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STOCKTONFWO:Water Tour for California Science and Technology Policy Fellows Program
California-Nevada Offices , November 9, 2011
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Attachment 1 - Water Tour handout
Attachment 1 - Water Tour handout - Photo Credit: Patricia Brandes, FWS
Water tour of the Delta participants with Pat Brandes.
Water tour of the Delta participants with Pat Brandes. - Photo Credit: Patricia Brandes
Discussion of the Delta Cross Channel with students from the California Science and Technology Policy Fellows Program.
Discussion of the Delta Cross Channel with students from the California Science and Technology Policy Fellows Program. - Photo Credit: Patricia Brandes

By Pat Brandes, Stockton Fish and Wildlife Office

The U.S. Fish and Wildlife Service Stockton Fish and Wildlife Office staff  recently spoke with students from the California Science and Technology Policy Fellows Program, on the role of the Delta Cross Channel in water conveyance and on juvenile salmon survival through the Sacramento-San Joaquin Delta. The briefing was part of a Water Tour of the Delta hosted on November 9, by the Sacramento Region Water Forum. FWS biologists explained how fish tagging studies have helped provide information on how the Delta Cross Channel influences juvenile salmon survival through the Delta.
 
The Delta Cross Channel is a water channel on the bank of the Sacramento River that diverts water from the river into a branch of the Mokelumne River. This 6,000-foot channel is key to maintaining a water quality balance. When the gates are open, fresh water is drawn from the Sacramento River for 15 miles to the San Joaquin River, then another 35 miles through Middle and Old rivers to the Tracy Pumpiing Plant.
 
The tour group met at the channel gates and learned how the Delta Cross Channel was built in the 1950s by the U.S. Bureau of Reclamation. 
 
Service biologists discussed the 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 and the juveniles must migrate downstream through the Delta to reach the ocean. 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).
 
Tour members heard about the results of studies by the Stockton Fish and Wildlife Office biologists that have shown a reduction in survival for juvenile salmon that are diverted into the interior Delta via the open Delta Cross Channel gates or Georgiana Slough. Early studies (using coded wire tag mark and recapture technology) show that survival is lower for juvenile salmon released into Georgiana Slough than those released on the main stem of the Sacramento River.
 
As a result of the early coded wire tag work done by the Stockton office, the DCC gates have been closed during key periods of juvenile outmigration to increase survival of the salmon through the Delta. More recently the Stockton FWO scientists have been using acoustic tag technology to more accurately determine the proportion of tagged juvenile salmon that enter the Delta Cross Channel and Georgiana Slough.
 
This newer technology also allows survival for specific routes to be estimated. Acoustic tag studies have found that closing the DCC gates do not always provide as large a benefit to fish as had been assumed in the past. They have also found that the proportion of salmon that migrate through Georgiana Slough and the open DCC is a function of downstream flow and the tides, with more fish 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.
 
The students on the tour asked thoughtful questions and were glad to see this example of science in action.


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



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