Lake Trout (Salvelinus namaycush) and Sea Lamprey (Petromyzon marinus) Populations in Lake Michigan, 1971–78

Abstract

Lake trout (Salvelinus namaycush) was exterminated in Lake Michigan by the mid-1950s as a result of the combined effects of an intensive fishery and predation by the sea lamprey (Petromyzon marinus). The widespread application of lampricide in tributary streams had greatly reduced the abundance of lampreys by the early 1960s, and a program to restore self-sustaining populations of lake trout through stocking of yearlings and fingerlings was initiated in 1965. Although the hatchery-reared fish spawned widely in Lake Michigan each year after 1970, no progeny were observed except in an isolated area in Grand Traverse Bay. During 1971–78, sea lamprey abundance was generally greater in Wisconsin than in other parts of the lake. However, the rate of occurrence of sea lamprey wounds on lake trout dropped dramatically there in 1978 after the Peshtigo River, a tributary to Green Bay, was treated with lampricide. Application of Lake Michigan wounding rates to a regression model relating mortality to lamprey wounding developed from Lake Superior data, yielded lamprey-induced mortality estimates in 1977 of 5% in Michigan plus Indiana (combined) and 31% in Wisconsin; corresponding estimates for 1978 were 5 and 15%.Key words: lake trout, sea lamprey predation, abundance, Lake Michigan