Title: (Re)Making connections: linking migratory fish and tributary ecosystems in the Great Lakes basin
Dr. Peter Mcintyre, UW-Madison, Center for Limnology
Abstract: Migratory fishes are capable of generating large nutrient subsidies to their spawning grounds,
but these effects are poorly understood for iteroparous species and at large spatial scales. Our research
uses suckers as focal species for understanding how breeding migrations by native fishes connect
ecosystem dynamics in the Great Lakes with their tributaries. We find that sucker migrations generate
substantial inputs of nitrogen and phosphorus to small tributaries of Lake Michigan, and can be important
even against a backdrop of moderate agricultural nutrient loading. These subsidies enhance nutrient
availability, primary productivity, and insect growth in tributaries. Fish migrations are frequently blocked by
dams and impassable road culverts, raising questions about the scale at which barrier removals would be
necessary to restore ecological connectivity in the Great Lakes basin. Using an optimization model to
maximize potential gains in spawning habitat from barrier removals, we find that restoration investments
are most efficient when prioritized at large spatial scales and allocated in large pulses rather than
sustained trickles of funding. Both dams and road culverts must be addressed to achieve efficient
restoration. Together, these field studies and basin-wide analyses show that relatively modest restoration
investments could accomplish major gains in ecological connectivity, thereby benefiting both native
migratory species and the ecosystems in which they breed.