Predation by Alewives on Lake Trout Fry in Lake Ontario: Role of an Exotic Species in Preventing Restoration of a Native Species

The role of non-native alewife predation on lake trout fry in inhibiting natural recruitment of stocked fish in Lake Ontario was studied. Laboratory studies showed that lake trout fry were eaten aggressively by alewives. Field studies at Stony Island Reef, Lake Ontario, showed that fry were available as prey from mid-April through mid-late May. Initial alewife capture at the site occurred in early May. Alewife predation could have caused high mortality of lake trout fry from spawning areas where alewives are abundant. Increased stocking of predatory salmonids might suppress the alewife and enhance lake trout fry survival, but suppression seems unlikely under current strategies that manage the alewife as forage for non-native salmonids. Management goals should focus on localized restoration programs at sites where alewives are not abundant in spring.