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November 29, 2023

In eighty feet of water, one mile off the Burlington shoreline, the research vessel Marcelle Melosira pulls in a trawling net. On the upper deck, a pair of winches turn slowly while the boat continues northwest, passing within swimming distance of the cliffs at Rock Point. The winches grow thick with cable while Professor Ellen Marsden looks expectantly down into the water. From the blackness, a gray form rises. It’s a netful of fish, a tangled, quicksilver heap of life.

Three undergrads—Jamie Loyst ’24, Nikolai Tang ’25, and Philip Hampson ’24—heave a crate of the fish onto an observation table and the other members of Marsden’s advanced course in fisheries biology crowd around in wool hats and rubber gloves. It’s below freezing on this late fall afternoon, and nobody is going swimming. Instead, they begin to sort the fish by species to take back to the lab. Most of them are alewife: flat, shiny, big-eyed invaders that arrived in Lake Champlain about twenty years ago. But mixed in are yellow perch, finger-sized rainbow smelt, some even smaller and squishy-looking sculpin, a few snake-like sea lamprey, handfuls of zebra mussels—and, like speckled majesty among the commoners, a bucket’s worth of lake trout.

These muscular trout are juveniles, puny compared to the ten-pound trophy specimens anglers pull out of the lake. Lake trout can live more than 25 years, with a rare few making it past 60. The largest lake trout caught in Vermont tipped the scale at over 35 pounds, while, last year, a gargantuan lake trout was hauled out of (and released back into) a lake in Colorado. It weighed 74 pounds.

The trout the students caught in the net today may, in a way, be more impressive. As the Marcelle turns to head for home on the Burlington waterfront, Ben Quigley ’24 is reviewing a data sheet. Of 21 “LKTs” (for “lake trout”) on his penciled list, 17 are marked “NC” (for “no clip”).  That means that more than 80 percent of these trout do not have a clipped fin to mark their origin from a fish hatchery. Instead, they were born wild in the lake. 

The short version of this story is that native lake trout were gone from Lake Champlain for more than a century—and now they’re back.  The longer version is a mysterious and hopeful ecological tale that Marsden and her many colleagues and students are helping to unravel, aided by sophisticated technology on the university’s new research vessel.

Lake trout, known to scientists as Salvelinus namaycush, are, technically, a freshwater char, sometimes called mackinaw, togue, siscowet, lean, touladi, longe, paperbelly or, in their dark forms, mud hen. By whatever name, they are a popular sport fish, a deepwater predator at the top of the food chain in many northern lakes, and native to Lake Champlain.

After 20 minutes of trawling near Burlington, undergraduate students on the lower deck of the Marcelle Melosira haul in the net and dump their catch onto an examination table for measuring and return to the lab.

Native in Lake Champlain, that is, until around 1900, when they disappeared. Nearly a century later, in 1996, Ellen Marsden arrived at ����̽̽ after years of studying fish in the Great Lakes—and began to ask what happened. “Why?” says Marsden, with her charming English accent, “To this day, nobody knows. Total mystery.” The State of Vermont began stocking trout in the 1950s and launched a sustained program in 1972. Tens of thousands of fish are released each year. The program is successful, in a way. The hatchery trout survive in the lake. After six or seven years, adult trout find mates, they successfully spawn eggs in the fall, and the eggs hatch in the spring—as Marsden’s meticulous research revealed. These babies find zooplankton and other food in the gravel shoals and rocks where they hatch. After a few weeks in these shallow waters, the young fish are big enough to head for deep water.

And that’s where trout mystery number two begins. “These young fish swim off—and then they’re never heard from again,” says Marsden. “Poof.” Were they eaten or malnourished or poisoned or starved? Marsden spent years exploring this disappearance (and learning more about the fish of Lake Champlain than, well, probably anybody) without finding a clear culprit—but, whatever the cause, the young trout never made it to adulthood.

 Or, rather, that was the story until 2015.

