The Role of Rivermouths and River Plumes in Young Fish Growth and Resource Utilization in Southern Lake Michigan

Great Lakes rivermouths and river plumes provide unique transitional habitats between tributary and lake systems. In Lake Michigan, tributaries deliver seasonally warmer, nutrient enriched water into the relatively oligotrophic nearshore, which likely promotes autotrophic and heterotrophic productivity. However, the influence of rivermouths and river plumes on fish recruitment is poorly understood. To evaluate how young fish utilize rivermouths, during 2011 and 2012, we measured water temperature and light, and collected zooplankton, benthic invertebrates, and larval and juvenile fish (primarily yellow perch, round goby, and alewife) at three rivermouths in southern Lake Michigan. We analyzed growth and stomach contents of larval and juvenile fish and explored patterns of stable isotopes δ¹³C, δ¹⁵N, δ²H, and δ¹⁸O of fish tissue and otoliths. Our results demonstrate spatial and temporal heterogeneity in physical and lower trophic level patterns within rivermouths. Furthermore, our preliminary characterization of rivermouth food webs indicates that young fish are utilizing a variety of tributary and nearshore resources. Additional investigation will further elucidate the role rivermouths and plumes play in young fish growth and survival in southern Lake Michigan.