Effects of predator and flow manipulation on Chinook salmon (Oncorhynchus tshawytscha) survival in an imperiled estuary

Abstract

We evaluated the effects of non-native, pi- scivorous fish removal and artificial flow manipula- tion on survival and migration speed of juvenile Chinook salmon, Oncorhynchus tshawytscha, emi- grating through the eastern Sacramento-San Joaquin Delta of California (Delta) using a Before-After- Control-Impact study design. Acoustically-tagged salmon survival increased significantly after the first predator reduction in the impact reach. However, sur- vival estimates returned to pre-impact levels after the second predator removal. When an upstream control gate opened (increasing flow and decreasing tidal ef- fect) juvenile salmon emigration time decreased and survival increased significantly through the impact reach. Though a short-term, single season experiment, our results demonstrate that predator control and hab- itat manipulation in the Delta tidal transition zone can be effective management strategies to enhance salmon survival in this highly altered system.