The Service determined on March 18, 2008 that a target OMR flow of -2,000 cfs would be protective of delta smelt. This is a continuation of last week's recommendation. The flow target is needed to protect delta smelt for the following reasons:
1) Recent salvage over the past week (March 10 through 16) has been lower than the past week, with 20 delta smelt caught at the export facilities. This indicates that actions taken over the past week to target an OMR flow of -2,000 cfs are benefiting the delta smelt by reducing entrainment at the facilities. Recent Spring Kodiak Trawl information has shown that some delta smelt continue to be distributed in the central and south delta and that spawning is likely occurring in these areas. With a high number of adult smelt already taken over the past two months based on last fall's low Fall midwater trawl index, the goal remains to minimize further entrainment or movement of delta smelt into the south delta.
2) Temperatures continue to remain in the spawning range for delta smelt, and spawning is likely occurring at a high rate. Larval delta smelt are likely becoming more numerous in the system and are easily 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.
The excedence of the target flows over the target of -3,000 during the week of March 10 did not have large effects to delta smelt. The three days of excedence were preceded by average OMR flows well below the -3,000 target and were followed by OMR flows below the target. The overall effect of the entire period with lower flows, a three day excedence, and lower flows again likely did not move delta smelt into the south and central delta where they could become vulnerable to entrainment.