In a March 2020 post, I described the status of the Delta smelt through 2019.  This post updates the status with the most recent 2020 information.  Delta smelt continue to be absent from the standard long-term surveys and their related indices.  However, some Delta smelt were collected in 2020 in selected locations of the Bay-Delta during focused intensive special surveys designed to find remaining survivors.  Larval and juvenile Delta smelt were collected in low numbers in the Bay and north Delta (Figure 1).  Pre-adult Delta smelt were also collected in summer trawl surveys (Figure 2).

The north Delta habitats where a few Delta smelt persevere continue to be plagued by constant stressful if not lethal water temperatures (Figures 3 and 4).

As I stated in a prior post, Delta smelt would benefit from increased net flows through the north Delta during the spring and summer.

Figure 1. Numbers of larval and juvenile Delta smelt collected in the spring Enhanced Delta Smelt Monitoring (EDSM) 20-mm nets. Source.

Figure 2. Numbers of pre-adult Delta smelt collected in the summer Enhanced Delta Smelt Monitoring (EDSM) Kodiak trawls. Source.

Figure 3. May through September 2020 water temperature and net tidally-filtered flow in the lower ship channel near Rio Vista. Note water temperatures fall 1-2ºC when net flows increase.

Figure 4. May through September 2020 water temperature and net tidally-filtered flow in Cache Slough near Rio Vista. Note water temperatures generally fall 1-2ºC when net flows increase.