Great Lakes Fishery Commission

New Study Concludes Invasive Sea Lampreys Can Be Controlled by the Release of Sterilized Males

In a study published in Scientific Reports, scientists with the U.S. Geological Survey, U.S. Fish and Wildlife Service, Fisheries and Oceans Canada, and Great Lakes Fishery Commission, demonstrated that sea lampreys—one of the most impactful invasive species in the world—could be controlled by the release of sterilized male sea lampreys just prior to spawning. This study is the first of its kind for a fish species and has relevance to vertebrate pest control programs worldwide. The research was funded by the Great Lakes Fishery Commission and Michigan Invasive Species Grant Program.

A man wearing a personal floatation device and waders stands in a river under a bridge. He is holding a tube-like fish about 15 inches long which is suctioned onto his hand.

Nick Johnson, USGS research ecologist and lead author of the study, holds an invasive sea lamprey captured in Michigan’s Inland Waterway, where the sterilization study was conducted. The sea lamprey is a fertile male, which was removed from the waterway prior to spawning. Photo credit: Andrea Miehls, Great Lakes Fishery Commission.

Sea lampreys are parasitic fish native to the Atlantic Ocean, which were first found in the Great Lakes in the mid-1800s. Each sea lamprey is capable of killing up to 40 pounds of fish during its parasitic stage. Because of the considerable harm that sea lampreys cause to economically valuable fish, Great Lakes sea lampreys have been controlled since the 1950s. The two primary control methods are lampricides and barriers to block the migration of spawning adults. Together, these methods have yielded a 90% reduction in sea lamprey populations since their historic highs in most areas of the Great Lakes, distinguishing the Great Lakes sea lamprey control program as one of the best in the world for an invasive, vertebrate species.

Though Great Lakes sea lamprey populations have been significantly reduced, there are many locations where implementation of traditional control methods is challenging or impractical due to physical, biological, chemical, or social reasons. Consequently, a suite of supplemental control methods are being evaluated in a multi-year, multinational initiative called SUPCON, funded by the Commission and Great Lakes Restoration Initiative. SUPCON is an integrated approach which uses an array of devices and techniques catered to the unique conditions of streams where sea lampreys spawn.

Six sea lampreys cluster together in the corner of an aquarium. Three sea lampreys are suctioned onto the glass, showing circular mouths filled with nearly 150 teeth. The profile of one sea lamprey is visible, showing a small eye and seven gill pores (openings). Two additional sea lampreys rest with their mouths partially closed.

Adult sea lampreys showing their toothy mouths which are used to suction onto fish and feed off the body fluids. Photo credit: Andrea Miehls, Great Lakes Fishery Commission.

One supplemental control method being tested by the SUPCON initiative is the release of sterilized adult male sea lampreys. In the study, sterilized male sea lampreys were released in Michigan’s Inland Waterway—a nearly 40-mile chain of rivers and lakes in the Northern Lower Peninsula that contains a landlocked population of sea lampreys. Sea lampreys likely established in this system due to a past breach of the lock and dam downstream on the Cheboygan River, a tributary to Lake Huron into which the Inland Waterway flows.

Sterilized male sea lampreys were released prior to the spawning season for five years (2017-2022 except for 2020 during the COVID-19 pandemic). Importantly, it should be noted that spawning sea lampreys no longer feed on fish. Instead, sterilized males spawn and then die shortly after. Though sterile, these males still behave like fertile males, including building nests in streams, attracting females to the nests, and releasing gametes in attempts to fertilize eggs. However, the eggs fail to develop, causing the fertile females to waste their reproductive effort.

A photo of a rocky river bottom. Among about a dozen rocks are grains of sand with small white spheres nestled in the interstitial spaces. The spheres are sea lamprey eggs.

Sea lamprey eggs—the small white spheres—nestled among sand and rocks in a spawning stream. Photo credit: Andrea Miehls, Great Lakes Fishery Commission.

"Like secret agents, sterile male sea lampreys blend into their social environments, thinking, moving, and acting like fertile male sea lampreys, yet the outcome of their spawning actions benefit sea lamprey control," said Nick Johnson, USGS research ecologist and lead author of the study.

Key to this research was the ability to overwhelm sea lamprey spawning populations in the Inland Waterway with sterilized males. "Our research team used a ratio of 35:1 sterile-to-fertile males. With this onslaught of sterile males, successful reproduction was suppressed to a small fraction of what it would be otherwise,” Johnson described. “The number of viable eggs in study streams decreased by 83-99% during the years sterile males were released."

"Though the landlocked population of sea lampreys in the Inland Waterway was an ideal location to test the efficacy of the sterile male technique, it’s not the only location where the method could be used," stated Johnson. According to the results of the research, sea lamprey control could be aided by the release of sterilized males in as many as 30% of streams where sea lampreys are found, strengthening the ability to keep this harmful invasive species in check.

A thin, brown creature that resembles an earth worm rests in a small metal basket. The creature is a larval sea lamprey.]

Lampricides—one of the primary methods used to control Great Lakes sea lampreys—target the larval life stage of sea lampreys (pictured here). Through the SUPCON initiative, researchers have shown that supplemental control methods, including the release of sterilized male sea lampreys, can suppress reproduction substantially. Photo credit: Andrea Miehls, Great Lakes Fishery Commission.

"Importantly, the release of sterilized males, and the broader SUPCON initiative, would be complementary approaches to traditional sea lamprey control methods," explained Ethan Baker, chair of the Great Lakes Fishery Commission. "Lampricides and barriers are highly effective at controlling abundant, dense populations of sea lampreys. As sea lamprey population sizes decrease through effective control, supplemental methods—such as release of sterile males—may result in further reductions."

"At the end of the day, vibrant fisheries, the valuable jobs that fisheries provide, and the health and prosperity of the Great Lakes are what SUPCON and the sea lamprey control program are implemented to protect," concluded Baker. "Eight states, one province, multiple tribes and First Nations, and millions of people call the Great Lakes home. Sea lamprey control, and the important scientific research conducted through SUPCON, protect this multinational treasure."

Reference:

Johnson, N.S., Lewandoski, S.A., Jubar, A.K., Symbal, M.J. Solomon, B.M., Bravener, G.A., Barber, J.M., Siefkes, M.J. 2024. A decade-long study demonstrates that a population of invasive sea lamprey (Petromyzon marinus) can be controlled by introducing sterilized males. Scientific Reports. 14: 12689. https://doi.org/10.1038/s41598-024-61460-1.

Read more Pulse on Science: Project Spotlights