Introduction
The North America Great Lakes basin is the largest surface freshwater resource in the world, having formed approximately ten thousand years ago from glacier activity and supporting over 120 native fish species. They are a vital resource providing water for consumption, recreation, power, along with fisheries for harvest (US Fish & Wildlife Service, 2021). However, due to human activity during the 1800s and early 1900s, the Great Lakes have been invaded by numerous invasive (exotic organisms that cause harm to the surrounding environment) species with one of the most prominent being the invasive Sea Lamprey (Petromyzon marinus).
The Sea Lampreys are a parasitic jawless fish that are native to the Atlantic Ocean. During the 1800s they made their way into the inland Great Lakes basin via manmade locks, shipping canals, and ballast water as humans navigated the region. They were first observed in Lake Ontario during the 1830s, Niagara Falls was a natural barrier to their dispersal however the Welland Canal constructed in the early 1900s allowed them to access the other Great Lakes with being spotted in Lake Erie in 1921 and then the other lakes later (Sullivan et. al., 2003) (US Fish & Wildlife Service, 2021).
Their introduction caused major destruction to the Great Lakes ecosystem, significantly reducing native fish populations especially the Lake Trout fishery. With a little over 1% of surface water on Earth being freshwater, it is vital to protect and preserve the health of these vulnerable ecosystems for humans and fishes alike.
Sea Lamprey Lifecycle
The Sea Lamprey lifecycle despite originating from the Atlantic Ocean have adapted since their introduction to the Great Lakes systems possibly due to their anadromous (migrate from sea/ocean to rivers to spawn) nature.
The Sea Lamprey grow in Great Lake tributary streams as larvae that filter feed on detritus and plankton for approximately 3-10 years (Great Lakes Fishery Commission 2a, 2021). They then metamorphize developing eyes along with oral disks and tongues with pointed teeth. They migrate downstream towards the lakes where they become parasitic juveniles, feeding on the blood of host fish for 12-18 months. As the winter months come, they stop feeding and migrate towards spawning stream where they become sexually mature adults and reproduce during the spring and early summer seasons. Once they spawn, producing up to 100,000 eggs in a spawning event, they die soon afterwards.
Sea Lamprey Impact on Great Lake Fisheries
The Sea Lampreys are most dangerous to other fish populations during their parasitic juvenile stage once they enter into the Great Lakes. Sea Lampreys attach to fish using their suction cup mouths, gripping onto the fish by digging their teeth into the body. They then feed on the fish’s body fluids by secreting an enzyme that stops blood clotting allowing them to continually feed on a host. As there is no co-evolutionary link in the Great Lakes as with fish in their native Atlantic Ocean, Sea Lamprey individuals can kill up to 40 pounds of fish during their 12-18 month feeding stage (Great Lakes Fishery Commission 2c, 2021).
Sea Lampreys mainly feed on large fish species such as Burbot, Lake Sturgeon, Whitefish, Chub, and Lake Trout (Salvelinus namaycush) which has drastically fish populations present in the basin. The Sea Lamprey invasion at its peak resulted in a drastic reduction of Lake Trout fishery harvest with the average catch being 300,000 pounds by the early 1960s, a drastic reduction from the 15 million pounds caught in the past (Great Lakes Fishery Commission 2c, 2021).
Once management programs were established in the 1970s and 1980s the suppression of Sea Lampreys was near immediate, with Lake Trout populations along with other species recovering however Sea Lamprey numbers have rebounded primarily in Lake Erie due to suspected migration from untreated larval populations (Sullivan et. al., 2003).
Current Management Efforts
Efforts are being made to reduce the invasive Sea Lamprey population in the Great Lakes basin and so far is the only worldwide example of a successful invasive aquatic vertebrate control program on an ecosystem-wide scale (Great Lakes Fishery Commission 2b, 2021).
Management program focus on the portion of the Sea Lamprey lifecycle in tributaries as larvae. Taking advantage of this information, biologists assess tributaries that contain larval Sea Lampreys to determine when and where pest control should be administered.
There are numerous methods that are utilized with the two most effective being lampricides and barriers.
Lampricides are the primary method used in targeting Sea Lamprey larvae in management programs. The lampricide TFM (3-trifluoromethyl4′-nitrophenol) and Bayluscide are most effective compounds found in controlling larvae after extensive testing. TFM kills larvae by disrupting energy metabolism of the Lamprey preventing them from developing further and migrating to the lakes. Bayluscide is combined with TFM in order to limit the amount of TFM required in tributary treatments. The most beneficial aspect of this method is that the compounds are lethal towards Sea Lamprey while being relatively harmless to other organisms.
Barriers prevent Sea Lampreys from migrating to spawning gravel and soft substrate types for larvae to burrow. Barriers function by stopping adult Sea Lampreys from accessing spawning grounds and limiting their habitat distribution. This method is effective with low-head barriers and trap and sort fishways designed to allow jumping and non-jumping fish species to still pass while Sea Lampreys are trapped.
References
1. Sullivan, W. P., Christie, G. C., Cornelius, F. C., Fodale, M. F., Johnson, D. A., Koonce, J. F., Larson, G. L., McDonald, R. B., Mullett, K. M., Murray, C. K., & Ryan, P. A. (2003). The Sea Lamprey in Lake Erie: A case history. Journal of Great Lakes Research, 29, 615-636.
2a. Great Lakes Fishery Commission. (2021). Sea Lamprey lifecycle. Available at http://www.glfc.org/sea-lamprey-lifecycle.php. (Last accessed 1 December 2021)
2b. Great Lakes Fishery Commission. (2021). Sea Lamprey control in the Great Lakes. A remarkable success!. Available at http://www.glfc.org/control.php. (Last accessed 1 December 2021)
2c. Great Lakes Fishery Commission. (2021). Sea Lamprey: A Great Lakes invader. Available at http://www.glfc.org/sea-lamprey.php. (Last accessed 1 December 2021)
4. U.S. Fish & Wildlife Service. (2021). Sea Lamprey control program. Available at https://www.fws.gov/midwest/SeaLamprey/. (Last accessed 1 December 2021)
5. Michigan Department of Natural Resources. (2021). Sea Lamprey: Vampires of the Great Lakes. Available at https://www.michigan.gov/dnr/0,4570,7-350-79135_101864-549964–,00.html. (Last accessed 1 December 2021)