Lessons in Rehabilitation Stocking and Management of Lake Trout in Lake Huron
James E. Johnson, Ji X. He, Aaron P. Woldt, Mark P. Ebener, Lloyd C. Mohr
Abstract.—Lake trout Salvelinus namaycush, the native keystone predator of the upper Great Lakes, were extirpated from Lake Huron in the 1940s. From 1973 to 2002, more than 42 million yearling-equivalent lake trout were stocked in Lake Huron. We use assessment catch rates and statistical catch-at-age models to evaluate stocking methods and whether objectives of rehabilitation stocking, including restoration of natural reproduction, have been achieved in western Lake Huron. A rise in survival after 1989 was probably due to vessel distribution of hatchery fish to offshore stocking sites and an increase in average condition of lake trout stocked during the early 1990s. Until 2000, however, excessive sea lamprey- and fishing-induced mortality permitted few lake trout to survive to spawning age, thus suppressing reproduction. In contrast, a reproducing stock of lake trout has been rehabilitated in Parry Sound, eastern Lake Huron, where fishing and lamprey controls were more effective and stocking rates higher. Beginning in 2000, more effective lamprey and fishing controls were implemented in western Lake Huron. Modeled spawning-stock- per-recruit estimates suggest that these measures produced conditions favorable for accumulation of lake trout spawning stocks. More effective management of mortality combined with recent improvements in stocking strategies should lead to improved prospects for reproduction in western Lake Huron.