Rine, K, M Wipfli, E Schoen, C Sticker, T Nightengale. 2016. Trophic pathways supporting juvenile Chinook and Coho salmon in the glacial Susitna River, Alaska: patterns of freshwater, marine, and terrestrial resource use across a seasonally dynamic habitat mosaic. Canadian Journal of Fisheries and Aquatic Sciences.
Contributions of terrestrial, freshwater, and marine-derived prey resources to stream fishes vary over time and space, altering the energy pathways that regulate production. In this study we determined large-scale use of these resources by juvenile Chinook and Coho salmon (Oncorhynchus tshawytscha and O. kisutch) in the glacial Susitna River, Alaska. We resolved spatial and temporal trophic patterns among multiple macrohabitat types along a 97-km segment of the river corridor via stable isotope and stomach content analyses. Juvenile salmon were largely supported by freshwater-derived resources, and secondarily by marine and terrestrial sources. The relative contribution of marine-derived prey to rearing salmon was greatest in the fall within off-channel macrohabitats, whereas the contributions of terrestrial invertebrate prey were generally greatest during mid-summer, across all macrohabitats. No longitudinal (upstream-downstream) diet pattern was discernable. These results highlight the large-scale spatial and seasonal patterns of energy flow and the dynamic interplay of pulsed marine and terrestrial prey subsidies to juvenile Chinook and Coho salmon in a large, complex, and relatively pristine glacial river.