Very Few Marked Delta Smelt Recovered at Skinner Fish Facility
Initial results from a three-year CALFED Science-funded research project showed that most delta smelt released into Clifton Court Forebay died there before they ever reached the louvers and screen at the State Water Project’s (SWP) Skinner Fish Facility where fish are salvaged for return to Delta waters.
This pilot project is the first experimental evaluation of the relation between delta smelt salvage at the Skinner Facility and underlying entrainment losses at the SWP in the south Delta. Fish are considered “entrained” when they enter a diversion point, which for the State Water Project is Clifton Court Forebay.
If corroborated by future tests, this could have implications for the management of Clifton Court Forebay and/or regulatory accounting of smelt loss at the SWP.
The Skinner Fish Facility was originally designed to salvage fish species other than delta smelt such as Chinook salmon and striped bass. Entrainment losses in Clifton Court Forebay and fish salvage efficiency have been estimated for these species in previous studies, but do not necessarily apply to delta smelt.
The study, led by Gonzalo Castillo of the US Fish and Wildlife Service, was designed to test the feasibility of a mass mark-recapture method to evaluate pre-screen losses and salvage efficiency estimates of juvenile and adult delta smelt at the SWP due to water exports in the south Delta.
“The number of marked juvenile and adult delta smelt recovered at the Skinner Fish Protective Facility was negligible when compared to the corresponding number of marked delta smelt released in Clifton Court Forebay,” Castillo said.
“Monitoring pre-screen losses of delta smelt in Clifton Court Forebay is critical to interpret the relation between salvage statistics and direct entrainment losses of delta smelt in the State Water Project.”
“Small variations in pre-screen loss can have major effects on delta smelt entrainment losses,” said Castillo. “For example, after fish were released in Clifton Court Forebay, the estimated average difference in pre-screen losses for these three experiments was less than 7 percent, but the total number of delta smelt lost in Clifton Court Forebay and the Skinner Fish Facility per recaptured fish varied dramatically (from 37 to 236 fish between consecutive adult experiments, and 3,602 fish for the juvenile experiment).”
More details on this project can be found at:
the U.S. Fish and Wildlife Service’s Fish and Wildlife Journal