Sea Lamprey Biology
Sea Lamprey Control
What is a Sea Lamprey?
The sea lamprey (Petromyzon marinus) is one of 31 species of lamprey found throughout the world and one of four lamprey species found in the Lake Champlain Basin. Lamprey are eel-shaped fish with a skeleton made of cartilage, not bone. They belong to a relic (primitive) group of jawless fishes called Agnathans.
Juvenile parasitic sea lamprey are 6 to 24 inches in length with smooth, scaleless skin that is mottled grey/blue to black, darker on top and fading to a lighter colored belly. Adult sea lamprey, preparing to spawn, are 14 to 24 inches in length and exhibit mottled dark brown/black pigmentation. Sea lamprey have two separated fins on their back (dorsal fins) and suction disk mouth filled with small sharp, rasping teeth and a file-like tongue. The sea lamprey is a jawless parasite that feeds on the body fluids of fish.
Sea lamprey, like many salmon, are "diadromous". They spend the early stages of their life in streams and rivers. The middle stage of their life is spent in the saltwater of the ocean or in a large freshwater lake. Then they return as breeding adults to spawn in the freshwater streams and rivers, and die shortly after spawning. Sea lamprey in Lake Champlain take about six years to complete this life cycle.
Life Cycle - How does it live and breed?
The blind worm-like larval lamprey, known as ammocoetes [am-mah-seats], can grow up to 5 inches long. They hatch from eggs in gravel nests in tributaries and drift downstream with the current. When they locate suitable habitat - usually silt/sand stream bottoms and banks in slower moving stretches of water - they burrow in and take up residence, filter-feeding on algae, detritus and microscopic organisms and materials. In the Lake Champlain Basin this stage of the sea lamprey's life cycle usually lasts 3 to 4 years; in other waters lamprey spend up to 10 years in their larval form.
Sometime in mid to late summer of their third or fourth year the ammocoetes undergo a dramatic change in both form and function. They develop eyes and a suction disk mouth, and become a smaller version of the adult sea lamprey. Also during this stage their kidneys change to allow them to live in saltwater. Once the ammocoetes´ change is complete, the newly transformed sea lamprey, known as a transformer, leaves its burrow and moves downstream towards Lake Champlain. The sea lamprey is then ready to begin the next stage in its life as a parasite of fish. The juvenile sea lamprey move into deeper water and begin to seek host fish on which to feed.
The juvenile sea lamprey uses its suction disk mouth which is filled with small sharp, rasping teeth and a file-like tongue to attach to fish, puncture the skin, and drain the fish's body fluids. An anticoagulant in their saliva ensures that the blood of the host fish does not clot while the sea lamprey feed. Often the host fish die from loss of blood, or infections resulting from stress. Fish that survive sea lamprey attacks will have decreased reproduction. Sea lamprey in Lake Champlain prefer landlocked Atlantic salmon (salmon), lake trout and other trout species, due to their small scales and thin skin. The same native fish species prized by anglers, and that are such an important part of the natural ecosystem of the lake.
Sea lamprey also feed on other fish species, including lake whitefish, walleye, northern pike, burbot, and lake sturgeon. The lake sturgeon is listed as a threatened species in New York and an endangered species in Vermont and it is likely that sea lamprey are affecting their survival. Most sea lamprey hosts are native fish species that have been part of the Lake Champlain Basin ecosystem for thousands of years
Mortality and Wounding of Host Fish
Studies on the Great Lakes show a 40 to 60 percent mortality rate for fish attacked by sea lamprey. Other studies have found that a single sea lamprey can kill 40 or more pounds of fish during its life. Even when fish survive the attacks, the fish populations will decline as the fish expend more energy on healing than on producing eggs and mating.
During periods when sea lamprey are abundant in Lake Champlain, anglers often catch salmon and trout with wounds or lamprey attached. Frequently these fish have multiple wounds, multiple scars and/or multiple lamprey attached to them. These high wounding rates indicate that sea lamprey are having a significant impact on the lake trout and salmon populations. Angler catches of lake trout and salmon in Lake Champlain were found to be just a fraction of catches in similar lakes, despite intensive stocking efforts by fishery agencies. Sea lamprey were preventing the restoration of these native fish species to Lake Champlain.
