Effects of Stream Temperature on Chinook Salmon Bioenergetics and Prespawn Mortality in the Columbia River Basin

Many populations of salmon migrate long distances and hold for weeks on fixed energy reserves prior to spawning.  The energetic costs of these behaviors is dependent upon climatic factors such as stream temperature and discharge, and are likely to be influenced by climate change.  We linked Columbia River spring Chinook salmon behavior and physiology during migration and holding to climate using empirical observations and a mechanistic bioenergetics model.  First, we evaluated the role of stream temperature, population density, and migration timing on prespawn mortality, where fish die after migration but prior to reproduction. Prespawn mortality rates were positively related to average August stream temperatures, and increased with spawner density.  Next, we modeled the energetic cost of migration in relation to water temperature, discharge, and the timing of migration.  Slowly migrating salmon arrived with less available energy for spawning.  Water temperature played a complex role in predicting migration duration, as travel rate increased with temperature in the tailrace below dams, but decreased with temperature in fishways through the dams.  Given the role that temperature plays in prespawn mortality and energetics, these modeled relationships will be used to predict future effects of increased stream temperatures on migration and spawning success.