Walleye Issues: Esocid Factors
October 10, 2019
While talking predator-prey dynamics with retired fishery scientist Jim Lilienthal, a thought occurred to me, as it probably had to him long ago, that every freshwater fish exists at the expense of others. Add humans into the mix and unexpected outcomes can elevate those “expenses.” For decades, anglers and darkhouse spearers have shunned the harvest of small pike, certainly in part because of the extra effort of removing pesky Y-bones. The targeted slaughter of large pike has produced just such an unexpected outcome, and possibly one of the great walleye dilemmas of a generation.
Fishery supervisor for the Minnesota Department of Natural Resources (MNDNR) for 28 years, Lilienthal’s mission, before and since his retirement in 2008, has been about improving pike fisheries in the Land of 10,000 Lakes. Following 30 years of field work, and nearly another decade of impassioned presentations to the state legislature since retirement, Lilienthal (a member of the Esocid Citizen Workgroup) and the Minnesota DNR convinced lawmakers to accept new pike regulations last year, perhaps three decades too late.
“In Minnesota, despite that darkhouse pike spearers represent only 2 percent of the angling public, members of the Minnesota Darkhouse & Angling Association wield a tremendous amount of clout at the state legislature,” Lilienthal says. “Leading up to 2014, no group had been more opposed to progressive pike management.” He says the group stance reversed course four years ago and became a key partner in helping pass new harvest regulations.
“We’ve known since at least the early 1980s that pike populations were out of balance, with fewer large fish and increasingly large numbers of small fish,” he says. “But every time we went to the legislature to ask about changing pike regulations over the years, we were always turned away and asked: ‘Why are you talking about pike when we need to be addressing walleye issues?’ Turns out, we were. Because the pike problem is a walleye problem if you don’t do anything about it.”
An Unbalancing of Scales
One of the first studies to uncover the links between populations of pike, perch, walleyes, and other species, biologists Dennis Anderson and Dennis Schupp discovered in 1986 that increasing abundance of pike led to declines in abundances of perch and walleye, as well as largemouth bass, black crappie, and sunfish in a North Central Minnesota lake.
Years later, suspicious of the effects of high-density populations of small pike, Lilienthal examined a large data set from North Central Minnesota lakes, a region that encompasses about 60 percent of the state’s counties. “It’s this zone that contains 93 percent of state’s problematic pike lakes that are also stocked with walleyes,” he says.
“My review of the most recent (2013) data revealed that 372 of the 722 (52 percent) North Central lakes stocked with walleyes had high density populations of northern pike, with more than 7 fish per gill-net lift,” he says. “When I looked at walleye gill-net catches I found that high-density pike lakes averaged walleye catches that were consistently 50 percent lower than in the lakes with lower-density pike populations. Not surprisingly, perch populations were in terrible shape in these same lakes.”
As biologist Tim Brastrup told me years ago, “Pike populations were never meant to mirror those of sunfish or other animals lower on the food web.” Putting the rarity and value of large pike into perspective, MNDNR research scientist Andy Carlson says: “In the heart of the walleye and pike belt in Central Minnesota, a 10- to 20-pound pike has become so rare that removing a single fish from a midsize lake can have a devastating impact on the fishery.” It’s a double-edged sword. Removing the genetics of a large spawning female prompts remaining smaller pike to mature and spawn at earlier ages, producing slow-growing pike at exponential rates. Also, large pike are excellent fishery “fixers,” keeping numbers of small pike in check via cannibalism. Large pike are effective predators on small pike predators.
Unwanted consequences result from unbalanced populations, be it pike, deer, or pine beetles. We shouldn’t be surprised when removing generations of large pike and reverting to high densities of small pike not only destroys the population balance of pike, but also reduces abundances of prey species such as yellow perch—a critical species for recruiting and sustaining walleye populations.
“Yellow perch are the primary buffer between small pike and their predation on juvenile walleye,” Lilienthal says. “We’ve also discovered that perch do a good job of keeping small sunfish in check via predation,” one more unexpected consequence of harvesting too many large pike.
“Looking further into the perch issue,” he says, “I examined 51 lakes over 500 acres in size, all with walleye stocking. Just 12 of the 51 lakes met population scenarios (based on catches in gill-net sets) indicative of a healthy perch-pike-walleye fishery: greater than 10 perch, less than 5.3 pike (where at least 29 percent were greater than 24 inches long), and at least 12 walleyes per gill-net lift. On the other hand, 23 of the 51 lakes had less than 2 yellow perch, greater than 7.8 pike (where 94 percent were less than 24 inches) , and fewer than 4.6 walleye per gill-net lift.
