Invasive Fish as Prey for Predators: To Manage for the Ecosystem or for Economics?

Fishery managers in the Great Lakes have overcome numerous impediments to maintaining recreational, commercial, and tribal fisheries, including overfishing, habitat destruction, and an initial wave of invasive species that included alewife Alosa pseudoharengus and sea lamprey Petromyzon marinus.  The destructive effects of these factors led to the loss of the native top predator lake trout from most areas of the Great Lakes by 1960.  Without strong top-down control, alewife populations exploded, creating nuisance die-offs.  Public demands for action, coupled with effective control of sea lamprey, allowed fishery managers to consider stocking Pacific salmon, especially Chinook salmon, to control the invasive alewife while simultaneously establishing a recreational fishery.  This effort was an unqualified success.   Chinook salmon consumed alewives, reducing their numbers such that die-offs did not occur.  At the same time, salmon grew rapidly and formed the backbone of a recreational fishery that today is conservatively estimated at $7 billion annually.  As new invasive species begin to alter the ecosystem yet again, however, this successful fishery management regime may no longer be viable.  Fishery managers face an interesting dilemma whether to manage in the short term for a popular and economically important sport fishery or to embrace ecosystem change and manage primarily for native fish species that appear to be better suited to the ongoing ecosystem changes.  Such dilemmas occur in throughout the world as fishery managers seek to balance economic pressure with changes in their respective ecosystems, often brought about by invasive species.