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STOCKTON FWO: Stocktonoffice participates in Water Tour for California Science and Technology Policy Fellows Program
California-Nevada Offices , November 10, 2010
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By Patricia Brandes

Fish Biologist, Pat Brandes, of the Stockton Fish and Wildlife office (STFWO) briefed students from the California Science and Technology Policy Fellows Program, on the role of the Delta Cross Channel (DCC) on water conveyance and juvenile salmon survival through the Sacramento-San Joaquin Delta.  The briefing was part of a water tour of the Delta hosted on Nov. 10, 2010, by the Sacramento Region Water Forum.  The group was introduced to California Water by Tom Gohring of the Water Forum and was told about The Water Forum Agreement and Collaborative Policy Making by Jeff Loux of the Center for Collaborative Policy (CCP) at Sacramento State.  The group also visited the Freeport Regional Water Project and the M&T Staten Ranch as part of their tour.

The group met in the field at the site of the Delta Cross Channel gates and received a presentation that explained to participants that the Delta Cross Channel was built in the 1950’s by the U.S. Bureau of Reclamation.  The Delta Cross Channel is designed to facilitate the movement of Sacramento River water through the interior Delta, via the Mokelumne River, to the south Delta for export purposes.  Brandes discussed the general life history of Chinook salmon in the Sacramento River basin, and the importance of the Delta to Chinook salmon in the Central Valley.  Adult Chinook salmon swim upstream through the Delta to spawn in the upper rivers.  The juveniles must migrate downstream through the Delta to reach the ocean.  She also explained that the Sacramento River basin is unique in that it has four races of Chinook salmon; winter run (listed as endangered by the Endangered Species Act (ESA)), spring run (listed as threatened by the ESA) and fall and late-fall runs (species of concern). 

The presentation focused on the results of studies conducted by the Stockton FWO on the impact of the Delta Cross Channel on juvenile salmon survival through the Delta.   Early studies using coded wire tag mark and recapture technology showed that survival is lower for juvenile salmon released into the interior Delta relative to those that migrate downstream via the main stem Sacramento River.  These results indicated that the open Delta Cross Channel may contribute to lower survival of out migrating juvenile Chinook salmon by allowing a greater proportion of fish to be diverted into the interior delta, than would be diverted with the Delta Cross Channel closed.  In recent years the STFWO has been using acoustic tag technology to more accurately determine how fish behave at various junctions in the Delta, and at the Delta Cross Channel and Georgiana Slough specifically.  This relatively new technology allows survival for specific routes to be estimated.   As a result of the early coded wire tag work done by the STFWO the Delta Cross Channel gates have been closed during periods of high abundance of out-migrating juvenile salmon.  Using the acoustic tag technology we have found that closing the channel gates does not always provide as large a benefit as has been assumed in the past.  Sometimes when the gates are closed a greater proportion of the tagged salmon enter the interior delta through Georgiana Slough than when the gates are open.   The proportion of salmon that migrate through the interior Delta through Georgiana Slough or the open Delta Cross Channel is a function of downstream flow and the tides.  More fish can be exposed to both diversions multiple times, when the flow is low and during a flood tide due to the fish moving both upstream and downstream during these times.

Brandes informed the tour participants of the studies that have been conducted to the date, associated with diversion of juvenile salmon into the interior Delta through either the Delta Cross Channel or Georgiana Slough.  Many of the students asked questions and were very interested in the information presented.  Sarah Foley, Director of the Water Forum was appreciative of Brandes helping the students understand some of the issues associated with California’s “plumbing.” 

Contact Info: Yvette Sky, (209) 946-6400 x301, yvette_sky@fws.gov



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