Hammond Bay Biological Station research ecologist Nick Johnson holds a sea lamprey, one of the most devastating invasive species in the Great Lakes. Johnson and collaborators are identifying which fish species sea lampreys parasitize in the Great Lakes through DNA analysis of sea lamprey excrement. (Andrea Miehls, Great Lakes Fisheries Commission.)
About 75 years ago, Great Lakes fish were nearly wiped out and the fishing industry as we know it completely eradicated. A so-called vampire was lurking, overpopulating and infiltrating the waterways of the region, putting the lakes at risk of becoming a graveyard of what once was.
In the 1830s, a parasitic fish, called the sea lamprey (Petromyzon marinus), found its way into the Great Lakes and latched onto helpless native fish, depleting them of life. Lampreys don’t have jaws or bones—their skeleton is made of cartilage. And no, they aren’t eels. Their mouth is what sets them apart with its razor-sharp circular sucking disk that drinks the blood of its victims.
Hammond Bay Biological Station research ecologist Nick Johnson holds a sea lamprey, one of the most devastating invasive species in the Great Lakes. Johnson and collaborators are identifying which fish species sea lampreys parasitize in the Great Lakes through DNA analysis of sea lamprey excrement. (Andrea Miehls, Great Lakes Fisheries Commission.)
Sydney Currier, the Aquatic Invasive Species Coordinator from the Invasive Species Centre (ISC) in Canada, says much of their work involves teaching the public about sea lamprey prevention. She says they have “leathery, scaleless skin in shades of grey or brown,” with sharp teeth and a “raspy tongue.”
Sea lampreys are native to the Atlantic Ocean, and historically, Niagara Falls—which separates Lake Ontario and Lake Erie—had prevented sea lampreys from traveling any further into the freshwater beyond the occasional sighting in Lake Ontario. That is, until the 1830s, when Ontario’s Welland Canal bypassed the Falls to create a shipping channel between Lake Ontario and Lake Erie. Over the course of the next century, the canal was reconstructed and expanded numerous times to allow for larger vessels, and in the 1920s, the sea lamprey gained access to Lake Erie.
By the 1940s, all eight of the Great Lakes had sea lamprey.
In the ocean, if a sea lamprey attaches to a whale, it’s not going to do any real damage. The lamprey will feed on the whale, but it will eventually drop off. In the Great Lakes, however, when an 18-inch-long sea lamprey attaches to a lake trout—which is approximately 24-36 inches in size—the fish doesn’t stand a chance.
Sea lamprey have almost 150 teeth. (Adult humans have 32 teeth, counting wisdom teeth). Sea lamprey can also replace their teeth as many as 30 times during their lives. (D. Brenner, GLFC)
And it doesn’t help that the sea lamprey has a robust appetite. A single lamprey can eat up to 45 pounds of fish in its lifespan. Only one in seven fish survives a lamprey bite.
Moreover, sea lamprey can lay 100,000 eggs, and do not have a natural predator in the Great Lakes ecosystem, meaning that the situation grew dire very quickly. The fish, with its leech-like shape and growing numbers, were feeding on 100 million pounds of fish annually. Lake trout in Lake Huron and the Georgian Bay had dwindled from 3 million pounds in 1940 to 760,000 pounds in 1946.
The nightmare could have continued if groundbreaking science hadn’t saved the region’s waterways, according to a new film The Fish Thief: A Great Lakes Mystery, created, written and produced by Lindsey Haskin in collaboration with the Great Lakes Fisheries Commission (GLFC) and narrated by Oscar-winning actor J.K. Simmons (who won the 2014 Academy Award for Best Supporting Actor in Whiplash).
“We have a long history of fishing,” says Haskin. “Native Americans in the Great Lakes region have fished for sustenance since prehistory. Fishing is an ingrained thing and an important source of protein for people. There are a lot of underprivileged people on the low end of the income scale who still go out and fish to have some food on the table.”
