YELLOWSTONE LAKE—By mid-October there was little sign of life at Bridge Bay Marina on the northwest corner of Yellowstone Lake. The fleet of fishing boats had been trailered away, the parking lot empty, the bathrooms locked. But nobody had wiped the whiteboard clean. 

A marked-up map just outside the staging area for an immense ecosystem restoration project showed where crews set nets. A tally left on the board from early September counted 204,300 slain exotic lake trout from the summer. By the time Yellowstone National Park’s lead fisheries biologist, Todd Koel, talked to WyoFile a month after the last whiteboard update, the cull had jumped by an additional 80,000 fish. 

The operation to drive down exotic lake trout populations in Yellowstone Lake relies on commercial fishing tactics used in places like the Great Lakes. Contracted and National Park Service boats stage out of Bridge Bay Marina. (Mike Koshmrl/WyoFile)

Another year, another big haul of exotic char netted from 136-square-mile Yellowstone Lake. 

This was not the game plan. 

Back in 2012, Yellowstone officials announced that after a decade of underestimating the nonnative fish, also known as mackinaw — which proliferated at the expense of native cutthroat trout — they’d finally scaled up their netting operations to a degree that would meaningfully drive down the lake trout population. By stringing up to 6,000 miles of gillnet throughout the big lake over the ice-free months, Koel and his crews sought to catch and kill half of all the lake trout dwelling in Yellowstone Lake every single year. 

At an expense of $2-3 million a year, they’ve succeeded on some fronts: More than 80% of mature, fish-eating lake trout have been eliminated, and there are anecdotal reports of some spawning cutthroat trout staging a comeback. The end goal was always causing a population crash. Models suggested a collapse would happen and the National Park Service narrative was that, after a sharp decline, Yellowstone could back off netting and turn to a less intensive and costly “population maintenance” method, like killing mackinaw eggs in spawning bed cobbles. 

The rising sun eclipses the shoreline of 136-square-mile Yellowstone Lake on an October 2022 morning. To keep lake trout populations low, a fleet of netting boats will continue operating on the high-elevation lake for years or even decades to come. (Mike Koshmrl/WyoFile)

But numbers of young lake trout have stayed high even after 11 straight summers of intensive netting. Koel now questions if that precipitous crash will ever come. 

“Into the foreseeable future, gillnetting is always going to be the cornerstone of suppression,” Koel said. “There is a component of it that will become more long-term operational, just like we maintain roads and do other maintenance.”

Netting, he said, is “just going to be a part of” Yellowstone. 

‘Environmental vandalism’ 

It’s not entirely settled how lake trout arrived in Yellowstone Lake, but the most accepted theory is that an angler caught some in nearby Lewis Lake, kept them alive in a livewell or bucket and drove down the highway to release them. At the time of lake trout’s 1994 discovery, Yellowstone Superintendent Bob Barbee called it “an appalling act of environmental vandalism.”

Todd Koel, Yellowstone National Park’s lead fisheries biologist, poses for a portrait in 2022. (Jacob Frank/National Park Service)

Koel has since posed an alternative theory: lake trout washed out of Jackson Lake and swam to Yellowstone Lake on their own, heading up Pacific Creek and down Atlantic Creek by crossing over the Continental Divide at the “Parting of the Waters.” 

Regardless of how they got there, the fish-eating char from the Great Lakes and Canada thrived. Within a couple decades, by 2012, there were nearly a million of them, according to Koel. Before lake trout, Yellowstone Lake was arguably the flagship cutthroat trout fishery on planet Earth, but as predation from the larger piscivore ramped up, the native trout population plummeted. The resulting story of ecological collapse is one for the history books: Researchers even drew lines from spawning cutthroats’ absence in Yellowstone Lake tributaries to higher grizzly bear predation on elk calves.  

Yellowstone started taking the invasive trout more seriously and ramped up its killing program upon a change of administration. The shift came in 2011, when Dan Wenk replaced retiring Suzanne Lewis as superintendent. 

“Dan Wenk said, ‘This is not going to happen, we’re not going to have this environmental disaster on my watch,’’” recalled Cody resident Dave Sweet, a Trout Unlimited volunteer who’s been a longtime spokesman and fundraiser for the Yellowstone Lake cutthroat restoration program. 

