Contribution of benthic and riparian macroinvertebrates to the diet of juvenile coho salmon and Dolly Varden in tributaries of the Copper River delta, south-central Alaska

During the summers of 2005 and 2006, 7 stream segments within the Copper River Delta, South-Central Alaska, USA were sampled via trapping and gastric lavage for juvenile coho salmon and dolly varden stomach contents to investigate the role of benthic and riparian macroinvertebrates in juvenile salmonid diet prior to habitat enrichment by returning adult spawners. 926 juvenile salmonids were sampled for stomach contents over the two summers. Results of sample enumeration and identification indicate that winged adult riparian insects and winged adult aquatic insects comprise the majority of the stomach contents of juvenile coho salmon (50 – 90%) within these habitats with Rhagionidae, Cecidomyiidae, Aphididae, Hymenoptera, and Chironomidae (aquatic) the dominant taxa. Juvenile dolly varden stomach contents were dominated by benthic organisms (50-80%), specifically larvae of Chironomidae, Simuliidae, Limnephilidae, and planorbid snails. Results of this study suggest that riparian macroinvertebrate inputs into freshwater habitats within the Copper River Delta comprise a significant and important portion of the diet of juvenile coho salmon during the summer period, and that juvenile coho salmon and dolly varden may alleviate interspecies food resource competition during the summer via adaptive feeding strategies.