March–April 2024

Mysterious Morphs

There’s only one species of lake trout in Lake Superior, but this shape-shifting fish has at least four distinctive morphotypes—and there may be more.

Chris Pascone

"Reel up fast!" My buddy Ethan Waytashek and fishing guide Grant Sorensen yell to me. We’re jigging for lake trout from a boat 120 feet above an offshore hump on Lake Superior, and the guys see a fish rocketing toward my lure on the scanning sonar. The moment I’ve been waiting for is here.

I crank the reel to impart a fleeing action to the jig, triggering the naturally aggressive trout to chase and hit it.

I instantly feel a tap and sweep my rod tip upward to set the hook. The rod doubles over, and the fight is on. My arms tire from a long tug of war before I finally reel the fish up to our waiting net. 

It’s definitely a lake trout—but not just any laker.

“Look at that short snout and that bulging belly,” Sorensen observes, admiring the fish.

“Check out that small head and those oversized eyes,” Waytashek adds.

We immediately discern it is likely not a lean lake trout, the most commonly caught and most studied type of lake trout in Superior, named for its slender, tapered shape. Instead, we believe the fish is a humper, a distinct form, or morphotype, of the same species, Salvelinus namaycush—which despite its widely used common name of lake trout is scientifically a separate genus known as char. Leans and humpers are two of the four different lake trout morphotypes, distinguished by their body shape, coloration, size, or other physical features, that fisheries biologists have identified in Lake Superior. The other two morphotypes are known as siscowets and redfins. This fascinating genetic biodiversity within the species has begun to attract the attention of fish experts and a few obsessive anglers like us—but in many ways the morphotypes still remain a mystery.

Among the scientists who’d like to learn more about them is Cory Goldsworthy, Lake Superior fisheries supervisor for the Minnesota Department of Natural Resources. “We’re still finding new things in Lake Superior,” he says. “We can’t say that all the different lake trout morphotypes have been described or even touched yet. For instance, only in the past few years has a spring-spawning siscowet population been discovered.”

The lake trout I’ve been lucky enough to catch today is humble in size, but not in beauty. October sunshine filters through its transparent yellow-tinged fins. Striking white vermiculations visually pop on the fish’s gray body in the low morning light.

Photos and smiles fill the boat as we admire this wild trout one last time before releasing it back to its rocky home.

A Product of Their Habitat. Later, I send photos of my catch to Goldsworthy, and he agrees based on the images that I indeed caught a humper. I’m ecstatic. Of the four known lake trout morphotypes in Superior, humpers are the least common.

Unlike their salmonid relative the humpback salmon, or humpy, which is named for a physical feature, the humper lake trout is so named for the habitat it prefers—the tops of the large seamounts, or humps, that rise from the depths of Lake Superior to heights that approach the surface. The redfin lake trout morphotype, with colorful fins that give it its moniker, also gravitates to these rises. It was on one of Superior’s largest seamounts, Superior Shoal, where Sorensen first started noticing something about the trout he was catching around these gigantic natural structures.

“Those fish were different than any I’d ever seen,” he says. “You see them come up from 20 or 30 feet down in the water and you’re like, ‘Wow, that’s a pretty cool-looking fish.’ That definitely stood out. Then you start to think, ‘Why are those fish different?’ And you see they’re in isolated locations.”

“The morphotypes are a product of their habitat,” says Goldsworthy, noting that 80 percent of Lake Superior is prime habitat for the siscowet, the most plentiful trout morphotype by far, which lives in the lake’s deepest waters. Abundant as they are, siscowet are largely ignored by anglers as they are hard to reach and their oily flesh makes them less desirable table fare. Lean lake trout, meanwhile, live at depths above 300 feet. They are the most catchable and commercially valuable lake trout because they inhabit near-shore waters where commercial and sport anglers can target them, and they are delicious to eat.

Though humpers are plenty edible, the few anglers who specifically pursue these morphotypes, like Sorensen, aren’t fishing to put dinner on the table. They’re catching and releasing them, as I did my humper, pausing a moment to admire these living examples of Lake Superior’s great biodiversity.

