Rehabilitation Stocking of Walleyes and Lake Trout: Restoration of Reproducing Stocks in Michigan Waters of Lake Huron

Abstract

AbstractLake Trout Salvelinus namaycush and Walleye Sander vitreus, native keystone predators of the upper Great Lakes, were nearly extirpated from Lake Huron in the 1940s. Efforts to restore these species in the Great Lakes constitute one of North American's largest‐scaled native keystone predator recovery projects. From 1973 to 2012 nearly 49 million yearling‐equivalent Lake Trout and 21 million spring‐fingerling Walleyes were stocked in western Lake Huron. We used assessment catch rates and biological data, statistical catch‐at‐age models, and harvest statistics to evaluate whether the objectives of rehabilitation stocking and management have been achieved in the Main Basin of Lake Huron, with emphasis on the period from 2003 to 2012. Key measures of progress were the biomass of older, spawning stock and evidence of natural reproduction. Until 2000, excessive Sea Lamprey Petromyzon marinus– and fishing‐induced mortality caused few Lake Trout to survive to spawning age. Lake Trout broodstock biomass rose after 2000 as these issues were more effectively addressed. Until 2004, Alewife Alosa pseudoharengus dominated the diets of Lake Trout, leading to low egg thiamine levels, which reduced the viability of Lake Trout fry. Adult Alewives were abundant enough to have limited reproduction by feeding on Walleye and Lake Trout fry. By 2004, Alewife had collapsed. The Walleye population is now rehabilitated in western Lake Huron and Walleye stocking ceased in 2006. Wild‐origin fish now compose nearly half of Lake Trout less than 8 years old. A combination of factors contributed these positive changes. Beginning in 2000, more effective Sea Lamprey and fishing controls were implemented. Seneca strain Lake Trout survived to spawning age better than other upper Great Lakes strains and became the principal strain stocked after about 1995. Removal of impediments to reproduction, combined with judicious stocking led to the Walleye recovery and improved prospects for the rehabilitation of Lake Trout in western Lake Huron.