Lake Michigan is home to an array of fascinating species, but there is one fish that strikes fear into the hearts of those who encounter it – the sea lamprey. With its eel-like body, circular mouth filled with sharp, jagged teeth, and reputation as a parasitic predator, the sea lamprey has earned a fearsome reputation as the “vampire of the Great Lakes.” However, while its appearance and behavior may seem terrifying, this invasive species poses no real threat to humans. Despite that, sea lampreys are a significant problem for Lake Michigan’s ecosystem, and efforts to control their population are ongoing. In this blog post, we’ll explore the life cycle of the sea lamprey, their invasive impact on Lake Michigan, and what is being done to manage their population.
The Life Cycle of the Sea Lamprey
Sea lampreys (Petromyzon marinus) have a unique and complex life cycle that contributes to their success as invasive species in Lake Michigan. They are native to the Atlantic Ocean, where they evolved as parasites, feeding on the blood and bodily fluids of other fish without typically killing them. In the ocean, the fish they parasitize have evolved to survive these attacks. However, when the sea lamprey made its way into the Great Lakes, it found a new home with a population of fish that had no natural defenses against their parasitic feeding habits.
The sea lamprey begins its life in freshwater rivers and streams. After hatching from eggs, the larvae, known as ammocoetes, spend several years burrowed in the sediment of streams, feeding on microscopic organisms. This stage of their life can last from three to ten years. Once they reach a certain size, the larvae undergo a dramatic transformation into the parasitic adult stage. As adults, they migrate to larger bodies of water, such as Lake Michigan, where they seek out fish to feed on.
The adult sea lamprey uses its sucker-like mouth, filled with sharp teeth, to attach itself to fish. It then rasps through the fish’s scales and skin with its rough tongue, feeding on the fish’s blood and body fluids. An enzyme in the lamprey’s saliva prevents the blood from clotting, which can cause the fish to bleed out or die from infection. Adult sea lampreys can live for about a year and are capable of killing up to 40 pounds of fish during that time.
Sea Lampreys: A Destructive Invasive Species

Photo Credit: Great Lakes Fishery Commission, Public domain, via Wikimedia Commons
Sea lampreys are not native to the Great Lakes, but their presence has had a catastrophic impact on native fish populations, particularly in Lake Michigan. Sea lampreys first entered the Great Lakes in the 19th century through man-made canals, such as the Welland Canal, which bypassed natural barriers like Niagara Falls. Once in the Great Lakes, sea lampreys found ideal conditions for spawning and feeding, leading to a population explosion.
The introduction of sea lampreys devastated Lake Michigan’s fish populations, particularly lake trout, which had no natural defenses against this new predator. By the 1950s, sea lampreys had nearly wiped out lake trout populations in Lake Michigan and Lake Huron. Other native fish species, such as whitefish and cisco, also suffered from the lampreys’ parasitic feeding.
The decline of these fish populations had a ripple effect throughout the ecosystem and the economy. Lake trout, for example, were a keystone species in the Great Lakes, playing a critical role in maintaining the balance of the food web. With the lake trout population decimated, other species began to proliferate unchecked, leading to further imbalances. Additionally, the collapse of the fishery industry due to the sea lamprey invasion caused economic hardship for communities that depended on fishing.
Scary Appearance, But Not Dangerous to Humans
One of the reasons sea lampreys are so feared is their appearance. These fish resemble something out of a nightmare, with their eel-like bodies, large round mouths, and rows of sharp, curved teeth. Their suction-cup mouths allow them to attach to prey, while their tongue, covered in sharp, rasping ridges, tears through the skin and scales of fish to feed.
It’s no wonder that people find the sea lamprey frightening. However, it’s important to note that while sea lampreys are parasitic predators to fish, they do not pose a serious threat to humans. The sea lamprey’s diet consists exclusively of cold-blooded organisms, meaning they have no interest in feeding on warm-blooded humans. Though there have been occasional reports of sea lampreys accidentally latching onto swimmers, these incidents are rare, and the bites are not life-threatening.
There is no documented evidence that sea lampreys in Lake Michigan intentionally target humans. Most of the time, sea lampreys are too focused on finding suitable fish hosts to notice swimmers. While their bites can be painful, they pose no long-term danger to people, and there have been next to no verified cases of sea lampreys causing serious harm to humans in Lake Michigan.
Why We Don’t Want Sea Lampreys in Lake Michigan
While sea lampreys may not be dangerous to humans, their presence in Lake Michigan is a significant problem for the ecosystem. Sea lampreys are extremely efficient predators, and their feeding can lead to the death of large numbers of fish. This not only affects the fish populations but also disrupts the entire food chain. Native species that once thrived in Lake Michigan have been struggling to recover ever since the sea lamprey invasion.
In addition to their devastating impact on native fish populations, sea lampreys reproduce prolifically. A single female sea lamprey can lay up to 100,000 eggs in a single spawning season. The combination of their high reproductive rate and lack of natural predators in the Great Lakes has allowed their populations to grow rapidly, making them difficult to control.
Controlling the Sea Lamprey Population
Given the destructive impact sea lampreys have had on Lake Michigan and the other Great Lakes, controlling their population has been a top priority for wildlife management organizations. The Great Lakes Fishery Commission (GLFC) has been spearheading efforts to reduce sea lamprey numbers and mitigate their impact on the ecosystem.
One of the primary methods used to control sea lamprey populations is the application of lampricides, which are chemicals designed to target and kill sea lamprey larvae before they can mature into parasitic adults. These lampricides are applied to streams and rivers where sea lampreys spawn, significantly reducing the number of lampreys that survive to adulthood. The most commonly used lampricides are TFM (3-trifluoromethyl-4-nitrophenol) and Bayluscide, both of which have been found to be highly effective at targeting lamprey larvae while minimizing harm to other species.
In addition to lampricides, physical barriers have been constructed in rivers and streams to prevent sea lampreys from migrating upstream to spawn. These barriers are designed to allow native fish to pass while blocking the movement of sea lampreys. Projects like FishPass, an experimental system that tests technologies for selectively allowing desirable fish species to pass while blocking invasive species, are also helping to control the sea lamprey population.
Trapping adult sea lampreys during their migration to spawning grounds is another method used to reduce their numbers. These traps target the adults as they move upstream, capturing them before they have a chance to reproduce. Combined with other control methods, trapping has proven to be an effective tool in managing sea lamprey populations.
Conclusion
The sea lamprey may look like the scariest fish in Lake Michigan, but its fearsome appearance is not indicative of a threat to humans. Though they are capable of causing significant damage to fish populations, sea lampreys are not dangerous to swimmers. Nonetheless, their presence in Lake Michigan has had a devastating effect on the ecosystem, particularly for native fish species like lake trout. Controlling the sea lamprey population remains a priority, and ongoing efforts by organizations like the Great Lakes Fishery Commission are crucial to protecting the health of the Great Lakes.
Through the use of lampricides, barriers, and trapping, significant progress has been made in reducing the sea lamprey population. However, continued vigilance is necessary to prevent this invasive species from once again wreaking havoc on the fishery. While the sea lamprey may not be the terrifying predator of humans that it appears to be, its impact on the Great Lakes is real, and efforts to control its population are essential for preserving the balance of Lake Michigan’s ecosystem.
Image Credit:
NOAA Great Lakes Environmental Research Laboratory via Flickrr