ANN ARBOR, Mich. —Travel restrictions associated with the COVID-19 pandemic caused a major pause in critical work to control destructive, invasive sea lampreys in the Great Lakes, according to the Great Lakes Fisheries Commission.
Now a study published in March in the journal Fisheries concludes that sea lamprey populations — and fish wounding — skyrocketed during the pause.
Sea lampreys are parasitic fish native to the Atlantic Ocean. Their populations spread into the Great Lakes in the mid-1800s and early 1900s, where they caused considerable harm to native fish, such as lake trout, whitefish, ciscoes, and walleye.
"Sea lampreys feed by suctioning onto fish, using their tongues to rasp a hole through the skin, and consuming the blood and juices that flow out," the fisheries commission notes.
Each sea lamprey is capable of killing up to 40 pounds of fish during its parasitic stage.
When populations peaked at nearly 2.5 million in the mid-1900s, sea lampreys were killing a 100 million pounds of fish each year.
Efforts to control Great Lakes sea lampreys began in the 1950s, eventually causing populations to plummet to only about 10 per cent of their historic highs.
$5-billion economic output
The fisheries commission says Great Lakes fisheries generate $5.1 billion in economic output each year and directly support 35,000 jobs in addition to hundreds of thousands of jobs related to tourism, navigation, and more.
Sea lamprey control is coordinated by the Great Lakes Fishery Commission in partnership with the U.S. Fish and Wildlife Service and Fisheries and Oceans Canada, with science support from the U.S. Geological Survey (USGS).
The fisheries commission says the sea lamprey control program is considered one of the most cost-effective and successful invasive species suppression programs in the world and an essential component of protecting economically valuable Great Lakes fisheries.
But the COVID-19 pandemic threatened that success.
With limitations on travel due to safety concerns in place during 2020-2021 for the primarily Michigan and Ontario-based control crews, "control efforts were greatly reduced", particularly at the geographic extremes of Lake Ontario and Lake Superior.
What followed was a unique situation that allowed scientists to answer key questions.
Are invasive sea lampreys still a threat to Great Lakes fisheries? Is sea lamprey control still necessary to suppress their populations?
A team of 15 scientists from six agencies found that the answer to both questions is yes.
The research team found that reductions in lampricide applications — a pesticide highly selective to lampreys — corresponded to a rapid increase in sea lamprey abundance.
In Lake Ontario, sea lamprey population sizes increased over an order of magnitude of 10 times.
“Like a coiled spring, sea lamprey populations bounced back quickly when control was relaxed,” said Dr. Ben Marcy-Quay, fish biologist with the U.S. Geological Survey, and lead author of the study.
Coho salmon
“We also looked at multiple fish species in Lake Ontario, including lake trout, Chinook salmon, coho salmon, and steelhead/rainbow trout, and found a substantially greater rate of sea lamprey wounds on fish following reduced treatment effort,” said Marcy-Quay.
“Wounding on Chinook and coho salmon, specifically, increased over 10-fold. Our findings support observations by the fishing public and fishery managers of fish riddled with sea lamprey wounds, some containing three or more wounds per fish.”
“When life gives you lemons, make lemonade,” quipped Dr. Nick Johnson, research ecologist with the U.S. Geological Survey, and co-author on the study.
“When the COVID-19 pandemic significantly reduced sea lamprey control for two years, our research team made the most of the situation by using it as an unplanned experiment to learn valuable information — nearly impossible to obtain otherwise — about the current impact of control on sea lamprey populations.”
“Ongoing, consistent sea lamprey control is critically important for preventing damage to Great Lakes fish by invasive sea lampreys,” said Ethan Baker, chair of the Great Lakes Fishery Commission and mayor of Troy, Mich.
“This research shows that sea lamprey control must continue each year to keep populations of this harmful invasive species in check. If we take our foot off the gas, even for a short while, sea lamprey populations will increase rapidly and cause considerable damage to fish.”
Baker concluded, “Fishing is a way of life in the Great Lakes region. The health and happiness of millions of people are tied to the lakes. Sea lamprey control is critical to safeguard the prosperity of the region.”
This research was conducted in collaboration by the U.S. Geological Survey, Fisheries and Oceans Canada, New York State Department of Environmental Conservation, U.S. Fish and Wildlife Service, Ontario Ministry of Natural Resources, and Great Lakes Fishery Commission.