Using Acoustic Tags to Estimate the Potential Impact of Exports on Juvenile Salmon Survival Through the Delta

The impact of the State Water Project (SWP) and Central Valley Project (CVP) water exports on juvenile salmon survival through the north Delta has been difficult to quantify. Coded wire tag (CWT) studies conducted by the USFWS have shown that juvenile Chinook salmon survival is lower in the interior Delta, compared to the mainstem Sacramento River, and potentially a function of water exports.  Newman and Brandes (2010), determined there was a significant amount of noise associated with the relationship between water exports and relative interior Delta survival – in part due to the lack of precision in survival estimates based on the recovery of coded wire tags.  In addition, the past CWT experiments have not been able to estimate how many juvenile salmon from the Sacramento River enter the interior Delta and consequently how water exports may impact survival through the entire Delta.  Since 2006, data have been obtained using VEMCO acoustic tags to determine 1) the relative difference in survival for smolts entering the interior Delta versus those migrating down the main-stem Sacramento River, 2) whether the relative difference in survival for juvenile salmon entering the interior Delta is potentially related to water exports, and similar to the relationship obtained using CWT’s, 3) the proportion of tagged fish migrating from Sacramento River that are diverted into the interior Delta with the Delta Cross Channel gates open and closed, and 4) where the mortality in the interior Delta appears to be occurring.  The information obtained from this study will help us better understand the potential impacts of water exports on juvenile salmon migrating through the Delta.