That year, Marsden was astonished to discover unclipped trout in her trawls. The young were, suddenly, surviving. “Turns out this was not a blip,” she says, “it was zero to sixty,” and this trend has continued in delightful fashion ever since. “Our summer gill net surveys have shown unclipped lake trout steadily increasing for the past five years. It’s a phenomenal success,” says Bernie Pientka ’94 G’00, a fish biologist for the State of Vermont, who had Marsden on his graduate committee and is now her close collaborator. In response, the state has reduced trout stocking levels from 82,000 per year to 57,000, “and now down to 41,000,” says Pientka. “It would be great to stop stocking completely if wild production goes up and continues.”

Enter trout mystery number three. “Now our problem is: what's going right with lake trout?” says Marsden—a professor of fisheries in the Rubenstein School of Environment and Natural Resources—as the Marcelle passes the Burlington breakwater and approaches its docking berth next to ����̽̽’s Rubenstein Ecosystem Sciences Lab at the Leahy Center for Lake Champlain. “It’s a much nicer question, but equally puzzling.” Working this puzzle has turned up a surprising and unsettling discovery.  “It’s bizarre, but the recovery of wild trout may depend on those,” she says, pointing to a Ziploc bag filled with alewife—those non-native, invasive fish that filled the trawling net.

Nikolai Tang ’25 and Jamie Loyst ’24 examine small trout-perch, a forage species that lake trout and other predators like to eat. But lake trout have also learned to feed on alewife; a pile of them lie below the students’ gloves. Alewife are a species native to the Atlantic ocean, but arrived in Lake Champlain through a canal in 2003. 

To some biologists and managers, this idea may “sound heretical,” says Marsden. That’s because invasive alewife in the Great Lakes—sneaking in from the ocean—have brought havoc. The first alewife in Lake Ontario were spotted in the 1870s and the invasion spread to the rest of the Great Lakes—through the Welland Canal that bypasses Niagara Falls, connecting Lake Ontario to Lake Erie—in the 1930s and ‘40s. By the 1950s, they were reproducing at rates beyond a rabbit’s wildest dreams, thanks in large part to the absence of lake trout that would have eaten them. The native trout had been wiped out by overfishing, pollution, and attacks by another invasive species, blood-sucking sea lamprey. Through the 1980s, and to this day, alewife have caused devastating losses of native fish in the Great Lakes, chowing on the young of trout, walleye, and other top predators that can regulate an ecosystem—while pushing out other forage fish, including smelt that are a primary food for lake trout.  No surprise, then, that the arrival of alewife in Lake Champlain in 2003 was met with dread. 

Instead, their invasion, complete by 2008, has aligned with the recovery of trout.  “What in the world is going on?” Marsden asks. “It's unnerving to think that an exotic species has made things better for these native trout.” But , post-doctoral scientists who worked at ����̽̽ with Marsden and others, indicates exactly that. They developed a computer model of the Lake Champlain food web. Drawing on twenty-five years of data about fish and other lake creatures, their diets and numbers, the ����̽̽ team studied how energy moves in the lake. In a study published in February, they conclude that alewife, rich in fats and plentiful in number, appear to have “jumped started” the recovery of trout, they write, by giving them more to eat. 

“Whoa, whoa, whoa. Be careful,” says Marsden when a certain science journalist wants to announce that we’ve finally found the wonder cure that rescued wild trout—and it’s an invasive pest fish.  “This line of thinking is playing with fire,” she says. “Invasive species in most places, most of the time, are bad news.”

And Marsden is cautious, even skeptical, at a deeper level too. “We're too ready to find a silver bullet,” she says. “In fisheries, for too long, we’ve focused on single species management. The problem is bigger than trout or alewife. It’s bigger than that, but our minds may not be that big.” Increasingly, science finds insight by paying attention to complex flows and whole systems—and that ubiquitous wildness that some people call chance. The new study provides a powerful example: the invasion of alewife in the Great Lakes was devastating to trout. In Lake Champlain, with a different history and starting suite of species, the invasion of alewife appears to have had the opposite outcome. 

