Minimizing opportunity costs to aquatic connectivity restoration while controlling an invasive species

Controlling invasive species is critical for conservation but can have unintended consequences for native species and divert resources away from other efforts. This dilemma occurs on a grand scale in the North American Great Lakes, where dams and culverts block tributary habitat access for desirable fish species and are also a lynchpin of long-standing efforts to limit ecological damage inflicted by invasive, parasitic sea lamprey. Habitat restoration and sea lamprey control create conflicting goals for managing aging infrastructure. Here, we use optimization to minimize opportunity costs to habitat gains for 37 desirable migratory fishes that arise from restricting sea lamprey access (0-25% increase) when selecting barriers for removal under a limited budget ($1-105M). Imposing limits on sea lamprey habitat reduces gains in tributary access for desirable species by 15-50% relative to an unconstrained scenario. Working around a sea lamprey access cap is costly for 30 of 37 species (e.g., an additional $20-80M for lake sturgeon), and often requires ≥5% increase in sea lamprey access to be feasible. Narrowly distributed species exhibit the highest opportunity costs, but also benefit more at lower cost from allowing small increases in sea lamprey access. Our results illustrate the value of optimization for limiting opportunity costs when balancing invasion control against restoration benefits for diverse desirable species. Such tradeoff analyses are essential for expanded efforts in the conservation community to restore connectivity within fragmented rivers without unleashing invaders