Fish Migration as an Ecosystem Linkages Between Western Lake Erie and Its Tributaries

Migratory fish can transport organic matter upstream through the release of gametes and deposition of carcasses, thereby creating an ecosystem linkage.  We examined potential river subsidies from western Lake Erie to its tributaries, because this system has large populations of migratory fish and differing tributary connectivity because of dams.  We sampled ¹³C and ¹⁵N stable isotopes from resident riverine fish and macroinvertebrates and three hypothesized basal food web sources: (1) benthic algae, (2) terrestrial vegetation, and (3) migratory fish.  We collected in spring and fall, 2011 at one site upstream and one site downstream of the first dam in three tributaries. Preliminary results from spring, 2011 show a clear difference in the isotopic makeup of food web sources, with migratory fish being enriched in ¹³C and ¹⁵N compared to terrestrial vegetation and enriched in ¹³C compared to benthic algae.  Terrestrial vegetation and benthic algae contributed to upstream food webs whereas downstream fish and macroinvertebrates were significantly more enriched in ¹³C than their upstream counterparts, indicating that subsidies from migratory fish are important to downstream river food webs.  In the future we will attempt to identify seasonal and spatial trends in tributary food webs and infer mechanisms driving food web structure.