Feeding Ecology of Juvenile Chinook Salmon in Shallow Freshwater Areas of the Lower Columbia River

Documenting the diet composition of juvenile Chinook salmon Oncorhynchus tshawytscha and associating that to the prey resources available in the shallow freshwater areas in the lower Columbia River could help to inform the efficacy of management actions aimed at recovery of the species in the basin. From March 2008 to April 2010, we characterized the diet of juvenile Chinook salmon and the prey composition available in the area of the Sandy River Delta, Oregon. The composition of prey items in the diet of juvenile Chinook salmon was based on foregut contents removed using a non-lethal lavage technique. Prey availability was characterized using drift, benthos and fallout collections. The diet composition of juvenile Chinook salmon varied spatially and temporally. Dipterans, hemipterans, and malacostracans contributed most consistently to the diets of juvenile Chinook salmon. Despite the significance of dipterans in salmon diets, and their dominance of the prey pool in most months, juvenile Chinook salmon largely selected against these invertebrates in all three prey pools. Both hemipterans and malacostracans were more sparsely represented in both diet and the three prey pools than dipterans. While hemipterans were largely selected against, malacostracans were periodically selected for in the diet of juvenile Chinook salmon. Management strategies that emphasize reestablishing juvenile salmon production may benefit by including restoration actions that promote the production of the prey items they consume while sustaining a robust and diverse food-web.