As animals swim, they push and pull on the surrounding water. This creates regions of high and low pressure around their body which can help move them along. Most animals — including humans — swim by pushing on water.
This generates positive pressure, which propels them forwards. But limbless lampreys also create little whirlpools — vortices of negative pressure — in front of their body as they snake their way through water. Did the power come from the front half of the animal — in the muscles behind the head — or was the whole body involved? These semi-paralysed lampreys could swim, but their bottom half followed passively. In their native Atlantic Ocean, thanks to co-evolution with fish there, sea lampreys are parasites that typically do not kill their host.
In the Great Lakes, where no such co-evolutionary link exists, sea lampreys act as predators, with each individual capable of killing up to 40 pounds more than 20 kilograms of fish over their month feeding period. Host fish in the Great Lakes are often unable to survive sea lamprey parasitism, either dying directly from an attack or from infections in the wound after an attack. Host fish that survive an attack often suffer from weight loss and a decline in health and condition.
The first recorded observation of a sea lamprey in the Great Lakes was in in Lake Ontario. Niagara Falls served as a natural barrier, confining sea lampreys to Lake Ontario and preventing them from entering the remaining four Great Lakes.
However, in the late s and early s, improvements to the Welland Canal, which bypasses Niagara Falls and provides a shipping connection between Lakes Ontario and Erie, allowed sea lampreys access to the rest of the Great Lakes.
Adults typically die within days after spawning. After larval lamprey ammocoetes hatch, they drift downstream to areas with slower water velocity and fine sand for them to burrow into. Ammocoetes will grow and live in riverbeds and streambeds for 2 to 7 years, where they mainly filter feed on algae.
The metamorphosis of Pacific lamprey from ammocoetes into macropthalmia juveniles occurs gradually over several months. This transformation typically begins in the summer and is completed by winter. Juvenile lampreys drift or swim downstream to the estuaries between late fall and spring. They mature into adults during this migration and when they reach the open ocean.
Adult Pacific lampreys are parasites: they use their sucker-like disc mouth to feed on a variety of marine and anadromous migrating to the ocean and back fish species.
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.
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. 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.
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