Energy and the Role of Shallow Tidal Freshwater Habitats for Juvenile Chinook Salmon

Shallow water habitats in the tidal freshwater portion of the lower Columbia River and estuary (LCRE) have for many years been cited as important to the growth and survival of juvenile salmon.  Yet until recently, empirical data describing the roles of these habitats for juvenile Chinook salmon have been scarce.  As a result, knowledge regarding energetic consequences of residence by Chinook salmon in shallow tidal freshwater is lacking.  Understanding factors that may regulate energy acquisition and gaining insight into how consumed energy is partitioned into metabolic pathways and growth under certain environmental conditions is critical to evaluate the suitability of certain habitats for juvenile salmon.  The goal of this research was to assess the ability of specific tidal freshwater habitats in the LCRE to support energy demands of juvenile Chinook salmon.  To this end, we applied a bioenergetics model to empirical data collected at sites near the Sandy River delta, Oregon.  Across sites, rates of consumption for simulation cohorts – defined by residence times – were generally moderate to high (i.e., proportions of maximum consumption > 0.50).  Mean specific growth rates and gross conversion efficiencies were positive, except during periods when water temperatures approached or exceeded 22°C.  Our results suggest tidal freshwater habitats in specific areas of the LCRE promote favorable consumption and growth for juvenile Chinook salmon throughout most of the year and highlight the need for restoration efforts that seek to maintain adequate ambient water temperatures and support prey production in perturbed tidal freshwater areas of the lower Columbia River.