Attention Lake Superior anglers: Minnesota DNR needs your fish samples

DULUTH — Lake Superior anglers, your Minnesota Department of Natural Resources fisheries team needs your help.

Fisheries biologists are in the midst of multiple scientific studies and need samples from as many fish from the Gitch as they can get, starting now as shore fishing and breakwall angling begin in earnest, and then into spring and summer as anglers hit the big lake trolling and ply the North Shore’s tributaries in waders.

Three different research projects need different samples:

• From all fish caught and kept in Lake Superior: The DNR is asking for all the leftovers after you take the fillets. It’s part of an ongoing study, called the Predator-Prey Project, to see what fish are eating. The DNR provides bags to submit the carcasses so that the stomachs can be analyzed.
• Fins clipped from released brook trout: Researchers want a pectoral fin for an ongoing study of coaster brook trout genetics. DNR biologists will briefly train and award a special permit to any anglers who want to volunteer to sample any brook trout they catch. 
• Scales from any rainbow trout caught in Lake Superior or its tributaries: Researchers are looking to make sure that the steelhead now being caught are indeed that preferred version of the migratory rainbow trout and not carrying the genes of Kamloops rainbow trout that had been stocked for years but which have been discontinued since 2017. Biologists will provide training on how to remove the scales, award a special state permit for the work and provide envelopes for each sample of scales.

Drop-off sites are located along the North Shore, and biologists are hoping to get samples coming in as soon as anglers hit the big lake.

“We really want to see what’s in these fish that the breakwall anglers and the early trollers are going to start catching any day now’’ as winter melts into spring, said Nick Peterson, Minnesota DNR Lake Superior stream fisheries biologist based at French River.

As the News Tribune first reported last fall, the population of cisco, or lake herring, along Lake Superior’s North Shore exploded to levels not seen in decades thanks to a huge hatch in 2022.

That’s good news if you're a lake trout looking for a meal, as those herring are probably 3 or 4 inches long right now. It might also be good news in a couple of years for North Shore commercial herring netters looking to sell fillets or cisco caviar.

It might be less good news for sport anglers whose lures will be competing with lots of real prey fish for action.

The cisco tsunami — there was also a big hatch of bloater and kiyi, other small fish that big fish love to eat — is the primary reason Minnesota DNR North Shore fisheries crews are continuing the Predator-Prey Project this year, and maybe into 2024 in Minnesota’s waters of the big lake, to find out which of the bigger predator fish in Lake Superior are gorging on cisco.

“We haven’t been able to look at diets during a time of a huge cisco boom like this, so we are going to keep the Predator-Prey Project going on our end of the lake,’’ said Nick Peterson, DNR fisheries biologist stationed at French River outside Duluth. “This is a once-in-a-lifetime, once-in-a-career for me, boom for cisco, and we really need to see what it does.”

Early results show this as the biggest hatch of cisco in at least 20 years, but a more precise tally will come this summer when the fish will be large enough to show up in test nets set by the U.S. Geological Survey.

It remains unclear what is causing the cisco boom after their numbers had been declining in recent years. There are fewer invasive smelt in the big lake, which could be leaving more food for the native cisco. Cisco spawning success appears to hinge on several factors, including winter ice cover (more ice is good) and wind speeds, and a few icier winters lately may have helped.

“Cold winters seem to mean better cisco reproduction,” said Cory Goldsworthy, Minneosa DNR Lake Superior fisheries supervisor.

Still, scientists don’t know exactly why their numbers go up and down or why this boom is so big.

The Minnesota effort of the Lake Superior Predator-Prey Project collected more than 4,400 fish skeletons from anglers from 2020-2022 and will continue through at least 2023 in Minnesota waters of the big lake.

Some 68 Minnesota anglers contributed fish, with most coming from charter captains in Duluth and along the North Shore, with some captains handing over nearly 500 samples over three seasons.

The skeletons represented 15 species, although lake trout were by far the most common, followed by coho salmon, Chinook salmon, pink salmon and walleye. The stomach analysis was conducted at Northern Michigan University and Lake Superior State University.