“I like the mystery, I like the unknown of these fish,” confesses Sorensen, who now fishes for morphotypes as a personal passion and spreads the word about them in his work as the host of the Superior Angling TV show on WDIO in Duluth. 

Lake trout brought Goldsworthy and Sorensen to know each other, first when the Superior Angling crew visited the Duluth DNR Fisheries office to film a segment about trout longevity, then as Goldsworthy came to appreciate the show’s focus on conservation and Sorensen’s firsthand knowledge and experience in finding trout morphotypes.

“It showed there are anglers out there boating fairly long distances over water to target redfin, humper, these different morphotypes that are very different-looking than, say, your lean lake trout,” says Goldsworthy. “And to see that level of acknowledgment of biodiversity, without having a harvest mindset to it, was just so cool to see.”

“I really like Grant’s work, because it’s putting a new light on ‘Hey, this is fishing too.’ It’s coming from a curiosity, a love of the resource, and an emotional attachment to natural resources.”

Back from the Brink. Lake Superior has the world’s largest wild lake trout populations.

Yet 65 years ago, the very existence of lake trout here was in peril. Overharvest of lake trout had already taken a toll on numbers, and then tragedy struck: invasive sea lamprey entered the Great Lakes. The lamprey almost extirpated all lake trout by the 1950s. Lake Superior was the only one to retain any wild trout populations.

The binational Great Lakes Fishery Commission was established in 1955, and just a year later scientists found a way to fight back against the sea lamprey: a chemical that kills off lamprey larvae when applied to tributary streams. Streams all around Lake Superior started being treated in 1958, and since then, the trout have come back. (See “A Superior Success Story,” January–February 2017.) Active conservation management around the lake, including harvest limits and massive native trout stocking programs that ended in 2016, has made lake trout rehabilitation a modern Lake Superior success story.

“We think we’re finally there now,” notes Goldsworthy. Today, there’s a large charter fishing industry and a revived commercial fishery on the North Shore. The Fond du Lac Band of Lake Superior Chippewa held its first tribal netting of lake trout on Lake Superior in 160 years last August. Anglers with a trout stamp can possess three lake trout in Minnesota waters of Lake Superior.

All of these measures of recovery, as positive as they are, are focused on lean lake trout.

“Our entire view of Lake Superior,” points out Goldsworthy, “is based on surveys that have been designed to monitor lean lake trout rehabilitation over the last 65 years.”

The Ecosystem View. Lost in the numbers-based lean lake trout rehabilitation effort was a holistic view of the lake ecosystem. Are there lake trout living at 1,332 feet, Lake Superior’s deepest spot? Yes. What do deepwater trout eat? Opossum shrimps (Mysida). How is global warming affecting cold-water lake trout? Under study. 

With the other four Great Lakes having lost much of their fish diversity in the 20th century, including the complete extinction of native lake trout, modern researchers are embracing Lake Superior’s relatively rich biodiversity. Researchers were aware of different morphotypes as early as the 1880s, and before that fishermen had often distinguished between lake trout types.

Shawn Sitar, a research biologist at the Michigan DNR Fisheries Research Station in Marquette, is one of the scientists studying lake trout morphotypes. He emphasizes the lake trout’s adaptability: “Animals, and life on earth, have a strong drive to persist. That’s why we see animals in the Arctic and in the deepest trenches in the ocean. We’re able to see that in lake trout. They’re adapted to their environment. That’s the difference between lake trout and salmon, which didn’t evolve here.”

This became evident when Chinook salmon were stocked in Superior, which, Goldsworthy says, was too deep, too cold, and too sparse in nutrients, compared to the warmer Great Lakes, to maintain high populations of the invasive alewife, the Chinook’s main prey fish.

The diversity of morphotypes is a genetically important adaptation for Salvelinus namaycush, according to Louise Chavarie of the Norwegian University of Life Sciences in Oslo, who did her postdoctorate research at Michigan State University on polymorphism among North American lake trout. She stresses the importance of genetic morpho­type diversity on her website: “Multiple forms within a species contributes substantially to the biodiversity in northern systems and has been associated with ecosystem resilience to disturbances (e.g., climate change).”

