Availability of lake trout reproductive habitat in the Great Lakes

A decades-long program to reestablish self-sustaining stocks of lake trout (Salvelinus namaycush) in the four lower Great Lakes produced excellent fisheries supported by stocked fish. These fish spawned widely and small numbers of their offspring were collected intermittently from Lakes Michigan, Huron, and Ontario, but no self-sustaining stocks were established. Irt this paper we address habitat sufficiency as a factor in the failure of stocked lake trout to established self-sustaining populations in the four lower Great Lakes. We present the previously unpublished results of lake trout spawning habitat surveys conducted at seven sites in the Great Lakes since 1987 and we compare them with the published results of similar surveys conducted at 24 other sites in the four lower lakes since 1981. Our evaluation indicates all but two of these sites can support the production of viable fry from spawnings by the shallow-water strains of lake trout that are stocked in the Great Lakes. However, some of the best spawning, egg, and fry habitat in the lower Great Lakes seems to be at deeper offshore sites that may be unattractive to these shallow-water strains. Thus, we suggest also stocking the lower four lakes with strains from Lake Superior that might more fully exploit the best spawning habitat at these deeper, offshore sites.