Prioritizing Barrier Removals to Restore Native Fish Migrations in Great Lakes Tributaries

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. The removal or modification of barriers can restore migratory pathways for these species, but removal costs and habitat gains differ markedly among potential projects. In the Great Lakes basin, 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 repair/removal on the basis of upstream breeding habitat. We found that the amount of accessible breeding habitat in the basin can be doubled for an investment of about $80m, a dollar amount well within the range of recent spending on Great Lakes restoration projects. That scenario would involve the removal or upgrade of numerous road crossings and a number of key problematic dams. We will discuss key factors that drive barrier prioritization, spatial patterning of priority projects, and future plans to incorporate invasive species (sea lampreys, gobies) into the model.