“The message is that it’s highly unlikely walleye stocking in these lakes will improve walleye numbers, no matter how many fingerlings, fry, or yearlings we stock,” he says. So unless we greatly reduce numbers of small pike and increase perch numbers, we might be simply feeding taxpayer dollars right into the tummies of small pike. Also, if you’re looking for a highly productive walleye lake, your best bet might be launch your boat on waters with relatively few pike and plentiful perch. Want better walleye fishing? Harvest as many pike under 24 inches as regulations allow.
Progressive Pike Removal
In Minnesota, new laws regulate harvest of pike in three separate regions. In the North Central region—the area encompassing Lilienthal’s research—anglers may, as of the 2018 fishing season, harvest a limit of 10 pike, with no more than two measuring longer than 26 inches, while all pike between 22 and 26 inches must be released.
“Before we can grow pike over 30 inches, we must first get them to reach 24 inches and then 26 inches, which is partially why we’re protecting pike of this size,” Lilienthal says. “The challenge, of course, is to convince anglers to harvest more pike under 22 inches.” Historically, creeling so-called hammer-handles isn’t something anglers have regularly practiced. A lot of us scratch our heads, wondering why folks would suddenly choose to harvest 10 of these smaller pike when they rarely chose to harvest three of them in the past—the maximum pike limit since 1948.2 It’s a question no one—angler or biologist—seems to know how to answer. Responses to this question always have the same theme: We have to change the way we view and choose to harvest small pike.
You can’t change angler perceptions overnight, nor their willingness to spend an extra few minutes carving out Y-bones. And yet, to many, pike tastes better than walleye. Many of my closest angling and guide friends believe, as I do, that pike offer perhaps the most delicious, distinctive flavor of all white-fleshed freshwater fish—firm, flaky, and slightly sweet.
Still, perceptions may never change. It’s why I asked Lilienthal about the idea of fish bounties, the practice of paying anglers to harvest undesirable fish. In places like the Columbia and Snake rivers in Washington, anglers earn $5 to $8 for every northern pikeminnow they kill. To protect juvenile salmon from predation by pikeminnows, the Washington Department of Fish & Wildlife instituted this highly controversial program in 1991. In 2017, one particular angler earned nearly $84,000 for killing 10,277 pikeminnows. Since 1991, over 4.77 million northern pikeminnows have been removed, with payments to anglers funded by the federal Bonneville Power Administration.
In a recovery effort of native cutthroat trout, the Coeur d’Alene Tribe paid 132 anglers nearly $8,000 to turn in 1,050 pike from Coeur d’Alene Lake, Idaho, over three years.
Lilienthal points to portions of southern Alaska, where illegal stocking of northern pike has threatened wild and stocked salmonids, and where regulations allow for unlimited pike harvest, including with line, spear, or bow. “Friends in Alaska have sent me photos of huge piles of pike removed by anglers in favor of salmon and trout,” he says. “You can’t believe how many fish are in some of these hauls.”
Many years ago, Lilienthal and DNR colleagues attempted numerous physical control measures, such as seining pike from waters where they are abundant and relocating them to new lakes, as well as placing barriers to spawning areas. “The effort and hours we spent on these projects were incredible, and it was never enough to alter the pike populations,” he says.
While seemingly extreme at first glance, measures such as paying anglers to harvest small pike shouldn’t be unreasonable in the state with the fourth highest taxes. Realistically, of course, it won’t happen—even though it may be the only reasonable way to reverse a plague of small pike and begin to restore the walleye fisheries where overabundant small pike may be having a negative effect.
Walleye Stocking Issues
Further exacerbating the dilemma of improving walleye fisheries, Lilienthal raises the concern over the condition of natural walleye rearing ponds—an issue with implications well outside Minnesota. Most walleye fingerlings that are stocked in Minnesota and in other states are reared in shallow, undrainable ponds stocked with fry in the spring and harvested in the fall with trap nets.
“In order for our rearing ponds to produce larger fingerling or yearling walleyes—the size that’s been most coveted for stocking—we need serious winterkills to occur, at least every few winters,” he says. “But increasingly warm winter temperatures haven’t allowed this to happen.”
Winterkills of small, shallow rearing ponds are critical because it eliminates undesirable species such as panfish and bullheads that both forage upon and compete with young walleyes for available prey. Dumping newly hatched walleyes into a pond with bullheads, bass, or other predators can quickly wipe out hundreds of hours of work that goes into collecting walleye spawn and incubating eggs in a lab.
Lilienthal suggests that stocking walleye fry—which don’t require rearing ponds—may be an effective practice, particularly when fishery managers target lakes or specific regions within larger lakes known for low pike numbers. “We saw this happen in one portion of Lake Minnetonka recently, where the DNR identified the lake’s northwest section as having low pike abundance and strong perch numbers,” he says. “Stocking walleyes here has helped build a strong local walleye fishery.”
That “Other” Esox
While overabundant pike have been shown to shape perch, walleye, and other fisheries at times, more fear and misinformation fuels muskie-walleye dynamics than that of sharks versus humans. Many folks who oppose muskies and love walleyes—particularly in Ontario and Minnesota—have employed some propaganda to keep muskies out of local lakes.