Anglers and charter captains turned in everything except the fillets and scientists have been looking into fish stomachs to see what the fish have been eating. Even if the stomachs were empty, other researchers collected samples of muscle from the fish to analyze carbon and nitrogen — called stable isotope analysis — that was conducted by a University of Minnesota Duluth graduate student.

So what do Lake Superior fish eat? Among the Minnesota-caught fish, pretty much anything and everything they can find.

Lake trout were by far the biggest eaters (especially the bigger, fatter siscowet lakers) dining on everything from shiner minnows and invasive ruffe to small walleyes, burbot (eelpout) and coho salmon. Scientists found parts of a snake in one lake trout stomach and, in another caught off Duluth, an entire, undigested Johnsonville bratwurst.

Across the big lake, state, tribal, federal and provincial agencies helped in the Predator-Prey Project as university scientists conducted the analysis. But contributions by anglers have been especially helpful in surveying salmon, which tend not to swim into DNR test nets that are normally set for lake trout and herring.

“Angler participation is critical for this to work,’’ Peterson said.

One early result of the Predator-Prey Project, now entering its fourth year, is that there is surprisingly little overlap between native fish and introduced species.

Native lean lake trout, fatty siscowet lake trout and walleye tend to feed on the higher end of the food chain, munching cisco (lake herring,) kiyi, smelt and other small fish, with some freshwater shrimp thrown in. They are mostly benthic feeders, down deeper in the water column.

But introduced species — coho, pink and Chinook salmon, especially — are eating mostly at the bottom of the food chain: small, freshwater shrimp and amphipods and even zooplankton and tiny plants. They are considered pelagic feeders, generally in shallower waters spread across the lake.

It would appear to be very good news that the stocked fish aren’t having an adverse impact on native species, said Jessie Hanson, a UMD graduate student.

Hanson took samples from 612 fish skeletons donated by anglers over the past three seasons analyzing levels of carbon and nitrogen. Those so-called stable isotope fingerprints showed the non-native salmon have been mostly eating snacks and not big meals

“They’re pretty much forced to find the small food because the native trout are taking the bigger prey,’’ Hanson said. “The introduced species (salmon) have found a different niche … they don’t seem to compete with the native species very much.”

Hanson said that finding has surprised some anglers she’s talked to.

“They are surprised that the salmon aren’t really eating fish very much,” Hanson said, noting she will continue to analyze samples at least through 2023.

It remains unclear if salmon might adjust their feeding to the explosion of cisco occurring along the North Shore.

“It will be interesting to see if they start to take advantage of that,’’ she said.

Hanson noted that the stocked salmon species are “taking whatever they can get” on Lake Superior, one reason they don’t grow nearly as large as ocean salmon which target bigger prey fish, or even as big as Lake Michigan salmon which have alewife to eat, an invasive species from the ocean that hasn't taken hold in Lake Superior.

In very cold, very infertile Lake Superior, the salmon just haven’t figured out how to find bigger prey that might fatten them up faster, Hanson said.

One reason might be that lake trout can live to be decades old while the longest-lived salmon live just five years “so they never get the chance to figure it out,’’ Hanson said. “And part of it is that Lake Superior (food for big fish) is just very limited. Lake Superior isn’t even a very good lake trout lake. … There’s not enough food.”

Hanson noted that while salmon aren’t competing against lake trout or walleyes for food, they are competing against each other. There is significant overlap between all introduced species — and big competition for food — including pink, coho and Chinook salmon, steelhead rainbow trout, brown trout and splake. Stocking more of those species, she noted, would create more competition between them.

Cory Goldsworthy, Lake Superior fisheries supervisor for the Minnesota DNR, said he expects salmon to munch more on cisco this spring and summer.

“They (cisco) just weren’t available for them the last few years,’’ Goldsworthy noted. “I think what surprised me the most was the fact we had these fairly big Chinook salmon that had nothing in their stomachs. … They were surviving on mysis (freshwater shrimp) and not finding fish to eat.”

