Seasonal Pattern of Differential Marine Survival of Barged to Run-of-River Juvenile Spring Chinook Salmon Explain By Counteracting Patterns of Smoltification and Fish Condition

To reduce mortality of juvenile spring Chinook salmon passage through the Columbia River hydrosystem, fish are transported from Lower Granite to Bonneville dams in barges. While barging eliminates direct hydrosystem mortality, it advances the marine entrance date of fish by weeks. Furthermore, hydrosystem passage delays run-of-river fish marine arrival. Thus, the hydrosystem differentially disrupts the natural timing of ROR and barged fish to the ocean. Correspondingly, the ratio of marine survival of barged to ROR fish changes from about one-half to two over the migration season. A model, based on seasonally improving smoltification status of barged fish and seasonally degrading condition of ROR fish,  predicts the differential survival ratio using river travel time of ROR fish and freshwater temperature exposures of barged and ROR fish.  The model, calibrated with fish condition and tagging studies conducted in 2008 and 2009 and validated with marine survival data from 2008-2012,  suggests the possibility that barged fish smoltification status, and therefore marine survival, might be improved by releasing fish above Bonneville Dam.