 “If someone asks, ‘how do I help this species?’ I say, ‘go restore the ecosystem!’” Marsden says. But to restore an ecosystem requires scientists to understand it deeply, “and there is so much we still don’t know about Lake Champlain. Keep in mind, a model is just a construct,” she says. “It's not the lake.”

The first research vessel of its kind, the electric-hybrid catamaran Marcelle Melosira, gets prepared for its next scientific outing. Docking downtown in Burlington, the boat is ����̽̽’s most distinctive outdoor classroom. Photo by ����̽̽ Spatial Analysis Lab

June 20, 2024 

The actual lake is growing dark, at 8:57p.m., on the longest day of the year. A purple haze sinks over the Adirondacks in the west, and fine rain begins to fall, making the steel rails and deck of the Marcelle glisten red under the boat’s lights.  Mia McReynolds, a Ph.D. student in her fourth year, Samantha Gonsalves ’26, and Nikolai Tang ’25 are untangling a specialized floating gill net. They’re part of a team getting ready to go out in search of alewife, the larger ones that may be fast enough to avoid regular trawling nets. The students will be out all night. 

The team wants to catch these fish so they can hear what they have to say. Well, not really, but McReynolds has deployed high-tech sonar platforms on the bottom of the lake that emit pings of sound through the water toward the surface. If a ping hits a school of fish, the sound bounces back, and the school’s size and location is recorded on a flash drive on the platform. To verify the sensor data, the team is catching actual fish so they can compare the results.

McReynolds wants to understand where, and how many, forage fish—like alewife and smelt—are in this lake, and in the Great Lakes too. Managers can’t do much to control the numbers of these fish directly, but they can control how many top predators—like trout and salmon—they stock, trying to balance the typical boom-and-bust lifecycles of these forage fish in the middle of the food web. Measuring populations with sonar on ships is a well-established practice in the ocean and Great Lakes. But is it accurate?

McReynolds knows that some fish hear boats coming and there’s good reason to think they do what any sensible fish would do: try to get out of the way. But then the questions begin to pile up: what species avoid vessels? And by how much? Are some fish being undercounted? And do different volumes of noise or boat speed or engine types affect fish differently? 

That’s where ����̽̽’s new, first-of-its-kind, $4.5 million research boat comes in. It’s an electric-hybrid catamaran that can run on batteries or diesel engine. “I have two platforms in Burlington Bay, and we'll pass over them every half hour,” says McReynolds—all night, following a pre-set research grid. Sometimes the boat will go fast, sometimes slowly; sometimes running its nearly silent electric motor, sometimes on louder diesel. “And all that time,” McReynolds says, “the platforms are collecting data about the fish, how they’re responding.” 

Before heading out for a full night of trawling, Ph.D. student Mia McReynolds (right), Samantha Gonsalves ’26 (center) and Nikolai Tang ’25 prepare a gill net. 

Four days later, on a flat and misty morning, the Marcelle is nearly stationary in Burlington Bay, with Old Mill barely visible to the east on College Hill, and, to the south, Juniper Island dipping in and out of fog. On the stern, just outside the Marcelle’s onboard classroom, Silva Sundberg ’24 pushes a lever connected to hydraulic lines and a steel crane that frames the back of the boat like a giant doorway pivots to about 45 degrees over the water so that rope hanging from a pulley can descend straight down. Deckhand Bo Barile ’26 switches on an aluminum drum and it slowly begins to wind in the rope while McReynolds and Jack Rice ’24 look expectantly down into the water. From the blackness, a bright yellow rectangle rises. It’s the world’s largest Lego. Well, at least that’s what it looks like. A plastic box—full of square holes and barnacled with devices, cables, and a long yellow tube—emerges from the water. McReynolds and the other students gently bring it on board. This is the sonar platform that’s been collecting data for a week. 

“These are the two transducers. They're sending out the pings and then listening,” McReynolds says, pointing to what look like a cooking pot and a neon-orange Roomba. They operate at two frequencies, 70 kilohertz and 200 kilohertz; the lower frequency is good at detecting fish. The higher frequency is better at finding plankton and Mysis shrimp, a key food for trout and other fish, she says. “I'm mostly interested in fish, but I'm also curious about plankton and how the layer of fish is chasing the plankton.” 

