It’s a brisk late-October morning, with a bright sun breaking through the fog clinging to the surface of Floods Pond, in Otis. Brad Erdman and Fred Seavey load gear into an aluminum skiff, and head out across the water.
A series of net floats comes into view in shallow water alongshore. Erdman and Seavey, both University of Maine graduate students, begin to check the submerged net.
In a trap at the business end of the net, Erdman finds a sleek 18-inch female arctic charr.
“This time of year they’re in their spawning colors," he says. "So they’ll have these dark backs, and kind of these brilliantly bright orange bellies, and their fins are like a brook trout, where you’ve got these orangish red colors to them, and white leading edges.”
This story is part of our series "Climate Driven: A deep dive into Maine's response, one county at a time."
Maine has the world's southernmost populations of Arctic charr, a landlocked fish left stranded here when the glaciers retreated. But the rare fish, once called blueback or Sunapee trout, are facing significant challenges, including a fast-warming climate.
As their name suggests, Arctic charr live primarily in northernmost waters, from Alaska to Greenland to Russia, where they are typically anadromous. Erdman says their presence in Maine lakes tells a story of dramatic climate change that began about 12,000 years ago.
“Maine was covered in ice, if you go back to the last glacial maximum," Erdman says. "And slowly, as the glaciers retreated, it filled in those depressions in the land, and they became lakes, and those Arctic charr were just chasing the glaciers as they left.”
As the glaciers left and the rivers warmed, some of the charr hunkered down in deep lakes with cold water, and have persisted here for millennia. Floods Pond is one of 12 lakes and ponds in Maine with remnant populations of charr. Other populations around New England have disappeared following introductions of non-native fish, which likely preyed on the charr, or competed with them for food and habitat.
But this pond has no non-native fish, and the habitat is protected by the Bangor Water District, which uses it as a water supply. So it’s ideal for this decades-long study of this unusual species.
Erdman puts the fish in a water-filled cooler to transport it to a makeshift lab on shore where it will be weighed and measured. At first, Erdman is surprised that there’s only one other charr in the net. And then he inspects the net and discovers why.
“Ah, that’s why we didn’t have many fish," he says. "So, in the process of the birds trying to get fish out of the net, they rip big holes into it, and it lets the fish out.”
The birds are loons and cormorants. And researchers say they have been feeding on the lakes later in the fall every year, as Maine’s climate warms.
“We’ve noticed over the years more and more times when we are finding fish with bird injuries," says University of Maine professor Michael Kinnison, who has been studying Maine’s arctic charr for 20 years. “And that probably reflects that those birds are now able to stick around longer, and they are coming into interactions with Arctic charr.”
He says it’s tough to predict how charr will be affected as a changing climate tips balances in aquatic ecosystems.
“And as you shift that balance, things that sometimes were prey become competitors, things that were predators that maybe were avoided because of the timing of the year are now coming into contact with the charr," Kinnison says. "And so this mismatch process kind of builds because different organisms respond to warming in different ways. And so it’s a complex problem.”
As a species, Kinnison says Arctic charr are remarkably plastic, meaning they can adapt to many different habitats and diets. In Maine, some populations specialize in eating snails, while others eat insects, and others prefer fish.
Christina Murphy, of the USGS Maine Cooperative Fish and Wildlife Research Unit, says their plasticity makes Arctic charr well-known in academic and scientific circles.
“So we use them all the time in evolutionary studies in general in fisheries," Murphy says. "And then to see them in Maine is really exciting, because you’re finally face-to-face with a really famous fish, within the fisheries and evolutionary world.”
Murphy and Kinnison and a colleague from the University of New Hampshire recently won a $1.5 million National Science Foundation grant to study how charr fit into the food webs in the Maine lakes where they persist, and how this might predict their vulnerability to climate change.
Although they keep a low profile, Murphy says Arctic charr are truly a keystone species in these lakes.
“For example in Floods Pond, they are one of the large predatory fish when they are adults in that system," she say. "So I think to underestimate their importance to a food web would be doing ourselves a disservice. Because the lakes that they persist in are structured with them there, and they are very important to keeping those lakes stable.”
Although a warming climate poses risks to charr, their most immediate threat is the introduction of nonnative fish species. Bob Mallard, of the Native Fish Coalition, says in addition to the species that are introduced illegally, he’s worried about the state's practice of stocking lake trout in Hancock County's Green Lake, which is also home to Arctic charr.
“It’s tough for me to sit here and be worried about climate and the impacts on charr," Mallard says, "when there are so many other things going on, right now.”
Back on Floods Pond, UMaine researcher Brad Erdman measures the 18-inch female charr, and inserts a tiny tag that will allow researchers to identify the fish if it is recaptured. Soon, he’s knee deep in the pond and ready to release her.
“Off she goes," he says, "make sure she swims off alright here.”
And as its forebears have done since the last ice age, the Arctic charr swims off into the cool waters of Floods Pond, and a tenuous future.
