Smelt -- Delta Actions Team Real-time Assessments

Biological

• Delta smelt life stages: Adult, Juvenile

• Abundance estimate: 6821 (95% CL: 1,477 to 20,185) as of the week of December 29, 2025–January 2, 2026

• Releases: A total of 163,349 cultured Delta smelt have been released for WY 2026. The most recent release of 24,606 fish occurred in Sacramento River at Rio Vista on Dec 16, 2025.

• Delta smelt count: 33 adult Delta smelt and 24 juvenile Delta smelt have been detected this water year. See Table 1 for recent detections, Figure 1 for spatial distribution, and Figure 2 for temporal distribution.

• Delta smelt salvage: 0 Delta smelt have been salvaged, and the cumulative seasonal salvage is 0.

Notes

• Since there are few recent detections of Delta smelt, estimation of distribution within the Delta is limited.
• As mentioned in EDSM reporting, fork length ranges reported for Delta smelt and longfin smelt life stages are defined by permit reporting purposes and are not intended to delineate cohorts or distinguish from hatchery or wild origin. See Table 1 caption for fork-length ranges for age groups of Delta smelt.
• See SacPAS SMT Page for additional details on releases and detection in surveys and salvage.
• Historical salvage trends can be found at: SacPAS Salvage Timing

Environmental

Real-time Assessment Thresholds

Evaluation

Delta smelt:

1. After the start of entrainment management, is JPF < 0 and is daily average turbidity ≥ 12 FNU in the OMR corridor (stations OBI, HOL, and OSJ)?

   No, these conditions will not be met this week.

2. Has the average water temperature at Jersey Point or Rio Vista not exceeded 53.6�F (12�C) for 3 consecutive days and/or has this action already been taken during WY 2026?

   Temperature at Rio Vista or Jersey Point has not exceeded the threshold. The Delta smelt adult entrainment management action has not yet been taken in WY 2026.

3. What is the evidence for the onset of Delta smelt spawning?

   Upstream migration for Delta smelt occurs between September and December and in response to “first flush” conditions (Sommer et al. 2011, Grimaldo et al. 2009). Migration typically ranges one to four weeks after flow and turbidity increases, based on salvage data (Sommer et al. 2011). Historically, detections of ripe Delta smelt began in January and peaked in February and March and the majority of Delta Smelt spawning occurs within a temperature range of 9-18˚C (Damon et al. 2016). Based on historical monitoring data from the past few years, first detection of larvae in the Central and South Delta has typically occurred by mid to late March. Based on historic data the migration is likely occurring now, and the onset of spawning has likely not yet occurred.

4. After the onset of spawning, have the following conditions occurred: JPF < 0, daily average turbidity is ≥12FNU in the South Delta, and PTM modeling indicates OMRI no more negative than -3500 cfs for at least 7 days would avoid ≥5% entrainment of the Delta smelt population at facilities after 30 days?

   The onset of spawning is unlikely to have occurred and JPF is not < 0 cfs.

Biological

• Longfin smelt life stages: Adult, Juvenile, NA, Larva

• Longfin smelt count: 277 adult, 439 juvenile, and 10 larval longfin smelt have been detected this water year. See Table 3 for recent detections, Figure 3 for spatial distribution, and Figure 4 for temporal distribution.

• Longfin smelt salvage: 0 longfin smelt have been salvaged, and the cumulative seasonal salvage is 0.

Real-time Assessment Thresholds

Evaluation

Longfin smelt:

1. If JPF < 0, what is the trajectory of annual loss of adult longfin smelt and is it likely to exceed 5% of the adult population estimate? Is South Delta entrainment expected to decrease due to a reduction in export pumping?

   JPF is not < 0 cfs and we have not detected any adult longfin smelt in salvage. The ZOI analysis indicates little change in the hydrodynamic footprint between current and forecasted flows this week. The analysis showed a 65 km difference in hydrodynamic footprint between OMRI of –3500 cfs and –5000 cfs, indicating a low risk of entrainment.

2. For larval and juvenile longfin smelt, if JPF < 0 cfs, do particle tracking models show a moderate to high difference in particle fates across different OMRI scenarios? Does Zone of Influence modeling show moderate to high changes in hydrodynamic footprint across different OMRI scenarios? Are these effects anticipated to cause a population decline?

   JPF is not less than zero. No PTM was run this week. ZOI modeling shows moderate changes in hydrodynamic footprint between OMRI scenarios.

3. Is there additional information or other analyses that should be considered in this evaluation?

   Additional information may be discussed if needed at the DAT call.