Variability of Juvenile Chinook Salmon Habitat in the Columbia River Estuary

Understanding the strong variability in the characteristics of supporting estuarine habitat might be critical to the preservation and restoration of Columbia River salmon. Metrics of habitat opportunity were introduced in the Salmon at River’s End report in 2005, and have since informed decisions in issues such as impacts of navigation improvements or hydropower operations. Here, we introduce an improved method to quantify juvenile Chinook salmon (Oncorhynchus tshawytscha) habitat, and to characterize its temporal variability in various estuarine reaches. Metrics are informed by fisheries data and sensitive to juvenile size, but are defined from physical variables—water depth, velocity, salinity, and temperature—obtained from 15 years of skill-assessed simulations of estuarine circulation. Simulation outputs are filtered through these metrics to calculate nursery and migratory habitat for four life stages of juvenile Chinook. We find that habitat differs strongly across the estuary, and is responsive primarily to river discharge in the upper estuary and to tides in the lower estuary. We also find nursery habitat to be sensitive to life stage, and to be roughly an order of magnitude less abundant than migratory habitat. Our analysis provides an improved baseline of contemporary variability of salmon habitat, against which to assess future changes.