The National Park Service has netted exotic lake trout in hopes of crashing Yellowstone Lake’s population of the species since the turn of the century, including intensive netting for 11 straight years. The operation has successfully eliminated over 80% of mature fish but remaining younger fish have responded with exceptionally high survival rates and have held on in high numbers. (Jacob Frank/National Park Service)

Under the new regime Yellowstone and its nongovernmental partners started sinking millions of dollars annually into its netting program. With increased resources and effort came increased catches, and soon a fleet of vessels using commercial fishing equipment were catching several hundred thousand of the invading salmonids every year. Until this point, there was annual netting — some 500,000 were killed in total from 2000 to 2010 — but it was limited and focused on juveniles around known spawning grounds on the western shorelines. 

Those early netting efforts essentially amounted to “fish farming” that had no effect on the population, said Mike Hansen, a retired fisheries professor who sits on a scientific review panel guiding Yellowstone Lake management. 

“I said, ‘Look, you guys need some adult help,’” Hansen said. “You need professionals, guys who learned how to fish in the Great Lakes where they destroyed lake trout populations.” 

Hit ‘em hard

The Park Service acted on the guidance. Starting in 2012, Yellowstone began contracting with a Wisconsin-based commercial fishing outfit, the Hickey Brothers, whose boats are still slaying lake trout in northwest Wyoming a decade later. Nowadays, a crew of 20 to 30 people operate a fleet of six gillnetting vessels that strategically fish Yellowstone Lake daily from ice-off to mid-October, Koel said. 

“We have 40 to 50 miles of net in the lake every day,” he said. “If you were to tie all the net lengths they set together from throughout the entire field season, it’s basically 6,000 miles of net. Enough net to stretch from Yellowstone to Italy.” 

That’s a lot of gear in the water of a “tiny lake,” by Hansen’s standards. 

“There’s no place to hide,” he said. 

Hickey Brothers and Park Service boats halted the population increase, then slowly reduced it. From 2012 to 2021 they netted, killed and sunk more than 3 million lakers  — six times greater than the prior decade’s take. Mackinaw now seldom survive past age 5 or so, Koel said, because they’re caught and killed before they get the chance. The difficulty in collapsing the population has come from impressive survival of the fish that don’t get caught. 

“Those guys [lake trout] are going to fight back with everything they’ve got, and that’s what they’re doing,” said retired U.S. Geological Survey fisheries biologist Bob Gresswell, who chairs the review panel. “The less adults, the higher the survival.” 

Large mesh nets in Yellowstone Lake are used to catch and kill mature lake trout, reducing those mature fish by over 80%. However, populations of juveniles, especially 2-year-old fish, have held much more steady despite a decade of intensive fishing with small-mesh nets. (Courtesy/National Park Service)

Researchers have examined this population response in depth. John Syslo, a National Oceanic and Atmospheric Administration research fisheries biologist, published on it in the Canadian Journal of Fisheries and Aquatic Sciences. He found that Yellowstone Lake mackinaw survive to breeding age at rates four to six times greater than in their native range. An alternative hypothesis explaining lake trout resilience, he wrote, is that early population models underestimated the abundance of larger, older lake trout. 

Expert optimism 

Yellowstone’s goal has been to reduce the population of lake trout down to 127,000 fish. In recent years, the netting boats are still catching in the realm of 300,000 fish annually. 

Gresswell, Hansen and the rest of the science panel predict it will take seven more years of netting at the current level to have a 90% chance of meeting the lake trout goal. Yellowstone could up its netting intensity by around 30% and get there sooner — by 2026 — the scientific panel found, but Koel says that’s not practical. 

“We’ve maxed out our capacity for boats and docks and housing for staff,” he said. “We don’t really have an ability to increase beyond where we’re at right now.”

“That was the way we thought about it early on — that we’re going to crash the population — but that’s not how it works.”

Yellowstone National Park lead fisheries biologist Todd Koel

Koel likens Yellowstone Lake’s slowly diminishing lake trout population to an airliner easing onto a landing strip. 

