Habitat Characterization of Southern Lake Michigan River Plumes: Implications for Fish Recruitment

Great Lakes rivermouths and river plumes provide unique transitional habitats between tributary and lake systems. In some estuarine and lacustrine ecosystems, river plume habitats enhance young fish growth and survival, thus increasing recruitment to adult populations. In Lake Michigan, fish recruitment is undoubtedly influenced by spatial and temporal environmental heterogeneity, but the relative importance of rivermouth and plume habitats for recruitment of many species is poorly understood. To thoroughly characterize the environmental conditions that young fish may experience in Lake Michigan river plumes, during 2011 and 2012, we measured physical variables, collected water, zooplankton, benthic macroinvertebrates, and larval and juvenile fish (primarily yellow perch, round goby, and alewife) at five rivermouths in southern Lake Michigan. We analyzed nutrient concentrations of water samples, and identified, enumerated, and measured invertebrates and larval fish. Additionally, we explored spatial and temporal patterns of stable isotopes δC, δN, δH, and δO to characterize rivermouth food webs. Our preliminary results indicate that physical (e.g., temperature, light) and lower trophic level (e.g., chlorophyll, zooplankton, and benthic invertebrate densities) conditions within rivermouths and plumes are suitable for young fishes.  Furthermore, stable isotope analyses of water samples indicate spatial heterogeneity within rivermouths. Additional investigation will further elucidate the role river plumes play in young fish growth and survival in southern Lake Michigan.