From stocking to self-sustaining? The return of Lake Champlain’s trout

Fish and wildlife researchers celebrate unexpected wild lake trout revival

By Zachary Matson

As a June heat wave scorched the Adirondacks, Lake Champlain’s deep water and a light breeze helped cool the Doré’s crew as they pulled a 450-foot-long gillnet and the handful of fish ensnared over 24 hours onto the boat’s small deck.

Bernie Pientka, a fisheries biologist with the Vermont Department of Fish and Wildlife, worked at a specialized table outfitted with weights, measures and a paring knife. Dave Gibson, the agency boat’s captain for over 30 years, readied a clipboard and data sheet, while two technicians and a graduate student untangled and sorted the fish into bins. 

It’s scaly, slimy, bloody and, for the fish, deadly work.

After thousands of years surviving the ebbs of oceans and ice sheets, development and pollution, the last native lake trout was lifted out of Champlain over 120 years ago. 

Today, after decades of stocking but no survival of lake-born trout, researchers are marveling at what they’re discovering in the cold depths—a rebounding population hatched within Champlain.

“We have a right vent, R.V., clip,” Pientka called out to Gibson.

The longtime colleagues recorded that the lake trout under Pientka’s knife lacked its right ventral fin. Hatchery workers snipped it off a few months before it was stocked. But lake trout with fins intact, once rare, are growing more common as trout establish a self-sustaining wild population.

Pientka measured length and weight and examined the body for sea lamprey encounters. The eel-like parasite feeds on the blood and body fluids of lake trout and harms their recovery. 

“Looks clean for lamprey wounds,” Pientka said. 

Pientka cut off the jawbone and handed it to Gibson. At the lab, they slice jawbone samples into wafer-thin segments to approximate age. “They put down rings like a tree,” Pientka said. 

Pientka split open the fish’s stomach to identify diet content and sex. “One alewife,” he told Gibson before tossing the trout overboard.

The art of research

This spring, Ellen Marsden, a fisheries biologist at the University of Vermont, stood on the deck of the Marcelle Melosira, UVM’s new research vessel. It arrived last summer when Captain Taylor Resnick steered the state-of-the-art boat up the Hudson River, through the Champlain Canal and docked beside the ECHO Center in Burlington.

Considered Lake Champlain’s leading lake trout expert, Marsden retired from teaching this year after nearly 30 years investigating the fate of the lake’s top predator. 

Placid waters shimmered under a clear sky. Water temperatures still dangerously frigid, Marsden and the rest of the crew donned heavy nautical life jackets as they set out not for lake trout but forage fish like rainbow perch, invasive alewife and slimy sculpin, the smaller species lake trout hunt.

Graduate student Shelby Scarfo is working to establish a new survey of the fish that play a critical role in the food web. Too few forage fish would threaten lake trout, while too many lake trout could crash the forage fish population. 

“We are making sure all of your babies have food,” Scarfo told Marsden.

With a new boat and a new crew taking on a new study, the plan didn’t quite pan out. 

“Ready for 50 feet,” Resnick said as he positioned the boat for 10 minutes of trawling. 

As they reeled in the trawl net, the line appeared to hook and snag. Hydraulics whirred and struggled. The heavy metal gates that guide the net dug into the lake bottom instead of skimming the lakebed. Rather than filling with fish, the net filled with sediment, and the winch labored.

“Oh, the fun of trawling,” Scarfo said. 

Fisheries research is often more art than science and more physical labor than art. The team convened an impromptu methodology seminar as Marsden explained how to tie a rope to the mud-filled net to leverage it open.

“Do you see what I mean?” asked Marsden, whose legacy includes a growing cohort of young researchers. “We fidget around until we’re free.”

“You’ve got to think outside the box,” Resnick said. “It’s too dangerous to not have teamwork.”

After clearing out the net and setting it back up, it was time to try again. 

“Same, same, but different,” Scarfo said.

“Cross your fingers and say your prayers to the fish gods,” Marsden added. 

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Prayers answered

Over the past 15 years, the fish gods have responded favorably. 

Scientists and lake managers knew for decades that stocked fish were surviving, growing, spawning and hatching fry. Anglers enjoyed a healthy lake trout fishery, all those fish with clipped fins, science’s way of identifying fish raised in hatcheries, while researchers watched as the lake-born, wild, fish swam into the void.

Since sustained stocking started in 1973, there was no evidence wild fish survived their first winter. That is until 2012.

Marsden and colleagues in 2015 found young unclipped lake trout cruising the 400-foot-deep lake—the oldest in their third year. 

