LAKE TROUT REHABILITATION IN LAKE-HURON

Efforts to restore lake trout (Salvelinus namaycush) in Lake Huron aft er their collapse in the 1940s were underway in the early 1970s with c ompletion of the first round of lampricide applications in tributary s treams and the stocking of several genotypes. We assess results of reh abilitation and establish a historical basis for comparison by quantif ying the catch of spawning lake trout from Michigan waters in 1929-193 2. Sixty-eight percent of this catch occurred in northern waters (MH-I ) and most of the rest (15%) was from remote reefs in the middle of th e main basin. Sea lampreys (Petromyzon marinus) increased in the early 1980s in the main basin and depressed spawning populations of lake tr out. This increase was especially severe in northern waters and appear ed to be associated with untreated populations in the St. Marys River. Excessive commercial fishing stemming from unresolved treaty rights a lso contributed to loss of spawning fish in northern Michigan waters. Seneca-strain lake trout did not appear to be attacked by sea lampreys until they reached a size > 532 mm. Ar sizes > 632 mm, Seneca trout w ere 40-fold more abundant than the Marquette strain in matched-plantin g experiments. Natural reproduction past the fry stage has occurred in Thunder Bay and South Bay, but prospects for self-sustaining populati ons of lake trout in the main basin are poor because sea lampreys are too abundant, only one side of the basin is stocked, and stocking is d eferred to allow commercial gillnetting in areas where most of the spa wning occurred historically. Backcross lake trout, a lake trout x spla ke (S. fontinalis x S. namaycush) hybrid, did not reproduce in Georgia n Bay, bur this genotype is being replaced with pure-strain lake trout , whose early performance appears promising.