For more information

Website:

www.glsc.usgs.gov

Publication:

Proceedings of the 1994 International Conference on Restoration of Lake Trout in the Laurentian Great Lakes: Journal of Great Lakes Research, v. 21, supplement 1, 1995.

Lake Trout Restored in Lake Superior after Lamprey Invasion

Highly prized lake trout have been successfully restored in Lake Superior through research of USGS scientists working closely with management agencies. This combined science and management approach is now being adapted to other lakes and species in a basin-wide effort to restore native fish species.

Lake trout historically were the top predator in Lake Superior and supported valuable commercial, subsistence, and sport fisheries. Starting in the 1920's, sea lampreys began to invade the upper Great Lakes, and their predation, combined with fishery exploitation, caused the collapse of most lake trout populations throughout the basin.

Given the scale of this ecological disaster, the Great Lakes Fishery Commission was established in 1955 to control sea lamprey and restore lake trout populations. Priority was given to Lake Superior, since lake trout populations had not been completely eliminated there. During the late 1950's and 1960's, the USGS Great Lakes Science Center in Ann Arbor, Michigan, worked closely with the Great Lakes Fishery Commission to identify a selective chemical to control sea lamprey larvae in streams.

After scientists tested more than 6,000 chemicals, they determined 3-trifluoromethyl-4-nitrophenol (TFM) the most suitable and developed it for field use. Shortly after TFM application to larval populations, sea lamprey numbers began to decline in Lake Superior, allowing for the reintroduction of lake trout through plantings of hatchery-reared fish and protection of remnant stocks.

Scientists measured performance of hatchery-reared lake trout as well as recovery of wild populations through long-term assessment programs developed by USGS scientists. These field programs were later assumed by State and tribal management agencies and used as a model to develop assessments in other jurisdictions.

Ongoing analysis of these important field data by USGS scientists, working with State, tribal, provincial, and other U.S. Department of the Interior agencies, led to the decision in 1996 to discontinue stocking federally produced hatchery lake trout in most areas of the lake. Results indicated that lake trout

restoration is well on its way in most areas of Lake Superior and that protection of self-reproducing wild lake trout populations from over-exploitation and sea-lamprey predation is the primary strategy to foster further restoration. Results from additional USGS research on the recruitment and survival dynamics of wild, remnant lake trout stocks also provide a benchmark to measure the performance of hatchery-reared fish in the other Great Lakes.

Progress of lake trout restoration in
the Great Lakes, 1970's to present.

Lake Superior - Lake trout are reproducing throughout the lake and in most Michigan, Wisconsin, and Ontario waters. The rate of reproduction is adequate to sustain the populations without additional stocking.

Lake Michigan - Spawning of stocked lake trout and subsequent production of young have been evident since the early 1970's. However, survival of young fish to adults has not been documented. Offshore reefs appear to be the most promising areas for establishing reproducing stocks.

Lake Huron - Stocked lake trout began reproduction on several nearshore reefs in 1981, and a small number of adults were evident in the annual assessments and creel catches. Intensive stocking of multiple strains on midlake reefs has resulted in the production of young lake trout each year since 1993.

Lake Ontario - Naturally produced two-year-old lake trout were present in many areas of the lake during 1995-97. Prior to this, spawning by stocked lake trout failed to produce detectable numbers of two-year-old fish although fry were detected as early as 1983.

Lake Erie - Lake trout stocking began in 1978 and abundance has been improving annually since 1992. Reproduction has not been detected, but lake trout are surviving to sexual maturity and offspring of stocked lake trout have been raised successfully in a hatchery.

Saga of the Sea Lamprey

Although more than 140 non-native species have entered the Great Lakes, the sea lamprey is considered the most harmful. During part of their life cycle, sea lampreys are parasitic, feeding only on the blood of fish.

They likely entered Lake Ontario from the Atlantic Ocean through the New York State barge canal system in the 1800's, and entered the upper Great Lakes after the Welland Canal was completed in 1829, allowing passage past Niagara Falls. By the 1950's, predation by sea lampreys and overfishing combined to exterminate lake trout in Lakes Ontario, Erie, Huron, and Michigan, and depleted stocks in Lake Superior. These declines caused economic devastation and a severe imbalance of predator and prey species.

Efforts to reestablish predators failed without sea lamprey control. Although application of a chemical lampricide, TFM, continues to be successful in most areas of the Great Lakes, the Great Lakes Fishery Commission has adopted an integrated pest management plan with the goal of using alternative methods for sea lamprey control. The USGS Upper Mississippi Science Center and Great Lakes Science Center are conducting research to reduce lampricide use and develop alternative methods of sea lamprey control. This USGS research is vital for restoring U.S. and Canadian commercial, recreational, and tribal fisheries in the Great Lakes.