The Relationships among In‐Channel Sediment Storage, Pool Depth, and Summer Survival of Juvenile Salmonids in Oregon Coast Range Streams

• Published in: North American journal of fisheries management 2004-08, Vol.24 (3), p.761-774
• Main Authors: May, Christine L., Lee, Danny C.
• Format: Article
• Language: English
• Subjects: Freshwater
• ISSN: 0275-5947; 1548-8675
• DOI: 10.1577/M03-073.1

The influence of channel aggradation on water availability and salmonid survival was investigated during the summer dry season in two Oregon Coast Range streams. Deep pools and a deformable streambed of coarse gravel were present in highly aggraded stream reaches. However, these thick, highly porous alluvial deposits caused surface flow to become intermittent, which stranded fish in drying channels. In gravel‐bed reaches with thinner alluvial deposits, pool depth was limited by the underlying bedrock, but pools were sustained by hyporheic flow throughout the summer dry season. In these moderately aggraded reaches, pool depth and area decreased throughout the summer, resulting in severe crowding of fish trapped in pools formed over small patches of exposed bedrock and isolated by dry, gravel‐bed riffles. Bedrock‐dominated stream reaches had slightly smaller pools but were most likely to contain continuous surface flow throughout the summer dry season; these reaches exhibited the smallest decreases in pool depth and area. Repeated snorkel surveys indicated that fish abundance in pools decreased by 59% during the summer, significantly higher losses occurring in gravel‐bed pools. Streambed substrate and partitioning of surface and subsurface flow may also have important implications for fish energetics due to differences in water temperature and food availability.