2023-Feb-13
Sea Lampreys in Lake Huron - They Just Won’t Go Away!
What are sea lampreys and why are they problematic?
Sea lampreys are an ancient form of a jawless fish with a toothed, funnel like mouth, that suck blood out of fish. They entered the Great Lakes through the St. Lawrence Seaway. During the 50’s, Lake Huron’s commercial fishing industry was verging on collapse. In particular, one of the most valued species, Lake Trout, a favorite sea lamprey meal, was nearing extinction.
The good news is Lake Huron’s sea lamprey population (once the largest in the Great Lakes with over 700,000 in the 1940’s and 1950’s) has been declining. For example, in 2015 the population fell to 70,000, well below the target of 90,000 set by the Great Lakes Fisheries Commission (GLFC), established in 1954 to oversee a Great Lakes sea lamprey control program.
Fig. 2 Lamprey wound on a trout – GLFC
Through GLFC’s efforts and bi-national partnerships, including First Nations, Upper Great lakes Management Councils and local fishing clubs, Lake Trout numbers, are holding steady and sea lamprey populations continue to decline. Most exciting, is evidence that “wild” Lake Trout are naturally reproducing in upper Lake Huron and Georgian Bay.
Despite this good news, Covid-19’s two-year travel restrictions, which prevented sea lamprey control treatments on most of Lake Huron’s tributaries, allowed a two-year spawning cycle for juvenile sea lampreys to migrate and prey on fish. GLFC’s fishery experts are now predicting sea lamprey numbers will bump up” for several years. With local commercial fishery operators and anglers recently finding more sea lampreys in their nets, and wounds on fish (figure 2), it suggests that lamprey numbers can rebound quickly when control treatments cease or are cut back.
Fig 3 Lampricide – GLFC
Fig 4 Low head-barrier – GLFC
With Covid-19 restrictions ending, fisheries staff are once again treating selected tributaries with lampricides (figure 4) such as TFM and Bayluscide. While these chemicals are effective when applied spring and fall, not all larvae can be treated. Barriers and traps can also be useful, such as a “low-head” barrier that blocks adult sea lampreys from entering into spawning areas, but allows other species to continue their passage.
Fig 5 trap and sort – GLFC
Another method is a “trap and sort” fishway (figure 5) which traps adults from entering spawning areas and prevents juveniles from leaving. Using barriers instead of chemicals reduces the risks to other aquatic species and allows fishery staff to count and monitor sea lamprey populations. Future deterrents may also include using lamprey “alarm” pheromones, which warn of impending danger, to prevent them entering spawning areas, or different pheromones that attract adults to spawning tributaries, where they can be captured. As sea lampreys may soon adapt to these controls, GLFC and Michigan State University have created a new 3.4-million-dollar research lab with the goal of finding new methods to reduce or eliminate the sea lamprey threat, such as altering their DNA.
So long as there are fish to prey on, sea lampreys will not be leaving northern Lake Huron and Georgian Bay, historically one of the most productive fisheries in the Great Lakes. Now with regular control treatment restarted, Sea lamprey numbers should eventually reach levels close or below targets set by the GLFC. Having fewer lampreys attacking fish is a major step in supporting a viable commercial and recreational fishery. Early evidence is already showing improvements to Lake Trout numbers.
Georgian Bay Association (GBA) will continue following GLFC’s research including the efforts of Ontario’s Upper Great Lakes Management Unit and others supporting the recovery of native fish species that are integral to Northern Lake Huron and Georgian Bay coastal communities’ jobs, tourism, and related businesses.
Written by Bill Steiss 01/25/23