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STOCKTON FWO: Evaluation of Pre-Screen Loss and Fish Facility Efficiency for Delta Smelt at the State Water Project
California-Nevada Offices , August 7, 2009
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 Mike Marshall and Phil Voong (USFWS) and Ryan Mayfield (CDFG) release delta smelt at the State Water Project at Clifton Court Forebay in February 2009. (photo: USFWS)
 Mike Marshall and Phil Voong (USFWS) and Ryan Mayfield (CDFG) release delta smelt at the State Water Project at Clifton Court Forebay in February 2009. (photo: USFWS) - Photo Credit: n/a

This photo shows the release locations of delta smelt at Clifton Court Forebay and recapture at the Skinner Fish Facility. (photo: California Department of Water Resources) 

This photo shows the release locations of delta smelt at Clifton Court Forebay and recapture at the Skinner Fish Facility. (photo: California Department of Water Resources)  - Photo Credit: n/a

by Gonzalo Castillo, Stockton FWO

The Stockton Fish and Wildlife Office and cooperators completed the final field phase of a three year CALFED Science project to test the feasibility of a mass mark-recapture method to evaluate entrainment losses of juvenile and adult delta smelt at the State Water Project (SWP) due to water exports in the south Delta. The SWP has a fish salvage facility, the Skinner Fish Facility (SFF), operated by the California Department of Water Resources (DWR).  The SFF was originally designed to salvage fish species other than delta smelt, before the water is pumped into the California Aqueduct.

 

Culture and marking of delta smelt and subsequent experiments were conducted in close collaboration with staff from the University of California (UC Davis), Fish Conservation and Culture Laboratory (FCCL); the California Department of Fish and Game; the UC Davis Interdisciplinary Center for Plasma Mass Spectrometry; the U.S. Bureau of Reclamation and DWR.

 

During 2009, researchers evaluated:

1) The percent of fish recaptured at the SFF of the total released at the entrance of SFF (fish facility efficiency);

2) The percent of fish recaptured at SFF of the total released at the entry point of Clifton Court Forebay (CCF), a reservoir for SWP exports (percent recovery);

3) The fish losses in CCF (pre-screen loss).

 

In addition, the potential that some salvaged delta smelt juveniles could have been produced by mark-released adult fish was investigated and will be reported subsequently. Mass mark-recapture experiments were conducted in February and March 2009 (adults) and June 2009 (juveniles).  All fish were calcein-marked and adults were additionally photonic and strontium marked at the FCCL, which is adjacent to the SFF.

 

Fish facility efficiency estimates declined in successive releases: February (52.0%), March (44.0%) and June (24%). The percent recovery of fish released in CCF declined greatly over time: February (2.98%); March (0.42%) and June (0.03%). Correspondingly, pre-screen losses increased in successive releases: February (94.2%); March (99.0%) and June (99.9%).

 

The main conclusions were:

1) Delta smelt can be readily mass-marked to quantify entrainment losses;

2) Entrainment losses of delta smelt could be much higher at times compared to other species previously studied at the SWP;

3) Pre-screen loss was overwhelmingly the largest source of mortality for delta smelt;

4) CCF entrainment monitoring is needed to better interpret and validate critical relations between salvage statistics and the magnitude and variability of direct delta smelt losses.


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



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