Stifling a sea lamprey comeback

The Great Lakes are one of Michigan’s greatest assets. They attract millions of local residents and visitors each year, many of whom partake in or benefit from its world-class fishery.

But few know the real story of the management that keeps the fragile fishery intact and benefitting the public. Without intense annual intervention by fisheries professionals, the Great Lakes fishery as we know it – generating $5.1 billion a year in economic activity – would collapse in less than a decade. Why is that?

The Welland Canal bypassing Niagara Falls forever changed fisheries management in the Great Lakes by allowing passage of organisms from the Atlantic Ocean. Sea lamprey used that connection, spreading throughout the lakes nearly 100 years ago, and are still at large.

Sea lamprey have the potential to devastate the Great Lakes fishery. It takes dedicated teamwork by multiple state, tribal, federal, and Canadian agencies to keep this invasive species under control.

While the sea lamprey resembles an eel, it is a jawless, parasitic fish that feeds on other fish species. One sea lamprey can kill up to 40 pounds of fish during its life. After colonizing the Great Lakes, sea lamprey nearly wiped out lake trout, causing their catches to decline by 98%. Similar destruction has occurred to other species.

It took a coordinated, binational effort to find a solution, made possible by the formation of the Great Lakes Fishery Commission (GLFC) in 1955 – the treaty organization responsible for sea lamprey control.

A chemical selectively toxic to sea lamprey (lampricide) was discovered that takes advantage of a vulnerability. Like many species that live in the Great Lakes, sea lamprey are migratory, spawning in rivers and streams that are connected to the Great Lakes. Larval sea lamprey bury themselves in the soft sediment of a streambed for three to six years before changing into parasitic juveniles and swimming downstream. Entering the Great Lakes, they begin to parasitize fish and rapidly grow for 12-18 months before returning to streams to spawn and then die. When they are confined to rivers as larvae, they are vulnerable to lampricide treatments that dramatically reduce their populations.

The peak of the sea lamprey invasion in the mid-20th century collapsed the Great Lakes fishery, but hope for restoration was found once sea lamprey control began. Decades of focused work by professionals with support from the public, as well as consistent federal funding and agency support, has led to the rebuilding of the Great Lakes fishery that continues to face challenges from the cumulative impact of a multitude of invasive species now prevalent in the Great Lakes.

Each lake is different in its physical characteristics and ecology, but recovery of fish populations has occurred in each. In a 2024 milestone, Lake Superior’s interjurisdictional management committee declared lake trout to be “fully restored” in the lake – a success story impossible without effective sea lamprey control.

Current management practices are highly effective at control but cannot eradicate sea lamprey, so control must be continued every year to keep their population in check. This was confirmed during the 2020-21 Covid pandemic, when sea lamprey control did not occur in Lake Ontario because of travel restrictions.

Sea lamprey numbers and the mortality rates of fish they attacked increased dramatically when the parasitic juveniles grown from larvae not treated in those missed years arrived in the Great Lakes. The economic loss associated with this two-year pause in Lake Ontario was conservatively estimated to be nearly $90 million. Across all the Great Lakes, the economic loss associated with reduced control during the pandemic was nearly $270 million. The lesson was learned: Sea lamprey control mustn’t stop. It’s just as important as ever.

That’s why the control program spends substantial time and money researching additional ways to control sea lamprey. Exploring new techniques to manage sea lamprey is just as important as continuing the current, effective control methods and could lead to advances. In human medicine, bacteria can develop resistance that makes antibiotics less effective as treatments for illness. The same risk exists if sea lamprey were to evolve resistance to lampricide. The threat to the Great Lakes fishery is real if control is no longer effective.

The Great Lakes fishery exists in a fragile balance that underscores the importance of ongoing federal, state, and local support for the agencies and partnerships that control the invasive sea lamprey and support this critical natural resource.

Funding to ensure the sea lamprey control program can effectively carry out its mission is vital to ensuring continuation of the benefits that the Great Lakes fishery brings to Michigan residents, visitors, and the health of the aquatic environment.