BURLINGTON, Vt. — Wild lake trout disappeared from Lake Champlain more than a century ago, vanished like ghosts from this 120-mile-long ribbon of water between Vermont and New York, pollution and overfishing having taken their toll.
But suddenly, the sleek and beautiful fish are back in growing numbers, reemerging in the lake’s cold, deep core.
The lake has been stocked with hatchery-raised trout for years, but their offspring rarely survived past infancy. Now, the lake-born population is growing quickly, although it could take a few more years for the resurgent population to advance beyond the juvenile stage.
The mysterious return has left scientists, state officials, and anglers elated but puzzled, unable to explain the sudden change.
“I’d like to think something good has happened,” said J. Ellen Marsden, a University of Vermont professor who is tracking the trout’s renaissance in a lake that stretches from Quebec to south of Fort Ticonderoga, N.Y.
Since Marsden discovered the first wild fish three years ago, their numbers have climbed steadily, from 24 percent of all lake trout collected in 2015, to 34 percent in 2016, to a projected 50 percent this year.
“Is this because of something we did? That’s something I can’t answer,” said Marsden, who clambered about the Melosira, the university’s 45-foot research boat, with the ease of a seasoned deckhand.
On a recent research trip, all but two of the 16 lake trout caught in a 20-minute trawl were wild juveniles. The remaining two, both older, came from Vermont’s robust stocking program — identified by a severed fin — that has supplied the lake with between 68,000 and 90,000 trout every year for the past two decades.
Until 2015, young wild trout apparently had run up against a mysterious obstacle that killed them well before the spawning age of 6 years old. Was it disease, predation, or starvation?
“We’ve been scratching our heads about why we weren’t seeing the wild lake trout showing up,” said Eric Palmer, Vermont’s fisheries director. “This is a good indication that something right is happening in Lake Champlain.”
Questions far outnumber answers, but researchers have a few theories on why wild trout are now thriving. An aggressive program to control sea lampreys, a non-native parasite that sucks blood and other fluids from trout, could be paying dividends, as could better sewage treatment and increased concerns about lake pollution.
“A little bit of this, a little bit of that, and it all adds up,” Marsden said.
Eric Howe, director of the nonprofit Lake Champlain Basin Program, which coordinates management of the watershed, is also unsure of the cause. But other fish in the lake have been rebounding, he said, and Lake Champlain’s overall health has “been holding its own.”
That represents a marked improvement from the past.
Deforestation in the 1800s allowed exposed soil to run off into the lake, along with phosphorous used for farming. Invasive species, such as the sea lamprey, also entered Lake Champlain, perhaps through newly built canals. With the stock declining, the last commercial fishery on the lake closed in 1917.
“We believe that lake trout were extirpated from Lake Champlain because of overfishing and habitat impacts from pollution,” Palmer said.
Those days are gone. Now, wild trout are being plucked for study by a net lowered by metal chains stretching 500 feet from the stern of the Melosira. The boat is captained by Steve Cluett, a veteran of Great Lakes research who was raised in Dennisport and helps nudge Marsden to explore different sections of the lake bottom.
Looking at her recent catch, Marsden found more evidence of the upward trend. The fish were spilled onto a work table, and she quickly separated the trout from a quivering mass of alewife and perch.
“It’s all good,” she said with a broad smile, raising her arms in mini-celebration.
Marsden checked the fins — wild or stocked? — then measured and recorded each fish before freezing them to stop digestion. The lake trout’s diet could provide vital clues to the mystery.
“You’re always asking why and trying to discover what the answer is,” said Marsden, a professor at UVM’s Rubenstein School of Environment and Natural Resources. So far this year, Marsden’s team has conducted 88 trawls.
A healthy, wild population of lake trout would be a financial boon for Vermont, which is spending $3.6 million this fiscal year on statewide fish programs and staff. The fish budget is disbursed across the state, but the Grand Isle hatchery on Lake Champlain costs $1 million by itself, Palmer said.
The key will be whether the wild lake trout live to spawning age, Marsden said. If that happens, and their numbers do not decline, their future is promising.
“If we could have the lake trout fishery support itself through natural reproduction, that would be wonderful,” Palmer said. “We would love to eliminate lake-trout stocking altogether.”
That milestone would bode well for the lake as a whole.
“If native fish are thriving, it’s an indication that things are going well in other parts of the ecosystem,” Palmer said.Brian MacQuarrie can be reached at firstname.lastname@example.org.