The lake trout, a federal trust species, was historically the top native predator fish in the Great Lakes and the mainstay of the early commercial fishery. A combination of over-fishing and predation by the exotic sea lamprey along with other contributing factors caused extinction of lake trout in all of the Great Lakes except Lake Superior where populations were greatly diminished and Lake Huron where an isolated, remnant population persisted. Managers have been deeply concerned about the lake trout and have instituted a variety of rehabilitation efforts. Because lake trout are a long-lived fish, effectiveness of management efforts are only determined through a long-term surveillance. Hence, the GLSC has conducted long-term gillnet assessment of native lake trout in Lake Superior and of hatchery-reared lake trout in all of the Great Lakes to evaluate the status of lake trout rehabilitation. As with our prey fish long-term data series, the lake trout database can provide a wealth of information in understanding lake trout population dynamics and movements. In addition, intensive research has been done on factors suspected of adversely influencing the establishment of self-reproducing, sustainable stocks of lake trout in the Great Lakes. Research has included evaluating the effect of various factors on survival of hatchery-reared trout, including rearing density, life stage at stocking, adult abundance on juvenile survival, season of stocking, genetic strain, and stocking method and location. Other research has included population modeling, observing geographic and bathythermal distribution and movements of adults and juveniles, verifying contaminant and energy uptake with laboratory and field diets and bioenergetic modeling, measuring growth and maturity, determining factors affecting fecundity, and understanding the role of thiamine deficiency in lake trout survival. Although many of the factors thought to influence survival of hatchery fish have been investigated, these studies have to be repeated periodically as fish communities change. We also demonstrated differential survival among genetic strains of lake trout in vulnerability to and survival from sea lamprey attack. As a consequence, hatcheries switched strain of lake trout used in rehabilitation program. Because of our observance of naturally produced larval lake trout on a mid-lake spawning reef in Lake Huron, that reef was declared a refuge.

Lake Trout Biology and Restoration Research Fact Sheet
PCBs and Mercury in the Great Lakes — Effects on Health of Lake Trout Fact Sheet