Temporal patterns of terrestrial and aquatic invertebrate prey abundance for juvenile Chinook salmon in a subdrainage of the Yukon River, Alaska

Terrestrial invertebrates are often an important food source for juvenile salmonids.  Seasonal inputs of terrestrial prey into streams and their abundance relative to aquatic-born prey are not well described, particularly in subarctic streams important for Chinook salmon production.  The objectives of this study-in-progress are to determine through time and in response to stream flow: 1) the seasonal influx of terrestrial invertebrates into the Chena River, central Alaska, 2) the proportion of aquatic and terrestrial prey in the drift, and 3) the predation on aquatic- and terrestrial-born prey by juvenile Chinook salmon.  We deployed surface pan traps to collect terrestrial invertebrate inputs into the river, collected drifting invertebrates via subsurface drift nets, and sampled juvenile Chinook salmon diets in two stream reaches within a 100-km section of river.  Juvenile Chinook salmon predominantly preyed upon chironomid midges, chloroperlid stoneflies, heptageniid mayflies, and some terrestrial invertebrates. Predation upon terrestrial prey increased in the fall.  Understanding the spatial and temporal dynamics of terrestrial invertebrate infall into streams, particularly as a function of environmental processes, is important for determining its role in aquatic food webs and in the production of Chinook salmon and other upper level consumers in riverine ecosystems.