Some of the fear stems from the notion that muskies selectively forage on walleyes to such a degree that fishing success suffers. The situation is this: Where they occur naturally and where they have been stocked in small numbers, muskies exist at such a low density that risk of potential impacts to any species is low.
Muskie management in Minnesota and Ontario, in particular, strives to maintain a muskie population density that rarely exceeds more than one adult for every 10 acres of water. Biologists call that a healthy muskie population. And yet, some folks imagine that one muskie is capable of munching walleyes by the ton.
In Gull Lake, Minnesota, muskies were stocked for the first time in 2016—2,000 fingerlings were stocked in the fall. During the same time frame, the lake received over 8.4 million walleye fry—or 4,200 walleyes for every one muskie. Even if muskies ate nothing except walleyes, the impact would scarcely be observable. But they don’t.
“Muskies, like other esocids, prefer soft-rayed fish, such as suckers and ciscoes,” says Dr. John Cassleman, Adjunct Professor at Queen’s University, Ontario, and one of the world’s foremost experts on muskellunge. “Years ago, I vividly remember looking into the muskie-walleye prey issue with a large sample of confiscated muskies from Eagle and Wabigoon lakes. There were of course a few large walleyes in their stomachs, but by and large, we saw many more of other species.”
Among at least a dozen food-habits studies—in Illinois, Ohio, Virginia, Wisconsin, Minnesota, Ontario, and New Brunswick—walleyes almost never comprised more than 5 percent of a muskie’s diet. One lake-specific study of Wisconsin muskies revealed that a single muskie was believed to consume up to 20 age-2 or age-3 walleyes per year.
“If you look carefully at all the data, you notice that muskie-walleye interactions typically only occur where muskies are at unnaturally high densities, or where walleyes are likewise, disproportionately abundant,” Casselman says.
Moreover, the aforementioned Wisconsin study is the exception rather than the rule, offset by evaluations of dozens of additional lakes in Ontario, Minnesota, and Wisconsin. In a Wisconsin study that examined the food habits of 1,092 muskies from 34 lakes, only five walleyes were found in stomachs.4 Rather, yellow perch made up 30 percent of the total number of prey consumed by muskies, while catostomids (suckers) made up 47 percent of their total food, by volume.
One of the more compelling recent studies, headed by Mike Knapp of the MNDNR, focused on 41 Minnesota lakes managed by muskie stocking. The study showed no significant difference (increase or decrease) in walleye abundance (catch-per-unit-effort, or CPUE) following muskie stocking. Eight of the lakes showed a significant increase in the walleye population post muskie stocking, while two lakes had a significant decrease. The study showed that white suckers, yellow perch, and ciscoes were the most important prey species. White sucker abundance tended to decline following muskie stocking and perch CPUE increased. Finally, a comprehensive 2005 study of 25 Wisconsin lakes concluded: “Because muskie abundances were positively correlated to walleye abundances, direct competition or predation is unlikely to be occurring betwween these two species.”
“In the mid-1970s, the Minnesota DNR stocked muskies in high numbers—almost like they were walleyes,” Lilienthal says. “So little was known back then and we took a ‘stock-and-see-what-happens’ approach. We’ve learned a lot since then, and we stock muskies in such low densities today that there are never enough of them in any lake to dent a local walleye population. In smaller stocked lakes, muskies don’t reproduce well, so those fisheries depend on stocking.
“Today, Minnesota has the lowest density stocking program of any state; the DNR has not documented a single a case in which a muskellunge stocking effort has significantly affected a walleye population. I’m a walleye fisherman who fishes walleye tournaments and I want to see walleyes thrive.”
Sometimes, ensuring the health of walleye populations means paying closer attention to other species, such as pike, as well as setting aside prejudices about other toothy Esox, and taking honest looks at the unintended consequences of our actions.
*In-Fisherman Field Editor Cory Schmidt writes for all In-Fisherman publications, often on conservation topics.
Anderson, D. W. and D. H. Sshupp. 1986. Fish community responses to northern pike stocking in Horseshoe Lake, Minnesota. Minn. Dept. Nat. Res. Investigational Report No. 387.
Pierce, R. A. 2012. Northern pike—ecology, conservation and management history. Univ. of Minn. Press.
Kerr, S. J. 2016. Feeding habits and diet of muskellunge. Ontario Ministry Nat. Res. and Forestry.
Bozek, M., and T. M. Burri. 1999. Diets of muskellunge in northern Wisconsin lakes. N. Am. J. Fish. Mgmt. 19:258-270.
Fayram, A. H., M. J. Hansen, and T. J. Ehlinger. 2005. Interactions between walleyes and four fish species with implications for walleye stocking. N. Am. J. Fish. Mgmt. 25:1321-1330.