DULUTH -- Researchers hope to inspect the stomachs of as many as 10,000 fish from across Lake Superior in the coming year to find out what they are eating, but they need your help to get the job done.

The Minnesota Department of Natural Resources fisheries crew that looks after Lake Superior is asking anglers to donate the leftover parts of any and all fish they catch on Gitche Gumee.

You can keep the fillets. They just want the rest — intact stomachs, spines and heads — refrigerated or frozen as quickly as possible and then dropped off at the French River office outside Duluth.

They aren't pretty, but the guts leftover after the fillets were removed from this small coho salmon caught last month will help fisheries biologists better understand what salmon eat, and when, in Lake Superior. (Photo courtesy of the Minnesota DNR)
They aren't pretty, but the guts leftover after the fillets were removed from this small coho salmon caught last month will help fisheries biologists better understand what salmon eat, and when, in Lake Superior. (Photo courtesy of the Minnesota DNR)

It’s called the Lake Superior PredatorPrey Project, part of a region-wide effort that includes Minnesota, Wisconsin, Michigan and Ontario as well as federal and tribal agencies and university researchers all looking at the relationship between predator fish and their prey in the big lake.

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They hope to find out if there’s enough food in the lake to go around and how much competition there is between predator species for specific prey species.

“We’re basically teaming up with all the other agencies around the lake to determine the feeding ecology of the fish in the lake. We want to know who’s eating who out there,” said Nick Peterson, Lake Superior migratory fish specialist for the Minnesota DNR. “It doesn’t matter how or when you catch the fish, we want them all.”

Contributions by anglers will be especially helpful in surveying salmon, which tend not to swim into DNR test nets that are normally set for lake trout and herring.

The participating agencies are members of the Lake Superior Technical Committee of the Great Lakes Fishery Commission. The project idea came from Cory Goldsworthy, Minnesota DNR Lake Superior Area fisheries supervisor.

“All of the agencies do our own diet content analysis for the predator fish. … But we want to standardize how it’s done now across the lake,’’ Goldsworthy said. That will allow an apples-to-apples comparison between the same species no matter where they are caught.

Goldsworthy said there’s some hint that small prey fish are getting eaten sooner, such as sculpin and rainbow smelt, that on average are considerably smaller now than a few decades ago. That would indicate increased competition among predator fish, especially as lake trout continue to rebound on the big lake after being decimated by sea lamprey in the mid-1900s.

The PredatorPrey effort started slowly last summer under COVID-19 constraints and only 70 samples were collected. Already this year more than 300 Lake Superior fish have been collected by Minnesota DNR, Peterson said. Nearly 200 have been processed and sent on to a lab in Michigan for results so far a mix of brown trout, chinook salmon, coho salmon, lake trout, clipped rainbow trout, splake, and cisco.

“It would be great to recruit a bunch more, particularly anglers who fish from Two Harbors and north,” Peterson said. “The project will continue throughout the year for sure and likely through the winter and spring of 2022.”

As of last week, 36 Minnesota anglers had signed up to participate. And the Lift Bridge Charter Association of six Duluth charter captains also are collecting fish guts from their clients' catch, so far contributing more than 125 samples for the project.

"We wanted to get all our guys in the association to help so we can get more samples to the DNR,'' said James Hall of James Addiction Charters, part of the Lift Bridge group. "Anything we can do to sustain the fishing in this lake, we want to help. This is our way of life. … Maybe it can help them understand the fishery a little better and maybe lead to more fish down the line."

Duluth angler Trevor Rodd with a chinook salmon he caught, the carcass of which he continbuted to the Lake Superior PredtorPrey project. (Photo courtesy of Trevor Rodd)
Duluth angler Trevor Rodd with a chinook salmon he caught, the carcass of which he continbuted to the Lake Superior PredtorPrey project. (Photo courtesy of Trevor Rodd)

Shawn Sitar, fisheries research biologist for the Michigan Department of Natural Resources, said predator fish diets will be analyzed at laboratories at Northern Michigan University and Michigan DNR’s Marquette Fisheries Research Station, while prey fish diets will be analyzed at the laboratory at Lake Superior State University in Sault Ste. Marie.

A final report on what they find will come out later, probably in 2023, and Sitar said enough new information likely will be gleaned to publish several scientific papers.

Sitar said the angler-contributed fish will be especially helpful to show what bigger fish are eating during fall, winter and early spring months when DNR survey crews can’t get out to net.

“We hope to be able to do this every five years on Lake Superior so we can capture those long-term trends in the food web of the lake,’’ Sitar said. “We want to see how their diets change, what kind of competition there is, how much overlap there is in what they eat.”

Michigan and Wisconsin researchers so far are netting their own fish for the samples. But because the Minnesota DNR doesn’t get a chance to net salmon very often, they are asking shore and boat anglers to volunteer for the effort — citizen scientists of sorts.

The DNR wants anglers to sign up for the program before donating samples. They’ll get detailed information on what fish parts are needed and participants will be given free storage bags. They can then drop off the bags at the DNR’s French River office where extra freezers have been brought in to store them.

The Minnesota DNR's French River fisheries office is collecting hundreds of angler-donated fish guts this year as part of a region-wide study of Lake Superior's predator-prey ecology. Anglers can sign up and then donate intact fish remains after the fillets have been removed. (Photo  courtesy of the Minnesota DNR)
The Minnesota DNR's French River fisheries office is collecting hundreds of angler-donated fish guts this year as part of a region-wide study of Lake Superior's predator-prey ecology. Anglers can sign up and then donate intact fish remains after the fillets have been removed. (Photo courtesy of the Minnesota DNR)

2021 PredatorPrey Project fish gut study

Sign up first!

  • Who can participate? All anglers who fish on Lake Superior.
  • How do you sign up? Contact Nick Peterson at the Minnesota DNR’s French River office, nick.peterson@state.mn.us or 218-302-3272.
  • What is needed? Everything that is left after you fillet your fish — the head, spine and all internal organs. The DNR will accept samples from all species harvested in Minnesota waters of Lake Superior at any time throughout the year — trout, salmon, walleye, herring (cisco), whatever.
  • DNR provides: Official PredatorPrey Project plastic fish gut bags and directions on how to collect and submit samples.
  • Drop-off sites: DNR French River office at 5351 North Shore Drive, Silver Bay Marina, Grand Marais Recreation Area.