Promotional poster for The Fish Thief. (Skyhound Media)
In 2009, Haskin—who grew up in the Detroit suburbs and went on to a successful production career in Denver and Los Angeles—wrote, produced and directed a two-hour public television film called Freshwater Seas: The Great Lakes about the history of the Great Lakes ecosystem. In the film, with input from the Great Lakes Fisheries Commission (GLFC), he spent about 10 minutes focusing on the sea lamprey. Subsequently, the GLFC offered him the opportunity to create a film entirely focused on sea lamprey, which would end up being his second long-form film about the Great Lakes.
Haskin says that since many of the people directly involved with sea lamprey were beginning to pass away, the crew hit the road and started filming. There wasn’t a time for a script or an outline—that would come later. It would end up taking them seven years to complete the film.
In TheFish Thief, Haskin interviews former fishers who saw and tried to kill lamprey while on boats and who experienced the stress of their livelihoods possibly being erased.
In the 1950s, the sea lamprey caused some native fish to go extinct, like the cisco fish species, which was last seen in Lake Michigan in 1952.
“As you know, fish and lamprey don’t carry passports,” says Greg McClinchey, director of policy and legislative affairs for the GLFC. “They don’t really care what side of the border they’re on.”
As a result, in 1954, the invasion of the lamprey forced Canada and the United States to establish the GLFC through a treaty at the Convention on Great Lakes Fisheries to help develop a binational coordinated body of science on which to make fishery management decisions. At the time, each area of the Great Lakes was conducting its own management without any consultation.
“We’ve spent the last 70 years working to keep the Great Lakes healthy and sustainable so that they still yield benefits for the individual states,” says McClinchey.
Through persistent efforts, a solution was eventually created to battle the otherworldly fish.
Trial and error
When Vernon Applegate and his team invented 3-trifluoromethyl-4-nitrophenol, a.k.a. TFM or lampricide, it was the 5,209th lampricide tested at the Hammond Bay Biological Station in Michigan. The research team had spent years of trial-and-error research attempting to create a pesticide that only affected sea lamprey, nothing else.
In The Death and Life of the Great Lakes, author Dan Egan describes Applegate and his team’s research as the “biological equivalent of a moon shot.” The crew would often receive various unlabeled or unknown chemicals from factories across the globe, as chemical companies zealously guarded their formulas in the event one became the lucrative poison that could defeat the lampreys. Their solution was to fill 10-liter jars with water, dropping two juvenile lampreys into each one, along with one rainbow trout, one bluegill and finally the poison.
Sea lampreys are a 350-million-year-old fish from the ocean and come from a saltwater environment, but they breed and live their formal larval years in freshwater streams. Because of this, they easily adapted to freshwater in the Great Lakes and maintained their behavior of moving into streams and rivers to lay their eggs. In 1958, the first TFM went into Mosquito River, a tributary of Lake Superior in Michigan’s Upper Peninsula. Mesh cylinders with lamprey larvae were placed downstream, and they were all found dead during the initial test.
James Moffett (left) and Vern Applegate (right) discuss the results of the TFM field test in the Mosquito River. (Courtesy of GLFC)
According to TheFish Thief, from then on, the GLFC began an all-out assault. Lake trout had not disappeared completely from Lake Superior, but in Lake Michigan and Huron, they were gone.
By the following autumn, all Lake Superior tributaries had TFM as well as some streams flowing into Lake Michigan and Lake Huron.
TFM is a restricted-use pesticide, which means that only a certified pesticide applicator applies it to freshwater streams in the Great Lakes basin. Since the lakes are too big, the GLFC controls lamprey populations in the rivers and streams. Through a schedule and a listing of hundreds of lamprey-producing rivers in the basin, the GLFC treats those rivers with lampricide to prevent them from moving into the lakes.
Lampricide is lamprey-specific. McClinchey explains that if he took a lake trout and put it in a lampricide container with a lamprey, in the morning, the lamprey would be dead, and the lake trout would be fine and unaffected.
TFM includes a similar compound found in human saliva. At a very specific concentration, when the water is at a certain pH level, the compound is introduced to the lamprey’s body, something that they have never been able to metabolize. As a result, the sea lamprey dies.
