The Service has determined that the following recommendation will be protective of delta smelt. The projects will implement a 7-day average OMR target of -2,500 cfs, and to limit increases in total project pumping to no more than 1,000 cfs on any given day. If, in the coming week, the combined adult delta smelt (expanded) salvage were to exceed 24, or if delta smelt were to be detected at either facility in the larval fish sampling on any two days, then Reclamation and DWR would modify operations to meet a 7-day average OMR target flow of -2,000 cfs within seven days of these events.
These flow targets are needed to protect delta smelt for the following reasons:
1. Delta water temperatures are about 17.5 degrees C (three station average of Mossdale, Rio Vista and Antioch) which is within the range of delta smelt spawning, which is 12-18 degrees C. Spawning is likely occurring throughout the delta and there are likely larval delta smelt as well as adult delta smelt in the system. To date, one larval delta smelt has been caught at the salvage facilities although none have been caught in sampling efforts in the delta, but this is probably due to the difficulty in catching small sized larval delta smelt. As these fish get larger, sampling efforts will become more effective at sampling larval delta smelt and will help give a more detailed picture of the current delta smelt distribution in the delta. There is concern that no larval delta smelt have been caught yet this season in the trawling efforts.
2. The goal remains to prevent delta smelt from becoming entrained into the south delta where they can become entrained at the facilities or succumb to high water temperatures later in the season. 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. Even though only one delta smelt was salvaged at the export facilities over the past week, there are still probably delta smelt in the central delta which could become entrained if actions to minimize OMR flows are not taken.
Particle tracking modeling was a tool used for this decision, and indicates that most larval delta smelt would not become entrained at the facilities at flows of -2,500 to -2,000 OMR.