After five more years of sustained wild fish survival, a cooperative of the New York Department of Environmental Conservation (DEC), Vermont Fish and Wildlife and U.S. Fish and Wildlife Service cheered the growing wild population and agreed to cut stocking levels. They reduced stocking again last year to 41,000, about 25% of historic levels. 

The success, though, leaves fisheries managers wondering when to hand the fishery over to the fish. Experts agree they should eventually stop stocking and let the emerging lake trout population sustain itself.

It’s a complicated calculus. Researchers don’t know what enabled wild fish to flourish, so it’s hard to know what to protect against.

Lake trout can live more than 30 years, so trends are slow to show in data, and the effects of the latest stocking reductions are still working through the population. There’s no playbook since few lake trout restorations anywhere have yielded a wild population. 

“It’s a new and exciting situation for us to be in,” said Rob Fiorentino, DEC Region 5 fisheries supervisor. “There’s nothing really written for us to work off.”

An Ice Age relic

Lake trout, Salvelinus namaycush, emerged a few million years ago during the last Ice Age.

The species survived in enormous and ever-changing lakes on the fringes of massive ice sheets, as a series of continental glaciers advanced and retreated across northern North America. Lake trout’s current distribution closely mirrors the limits of the era’s final glacial advance.

Lake Vermont, one of the massive lakes to form around 18,000 years ago in the wake of the last glacier, filled the Champlain Valley with shorelines 600 feet higher than today’s more modest Lake Champlain.

Around 13,000 years ago, the lake turned temporarily to an inland sea, the Champlain Sea, connected to the Atlantic Ocean along the St. Lawrence River valley. Depressed from the weight of the ice sheets, the Champlain Valley rested below sea level and flooded as melting glaciers raised worldwide ocean levels. 

By 10,000 years ago, the Champlain Sea freshened. With ice gone, the land rose to form a lake and locked in today’s native fish roster. 

When Samuel de Champlain showed up in 1609, lake trout thrived in the lake, as they did during Revolutionary War naval battles. In 1832, the Champlain Canal opened access from the Hudson River and Great Lakes systems to Lake Champlain, inviting decades of successive plant and animal invasions. The lake is now home to 15 non-native fish species and over 50 invasive species.

Widespread construction of dams and causeways during the late 19th century cut access to important habitat. Agriculture and land development increased pollution and a small commercial fishery persisted until 1913. 

By 1900, scientists estimate, the lake’s native lake trout were gone. 

Stocking program

Every year, the management cooperative stocks tens of thousands of lake trout into Lake Champlain, many dumped directly off ferries between Vermont and New York. 

It all starts with a 48-quart Igloo cooler. The boating cooler can carry 78 beer and soda cans—or more than 60,000 lake trout eggs. 

Paige Blaker leaves the Ed Weed Fish Culture Station on Grand Isle and drives to Salisbury, to Vermont’s broodstock of 450 lake trout, the parents of the 41,000 seven-inch trout fingerlings scheduled to be stocked this fall and next spring.

Blaker asks for about twice the number of eggs as she needs fish so keeps two coolers on hand. Less than 10 pounds of eggs will hatch and grow into over 5,000 pounds of lake trout before getting dropped into the lake.

“As much as I love hatching lake trout, in a perfect world I don’t have a job,” said Blaker, fish culture supervisor at Ed Weed. 

New York contributed its own hatchery fish until last year, ending its stocking as a logistics efficiency agreed to by the management cooperative.

Those fish, the Seneca strain from eggs gathered at Cayuga Lake and raised at the Chateaugay hatchery, used to be stocked each spring.

Recently, Ben Marcy-Quay, a former postdoctoral fellow working with Marsden, made a discovery about the closed New York hatchery program. Through genetic analysis, he found that a significant majority of the stocked fish that survived in the lake and produced offspring that have lived on as wild trout trace their roots to New York.

Around 87% of the wild fish are genetically linked to the fish New York stocked, Marsden said of soon-to-be-published findings. 

Marsden predicted the wild population would continue to rise and that managers could soon halt stocking. 

“Every sign points to this being a recovery, not an accident,” she said. 

Finishing its fifth summer, Vermont conducts the gillnet survey in south, north and central sections of the lake, collecting measurements on around 100 fish per section, the fewest researchers can sacrifice in the name of reliable data. 

Survey results show a striking rise in the proportion and number of unclipped fish caught each year, marking another high this summer.

“I just want to know: Why now? What’s going right?” Marsden said. “I spent 20 years trying to figure out what went wrong, and now we are trying to figure out what went right.”

A nasty parasite

Sea lamprey make convenient villains. When the parasitic fish morphs into its adult form, its mouth forms a suction cup ringed with tiny, tack-sharp teeth. Its tongue is lined with more, smaller teeth. It uses its mouth to latch on to lake trout, salmon, sturgeon and other fish, sucking sustenance from its host.