“We know how to kill fish, but what’s really hard is killing only a specific fish,” says McClinchey.
TFM is applied to waterways every three to five years. Folks from the U.S. Fish and Wildlife Service walk the streams with electric backpacks and scoops with long poles as they shock the bottom of the stream. This stimulates the lamprey larvae to come out of the muck. Then stream surveys are done to look at the larval populations to see when TFM should be introduced to the area again.
Agent with the U.S. Fish and Wildlife Service conducts an assessment to determine sea lamprey abundance. A minor electric current is administered through a backpack shocker to draw larval lamprey out of the stream bed. (Courtesy of GLFC)
For lake swimmers, they may be alarmed to hear that a chemical is being introduced to their waterways. However, lampricide has another fascinating property. It’s photosensitive, which means that when it’s exposed to sunlight, it breaks down and is gone without accumulating in the environment.
“When I say we’re lucky to have found it, that’s a huge understatement because otherwise, had we not found this in the 1950s, we wouldn’t have fish in the Great Lakes today,” says McClinchey.
U.S. Fish and Wildlife Service agent deposits TFM bars as part of a treatment on the Manistee River in Michigan. (Courtesy of GLFC)
Lampricide isn’t the only method for killing the fish, however. The Commission uses barriers and traps throughout the rivers and streams.
In 2024, a behavioral ecologist and two engineers commissioned by the GLFC at Michigan State University launched their plan for a new fish barrier in Traverse City that’s been called the “Holy Grail” of invasive species control. For the next decade, the team will work to create a barrier, called FishPass, that sorts and allows desirable fish to pass, while blocking invasive species like sea lamprey.
McClinchey says the exact number of sea lamprey presently in the Great Lakes is unknown, but, “What I know is that we kill between 8 and 9 million a year. We have reduced their population numbers by about 90% of what they were during their high levels.”
If the TFM efforts ended today and the GLFC dissolved its program, there would be an estimated three to five years of fishing left in the Great Lakes before all of the fish would be gone.
McClinchey says just thinking about this possibility sends a shiver up his spine. “As someone who grew up on a farm on the coast of Lake Huron, I could not imagine a circumstance where there’s no fish in the Great Lakes. It’s unfathomable.”
Funding cuts and the future of TFM
The Great Lakes can’t afford to have the GLFC take their foot off the gas. During the Covid-19 pandemic in 2020 and 2021, the program was reduced to a partial control program, and there was a 300% increase in sea lampreys due to relaxed controls.
The one-year pause illustrated the importance of lampricide, as leaving sea lamprey to their own devices would be catastrophic.
In February 2025, the U.S. Fish and Wildlife Service, with which the GLFC works on the American side of the border, experienced staffing reductions under the Trump administration, which impacted the ability to deliver the lamprey control program going into the new year.
In March, U.S. Reps. Mike Quigley (D-Ill.-05) and Bill Huizenga (R-Mich.-04) proposed the Great Lakes Fishery Research Reauthorization Act to continue funding scientific research to stop sea lampreys and other invasive species from infiltrating the freshwater lakes. The bill will maintain current research for another five years.
“It’s on us to preserve our natural resources for future generations,” said Quigley in a press statement.
The GLFC is jointly funded by Canada and the U.S., and at this point, there is no indication or signal that the program is in jeopardy. It has immense support from the Great Lakes congressional delegation.
“I’ve never gone to a single meeting and been told by anyone, ‘Man, do I hate the Great Lakes’ or ‘Man, am I cheering for the sea lamprey this year,’ ” McClinchey says. “We’re all rowing in the same direction. The congressional support has been amazing.”
Lampreys aren’t bad news everywhere, though.
There are four other species of lamprey besides the sea lamprey: the chestnut, the silver, the American brook and the northern brook. These types of lamprey belong in the Great Lakes and have a place in the ecosystem and the food web (the American brook and the northern brook are non-parasitic).
Lampreys are native in freshwater systems in other parts of the country such as North Carolina, where five lamprey species return to spawn. They are prey to Blue Herons, make nutrients available to organisms and are filter feeders that eat algae.