“It’s not going to, all of the sudden, fall out of the sky and crash,” he said. “That was the way we thought about it early on — that we’re going to crash the population — but that’s not how it works.” 

Hansen is more hopeful. Give it time, he said.

“The Park Service has been wringing its hands over the fact that the juvenile fish are still hanging on,” he said. “As you drive the adults down, conditions for the survival of the babies actually improves, but the recruitment we’re seeing cannot be sustained. If you kill all the adults, then you won’t have any babies — that’s the theory of a crash.” 

The unknown, he contended, is how low the crash goes and what intensity of netting is required to keep lake trout at trace levels. When the Idaho Department of Fish and Game went after nonnative lake trout in Lake Pend Oreille, they were successfully able to crash the population via netting, reducing it by 84%. Hansen has researched this Idaho Panhandle fishery and his modeling suggests that the state agency could reel back its netting effort by 76-86% and still “keep the population in a stranglehold.”

Yellowstone National Park has used telemetry, enabled by GPS-tracked fish like this one, to better understand how lake trout move around in Yellowstone Lake. (Jacob Frank/National Park Service)

But Yellowstone Lake is a “different lake,” Hansen said. There’s already been an order of magnitude more lake trout caught and killed in Yellowstone than in Lake Pend Oreille, and Yellowstone Lake is a “probably a better lake” for juvenile survival, he said.

Even if Yellowstone Lake’s 127,000-fish goal were achieved, the science panel’s most recent modeling suggests the Park Service could only cut back on netting by 21-26% from the current level of effort in order to maintain low numbers. 

Forever netting

That could mean a multimillion-dollar expense saddling 150-year-old Yellowstone for perpetuity. All told, the park is sinking between $2.8-3 million into its Yellowstone Lake program annually, Koel said, though that figure encompasses research not related to netting. 

There are three big pots buoying the effort. Around $1 million of netting revenue a year is generated from the sale of Yellowstone fishing licenses, which recently saw a major price hike explicitly to fund lake trout netting. Another smaller chunk of the annual expense is covered by gate fees, Koel said.

The park’s nonprofit partner, Yellowstone Forever, has also contributed around $1 million a year. The organization’s staff did not respond to WyoFile’s request for an interview, but Sweet, with Trout Unlimited, said that fundraising for interminable lake maintenance has become a “tougher sell” to donors than a one-time project. 

“It’s a harder story when you have to say, ‘Hey, look, a crash doesn’t mean it’s the end,’” Sweet said. “You can only go out there and ask donors for a million bucks a year for so long.”

An illegal introduction of lake trout to Yellowstone Lake nearly three decades ago has led to the ecological collapse of the cutthroat trout-dominated system and tens of millions of dollars in expenses suppressing the non-native species. Some biologists theorize that intensive netting to hold lake trout populations low will be necessary for the foreseeable future. (Todd Koel/National Park Service)

Yellowstone has about emptied its quiver in the effort to find an effective suppression complement to netting. Most of those efforts have targeted lake trout in their earliest life stage: as embryos in eggs. Spawning bed sites cover just .03% of the lake surface, so the theory is that hitting an entire concentrated age class of fish in these relatively small areas could have an outsized effect.  

To kill off eggs, researchers have toyed with using electricity, suction-dredging, sediment and even lake trout carcasses — both whole and ground up. The latter method worked because of decay: Rotting fish matter stripped the water of oxygen, suffocating the eggs. Perhaps the most promising technique debuted to date is a trial of an airborne application of custom-made soy pellets, flung from a seed spreader dangling from a helicopter.

Although egg mortality at Yellowstone Lake test plots has approached 100%, Gresswell, on the science panel, said these methods are not proven. 

“We know it kills fish, but is it having a population effect?” he said. “I’ve not seen any data to suggest that it is successful or isn’t successful.”

Another solution the future might deliver is using “super male” lake trout in Yellowstone Lake, Gresswell said. These YY chromosome fish have been exposed to hormones and selectively bred so that they produce almost exclusively male offspring. While there’s promise that the technique can eradicate non-native populations — the Wyoming Game and Fish Department is testing it on brook trout in a small stream south of Jackson — the prospect of YY fish working on hundreds of thousands of lake trout in a nearly 400-feet-deep lake is more questionable. 

