Sea Lamprey

Other names for the sea lamprey: lamprey eel, stone sucker, nannie nine eyes (UK); Danish: havlampret; Dutch: zeeprik; Finnish: merinahkiainen; French: lamproie marine; Italian: lamprea di mar; Norwegian: havnioye; Portuguese: lampreia do mar; Russian: morskaja minoja; Spanish: lamprea de mar.

Overview

Lampreys are one of two groups of jawless fish (the other being hagfish), which are the most primitive true vertebrates. They are members of the Petromyzontidae family. Jawless fish are fishlike vertebrates that resemble eels in form, with a cartilaginous or fibrous skeleton that has no bones. They have no paired limbs and no developed jaws or bony teeth. Their extremely slimy skin lacks scales. Fossils of lampreys have been dated back 280 million years.

The jawless, eel-like lampreys are just as ugly as their hagfish (see) cousins in form and feeding habits; they differ in other respects, however. Hagfish are strictly marine, whereas lampreys are either totally freshwater inhabitants or, if they live in the sea, they return to freshwater rivers to spawn.

Lampreys have a large sucking disk for a mouth and a well-developed olfactory system. The mouth is filled with horny, sharp teeth that surround a filelike tongue. A lamprey’s body has smooth, scaleless skin, two dorsal fins, no lateral line, no vertebrae, no swim bladder, and no paired fins. Lampreys have no prominent barbels on their snout; their eyes are well developed in the adult and visible externally; there are seven external gill openings on each side; and the nasal opening is on the upper part of the head.

Whereas hagfish scavenge dead or dying fish and secure their nourishment by entering the body cavities of their victims, literally consuming them from inside outward, lampreys are usually parasitic. The lamprey attaches itself to the side of a live fish by using its suctorial mouth; then, by means of its horny teeth, it rasps through the victim’s skin and scales and sucks the blood and body juices. The lamprey’s mouth glands produce anticoagulating secretions, thereby assisting the flow of blood. After exhausting the blood supply of its weakened or dying host, the lamprey seeks another fish to attack.

There are reportedly 31 species of lampreys worldwide. Not all are parasitic, however. Sixteen are small, inconspicuous, nonparasitic filter feeders in freshwater streams. Of the parasitic species, nine are anadromous, living as adults in the ocean and returning to freshwater to spawn. Most parasitic types attain a length of roughly 12 inches. The marine, or sea, lampreys (Petromyzon marinus), are the largest, some capable of reaching a maximum length of 36 inches.

Lampreys spawn in the spring. They ascend streams where the bottom is stony or pebbly and build shallow depressions by moving stones with the aid of their suctorial mouths. Usually, the male and female cooperate in constructing the nest. When ready to spawn, the pair stir up the sand with vigorous body movements as the milt and eggs are deposited at the same time. The eggs stick to particles of sand and sink to the bottom of the nest. The pair then separate and begin another nest directly above the first, thereby loosening more sand and pebbles, which flow down with the current and cover the eggs. The procedure is repeated at short intervals until spawning is completed. The adults die after spawning.

After a period of several days, depending on the species and water temperature, the young appear and drift downstream until they are deposited in a quiet stretch of water where they settle down and burrow into the bottom to spend several years as larvae (called ammocetes). In this stage, they feed on materials strained from the bottom ooze. When they reach a few inches in length (this varies with the species), the ammocetes transform during late summer or fall into adultlike lampreys, complete with a sucking disk and circular rows of horny teeth.

The sea lamprey is most notorious as a despoiler of valued sport and commercial fish. It ranges the eastern Atlantic from Iceland and northern Europe (including the North Sea and the Baltic, western Mediterranean, and Adriatic Seas) to northern Africa. It ranges the western Atlantic from southern Greenland, Labrador, and the Gulf of St. Lawrence south to the Gulf of Mexico in Florida. It is landlocked in the Great Lakes, the Finger Lakes, Oneida Lake, and Lake Champlain. It breeds exclusively in freshwater.

Young lampreys, when in saltwater or en route to saltwater, are white underneath and blackish blue, silvery, or lead-colored above. Large specimens approaching maturity are usually mottled brown or dressed in different shades of yellow brown and various hues of green, red, or blue. Sometimes they appear black when the dark patches blend with each other. The ventral surface may be white, grayish, or a lighter shade of the ground color of the dorsal surface. Colors intensify during the breeding season.

Mature sea lampreys are from 2 to 21/2 feet long. The maximum recorded length is nearly 4 feet, and the maximum weight 5.4 pounds. Reproductive activity is the same as in other lampreys. A single female may contain 236,000 small and spherical eggs.

Little is known of lamprey habits in the sea, except that they are extremely aggressive in their attacks on other fish and are capable of swift travel by body undulations similar to that of an eel. Lampreys do not take the angler’s lure or baits but may be accidentally caught in freshwater; they are often seen by trout anglers in shallow water, and are sometimes attached to the bodies of trout or salmon that are caught by anglers. Although lampreys are usually close to land during their stay in the sea, they sometimes stray far offshore to water hundreds of fathoms deep. The sea lamprey is tolerant of a wide range of temperatures and water salinities, ranging from freshwater to that of full oceanic saltiness.