Ellen Marsden retired in May. “I’m fully emerita in September and then will be sailing off,” she says with a cheerful laugh, though she’ll continue to do research for a while. But her approach to fisheries science seems to be powerfully present in the next generation of ����̽̽-trained fisheries scientists—like Mia McReynolds. “Why am I interested in plankton too?” McReynolds asks. “Because I want a more complete picture.” 

What McReynolds will learn from the sonar data is not just relevant to biologists on Lake Champlain: the managers of the $7 billion fisheries economy in the Great Lakes depend on accurate data about food supplies to make decisions. “In the Great Lakes, these annual indices of forage fish, like alewife and smelt, feed directly into a model that tells them how many salmon and trout and other fish to stock,” McReynolds say. “And so if those surveys are biased or we don't really understand interactions, it could cause a problem with management.”

Brand-new Ph.D. student Amane Takahashi helps McReynolds untie the ropes and shackles connected to the platform, while Sundberg, an environmental science major who just graduated, fills out a field data sheet about the platform recovery.  “I think the world of fisheries is really cool just because there's so much unknown,” Sundberg says. “We don't know a lot about fish because it's hard to find out.”

Ph.D. student Anna Schmidt (left) and Silva Sundberg ’24 prepare water samples for initial analysis in the Marcelle’s on-board lab. The water was collected in the instrument behind Schmidt, a rosette sampler, that snaps shut at numerous depths in the lake, successively taking water into one its 23 bottles.

August 20, 2024

Near Schuyler Reef, five miles due west of Burlington’s Rock Point, on the New York State side of Lake Champlain, a cool breeze blows, crinkling the surface, and splashing water gently against the hull of the Marcelle. The sun pops out between clouds and the lake seems at ease. But ����̽̽ postdoctoral scientist Bianca Possamai has brought a team here for the day to collect water samples to better understand what’s happening beneath the surface—where a gigantic rogue wave roars north and south, overtopping mountains. 

One of the most powerful and little-known features of Lake Champlain (as well as other lakes and parts of the ocean), the wave is called a seiche (pronounced “say-sh”). It begins with wind. If it blows hard enough, long enough, water will literally pile up at the downwind end of the lake—usually just a few inches but sometimes a foot or more. Then the wind abates, and, like a sloshed bathtub, the water will rock back and forth along the length of the lake. This “surface seiche” on Lake Champlain takes about four hours to complete the journey. But far more powerful is what happens below the surface, especially during the summer. There, an “internal seiche” develops. As the wind piles surface water up at one end, the line between this sun-warmed water on the top of the lake and the cold water underneath—a sharp boundary called the thermocline—tips away from the direction of the wind. The dense, cold water piles up on the opposite end of the lake. Now these divided layers of water—like two huge, stacked slabs sliding on grease—rock back and forth along the teetertottering thermocline, creating a gigantic wave that runs from one end of the lake to the other.  This invisible current takes one to three days to travel the full length of Champlain, moving water and nutrients as it goes—and then it sloshes back in the other direction.

Possamai, a Brazilian who trained as an oceanographer and now collaborates with Marsden and Stockwell, wants to know what this current is doing—particularly when it hits underwater mountains, like Schuyler Reef. In the ocean, deep currents run into steep mountains, called seamounts. With nowhere else to go, these currents are forced to the surface, bringing nutrients up from the cold depths into the sunlit layers—and making seamounts into biological hotspots, where plankton can grow and many species feed, reproduce, and find refuge in the middle of the ocean. Possamai thinks something similar may be at work in Lake Champlain. 

That’s why she’s about to lower a $200,000 tool, called a rosette sampler, into deep water on the edge of Schuyler Reef. A metal ring with 23 remotely controlled bottles, the rosette will plunge 200 feet to the bottom and then come slowly back up, collecting water samples at numerous depths, guided by Possamai in the Marcelle’s onboard lab. 

