyons and Avelallemant, all members of an ad hoc team the DNR fisheries program has pulled together to work on the issue, hope the plan also helps biologists learn more about what is causing population shifts in the two species, including the effectiveness of stocking large walleye fingerlings. Such information will be critical for addressing future problems and helping the Department of Natural Resources allocate its shrinking resources in the best way.
And the findings that emerge from the walleye recovery plan are just the start of the research and discussions that are needed, they say.
"We have more work to do analyzing data and forming policies before June 2010 9 we can continue efforts to change bass populations through angling regulations," says Avelallemant.
Specifically, he says, we need to look further at:
DNR Fisheries Biologist Frank Pratt in Sawyer County is convinced that once walleye decline, if largemouth bass are waiting in the wings, walleye recovery is severely impeded and further management activities are warranted.
One thing that all seem to agree on, however, is that anglers hold the key in the walleye recovery plan. We need anglers' help, Fayram says. "We don't know if we have the capacity to flip it back or fight it in the target lakes," he says. "We don't know if anglers will keep enough bass to make a difference." One potential difficulty is that reducing fish populations a little can increase consumption by the remaining fish with every remaining fish growing faster and eating more.
"We just have to kick it, and kick it hard enough," he says.
Lisa Gaumnitz is the public affairs manager for DNR's Water Division including the Fisheries and Habitat Program.