Sensitivity of survival to migration routes used by juvenile Chinook salmon to negotiate the Sacramento-San Joaquin River Delta
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Populations of juvenile salmon emigrating from natal rivers to the ocean must often traverse different migratory pathways that may influence survival. In regulated rivers, migration routes may consist of a network of channels such as in the Sacramento-San Joaquin River Delta, or of different passage structures at hydroelectric dams (e.g., turbines or spillways). To increase overall survival, management actions in such systems often focus on altering the migration routing of fish to divert them away from low-survival routes and towards high-survival routes. Here, we use a 3-year data set of route-specific survival and movement of juvenile Chinook salmon in the Sacramento-San Joaquin Delta to quantify the sensitivity of survival to changes in migration routing at two major river junctions in the Sacramento River. Our analysis revealed that changes in overall survival in response to migration routing at one river junction depended not only differences in survival among alternative routes, but also on migration routing at the other river junction. Diverting fish away from a low-survival route at the downstream river junction increased population survival by less than expected, given the difference in survival among routes, because part of the population used an alternative migration route at the upstream river junction. We also show that management actions that influence only migration routing will likely increase survival by less than actions that alter both migration routing and route-specific survival. Our analysis provides an analytical framework to help fisheries managers quantify the suite of management actions likely to maximize increases in population level survival.
KeywordsMigration Telemetry Juvenile salmon Sacramento-San Joaquin Delta Survival
Funding for R.W.P’s involvement with this project was provided by a CALFED Science Fellowship, Agreement No. U-04-SC-005 with the California Bay-Delta Authority. Tagging of juvenile salmon, ultrasonic station deployment and interrogation, and tag-detection database maintenance were supported by a grant from the California Bay-Delta Authority by Agreement No. U-05-SC-047. We thank the staff of Coleman National Fish Hatchery for providing the late-fall Chinook and logistical support for this study. Staff of the Stockton U.S. Fish and Wildlife Office gratefully assisted with fish transportation and release. We thank two anonymous reviewers for comments that substantially improved this manuscript.
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