Effect of Migration Pathway on Travel Time and Survival of Acoustic‐Tagged Juvenile Salmonids in the Columbia River Estuary

Abstract

AbstractWe applied acoustic telemetry methods to characterize migration pathways and estimate associated travel times and survival probabilities for juvenile Chinook salmon Oncorhynchus tshawytscha and steelhead O. mykiss migrating downstream through the Columbia River estuary (from river kilometer [rkm] 86 to rkm 8). Acoustic‐tagged fish were detected as migrating in the navigation channel and in off‐channel areas at each of the estuarine reaches we examined during May–August 2010. However, the majority of fish traveled in the main navigation channel from rkm 86 to rkm 37, at which point most fish left the river‐influenced navigation channel; crossed a broad, shallow tidal flat; and migrated the final 37 km in a secondary channel, which was characterized as having greater tidal transport than the navigation channel. The pathway used by acoustic‐tagged smolts to migrate through the estuary affected their rate of travel. In most reaches, navigation channel migrants traveled significantly faster than fish that migrated through off‐channel areas. Contrary to observations from previous studies, smolts that migrated through off‐channel areas at a slower rate did not experience lower survival than their cohorts that used the navigation channel. Although no significant differences in survival probability were observed between navigation channel migrants and off‐channel migrants, areas of high mortality were identified between rkm 37 and rkm 8. Dispersion of juvenile salmonids into multiple pathways during downstream migration can be beneficial in terms of increased expression of life history diversity and resiliency to environmental perturbations. Our results, which document juvenile salmon migration pathways and associated travel time and survival through a large estuary, can be used to focus future research and management activities in areas identified as having high mortality and therefore can be used to aid in the recovery of Endangered Species Act‐listed salmon populations.