Session C1: Prioritizing Barrier Removals in Great Lakes Tributaries: Balancing Tradeoffs Between Native and Invasive Fish Species

Abstract Tributaries to the Great Lakes are highly fragmented by dams and road crossings that act as potential barriers to migratory fishes, restricting their access to historical riverine spawning grounds. There is growing investment in removing or modifying barriers to restore native fish migrations and ecosystem function, but these efforts may also increase available habitat for invasive sea lamprey. The restoration community lacks a systematic method for comparing these costs and benefits to assess which barrier removal projects would offer the greatest return on investment. To address this problem, we developed a basin-scale mathematical optimization model to prioritize barriers for removal on the basis of upstream breeding habitat for both native and invasive fishes. We parameterized the model using an extensive database of dams and road crossings; economic models of projected barrier removal and lampricide application costs; and historical data describing distributions of native and invasive species. We describe trade-offs resulting from increased habitat access for native migratory fishes and sea lamprey that would accompany different barrier removal scenarios. We further discuss the sensitivity of the model to uncertainty in estimates of tributary suitability for native and invasive species and investigate the benefit of simultaneously planning barrier removal and lamprey management actions