Dynamic Migratory Conditions and Hydropower Production Effects on Adult Sockeye Salmon Navigation in a Fraser River Tributary

Cumulative effects and the underlying mechanisms of slowed and unsuccessful migration of wild adult salmon in regulated rivers are not well understood. We combined radio telemetry, thermal loggers, and individual physiology to examine the migration success of salmon navigating through a regulated river in British Columbia. Over two years, we continuously monitored survival of 582 sockeye salmon as they encountered olfactory, thermal, and physical barriers passing from the Fraser River into the Seton River, and ascended the Seton Dam enroute to spawning grounds. Dam passage (2013 - 52%, 2014 - 89%) was consistent with previous studies (2005 - 78%, 2007 - 66%, 2012 - 62%) and survival to spawning grounds (2013 - 38%, 2014 - 66%) was not associated with longer passage times at the dam. However, slower migration to passing the dam and higher concentrations of blood lactate were associated with a reduction in survival to spawning grounds. These results provide evidence for cumulative effects of barriers, and environmental and physiological stress on individuals, and should be considered when monitoring adult salmon migration in regulated rivers. We discuss our results in the context of evaluating current hydrosystem operations and whether operational changes can improve fish passage to spawning grounds.