Estimating survival and migration of coded wire and ultrasonic tagged late-fall Chinook smolts during their passage through Delta of the Sacramento – San Joaquin watershed
Introduction:
The impact of the State Water and Central Valley Project exports on juvenile salmon survival through the Delta has been difficult to quantify. Coded wire tag (CWT) studies have identified that survival is less in the interior Delta and potentially a function of exports. Although these past CWT experiments have provided useful data, they have not been able to estimate how many juvenile salmon from the Sacramento River enter the interior Delta and consequently how project exports impact survival through the entire Delta. This experiment paired an old technology (CWT’s) with a newer one (sonic tags) to estimate the survival of juvenile salmon through the Delta and compared the results. The ultrasonically tagged fish also provided information on how the juvenile salmon split at various channels as they migrated through the Delta. By releasing sonic and coded wire tags with the Delta Cross Channel (DCC) gates open and closed, we were able to see how survival and migration routes varied with DCC operation. The information obtained from this study will help us better understand the ramifications of project exports for juvenile salmon migrating through the Delta.
Objective:
The project has three specific technical objectives:
- Compare estimates of survival through the Delta using two independent methodologies – ultrasonic telemetry and coded wire tag mark and recapture methods.
- Determine migration pathways for juvenile salmon released at Sacramento as they migrate through the Delta
- Determine how survival and migration behavior differs with the Delta Cross Channel gates open (December release) versus closed (January release).
- Model survival and distribution probabilities
- Develop a statistically robust study design to determine survival and distribution probabilities for future studies
Methods:
In December of 2006 and January 2007, paired groups of juvenile salmon with ultrasonic and coded wire tags were released at Sacramento. The experiment used late-fall juvenile Chinook salmon obtained from Coleman National Fish Hatchery, situated on Battle Creek; a tributary of the upper Sacramento River. The tagged fish were transported to the release site and held in net pens until release. The December release was transported to the West Broderick Boat Ramp and held and released just downstream at a dock across from Old Sacramento. The January release was transported to, held at and released from the Discovery Park boat ramp. Sixty-three and 80 ultrasonically tagged juvenile late-fall salmon were released in December and January, respectively. The groups of ultrasonic tagged fish were paired with batches of approximately 70,000 coded wire tag fish. The paired groups were released at four discrete times, each on a slack tide, just prior to the ebb or flood tide over a 24 hour period. Releases were made in this manner to approximate the average condition of movement into the Delta over the tidal cycle.
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