Effects of the proposed California WaterFix North Delta Diversion on survival of juvenile Chinook salmon (Oncorhynchus tshawytscha) in the Sacramento-San Joaquin River Delta, northern California

Survival of out-migrating juvenile Chinook salmon (Oncorhynchus tshawytscha) in the Sacramento–San Joaquin River delta, California, USA, varies by migration route. Survival of salmonids that enter the interior and southern Delta can be as low as half that of salmonids that remain in the main-stem Sacramento River. Reducing entrainment into the higher-mortality routes, such as Georgiana Slough, should increase overall survival. In spring 2014, a floating fish-guidance structure (FFGS) designed to reduce entrainment into Georgiana Slough was deployed just upstream of the Georgiana Slough divergence. We used acoustic telemetry to evaluate the effect of the FFGS on Chinook entrainment to Georgiana Slough. At intermediate discharge (200–400m3 s–1), entrainment into Georgiana Slough was five percentage points lower when the FFGS was in the on state (19.1% on; 23.9% off). At higher discharge (>400m3 s–1), entrainment was higher when the FFGS was in the on state (19.3% on; 9.7% off), and at lower discharge (0–200m3 s–1) entrainment was lower when the FFGS was in the on state (43.7% on; 47.3% off). We found that discharge, cross-stream fish position, time of day, and proportion of flow remaining in the Sacramento River contributed to the probability of being entrained to Georgiana Slough.

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Comparison of Length-at-Date Criteria and Genetic Run Assignments for Juvenile Chinook Salmon Caught at Sacramento and Chipps Island in the Sacramento–San Joaquin Delta of California

San Francisco Estuary and Watershed Science ◽

10.15447/sfews.2021v19iss3art2 ◽

2021 ◽

Vol 19 (3) ◽

Author(s):

Patricia Brandes ◽

◽

Brian Pyper ◽

Michael Banks ◽

David Jacobsen ◽

...

Keyword(s):

Chinook Salmon ◽

Oncorhynchus Tshawytscha ◽

Central Valley ◽

River System ◽

Population Status ◽

Juvenile Chinook Salmon ◽

Late Fall ◽

San Joaquin River ◽

Juvenile Chinook ◽

Specific Timing

There are four distinct runs of Chinook Salmon (Oncorhynchus tshawytscha) in the Central Valley, named after their primary adult return times: fall, late-fall, winter, and spring run. Estimating the run-specific composition of juveniles entering and leaving the Sacramento–San Joaquin Delta is crucial for assessing population status and processes that affect juvenile survival through the Delta. Historically, the run of juvenile Chinook Salmon captured in the field has been determined using a length-at-date criteria (LDC); however, LDC run assignments may be inaccurate if there is high overlap in the run-specific timing and size of juveniles entering and leaving the Delta. In this study, we use genetic run assignments to assess the accuracy of LDC at two trawl locations in the Sacramento River (Delta entry) and at Chipps Island (Delta exit). Fin tissues were collected from approximately 7,500 juvenile Chinook Salmon captured in trawl samples between 2007 and 2011. Tissues were analyzed using 21 microsatellites to determine genetic run assignments for individuals, which we compared with LDC run assignments. Across years, there was extensive overlap among the distributions of run-specific fork lengths of genetically identified juveniles, indicating that run compositions based on LDC assignments would tend to underestimate fall-run and especially late-fall-run compositions at both trawl locations, and greatly overestimate spring-run compositions (both locations) and winter-run compositions (Chipps Island). We therefore strongly support ongoing efforts to include tissue sampling and genetic run identification of juvenile Chinook Salmon at key monitoring locations in the Sacramento–San Joaquin River system.

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