“They are not a face even a mother could love,” said Stephen Smith, a fish biologist with the U.S. Fish and Wildlife Service. 

During the 12 to 18 months lamprey spend feeding, before migrating into one of at least 25 tributaries to spawn and die, scientists estimate a single lamprey can kill up to 40 pounds of fish. 

Trout researchers track lamprey wounds as a proxy for the problem. In 2006, the rate reached 99 wounds per 100 lake trout. That fluctuating rate dipped below 25 per 100 for the first time in 2022.

The management cooperative initiated an experimental lamprey control program in 1990, the apparent success of which instigated the first major reduction in lake trout stocking numbers, from over 170,000 a year to around 83,000 in 1995, a level sustained until recent cuts.

After adult lamprey feed in the lake, they are drawn to tributaries to spawn in late spring. Lamprey larvae live in the streams for three to seven years, burrowing into sediment and filter-feeding on algae.

They grow from the size of a fingernail clipping to a pencil, roughly six inches long, Smith said. Before the lamprey can migrate to the lake, the wildlife service and its partners in New York and Vermont, work to kill as many as possible. 

Rotating between three zones of the lake on a four-year cycle, managers treat over two dozen tributaries with a chemical lampricide to kill most of the larvae.

They use temporary barriers and traps to prevent adults from entering the rivers. Researchers survey each of the lake’s more than 200 tributaries once every four years to monitor lamprey reproduction. 

“Eradication is not really possible,” Smith said. “This will be a program into the future.”  

Revival mystery

The explanation for the sudden survival of lake trout born in Lake Champlain remains a mystery. Perhaps the persistence of lamprey control is paying dividends. Maybe improvements to wastewater treatment plants that discharge to the lake strengthened water quality. Or, multiple factors are at play.

One theory from Marsden and her colleagues runs counter to the standard model of invasive species. According to the common narrative, invaders enter new ecosystems with behaviors misaligned with the local ecology, outcompeting natives, disrupting fragile relationships and devastating food webs. 

In Wyoming’s Yellowstone Lake, for instance, efforts to protect the native Yellowstone cutthroat trout have been stymied by an invader from the East Coast: lake trout.

The voracious and long-lived species desired in Lake Champlain is unwelcome in Yellowstone. While control efforts show signs of progress, lake trout continue to disrupt the regional ecosystem.

Unlike lake trout, cutthroats migrate up tributaries and are important food sources for bears and other animals. As their numbers declined, bears preyed on elk calves.

In Lake Champlain, the successful takeoff of wild lake trout followed the 2003 invasion of alewives, an Atlantic Ocean fish. Alewives have since come to dominate the forage base, displacing rainbow smelt as the primary food source. Alewives threaten zooplankton, prey on trout and salmon eggs and exacerbate thiamine deficiency in native fish. 

But, at least for lake trout, they could also provide an important boost. Alewives are more energy-dense than smelt, and Marsden’s team theorizes the alewife invasion helped “jump-start” wild lake trout success.

“Things are complicated,” said Justin Lesser, a postdoctoral fellow working with Marsden. “‘You can’t always look at them as all good or all bad.”

Attacking from below

Lake Champlain at times feels like the inland sea it once was. Windswept, open, almost oceanic compared to other Adirondack lakes—its underwater topography no less impressive than the glacier-carved peaks and valleys that roll upward from its western shores. 

Lake trout use that rugged waterscape to their advantage as they stalk prey from the depths. They hunt for food near shoals and underwater islands, where they can ambush prey. 

That’s where Scott Thurber, who charters fishing tours out of Plattsburgh, looks for lake trout.

He records the location of his catches on a map. Some days, though, the fish aren’t biting.

“They are not making it easy today,” Thurber said in early July as he shuttled between favorite spots around Valcour Island.

Thurber has been fishing Lake Champlain for over 50 years, learning from his grandpa who fished the lake when there were no lake trout. After retiring as a Saranac Lake police officer, Thurber started his charter business, Irish Raider Outfitters. 

His sonar and GPS reveals the activity below. The right kind of blip on the screen indicates a lake trout nearby.

“It’s like a video game,” he said. 

When he catches a fish, Thurber immediately inspects the fins, hoping he pulled in a wild one before releasing it. He said he is catching more and more unclipped lake trout. To his eye, they shine brighter with more distinctive coloration than their hatchery-raised counterparts. 

After striking out at a handful of deep holes, Thurber motored to “The Alamo”— his last stand. 

“I think this is the spot,” he insisted.