The Lamprey: Vicious invader of the Great Lakes
By Robert A. Hedeen, Naturalist
The sea lamprey is the most primitive of all vertebrate animals (with backbones). This primeval creature is sometimes called the lamprey eel because of its superficial resemblance to a true eel, but this is a misnomer. The eel is a bona fide bony fish and much higher on the evolutionary scale. The lamprey does not have a bone in its body. Its primitive internal supporting structure is composed entirely of a rubbery tissue called cartilage. The body of the sea lamprey is smooth, shiny, and lacks scales. It may grow to a length of three feet, looks like a length of garden hose, and swims like a snake.
The sea lamprey normally lives in the north Atlantic and Pacific Oceans, but ascends to clear, fresh water streams to reproduce. After spawning, the adults die. A lamprey egg hatches into a juvenile called an ammocetes. This larval lamprey is blind and toothless and looks like a small worm. It lives in the sand and mud of the stream bottom for several years and then metamorphoses into an adult with eyes and teeth and then moves into the large body of water from whence its parents came.
The adults feed on large fish in a most vicious and sadistic way. Lampreys do not have jaws but, rather, have a round, suction cup-like mouth full of sharp, horny teeth that grow from the surface of the mouth. A rasp-like tongue is also laden with sharp teeth. An anatomical adaptation allows them to attach the sucking mouth firmly to a fish and bring in oxygenated water at the same time through external gill slits.
The sharp teeth on the tongue then go to work rasping away at the tissues of its unfortunate victim. When the predators appetite is appeased, it releases the suction and proceeds to digest its meal of fish blood and tissue. A large, round, gaping wound on the side of the victim usually insures its eventual death.
Sea lampreys gained access to the Great Lakes when the Welland Canal was dug in 1829 and a passage from Lake Ontario to Lake Erie was created. Recall, Lake Ontario is connected to the North Atlantic by the St. Lawrence Seaway. The canal circumvented Niagara Falls, and the heartland of North America was opened to sea-going vessels.
The lampreys that had previously been confined to Lake Ontario and the Atlantic quickly followed the ships into all parts of the Great Lakes System. Later generations of these pioneering lampreys no longer needed to return it the sea and, instead stayed in the lakes and fed upon large fish such as lake trout and whiting.
The affect was devastating. For example, between 1936 and 1948 the catch of lake trout from Lake Huron fell from 1,720,000 pounds to less than 5,000. By the 1950s most of the lake trout and walleyes in Erie, Huron, Michigan, and Superior, had been killed and commercial and sport fishing in these imposing bodies of water was a thing of the past.
With the large trout and walleyes almost nonexistent in the lakes, huge populations of alewives and other small prey fishes, on which the predators normally fed, resulted, and annual die offs of these species polluted the lakes and the shorelines. Unfortunately, Alewives are too small to interest the voracious lamprey and they escaped predation.
Biologists from state and federal agencies tried for years to devise a method of controlling lamprey populations. One promising means of control was to erect electric barriers across the mouths of the streams the adults entered to spawn. Though some measure of control was achieved with these electrically charged weirs or fences, they were hazardous, costly, and difficult to maintain. Then, researchers discovered a chemical called TFM which, when applied to the stream in which breeding occurred, killed the lampreys but did not harm other fish or aquatic life in the watercourse.
TFM, though expensive, proved to be a magic bullet, specific for lampreys, and its use caused a sharp decline in the number of lampreys in the lakes. By the mid 1960s the lamprey problem was so alleviated that lake trout, coho salmon, and other species could be planted and have a good chance to survive. Now salmon and trout fishing on the lakes is a thriving industry from the standpoints of both the sport and commercial fisherman.
The story of the invasion of the Great Lakes and the subsequent destruction of native species is just another example of what can occur when Man in his infinite wisdom alters natural ecosystems that have delicately evolved over untold thousands of years. Before an alien species is introduced into a biologically balanced system, many things must be taken into consideration. We were recently reminded of this when we read about the introduction of the Asian, predatory snakehead fish into some waters of this country where it has no natural enemies and can rapidly reproduce and eventually eliminate native species. Constant vigilance is required.
At one time sea lampreys were used as food in New England, and smoked lamper eels were relished as a delicacy. Too bad the taste for lampreys did not develop in the region of the Great Lakes.