The Service determined on March 11, 2008 that a target OMR flow of -2,000 cfs would be protective of delta smelt. This flow is needed to protect delta smelt for the following reasons:
1) 72 adult delta smelt were taken at the salvage facilities for the week of March 4 through March 10. This indicates that delta smelt continue to be distributed in the central and south delta and that spawning is likely occurring in these areas. Target flows reduced from -3,000 to -2,000 cfs are expected to reduce the number of delta smelt entrained at the facilities.
2) Delta water temperatures are now above 12 degrees C, therefore, larval delta smelt are likely becoming more numerous while at the same time they are moving up from the bottom of the channel into the middle and upper portion of the water column where they are more readily transported by flows. Since larval delta smelt are not strong swimmers, a flow of -2,000 cfs is needed to minimize or reduce the number of larval delta smelt who are transported into the south delta where they may become susceptible to entrainment or lethal temperatures later in the season.
Particle tracking modeling was one of the tools used for this decision and indicates that most particles from the central delta would not become entrained at OMR flows of -2,000 cfs.