University of Vermont

Rubenstein Ecosystem Science Laboratory

Listening to Lake Trout to Build a Sustainable Population

Ellen Marsden handles a lake trout

Under the surface of Lake Champlain, dozens of lake trout are making weird noises. That's because transmitters, about the size of a AA battery, have been surgically implanted inside these fish. As they swim around, the transmitter sends out a high-pitched "ping." You — and the fish — can't hear it, but receivers on the bottom of the lake can. And this lets scientists track the movements of the fish, whether they're cavorting off the Burlington waterfront or brooding in Mallets Bay.

Listening to lake trout is just one research project supported by this technology, the Champlain Acoustic Telemetry Observation System (CATOS), created by Professor Ellen Marsden, Ph.D., and Professor Jason Stockwell, Ph.D., at UVM's Rubenstein Ecosystem Science Laboratory. CATOS, which is modeled after a similar system in the Great Lakes (GLATOS), began with 12 acoustic receivers deployed throughout the lake. Another 14 will be added in 2014, with plans to continue expanding coverage.

Why do we care about the movement of lake trout? "All of the lake trout you see out in Lake Champlain right now are stocked fish," says Marsden. Lake trout, which disappeared from Lake Champlain around 1900, have been stocked by the state since 1972. "The goal is to restore a self-sustaining population," Marsden says, since lake trout play an important ecological role as a top predator. "Why pay for something that could be naturally produced?"

Little is known about why the trout disappeared more than a century ago. For more than a dozen years, Marsden has been trying to find out what's preventing them from thriving today. To do this, she's employed other technologies, like underwater, remote-controlled video, to learn more about the fish's habits and habitat. The data collected suggest that all is well for the naturally spawned young lake trout up to about four weeks of age. The trout are spawning successfully, eggs deposited in November are hatching successfully in April, and plenty of fry are emerging out of the substrate. "Now, we're continuing to push that research forward to understand what happens to those fry as they progress through life," she says.

There are three factors that could be affecting the fish: disease, predation and starvation. "We're fairly confident there aren't any diseases we don't know about in the lake," Marsden says. So that leaves the other two to explore. With the addition of exotic species into the lake, predation could be a possibility. And while young fish are feeding successfully on the reef, there may be a food supply imbalance in deeper waters leading to starvation. "It's hard to find that smoking gun," Marsden says. "At about four weeks old, they leave the spawning reef, and they should be going off into deeper water. It gets very hard to follow them at that point."

CATOS will help researchers find new spawning sites, learn more about lake trout spawning behavior, and uncover the movements of the fish throughout the year — all putting Marsden closer to solving the mystery of what's happening to Champlain's lake trout.