For decades, the question has loomed whether Lake Superior’s coastal “coaster’’ brook trout are a separate species from the brookies found in streams isolated from the big lake.

It turns out they are genetically identical, according to ongoing genetic research by the Minnesota DNR that found no difference between brookies swimming in rivers above barriers and those brookies swimming in the lower mouths of rivers and Lake Superior itself.

Minnesota’s coasters are essentially brookies that wash down the river and get pushed over the barriers, such as big waterfalls, during flood events, Peterson noted.

The genetic research capabilities are getting so good that scientists can pinpoint exactly which source river each coaster brook trout originated from. And they are finding there likely isn’t any reproduction going on below the barriers.

“That’s our hypothesis now,’’ Peterson said

So far, the research has focused on just a limited number of fish netted in a few North Shore streams. Biologists are expanding the study to more streams and need more samples.

“Anglers can sample much bigger fish than we are catching in our nets, so we need their help,’’ Peterson said.

The DNR can get all the genetic material they need from a small pectoral fin on the brook trout, which the fish won't miss much once it's released to keep swimming.

The more researchers can pinpoint where the brookies are originating from, the more they can protect those streams — even small pockets of stream habitat — to protect the population.

“If we can find where the cold water sources are (that) they like to be near, if we can preserve habitat that’s left, then we can help out the population,’’ Goldsworthy said.

Coasters may have reproduced in the lower rivers near Lake Superior back in the 1800s, when they were said to swarm around Lake Superior tributaries and when habitat was much better. Since then, logging, fires and development have destroyed most of the old-growth cedar forest that once shaded and protected the lower North Shore streams.

“They probably had the habitat then to successfully spawn in the river (mouths) and reproduce,’’ Goldsworthy said. “But we aren’t seeing that happen now.”

The Minnesota DNR stopped stocking the Kamloops version of migratory rainbow trout in Lake Superior in 2017, concerned that they were mingling with steelhead and diminishing the wild genetics of Lake Superior’s naturalized rainbows. That angered many shore anglers who had enjoyed casting for Kamloops. But the move buoyed river anglers who prize the pure steelhead version of the trout.

Previous studies showed that the loopers were indeed breeding with the steelhead. And that worried fisheries biologists (and steelheaders). Now that no new loopers are being stocked, the last remaining loopers should be either dying out being caught. That should mean the steelhead genetics — genes from naturalized wild fish from Lake Superior — are holding true. (Steelheads were introduced more than 100 years ago but aren’t native to the lake.)

And that's why biologists are asking for anglers who catch any rainbows to get signed up, get trained, get a permit and submit scale samples from the fish they catch and release. (Only clipped-fin, stocked steelhead can be kept in Minnesota waters.).

“Our assumption is that the Kamloops (genetics) are fading fast with the last few fish out there. But we want to make sure that’s what's happening, so we need the samples,’’ Goldsworthy noted.

• Who can participate? All anglers who fish on Lake Superior. You must sign up first.
• 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. 
• What species? The DNR wants samples from all species harvested in Minnesota waters of Lake Superior at any time throughout the year: trout, salmon, walleye, cisco (lake herring), eelpout, etc.
• DNR provides: Official Predator-Prey Project plastic fish gut bags and directions on how to collect and submit samples.

• Who can participate? All anglers who fish rainbow trout on Lake Superior and its North Shore tributaries. You must sign up first.
• 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’s required? Brief training and a state permit to take scales from a live fish.
• What is needed? Scales from the trout taken just above the lateral line.
• DNR provides: Official envelopes and directions on how to collect and submit samples.

• Who can participate? All anglers who fish brook trout on Lake Superior and its North Shore tributaries. You must sign up first.
• 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’s required? Brief training and a state permit to take a pectoral fin from a live fish.
• What is needed? One pectoral fin from a live fish to be released. 
• DNR provides: Official envelopes and directions on how to collect and submit samples.