Transportation of acoustically tagged fish from hatchery to release site. (photo: USFWS)

Tempering acoustically tagged fish prior to release into the San Joaquin River. (photo: USFWS)

by Pat Brandes and Shannon Brewer, Stockton FWO

During 2008, the Stockton Fish and Wildlife Office (FWO) participated in juvenile Chinook salmon survival studies.  Acoustic tags were used as a tool to better estimate survival of juvenile salmon through the Sacramento-San Joaquin Delta.  During the Spring, the Stockton office participated in a collaborative study called the Vernalis Adaptive Management Program (VAMP).  The objective of VAMP is to estimate juvenile survival in the lower San Joaquin River in relation to discharge and water project exports. The VAMP study has been conducted annually since 2000 using coded-wire-tagged salmon, but low returns of adult salmon in Fall 2007 prevented use of coded-wire tags because of the number of study fish required for adequate sample size.  The Stockton office participated by assisting in tagging 1,000 fish used in the study with acoustic transmitters and acclimating and releasing the fish over four temporal periods at two release sites. In addition, the Stockton office helped to maintain the receiver array and collect stored data from eleven of the acoustic receiver stations deployed throughout the Delta.  

The Delta Cross Channel was built in 1951 in the north Delta to facilitate the movement of Sacramento River water into the interior Delta for pumping by the Central Valley Project and State Water Project.  During Fall 2008, a separate acoustic-tag study was implemented in the north Delta to estimate survival of juvenile Chinook salmon in relation to gate positions (open or closed).  Earlier mark and recapture studies indicated survival was lower for juvenile salmon that migrate though the interior Delta compared to those that migrate via the Sacramento River; however, it is unclear what proportion of juvenile salmon enter the interior Delta through the Delta Cross Channel.  This is the third year that we have implemented this study.  Survival via specific migration routes is being modeled by CALFED Science Program fellow Russ Perry from the University of Washington. 

The Stockton FWO is collaborating on a separate, but related effort, with the U.S. Geological Survey (USGS).  The North Delta Salmon Outmigration Study Primary Investigator is Jon Burau of the USGS who is being assisted by the Stockton FWO.  The ultimate goal of this study is to predict likely survival rates of juvenile salmon in relation to migration routes.  It is similar to the previous study because it relates survival to gate positions, but it is a much larger effort with nearly 6,000 fish being tagged and released.  In addition, this study will examine hydrologic patterns at gate locations in relation to salmon movement.  The Stockton FWO is providing logistical support as well as biologists to assist with curation, tagging, holding, and releasing salmon 24-hours per day throughout the duration of the study.