Sea lampreys were considered a delicacy in Europe during the Middle Ages. Also, at one time, large numbers were caught for human consumption in New England, especially in the Connecticut and Merrimack Rivers. Today a few are eaten as table fish, but in general the only value the lamprey has is in its larval form as a bait for anglers.

Commonly, but erroneously, lampreys are known or referred to as “lamprey eels.” They are not true eels (see) of the family Anguillidae. For easy differentiation, eels possess jaws and pectoral fins; these are lacking in the lamprey.

Sea Lampreys in the Great Lakes

A lake trout from Lake Michigan bears a scar made by a lamprey.

Several different types of native lampreys (including the silver lamprey, the American brook lamprey, and the northern brook lamprey) exist in the Great Lakes, but the exotic sea lamprey (Petromyzon marinus) is far larger and more predaceous than native lampreys. None of the Great Lakes lampreys have traditionally had any economic value.

Sea lampreys are native to the Atlantic Ocean and Lake Ontario but not to the upper Great Lakes. Sea lampreys entered the Great Lakes system in the 1800s through man-made locks and shipping canals. Prior to the opening of the Welland Canal in 1829, and prior to its modification in 1919, Niagara Falls served as a natural barrier to keep sea lampreys out of the upper Great Lakes.

Sea lampreys were first observed in Lake Ontario in the 1830s. They did not invade Lake Erie prior to the improvements of the Welland Canal in 1919; sea lampreys were first observed in Lake Erie in 1921. After spreading into Lake Erie, sea lampreys moved rapidly to the other Great Lakes, appearing in Lake St. Clair in 1934, Lake Michigan in 1936, Lake Huron in 1937, and Lake Superior in 1938. By the late 1940s, sea lamprey populations had exploded in all of the upper Great Lakes, causing severe damage to lake trout and other critical fish species.

Sea lampreys attach to fish with their ******* disk and sharp teeth, rasp through scales and skin, and feed on the fish’s body fluids, often killing the fish. During its life as a parasite, each sea lamprey can kill 40 or more pounds of fish. Sea lampreys are so destructive that under some conditions, only one out of seven fish attacked by a sea lamprey will survive.

Of the 5,747 streams and tributaries of the Great Lakes, 433 are known to produce sea lampreys. Adult sea lampreys move into gravel areas of tributary streams during spring and early summer. They build nests and lay eggs before dying. After the eggs hatch, small, wormlike larvae are swept downstream from the nest and burrow into sand and silt. The larvae feed on bottom debris and algae carried to them by stream currents. During this stage, which can range from 3 to 17 years, larvae grow to about 6 inches. After the larval life stage, sea lampreys enter their parasitic phase and migrate into the open waters of the Great Lakes. Sea lampreys spend the next 12 to 20 months there (not migrating to saltwater) feeding on fish. The sea lamprey’s life cycle, from egg to adult, averages about 6 years, and may last as long as 20 years.

Sea lampreys have had an enormous negative impact on the Great Lakes fishery. Because they did not evolve with naturally occurring Great Lakes fish species, sea lampreys’ aggressive, predacious behavior gave them a strong advantage over native fish. Sea lampreys prey on all species of large Great Lakes fish such as lake trout, salmon, rainbow trout (steelhead), whitefish, chub, burbot, walleye, and catfish.

Sea lampreys were a major cause of the collapse of lake trout, whitefish, and chub populations in the Great Lakes during the 1940s and 1950s. These fish were the mainstay of a vibrant and important fishery. Before the sea lamprey’s spread, the United States and Canada harvested roughly 15 million pounds of lake trout in the upper Great Lakes each year. By the early 1960s, the catch was only about 300,000 pounds. In Lake Huron, the catch fell from 3.4 million pounds in 1937 to almost nothing in 1947. The catch in Lake Michigan dropped from 5.5 million pounds in 1946 to 402 pounds by 1953. The Lake Superior catch dropped from an average of 4.5 million pounds to 368,000 pounds in 1961. During the time of highest sea lamprey abundance, up to 85 percent of fish somehow not killed by sea lampreys exhibited sea lamprey wounds. The once thriving fisheries were devastated.

In 1958, scientists discovered that TFM (3-trifluoromethyl-4-nitrophenol) was selectively effective in controlling sea lampreys without signi-ficantly impacting other species. Since its discovery, TFM has been used to suppress populations of sea lampreys in the Great Lakes (and also in other areas) by killing their larvae. As a result, sea lamprey populations in the Great Lakes have been reduced by 90 percent from their historic high numbers of the 1940s and 1950s. Decades of exhaustive tests have shown that at the dose needed to kill sea lampreys, TFM is nontoxic or has minimal effects on aquatic plants, fish, and other aquatic organisms, and is nontoxic to humans and other animals.

Despite this success, due to the high cost of TFM and in response to concerns about the use of chemicals, the Great Lakes Fishery Commission and its agents are reducing reliance on the lampricide by 50 percent by the year 2001. The lampricide is being applied more selectively, and alternative control methods, such as traps, barriers, and sterile-male release, are being employed.