En route temperature use and bioenergetics of different migration strategies in a population of summer-run Chinook salmon

By using in situ temperature loggers combined with radio telemetry of fish position, we recreated the thermal histories of 27 summer-run Chinook salmon dwelling in a hydropower impacted river system in British Columbia. We assessed to what extent behavioural thermoregulation was occurring during the upriver migration, as well as estimated the amount of acquired thermal units each migrant had accrued during their freshwater migration.  There was little evidence that fish were able to behaviourally thermoregulate while in the river.  However, fish that migrated through the river and held in a lake prior to spawning were able to select cooler temperatures.  We also determined that for fish that only used the river portion of the system, their daily mean internal temperatures were almost 3 °C higher than fish that used both the river and the lake.  We also quantified the proportion of time that fish were exposed to temperatures that were approaching their thermal limits.  We used bioenergetics modelling to determine the potential fitness-level consequences of different migration strategies and thermal conditions.