The Sea Lamprey: The Parasite That Collapsed the Great Lakes Trout Fishery

The sea lamprey may be America's first destructive invasive species. This primitive, parasitic fish from the Atlantic reached the Great Lakes in the 1830s, and within a century the lakes' trout fishery had collapsed — largely because of it.

An ancient design

The sea lamprey is one of the most primitive of all vertebrates, native to the northern and western Atlantic Ocean. Because of its shape it is sometimes called a "lamprey eel," which is inaccurate. Unlike bony fishes such as trout, cod and herring, lampreys have no scales, fins or gill covers. Like sharks, their skeletons are cartilage. They breathe through a row of seven pairs of tiny gill openings behind the mouth and eyes.

An efficient killer

What makes the sea lamprey so deadly to lake trout and other bony fishes is its mouth: a disc-shaped suction cup ringed with sharp, horny teeth. It latches onto a fish, then uses its rough tongue to rasp away the flesh and feed on the host's blood and body fluids. A single lamprey kills about 40 pounds of fish every year.

The invasion

Sea lampreys entered the Great Lakes in the 1830s through the Welland Canal, a key section of the St. Lawrence Seaway. Within a decade they had reached all five Great Lakes and were preying on commercially important fish — trout, whitefish, perch and sturgeon. Within a century, the trout fishery had collapsed.

Keeping them in check

Today the Great Lakes Fishery Commission coordinates sea lamprey control, carried out by the U.S. Fish and Wildlife Service and Fisheries and Oceans Canada:

• Barriers and traps in the streams that feed the lakes block lampreys moving upstream.
• Lampricides, special chemicals, target lamprey larvae but are harmless to other aquatic life.
• Scent. Sea lampreys communicate with odors, or pheromones, and scientists have recreated these odors to make control methods work better.

Sources

Based on "What is a sea lamprey?" from NOAA's National Ocean Service, reviewed for NOAA by Ted Lawrence, PhD, of the Great Lakes Fishery Commission; a work of the United States government in the public domain.