Leans, siscowets, humpers, and redfins all contribute to what Chavarie terms a “portfolio effect,” meaning that the various morphotypes give Lake Superior’s lake trout more stability in a changing ecosystem.

Goldsworthy is eager to learn more about how morphs fit into the big lake’s big picture.

“These different morphotypes are part of the overall ecosystem of Lake Superior, so they have a role in that ecosystem,” he says. “And for us, as fisheries managers, to better understand their role where they fit, it’ll help us manage the lake based on ecosystem management principles, where we’re managing for all of the native fish that are out there.”

More research into morphotypes could benefit the other Great Lakes, too. Goldsworthy is among the resource managers from state, federal, and tribal agencies that make up the Great Lakes Fishery Commission, and he serves as the head of the commission’s Lake Superior Technical Committee.

“In all of the other Great Lakes, lake trout were wiped out due to overfishing and sea lamprey,” he explains. “So Superior is the last Great Lake that has any of these existing morphotypes remaining. And there’s a big push in the other Great Lakes to reestablish some of these extant morphotypes—so the more we know about those fish in Lake Superior, the better chance rehabilitation efforts in the other Great Lakes will be successful.”

Very Special Fish. Scientists and fisherfolk alike are seeing the importance of preserving the biodiversity of Lake Superior’s lake trout morphs. Sorensen is a strong voice for conservation on Superior Angling. It’s these fishes’ natural beauty and variability that intrigues him: “They’re very special fish. They’re just gorgeous.”

To be clear, catching a humper or redfin morphotype on Lake Superior is a very challenging and specialized fishing endeavor. It takes a big, fast boat and a lot of technological know-how to navigate to the offshore humps where they gather, and it takes a lot of guts and desire to risk being so far offshore with nobody around for miles. The fish are stunning, but those who pursue them understand how hard they are to catch.

Sorensen realizes he is part of a small club. He knows of only a few other anglers who pursue these morphotypes, and he doesn’t guide fishing clients to them.

“I don’t want to exploit those areas. It’s not worth it,” he says. “A lot of these offshore places—you just can’t guide them. It’s just too much, too far from home. We go closer to shore, in Wisconsin, where the fish are plentiful. But it’s not common that you see those rare morphotypes there.”

While Goldsworthy is cheered to see conservation-minded anglers gaining interest in Superior’s humpers and redfins, as a resource manager, he wants to learn much more about all the morphotypes, including the very abundant but little-studied or -caught siscowet.

“We need to get better at siscowet. We know very little about siscowet even though they’re by far the most abundant lake trout in Lake Superior. We sample them once every three years at one location in Minnesota. We need to shift our perspective to be prepared to manage in the future, rather than looking back at the past.”

“We’re trying to better understand the ecosystem as a whole. As the chair of the Lake Superior Technical Committee, I’m trying to get us to start to talk about this. Let’s look forward 50 years and see if the surveys we’re doing now are going to give us the information we need to manage in the future.”

Mysteries to Unravel. Lake trout are the most important recreational fish in Lake Superior. They are sought for their trophy size, for their good looks, and, more recently, for the diversity within their species. Lakers are also Superior’s most mysterious fish: Their manifold morphology can vary even from one reef to the next. This makes the moment you lay eyes on each one a new thrill, every time.

Sorensen has a specific spot on Superior where he catches a distinctive type of redfin trout that he terms “butterflies” due to their winglike fins.

“Their front pecs [pectoral fins] are just massive. They don’t even look real,” Sorensen says, speculating that the oversized appendages allow them to conserve energy by riding currents in search of food in their spartan habitat, 55 miles offshore.

Is the butterfly possibly a newly described morph to fisheries science? Are those pecs adapted in the way that he speculates? Mysteries still abound when it comes to morphs, which is what keeps Sorensen looking for them.

 “I’ve driven 45 miles in the boat to look for structure, never found it, and went home. That’s what I do. I like it. I enjoy the mystery. Especially on Superior—there’s just so much water to explore.”