Native Fish Migrations Deliver Nutrient Subsidies to Great Lakes Tributaries

Fish migrations can deliver materials and energy against stream currents and provide important subsidies to stream ecosystems. There is an extensive literature on Pacific salmon, which are semelparous, showing that marine-derived nutrients are incorporated into all stream and riparian trophic levels where salmon migrations occur, and that these nutrients can spur productivity. In contrast, there is little research on the role of iteroparous fishes. I investigated the effects of iteroparous sucker (Catostomidae) migrations on nutrient dynamics, algal growth, and caddisfly (Limnephilidae: Limnephilus spp.) growth in a small, oligotrophic Lake Michigan tributary, using experimental barriers to establish reaches with and without a sucker migration. Soluble reactive phosphorus and ammonium became elevated during the sucker migration at treatment reaches relative to reference reaches while nitrate dynamics did not differ between treatments. Algal and caddisfly growth were higher in reaches receiving a sucker migration. Limnephilus in enclosures with a sucker carcass became rapidly enriched in δ15N and δ13C indicating assimilation of sucker materials. Stable isotope data from the field suggest assimilation of sucker N but not C, but this result could not be confirmed statistically due to gaps in the data. This study suggests that iteroparous fish migrations can provide important nutrient subsidies to stream ecosystems. Suckers are restricted from much of their historic spawning range by anthropogenic barriers; my results suggest that restoring connectivity in the Great Lakes Region would restore this important process to a state more closely resembling natural conditions.Master of ScienceNatural Resources and EnvironmentUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/77587/1/Evan Childress Thesis.pd