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Smelt Status – Spring 2022

Initial 2022 late winter surveys indicate modest improvement in longfin and Delta smelt populations. Previous posts outlined the grim status of the two species.1

Delta Smelt

Five larval Delta smelt were captured in the first 20-mm survey of 2022. They were captured in the Cache Slough Complex in late March (Figure 1). After more of the survey is processed, further numbers of recently hatched larvae may be noted, indicating a slight improvement in the nearly extinct population.

Longfin Smelt

Larval longfin smelt were widely collected in the late February Smelt Larva Survey (Figure 2). Highest densities were in the low-salinity zone (Figures 2 and 3). Numbers were higher than in recent years, likely reflecting good early winter condition after high December Valley-wide precipitation.

These modest improvements in the endangered smelt populations will likely be short-lived as the State Board enacts the Temporary Urgency Change Petition (TUCP) of the Department of Water Resources and the Bureau of Reclamation in response to the winter 2022 drought. The TUCP will further reduce freshwater outflow and move the low-salinity zone upstream into the Delta (Figure 4 and 5). Depleted reservoir storage resulting from excessive storage releases to water contractors in 2020 and 2021 created the need for the petition. Despite the depleted reservoir storage, less extreme measures are possible that would provide some protection for the smelt, as discussed in an April 5 post.

Figure 1. Partial results of late March 2022 20-mm Survey, showing location of 5 identified Delta smelt larvae in Cache Slough Complex.

Figure 2. Results of late February 2022 Smelt Larva Survey, showing density of longfin smelt larvae collected in Bay-Delta survey region. Red outline is area of low-salinity zone (2000-8000 EC).

Figure 3. Plot of longfin smelt larvae catch per 1000 cubic meters sampled in late February Smelt Larva Survey (shown in Figure 2). Red curve shows that larvae were concentrated in the low-salinity zone (2000-8000 EC).

Figure 4. Salinity at confluence of Sacramento and San Joaquin Delta channels in eastern Suisun Bay in late winter – early spring 2022.

Figure 5. Calculated Delta outflow in late winter – early spring 2022.