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March 06, 2013

Great Lakes Invasives: Sea Lampreys

Sea lampreys, Petromyzon marinus, were the Great Lakes’ first notorious invasive species. Originally from the Atlantic Ocean, they entered the Great Lakes through water diversions built for ships to bypass Niagara Falls. Able to survive in both fresh and salt water, these primitive fish may look like eels to the untrained eye, but they’re closer to vampires as they feed on the blood of host fishes.

The sea lamprey has a multistage life cycle lasting several years. As a small harmless larva, a lamprey lives in a freshwater tributary, buried in the mud and feeding on microscopic materials. As it starts to develop into an adult, it migrates toward the open water of the Great Lakes.

An adult sea lamprey is long—about 2 feet—and lean, with mottled black or brown scales, seven pairs of gill openings and two dorsal fins. But its signature feature is a gaping, disk-shaped, sucking mouth filled with rings of sharp, hooked teeth that radiate out from a rasping tongue. Horrific as that image is, sea lampreys’ effect on Great Lakes fishes is much worse.

In open water, a lamprey attaches to the side of a fish with its suction-cup mouth. With its small teeth, it pierces and hooks onto the side of a host fish, and it uses its tongue to rasp through the skin to consume the blood. The lamprey’s saliva contains an anticoagulant to maintain the blood flow as it feeds. Over the course of a few hours, days, or weeks, it consumes its host’s body fluids, dropping off when it’s satisfied. While the lamprey doesn’t kill its host outright, the afflicted fish can be so weakened that it dies later. This parasitic stage lasts for about a year, until the sea lamprey travels back upstream to spawn. Soon after spawning, it dies.

Invasion and control

Invasive species are organisms outside of their native range that do economic or environmental harm. Sea lampreys are successful in the Great Lakes for several reasons: They lack natural predators, females spawn up to 70,000 eggs, and they are resilient and can survive in both fresh and salt water.

Sea lampreys most likely entered the Great Lakes shortly after improvements to the Welland Canal, between Lake Ontario and Lake Erie, were completed in 1919. The canal lets ocean-going cargo ships into the other Great Lakes from Ontario by bypassing Niagara Falls. Although it’s possible sea lampreys had already invaded Lake Ontario by way of the St. Lawrence River, the reconstruction of the canal was like opening the floodgates, and by 1939, sea lampreys were in all of the lakes. Lake trout, the main predatory fish species in the Great Lakes at the time, was their primary host species. Fewer than one in seven lake trout survive a lamprey attack. A combination of overfishing and then the introduction of the sea lamprey decimated lake trout populations, and the natural balance of the Great Lakes food web was dismantled.

Several control techniques were developed for sea lampreys, targeting the fish at different life stages. To destroy the larvae, a lampricide chemical is applied to infested streams and tributaries. The chemical disrupts the larval lampreys’ development but does not cause significant harm to other aquatic organisms. Another control technique uses barriers to block or catch adult lampreys swimming upstream to spawn. A program that releases sterilized male lampreys has proven to be successful in reducing populations.

“It costs around $18 million a year to keep their numbers under control,” says Dr. Philip Willink, Shedd Aquarium senior research biologist.

We may be controlling the sea lamprey population in the Great Lakes, but these vampires are here to stay. The lesson from the sea lamprey story is that the best protection against invasive species is prevention: Don’t let them get into the lakes in the first place.

Meet more invasive species as we continue our observance of National Invasive Species Awareness Week, through March 8.

Sam Bugg, Daniel P. Haerther Center for Conservation and Research

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