Migration is often the most perilous stage of an organism’s life. In the case of the declining populations of Chinook salmon (Oncorhynchus tshawytscha) in California’s Central Valley, juvenile emigration from riverine origins to the ocean is a period of high mortality. Specifically, natural and anthropogenic factors within this system have been known to affect emigrating juveniles (smolts) movement and mortality rates. Knowing which variables influence movement and mortality and to what extent help in understanding how environmental factors shape migratory behavioral ecology. Additionally, in a system shared by four runs of Chinook salmon with different migration strategies and varying abundance over time, this information will provide comparative insight into the evolution and requirements of different migration strategies.

Advances in the miniaturization of acoustic telemetry have allowed the tagging and tracking of juvenile Chinook salmon throughout the Sacramento River watershed to the Pacific Ocean. This was made possible by an array of 330 acoustic monitors placed throughout the watershed, allowing for high spatial resolution movement and mortality estimates. I have tagged and released 200 to 300 late-fall run Central Valley Chinook salmon every year for three years from winter 2006/2007 to winter 2008/2009.

Results/Conclusions

The average movement rate for late-fall run Chinook salmon smolts emigrating through the Sacramento River watershed was 30.4 ± 19.6 km×d^-1. Movement rates were relatively faster in the upper Sacramento River than downstream in the Sacramento-San Joaquin Delta and Estuary. Of the fish released near the first barrier to anadromy, 4.3 % successfully made the 500 km migration to the Pacific Ocean, taking an average of 26.8 d. Mortality was about 80 % in the first 150 km of the upper reaches of the Sacramento River, 33 % within the lower 300 km of the river, and 60% in the estuary (85 km).

Preliminary analyses of the effects of environmental variables on movement have shown that the Chinook salmon smolts exhibit strong diel patterns, and that increases in movement rates correlate with increases in pulse flows due to storm events. Preliminary analyses of mortality patterns have shown that the presence of anthropogenic water diversions and dams explain some of the variability in mortality rates.

The knowledge provided by data analyses from this study will elucidate migration dynamics of this ecologically and economically important species. These findings will allow more efficient management of the imperiled fishery, and potentially allow predictive power for future cohorts based on conditions alone.