Resource Subsidies for Young Fish in Lake Michigan Rivermouths

Rivermouth consumers derive energy from spatially diverse habitats. Trophic linkages between tributaries and coastal zones can facilitate complex food webs, where fish benefit from subsidies that originate in adjacent systems. In Lake Michigan, tributaries deliver seasonally warmer, nutrient enriched water into the relatively cool, oligotrophic lake. Mixing zones within rivermouths may provide important nursery habitat for fish. Despite burgeoning interest in nearshore Great Lakes ecosystems, energy dynamics and nutrient transfers in rivermouths are understudied. To explore resource utilization by fish in three southern Lake Michigan rivermouths, we characterized trophic interactions among young round goby, yellow perch, alewife, and their prey. Fishes were analyzed for gut contents and stable isotopes of carbon, nitrogen, hydrogen, and oxygen of tissue. To further explore trophic linkages, we quantified fatty acid signatures of fish tissue and prey. Our results reveal that young fishes utilize a variety of tributary and nearshore lake resources. Fishes consumed similar prey types across habitats; however, isotope and fatty acid results suggest habitat-specific resource use. These transitional habitats may facilitate early-life growth and survival of Lake Michigan fishes. Our investigation likely has broader implications for the recruitment of these ecologically and economically important fishes throughout the Laurentian Great Lakes.