What fish eat can reveal changes in Lake Superior’s food web

A fish carcass that might otherwise be disposed of may instead help fisheries biologists with the Minnesota Department of Natural Resources better understand Lake Superior’s ecosystem and dynamic food web.

That’s the idea behind the agency’s Predator-Prey Project, which for more than six years has relied on anglers donating remains of their catch for research.

The project began in 2020 when staff at the Lake Superior Fisheries Office in French River near Duluth saw an opportunity to gather more information about prey resources, predator-prey dynamics, and ecosystem health to help guide fisheries management.

Since then, anglers have donated more than 10,000 fish carcasses, giving biologists access to samples they might not otherwise collect.

Anglers submit fish carcasses in Minnesota DNR’s Predator-Prey Bags | Photo by Minnesota DNR

The DNR works with charter captains and recreational anglers along the North Shore, from Duluth to the Canadian border. After a day on the water, anglers and guides place their catch remains in a special Predator-Prey Project bag provided by the DNR.

The project targets several species that are rarely encountered during the DNR’s standard surveys, including siscowet lake trout, pink, coho, and Chinook salmon, brown trout, and steelhead.

“The gap that this helps us bridge is that these are not species we’re going to encounter in our regular sampling, and we’re able to get those samples with the help of the public,” said Nathan Beckman, a fisheries biologist with the DNR’s Lake Superior Fisheries Office.

The DNR collects stomachs, tissue samples, and otoliths, or ear bones used for aging. Stomach and tissue samples are then sent to research partners for analysis, providing information about what fish are eating and where they fit within Lake Superior’s food web.

So far, the research has shown that siscowet and lean lake trout occupy a high position in Lake Superior’s food chain.

“They occupy the highest level of the food chain, and that they are distinctly different than all the non-native introduced salmonids,” Beckman said.

Beckman said the research has also shown that non-native species, including pink, coho, and Chinook salmon and brown trout, tend to be more selective in what they eat and generally have shorter lifespans than native species.

That information helps fisheries managers better understand prey availability and how changes in prey populations can ripple through Lake Superior’s food web.

And sometimes, the contents of a fish’s stomach are surprising.

“We have a long list of odd things we’ve found over the years,” Beckman said.

Researchers have found black crappie, pieces of a duck, various terrestrial animals,like moles and rats, and an entire bratwurst.

Researchers found an entire Johnsonville brat in Siscowet stomach | Photo by Minnesota DNR

They’ve also found human garbage.

“We found nicotine pouches, cigarette butts, random pieces of garbage-you name it, we found it,” Beckman said.

Beyond the unusual items found in some fish stomachs, the project has also helped researchers track broader changes in Lake Superior’s food web.

One of the most significant developments researchers have tracked is the effect of a major boom in Cisco populations, an important prey species in Lake Superior.

Beckman said the abundance of Cisco was followed by dramatic changes in the size of Chinook and Coho salmon, including several state-record coho catches.

“We saw dramatic shifts in both Chinook and Coho salmon size in a very short period of time in what we believe is a response to that Cisco boom,” he said.

The salmon have since returned to sizes closer to what Beckman described as normal for Lake Superior. Researchers are now studying the lingering effects of the Cisco boom and watching for signs of another increase in Cisco abundance.

“So we’re hopeful that future Cisco booms could replicate the same conditions,” Beckman said. “It gives us the ability to kind of predict.”

Beckman said the Predator-Prey Project has been particularly valuable over the past six years because researchers can study the before, during, and after of increased Cisco abundance, giving them a longer-term look at changes in Lake Superior’s food web.

The project is intended to continue in the years ahead and, with continued support from anglers, help fill gaps in understanding the predator-prey dynamic in Lake Superior.

Beckman said anglers interested in participating can contact the Lake Superior Fisheries Office for collection bags and instructions.

“It’s garbage, anyways. You’re just going to throw it out, so why not donate it to science, right?” he said.

WTIP’s Kalli Hawkins spoke with Nathan Beckman, a fisheries biologist with the DNR’s Lake Superior Fisheries Office about the ongoing Predator-Prey Project. Audio below.

Kalli Hawkins September 19, 2026