| Movement and survival rates of Butte Creek spring-run Chinook salmon smolts from the Sutter Bypass to the Golden Gate Bridge in 2015, 2016, and 2017 - :20687 | National Marine Fisheries Service (NMFS)
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Movement and survival rates of Butte Creek spring-run Chinook salmon smolts from the Sutter Bypass to the Golden Gate Bridge in 2015, 2016, and 2017
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Movement and survival rates of Butte Creek spring-run Chinook salmon smolts from the Sutter Bypass to the Golden Gate Bridge in 2015, 2016, and 2017
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  • Description:
    California’s Central Valley (CCV) Chinook salmon stocks have declined substantially since the mid-1800s with most of them listed as threatened or endangered, or heavily supplemented by hatcheries. Butte Creek supports the largest population of CCV wild spring-run Chinook, and represents an important component of this ESU. However, little information exists on Butte Creek juvenile mortality during out-migration to the ocean, which is considered a critical phase to the overall population dynamics. We used the high resolution Juvenile Salmon Acoustic Telemetry System (JSATS), and a mark-recapture modeling framework to track the movement and estimate survival of migrating wild Chinook salmon smolts from lower Butte Creek to the Golden Gate Bridge in three distinctly different hydrologic periods (spring of 2015, 2016, and 2017). The fish tagged were a mix of genetically identified spring- run and fall-run Chinook juveniles, which were not visually distinguishable. Our results show that outmigrant smolt survival and receiver detection strongly varies by location and year. The highest survival of these outmigrant juveniles to the Golden Gate Bridge was observed in 2017 which was the wettest year of our study, and survival was extremely low in 2015 and 2016 (0.7% in 2015, 2.0% in 2016, and 10.0% in 2017). We observed that survival and migration varied significantly among years and regions; fish migrated faster and experienced higher survival in 2017 than in 2015 and 2016; fish migrated faster and experienced higher survival in the lower Sacramento River than in the Sutter Bypass, Delta and Bay. We also showed that release date and Delta flow are significantly correlated with survival rates of these outmigrating smolts. These results are largely driven by 2017 data. Indeed, 2017 tagged fish were released a month later than those in 2015 and 2016, and Delta flow and smolt survival were significantly higher than in the previous two years. More tagging years including measurements of more potentially important environmental factors (such as turbidity) are required to robustly identify the influence of various factors on Butte Creek spring-run Chinook outmigrant smolt survival.

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