Migration route selection of juvenile Chinook salmon at the Delta Cross Channel, and the role of water velocity and individual movement patterns
We examined movement tracks of ultrasonic-tagged juvenile Chinook salmon (Oncorhynchus tshawyscha) smolts at the juncture of two migratory pathways. This migratory juncture occurs where the Delta Cross Channel splits from the Sacramento River in California’s Sacramento–San Joaquin Delta. Smolt tracks were analyzed to compare the importance of river flow and individual parameters in migratory route selection. The two routes differ significantly in smolt survival probabilities (Perry et al. N Am J Fish Manag 30:142–156, 2010), thus a clearer understanding of the variables contributing to route selection will be valuable for management of this declining species. A comparison of the two migratory groups showed that fish remaining within the Sacramento River: 1) Encountered the migratory juncture when river water velocities were much higher than those in the Delta Cross Channel (p < 0.0001), 2) showed more direct swimming paths (p = 0.03) and 3) migrated at higher speeds (p = 0.04). Logistic regression models showed that the ratio of mean water velocity between the two routes was a much stronger predictor of ultimate route selection than any other variable tested. However, parameters for both the lateral position of smolts within the river and smolt size added predictive power to the final model. Our results suggest that river flow remains the most important variable for predicting smolt migration route, but note that knowledge of individual smolt attributes and movement patterns can increase our predictive ability.
KeywordsUltrasonic telemetry Positioning system Sacramento–San Joaquin Delta Water velocity
We thank the U.S. Fish and Wildlife Service and the staff of Coleman National Fish Hatchery for providing the late-fall Chinook and logistical support for this study. Thanks also to those from the National Marine Fisheries Service who conducted tag implantation surgeries: Arnold Amman, Cyril Michel, Heidi Fish, and Gabriel Singer. Gabriel was also invaluable for his work in the field, helping to maintain and download the ultrasonic positioning array. In addition, we are grateful to the staff of the U.S. Fish and Wildlife Service in Stockton, CA for assisting with tagging, and transport, holding, and release of tagged fish, as well as staff from the USGS Columbia River Research Lab who also assisted with the release of fish. Finally, many thanks to those of the UC Davis Biotelemetry Lab who worked in the field to maintain and download ultrasonic monitors located throughout the Central Valley and Bay-Delta region, especially Michael Thomas and Eric Chapman.
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