Progress Toward Restoration of Naturally Reproducing Top Predators and Self Regulation of Lake Huron's Fish Community, a Case Study

At the 2003 “Propagated Fish in Resource Management” symposium we presented case studies on role of stocking in rehabilitation of walleye and lake trout populations and biomanipulation of Great Lakes ecosystems.  At that time (2003), lakes Huron and Michigan were reliant on stocking for maintenance of predator-prey balance and for sustaining recreational fisheries valued at nearly $1.7 billion/yr.  Spawning stocks of lake trout, Chinook salmon, and walleyes had been re-established, but reproduction of these species remained low.  More recently in Lake Huron, marking hatchery fish with oxytetracycline led to the finding that upwards of 80% of Chinook salmon of the 2000-2008 year classes were of wild origin.  In 2004, alewives collapsed which caused the introduced Chinook salmon to decline but reproduction of native walleyes and lake trout to rise sharply.   Relief from chronic thiamine deficiency caused by alewife-dominated diets probably contributed to rising reproduction.  Central Lake Huron’s walleye population is now considered to be recovered.  Due to the decline of the Chinook salmon population, fishing effort fell and shifted from salmonids to percids.  As reproduction rose and stocking success declined, agencies sharply reduced or ceased stocking of several species.  If sustained, recent events will represent regime shift to a top-predator configuration resembling what prevailed prior to system collapse.  The restoration of top-down controls could lead to a more resilient fish community with lower management costs to resource agencies, but also with lower economic benefits from its recreational fishery.   Hatcheries have played a key role in this ecosystem recovery.