In many places around the world lamprey is a delicacy or a part of the community that in some cases dates back to the Middle Ages and before.
Did you know?
Pacific lamprey (a species distinct from the sea lamprey) have cultural and ceremonial significance for Native Communities in the Pacific Northwest, like the Yakama, Umatilla, Warm Springs and Nez Perce Nations. Pacific lamprey are used in rituals and for medicinal purposes for skin conditions like boils, sores and rashes. They are also used for wound healing and as an ailment for arthritis and stomachaches. Pacific lamprey are considered elders and relatives in some Native communities.
In Gloucester, in the United Kingdom, there’s a tradition that every time the British Sovereign has a significant event like a birth, wedding or coronation, the sovereign is presented with a sea lamprey pie. The pie is a puff pastry made to look like a cathedral, filled with sea lamprey. In Azerbaijan, locals eat Caspian lamprey cooked in oil or in a stew. Sea lamprey in Portugal is a replacement for beef, marinated in its own blood and served with rice. In March, approximately 30,000 people visit the village of Montemor-o-Velho for the Lamprey and Rice Festival. And Padrón, Spain, has their own Lamprey Festival where restaurants in the area serve sea lamprey from the Ulla River.
When asked why we don’t simply eat the lamprey in the Great Lakes—“if we can’t beat them, eat them” as they say—McClinchey says that the problem isn’t with sea lamprey, but with how humans have treated the Great Lakes. Because sea lamprey feed at the top of the food chain, eating “fish that eat fish that eat fish,” he says, “they concentrate mercury and other heavy metals, which is part of the terrible legacy of the Great Lakes.”
The Great Lakes were not always treated the way they are today. It wasn’t until 2002 that Presque Isle Bay in Lake Erie off the Pennsylvania coast was the first U.S. Area of Concern to be declared in a recovery stage.
Even if lamprey were safe to eat, says McClinchey, “We would want to be careful about promoting a food industry that has the potential to wipe out fish in the Great Lakes in 5 years.”
Are the Great Lakes safe for now?
The Great Lakes are home to 186 invasive species.
“Sea lamprey is just one of them,” McClinchey says. “Those who don’t understand the past are doomed to repeat it. We don’t need any more invasives to come in.”
Asian carp was the last new invasive species to enter the basin in 2017, and that’s due to the public’s awareness and federal and state levels taking precautions.
McClinchey says TheFish Thief has a message everyone needs to know:
Sometimes when we come home, we bring little friends with us, and we need to make sure that we do everything possible to prevent any new invasives from coming into our ecosystem. There are things that every single one of us can do as individuals to prevent the spread of invasive species.
Currier says if you catch a fish with a sea lamprey attached to it, “do not return it to the water.” She instructs fishers to “kill it and put it in the garbage.” All sea lamprey sightings should be reported to EDDMapS or iNaturalist.
Many fishing or boating rules already include ways to prevent the spread of invasive species, such as avoiding dumping bait buckets from one body of water into another and washing boats before entering a new body of water. These types of reminders and daily knowledge keep the Great Lakes great.
For Haskin, fishing and the Great Lakes appeal to people from “all walks of life.” He hopes his film shows the public how important natural resources are to economies, even small town economies on both sides of the U.S. and Canadian border, and how science and government can work to help people protect the things they enjoy.
Saving the Great Lakes and the ecosystem within the streams and tributaries crosses political, racial and socioeconomic lines. When it comes to saving the fish in the Great Lakes, it’s a shared commonality between environmentalists and conservationists alike. Fishers want to fish, and environmentalists want the lakes to thrive. It’s a moment where these groups of people, who oftentimes come from differing political backgrounds, can agree.
Overall, Haskin hopes his film helps people learn about the history of lamprey and how we can continue to stay in the fight.
“It’s a story about human tenacity and about human persistence in the face of challenges,” says Haskin. “It’s a human story about, if at first you don’t succeed, try, try again, and in that way the story has a happy ending.”
The Fish Thief is available to stream, download, or rent on Apple TV, Amazon, Google, YouTube and Tubi.