“I’m not saying that it’s a silver bullet,” Gresswell said, “but it’s another tool that, in combination with gillnetting, might get us where we want to go.” 

Reframing success

The park’s 2011 native fish conservation plan identifies the recovery of Yellowstone Lake’s cutthroat trout as its top priority. Specifically, it sets a goal to recover the native species to the average abundance in the five years after its nemesis the lake trout was discovered. 

Mature lake trout, like these fish photographed in 2012, have declined dramatically in Yellowstone Lake, but numbers of 2- to 4-year-old fish have held much more steady. (Mike Koshmrl/WyoFile)

Clear Creek, a lake tributary, was used as the barometer for meeting the goal. In the late 1990s nearly 13,000 cutthroat a year were tallied traveling up the stream in the springtime to deposit their eggs, but the run subsequently collapsed to nearly zero spawners. Monitoring of that lake tributary has since ceased, though the science panel has called for the Park Service to reinitiate the springtime counts as soon as possible. 

Gresswell worries that the goals lined out in the decade-old plan are out of reach. 

“I used to say it’s cutthroat that are going to determine when we get there, but I’ve changed my mind on that,” he said. “We will never go back to the 1970s and ‘80s, at least in our lifetime … because climate’s going to make a difference.” 

Big, but not too big, runoff years that cutthroat tend to thrive on are likely to become less commonplace in the Yellowstone River basin, according to the latest climate science, he said. 

There’s also the reality that even reduced populations of lake trout will continue to prey upon and shape the cutthroat fishery, Gresswell said. “The whole system has changed,” he said. 

Koel is trying to get a better grip on how cutthroat trout have responded to tens of millions of dollars of lake trout netting. Standardized lake-wide gillnetting (geared not toward killing but sampling numbers) suggest that cutthroat abundance has stayed mostly flat over the past decade, though two graduate students are currently focused on refining population estimates with better science, he said. 

What’s clearer is that cutthroat size has increased dramatically, Koel said. It’s a product of there being fewer fish competing for the same food resources. 

“An individual cutthroat 20 inches or bigger weighs twice what one did at that same length before the lake trout invaded the lake,” Koel said. “That’s pretty cool. From an angler’s perspective it’s really nice.” 

Pre-dawn steam rises from the West Thumb Geyser Basin along the west shore of Yellowstone Lake on an October 2022 morning. (Mike Koshmrl/WyoFile)

That’s a nice silver lining to Sweet, who admitted being frustrated by the lake trout’s unexpected resilience and the prospect of heavy perpetual netting. “I was discouraged,” he said, “until I spent some time on the boat with Bob Gresswell and Mike Hansen.”

Meanwhile, the National Park Service has signaled steadfast commitment to a costly endeavor that’s already spanned decades with no end in sight.   

“We can’t walk away from the effort,” Koel said, “and we’re not going to.” 

Correction: This story has been updated to correct a comparison Mike Hansen drew between Yellowstone Lake and Lake Pend Oreille. —Ed.

Mike Koshmrl

Mike Koshmrl reports from Jackson on state politics and Wyoming's natural resources. Prior to joining WyoFile, he spent nearly a decade covering the Greater Yellowstone Ecosystem’s wild places and creatures...

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  1. By gutting, and throwing them back into the lake, aren’t they essentially feeding the survivors? I agree with Dewey that more could be done with these netted fish.

  2. About twenty-five years ago, now retired WGFD fish biologist Ralph Huddleston showed me an entry in official NPS records demonstrating that in July 1910, 10,000 lake trout fry from Michigan were released into the Yellowstone River above the falls. The fish likely came to Mammoth by train and were then being transported by wagon or pack train in milk cans to Lewis Lake. Ralph speculated that is was hot and the fry were in distress, so rather than letting them die the packers dumped them in the river. Evidently, the NPS took the position that the records were in error and that it was really Great Lakes whitefish which were dumped in the river, but why would whitefish be imported from Michigan when they were already native in the Yellowstone drainage? I think that instead of ‘bucket biologists” it was NPS that introduced lake trout to Yellowstone Lake.

