Indirect management of invasive species through bio-controls: A bioeconomic model of salmon and alewife in Lake Michigan

Invasive species are typically viewed as an economic bad because they cause economic and ecological damages, and can be difficult to control. When direct management is limited, another option is indirect management via bio-controls. Here management is directed at the bio-control species population (e.g., supplementing this population through stocking) with the aim that, through ecological interactions, the bio-control species will control the invader. We focus on stocking salmon to control invasive alewives in Lake Michigan. Salmon are valuable to recreational anglers, and alewives are their primary food source in Lake Michigan. We illustrate how stocking salmon can be used to control alewife, while at the same time alewife can be turned from a net economic bad (having a negative shadow value) into a net economic good (having a positive shadow value) by providing valuable ecosystem services that support the recreational fishery. Using optimal control theory, we solve for a stocking program that maximizes social welfare. Optimal stocking results in cyclical dynamics. We link concepts of natural capital and indirect management, population dynamics, non-convexities, and multiple-use species and demonstrate that species interactions are critical to the values that humans derive from ecosystems. This research also provides insight into the management of salmon fisheries in the Great Lakes.