Since the 1950s, the Great Lakes Fishery Commission has used a lampricide to control the population of invasive sea lamprey. But recent research notes the amount needed to eliminate larval lamprey changes based on water temperatures, which may pose a problem in the future.
The lampricide is called TFM for the trifluoromethyl part of the compound. TFM is toxic to more species than just sea lamprey, including native fish. But because lamprey are worse at processing the substance, the other species typically survive treatments that kill lamprey larvae, according to Hugo Flávio, a researcher at Wilfrid Laurier University in Ontario.
Flávio presented on this topic at the Joint Aquatic Sciences Meeting held in May 2022 in Grand Rapids, Michigan. Prior to TFM’s usage, sea lamprey had a devastating effect on Great Lakes fish populations, killing native species that aren’t adapted to surviving their attacks. The lampricide eliminates around 95 to 99 percent of all sea lamprey in the Great Lakes, keeping the population in check and ensuring other fish species can survive and thrive.
Flávio said research dating to the 1960s found that TFM’s effectiveness appeared to wane during summer months unless applied in higher concentrations. In recent years, that’s led to research looking at how warming waters under climate change may affect its use.
While factors like alkalinity also affect how well TFM works, a study published in 2021 affirmed that water temperature was the primary driver impacting the variation in TFM effectiveness over different seasons, he said. That led Flávio to begin looking at the temperature range where larval sea lamprey are best positioned to survive TFM treatments.
As a parasitic species with a native range spanning much of the North Atlantic Ocean and connecting freshwaters, sea lamprey have a variety of water temperatures that they can live in, Flávio said. In contrast, native species in the Great Lakes have a smaller range and have evolved to specific temperatures historically found in those waters.
“We know the Great Lakes are warming up, and we also know the sea lamprey are responding to this warming,” Flávio said. “Spawning season, for example, is getting earlier because of the spring temperatures.”
Flávio’s research involved exposing larval sea lamprey to different water temperatures and activity levels to determine their optimal range for survival —and to survive standard lampricide treatments. While sea lamprey die at around 31 to 33 degrees Celsius (about 28 degrees Fahrenheit), there was little information on what temperatures they thrive in below that point.
Flávio designed a series of chambers to contain larval sea lamprey at a given water temperature, measuring their oxygen usage while they were at rest and when active. The rates that sea lamprey use oxygen closely match the effectiveness of TFM at different temperatures, making it a useful measuring stick, he explained.
This research affirms previous studies that showed sea lamprey have a high tolerance for warm temperatures, he said. “Larval sea lamprey show a wide thermal range, indicating that their tolerance to TFM will likely continue to increase as water temperatures in the Great Lakes rise.”
While this information is useful for updating TFM treatment tables to account for higher temperatures, other species also must be considered, Flávio said. Students at the university are researching how rising temperatures and a required increase in TFM concentrations would impact native species.
“We’re worried that while the lamprey are getting better (at surviving lampricide treatments), the native species might approach that inflection point where things break down, and they become less tolerant to TFM.”
Flávio said reaching a point where TFM treatments would end up killing the species they’re designed to protect would lead to a “complicated standstill” in managing sea lamprey populations. While there are other methods to reduce populations, lampricide remains one of the best tools available to managers. Once more information is available on how native fish can handle TFM at higher temperatures, managers can begin to determine the best way to apply TFM in changing conditions.
Flávio said once that additional work is complete, he and the other researchers intend to formally publish their findings, ideally next year.
