The Role of Geomorphic and Hydrologic Processes in Structuring Spawning and Rearing Habitats for Chinook Salmon in a Boreal Stream Ecosystem

Across the Yukon River basin, a recent downturn in Chinook Salmon returns has led to hardship among user groups and an increased interest in better understanding how physical processes affect freshwater survival and population persistence within this important commercial, recreational, and subsistence fishery. Here we present the results of our recent work in the Chena River basin, interior Alaska, where we used field-based investigations and a suite spatially-explicit models to assess Chinook Salmon spawning and rearing habitat quality and dynamics. Based on a digital landscape model and occupancy estimation from environmental DNA sampling we found a strong effect of interannual variability in flow conditions on tributary rearing habitat use. However, model-derived flow metrics were less useful in predicting counts of adult salmon in core and peripheral spawning habitats relative to annual escapement and habitat spatial structure. Finally, using spatially-constrained clustering and a rainfall-runoff hydrologic model we estimated ecological flow metrics in spawning and rearing habitats under historic and future climate conditions. Knowledge of the distribution, amount, and relative importance of habitat features within freshwater networks gained by studies such as ours will be critical for conservation and management of Alaskan Chinook Salmon stocks under a warmer and more variable climate.