In the spring, sexually mature adult sea lamprey migrate up tributaries to spawn. They locate spawning streams by following pheromones (naturally produced chemical attractants) released by ammocoetes living in those waters. A pair of male and female sea lamprey build a nest, called a redd, in a gravel stream bottom in section of flowing water. The female lays tens of thousands of eggs and the male fertilizes them, then having completed this act the sea lamprey die. The eggs lie in the small spaces between the gravel, and are provided oxygen by the flowing water. Weeks later the eggs hatch and the complex life cycle of the sea lamprey begins again.
Sea Lamprey in Lake Champlain
Prior to the 1800s native Atlantic salmon and lake trout were abundant in Lake Champlain. Early explorers and settlers reported salmon runs in the tributaries that were so abundant that "salmon were harvested by the wagon load with pitchforks." While not so graphic, historical accounts of large and plentiful lake trout were reported as well. However, by the mid 1800s over fishing, pollution and damming of tributaries had eliminated native salmon from Lake Champlain, and lake trout disappeared from the lake by 1900.
During the late 1800s and early 1900s numerous attempts were made to restock trout and salmon, but all failed. In the late 1950s and 1960s New York State began experimental stockings of lake trout and salmon with some limited success. It became clear that one of the factors limiting the success of stocking was parasitism by sea lamprey.
A non-native species?
The sea lamprey was first noted in Lake Champlain in 1929 by J.R. Greeley, who reported that sea lamprey were found in moderate numbers at that time. It is not clear if, or for how long, sea lamprey had existed in Lake Champlain prior to this time. Taking into account that salmon and trout were sought by both the native people and settlers as a source of food, and later for commercial purposes, coupled with the obvious signs of lamprey parasitism - wounds, scars and attached lamprey - the lack of mention of lamprey in the oral and written history is consistent with the position that sea lamprey may be a non-native invasive species.
If sea lamprey are invasive, they are thought to have entered Lake Champlain during the 1800s from the Hudson River Estuary through the Hudson/Champlain Canal or possibly from the St. Lawrence River through the Richelieu River - both the Hudson and the St. Lawrence Rivers empty into the Atlantic Ocean.
Or a native species?
Three recent genetic studies provided evidence to support the position that sea lamprey may be native to Lake Champlain and existed in the lake for around 10,000 years. If true, the lamprey may be having a detrimental impact on salmon and lake trout because the original Lake Champlain strains of these fish that may have evolved with the sea lamprey disappeared in the late 1800s.
Habitat degradation, water pollution, and dams on almost every tributary in the basin during the last two centuries may have kept lamprey numbers low. Recent improvements in habitat and water quality, along with the annual stocking of their preferred hosts, may be providing lamprey with a new opportunity to prosper. If native to Lake Champlain, sea lamprey either remained in the lake as a remnant population after the retreat of the "Champlain Sea" or migrated into the lake via the Richelieu River.
Does it matter?
Regardless of whether the sea lamprey is native or not, due to the severity of the impacts that sea lamprey currently have on the Lake Champlain fishery and ecosystem, and the social and economic impacts on the people who live in the Lake Champlain Basin, sea lamprey populations must be controlled to balance the Lake´s ecosystem and restore its world class fishery.
Other lamprey species
Three other lamprey species are found in the Lake Champlain Basin. Two species - the northern brook lamprey and the American brook lamprey - are non-parasitic filter feeders similar in size and habits to sea lamprey ammocoetes. The silver lamprey is parasitic, but does not have the negative impact on the Lake Champlain fish community that the sea lamprey does, due to its smaller size and fewer numbers.
Sea lamprey are an ancient fish, with a complex life cycle and mouth parts that are well adapted for their parasitic life. The elimination of this species from Lake Champlain is neither desired nor possible. However, their population must be reduced to lessen their negative impacts on the Lake Champlain fishery to an acceptable level, to balance the Lake Champlain Basin ecosystem and its world class fishery.