Modeling Stream Habitat Dynamics and Coho Population Viability in Oregon Coastal Rivers

Freshwater habitat degradation is linked to declining abundances of Oregon coastal Coho salmon populations, yet it is difficult to assess how habitat quality changes with land management.  We are developing a habitat-based, Coho life-cycle model in which freshwater habitat quality is influenced by upstream and upslope processes.  Our modeling approach consists of using the output of a dynamic landscape model to estimate Coho salmon habitat capacity by reach and life stage.  Coho population dynamics are simulated using the resulting habitat capacities in a spatially explicit life cycle model.  Currently, we are using land management scenarios developed in the Coastal Landscape Analysis and Modeling Study to simulate forest dynamics across the landscape.  Wood inputs to the stream are from riparian and upslope processes (e.g., tree mortality and debris flows) and modeled sediment sources are landslides and debris flows.  We have calibrated our habitat capacity component to Oregon Department of Fish and Wildlife’s Habitat Limiting Factors model.  In the habitat-based life cycle model, each reach represents a population through a 3-year life history cycle that includes estimates of egg, summer parr, smolts, adults, and spawners for each modeled stream reach.  Summer habitat capacity influences the egg-to-parr survival rate and winter habitat capacity is used to calculate the parr-to-smolt survival rate.  We are currently evaluating model performance with validation and sensitivity analyses.  Our first application of the model assesses patterns of distribution and extinction risk of selected Oregon coastal Coho populations under different landscape management scenarios.