Hydropower peaking and stalled salmon migration are linked by altered reservoir hydraulics: A multidisciplinary synthesis and hypothesis

Adding variable renewable energy (solar, wind) in electricity portfolios will increase need for fast grid responses through hydropower peaking. Over 60 years of daily hydropeaking by four dams on the lower Snake River, United States America provide an example long-term environmental impacts. Downstream-migrating Chinook salmon (Oncorhynchus tshawytscha) subyearlings that normally transit dammed river summer slowed their migration into autumn with about one-third those delayed overwintering reservoirs. Specific cause stalled is controversial, options including evolution a new migratory strain and action environment individual migrants. Analysis archived dam data shows evidence reservoir seiches (standing waves waterbody oscillations) caused within-day peaking during October–February period migration. Analyses limnological literature identified typical water movements analyses biological effects fish kinematics (shape, motion) changing flows fish's immediate proximity. Process-focused inference predicts anomalous fish-migration behavior seiche hydraulics, which matches fish-tracking obtained others Lower Monumental Reservoir. Fish tracks include upstream swimming (‘downstream’ reverse flows) periods disoriented to repeatedly flows. This multi-disciplinary, process-focused synthesis yields testable hypothesis seiche-flow hydraulics River reservoirs from contribute known out-migration delay late-migrating fall subyearlings. As causes downstream elsewhere North Europe, species may be susceptible similar delays population effects.