“Schuyler East?” says Taylor Resnick, the captain of Marcelle. “Yes, East, good,” says Possamai. About an hour later, Possamai, visiting scientist Renan Machado, and Ph.D. student Anna Schmidt intently watch a graph of temperature and depth data coming up from the rosette. Possamai clicks a mouse each time she wants one of the bottles to close. As the device approaches 90 feet, the temperature spikes from about 40 degrees Fahrenheit to the low 70s just 30 feet later. The rosette is passing through the thermocline. Soon, Sam Nieder ’25 and Silva Sundberg are easing the rosette back onto the boat and the team gets to work taking water samples from each bottle into the boat’s lab to filter, measure, and prepare for tests of plankton and nutrients.

Possamai has identified Schuyler Reef as one of several “lakemounts,” as she calls them: very steep mini-mountains that rise from the bottom of the lake—which can be more than 300 feet deep—to a pinnacle just below the surface. “You can take an oar and touch bottom here,” says Captain Resnick. “It's pretty weird.” Possamai thinks that the seiche may bring enough nutrients up from below to make these lakemounts into biological hotspots and fish nurseries in the middle of the lake. They might even be unknown spawning sites for lake trout.

But nobody knows, since the ecology of lakemounts is almost entirely unstudied. 

Post-doctoral research scientist Bianca Possamai has studied seamounts in the ocean. These submerged mountains rise near the sunlit surface, making a home for many plants and animals. Now she’s turned her attention to the middle of Lake Champlain, wondering if the same might be true of “lakemounts,” pinnacles that rise from the bottom, where shallow-water animals may thrive—perhaps including juvenile lake trout.

“We’re trying to see if lakemounts really do have a lot of production going, especially at the end of the summer, when the other shallow waters in the lake may have already used up their nutrients,” she says. If that’s true here on Lake Champlain and in other waters, lakemounts and their ecosystems will be important to protect. The team hasn’t found any spawning lake trout yet, but they have found lots of other critters, including arthropods that are normally only found in near-shore waters.

The first fish evolved about 530 million years ago during the planet’s great diversification of complex life, the Cambrian Explosion. By about 415 million years ago, some fish had made their way into fresh water. Lake trout are believed to have diverged from other fish species in the Salvelinus group around two or three million years ago, probably as a result of the surging and retreating of glaciers during the last Ice Age. Numerous populations and strains of lake trout have been scattered across northern terrain for untold millennia, becoming exquisitely at home in their own lakes. 

There’s evidence that paleo-hunters were eating lake trout from Lake Champlain 10,000 years ago. But the trout that are now swimming in Lake Champlain do not have a long history here. Their genetics comes from other places, including Seneca Lake in upstate New York and mixed lineages from the hatchery. “We've set out with a goal to restore a lake trout population, like the one that was here,” says Stephen Smith G’06, one of Marsden’s (many) former graduate students, and now a fish biologist for the U.S. Fish & Wildlife Service in Essex, Vt., who works on lake health and lamprey control. “Now, it's not the same fish exactly, because those are gone, but it's as close as we can get.”  

What, then, should we think about the unclipped trout that Marsden’s students caught? In some obvious and encouraging ways, they’re making it work: reproducing, feeding on alewife, doing their job as apex predators in a complex food web. They’re back, and the restoration of native species is cause for celebration, even if the genetics of these fish come from afar—and the lake to which they have been returned has many species in it that weren’t there in 1900. And what of alewife? Ellen Marsden says that alewife will never be native in Lake Champlain. “We introduced them to a system in which they did not appear naturally,” she says, “and they have altered the system.” David Quammen’s warning in 1998, that Earth is fast becoming a planet of weeds, grows only more urgent as humans transport species on ships and planes every which way. And yet alewife are in Lake Champlain and don’t seem likely to go away. Lake trout may now depend on them. “We are re-creating ecosystems wholesale,” Marsden says. “What do we call them in a thousand years when half the native species are extinct and half of the self-sustaining species are non-native?” There are so many questions that a case can be made for this answer: slow down and stare in wonder into the black water from which sprang the tangled, quicksilver heap that is life.