    1. Hal, I think you’re correct. Myself, I’ve seen a copy of the same Ledger from the early 1900’s. There were also many other ‘exotic’ fish transplanted in the Park and I believe even Largemouth Bass were stocked in Yellowstone Lake. I believe Rainbow trout, also, which ended up hybridized into the native population of Cutts. Todays Yellowstone Cutt is probably 0.00001% Rainbow

  3. open the lake to ice fishing and commercialize the netted lake trout catch why spend our money when folks will pay for the product?

  4. In my opinion this is first class reporting. I was impressed that the reporter took time to explain that in reality, despite what the NPS has said in the past, they don’t know how the lake trout got into Yellowstone Lake. That is more truthful than categorically saying it was rogue anglers.
    I read a book published I think around 1920 called “Flora And Fauna Of Yellowstone.” In this book the author refers to Park records that state that 10,000 “Lake Trout” were stocked in the “Yellowstone Lake Estuary” around 1910 or so. Could this be the source of lake trout in Yellowstone Lake? Who knows? But I appreciate Mike Koshmrl taking time to point out that it may, or perhaps may not, have been rogue anglers. In any case, the more important point is how to knock them down to bring back the world class cutthroat fishery. Great reporting here!

  5. There is a way to pay the entire cost of the annual Yellowstone Lake Trout gill netting operation and have plenty of money left over for other conservation programs, but it will require new thinking and an act of Congress.
    Yellowstone might want to get into the gourmet canned cat food business.
    What this well researched article fails to mention is what the commercial gill netters do with the tens of thousands of Mackinaw they net. The fish are killed then literally eviscerated on the boats ; the guts and carcasses heaved over the side back into the lake to decompose , supposedly providing nutrients to the aquatic food chain. That’s the holistic ecological theory applied . The seagulls and American pelicans that follow the gill boats love it. I’m skeptical , since the invasive trout are not native to the receiving waters to begin with.There must be some other way to recycle the tons of deceased unwanted lunkers.
    When I was in Thailand years ago I observed entire fleets of fishing trawlers accompanied by larger factory ships heading out into the Gulf. Not only did they net fish, the hauls were processed aboard the boats and came ashore in cans. (Think tuna and squid ) . Floating factories.
    How could this work in Yellowstone? Factory boats are likely not practical nor acceptable, but processing the modest daily Lake Trout hauls onshore in a carefully controlled mechanical setting might work. It wouldn’t be a large operation… ten employees, a dock , and a ~50 x 75 foot building at the old Lake Hotel boathouse on the water or the Bridge Bay service yard a short ways inland should suffice. A temporary modular facility trucked in, perhaps. This need not be complicated .
    The goal is to repurpose thosa tons of fresh caught Yellowstone mackinaw trout into 100% natural organic gourmet cat food , branded as Yellowstone, sold exclusively by nonprofits to support conservation and pay for the gill netting. As it is now, a precious commodity is literally being thrown back into pristine Yellowstone Lake as waste fish , in the name of conservation. At the same time as the Park is engaging or enabling all manner of industrial tourism elsewhere 24/7/365.
    I envision stylish 5 ounce faux-gold rimmed cans with an artful green label selling coast to coast in America at the better establishments for maybe $ 2.00 per can … certified clearly marked as ‘ All proceeds go to support Conservation in the world’s first National Park ‘. Buy it in packages of six cans or an entire case and you have a perfect point of sale opportunity to include literature on the delightful blend of economics and ecologics . Instead of budgeting millions annually to fund a dead end closed loop one way gill net operation, this quasi-public cat food production and supply-side marketing would provide a sustainable way of attaining several worthwhile goals without bending or breaking the National Park ethic too much, to my mind anyway . Certainly no more than occurs already in other venues. ( Hint: leave Xanterra completely out of all this ).

    Full disclosure: I have four cats. They approve this message.

  6. I find this so interesting, when did they decide Lake Trout were a problem? I remember my family going to Yellowstone in the mid 40s to mid 50s with an uncle and his family. My uncle was an avid fisherman and he trolled for “Lakers” on Lewis and Yellowstone Lakes from his boat.