Category Archives: Smelt

Longfin Smelt 2021

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In a 6/15/21 post, I had a grim outlook for longfin smelt for the summer of critical drought year 2021.  My concern has proven warranted.

The June Townet Survey (6/7-6/10) found longfin juveniles concentrated in the Sacramento River channel of the western Delta (Figure 1) in water temperatures of 19-21ºC (Figure 2), very close to stressful, low growth, poor survival conditions for longfin (>20ºC).  The area was within the low salinity zone, where juvenile smelt concentrate in spring.  In conditions of low Delta outflow in drought years like 2021, the low salinity zone encroaches into the western Delta, where the zone is prone to warming without the cooler Bay air temperatures.  The zone remained in the western Delta through the summer of 2021, with sustained water temperatures of 21-23ºC.

The September Midwater Trawl Survey collected only one longfin smelt, a minimum catch for that survey (Figure 3).  This catch total was similar to those observed in late summer of other drought years (07-08, 15, and 20).

A 2017 paper by UC Davis scientists concluded that extinction of Delta smelt and longfin smelt was not inevitable if the necessary recovery actions were soon implemented.  The paper’s recommended actions have as yet not been implemented, and conditions have even become worse in recent years, especially in the 2021 drought.  Delta smelt are now virtually extinct in the wild, with longfin smelt likely to follow soon.

Figure 1. Catch per unit effort of longfin smelt in survey #1 of CDFW/IEP Townet Survey in June 2021.

Figure 2. Water temperature in lower Sacramento River channel in western Delta in early June 2021.

 

Hatchery Delta Smelt 2021

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Efforts continue to gain approval for releasing hatchery-raised delta smelt in the San Francisco Bay-Delta Estuary. However, given a poor prognosis for a successful introduction, the chances of approval are not good.1  The biggest obstacle is the absence of a location to release the hatchery-raised fish that will allow their survival and thus contribute to the species’ recovery. Another problem is the potential detrimental effect on the remaining wild smelt from genetic compromise.

To me, the answer to the second issue is clear. With few if any “wild” delta smelt left on Earth, it is essential to get as many hatchery smelt out into the wild as soon as possible to save the species. Let the genetics get worked out later by Mother Nature.

Two locations for release of hatchery smelt seem most plausible: the low salinity zone in the west Delta/eastern Suisun Bay and the Deep-Water Shipping Channel in the north Delta. These are primary late spring and early summer nursery areas that are most likely to have the right habitat conditions (water temperature and low salinity) and food supply. These two locations were the last known concentrations of juvenile delta smelt (Figure 1) from the last strong adult spawn in 2012 (Figure 2).

The better of the two sites is the eastern-Bay/west-Delta location, because the ship-channel gets too warm by summer (Figure 3). In contrast, the region between Collinsville in eastern Suisun Bay and Decker Island in the west Delta is cooler and within the low salinity zone (Figures 4 and 5). A nighttime near-bottom release into cooler, deeper channel waters would give the hatchery smelt at least a minimum opportunity to acclimate to the warm Bay-Delta waters.2

Figure 1. Last known prime late spring and early summer nursery area of delta smelt (2012, 20-mm survey). Red lines denote approximate location of X2 (~2000-4000 EC) at the time.

Figure 2. Adult delta smelt catch index from monthly winter trawl surveys 2002-2021.

Figure 3. Water temperature (ºC) and salinity (EC) in spring 2020 in Deep Water Ship Channel.

Figure 4. Water temperature (C) and salinity (EC) in spring 2021 in Sacramento River channel near Collinsville in eastern Suisun Bay.

Figure 5. Water temperature (ºC) and salinity (EC) in spring 2021 in Sacramento River channel near Decker Island in the western Delta.

Longfin Smelt 2021 – Another Poor Year

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The Bay-Delta longfin smelt population, listed as threatened under the California Endangered Species Act, is having another poor year because of the Bay-Delta habitat conditions in critically dry year 2021. Winter spawning and early rearing habitat conditions were poor due to low Delta outflow. Spring conditions have been similarly poor, with low Delta outflows and high water temperatures. Summer conditions will be even worse.

Winter

As in prior dry years, longfin spawned in the Delta in winter 2021. Their newly hatched pelagic larvae accumulated in the low salinity zone in eastern Suisun Bay close to Chipps Island near the city of Pittsburg (Figures 1 and 2). In wetter years, longfin larvae accumulate further west in western Suisun Bay and San Pablo Bay, and are also more likely to spawn in Bay tributaries, especially the Napa River. With Delta export pumps diverting about one-third of winter freshwater inflow to the Delta and Bay, significant numbers of larval longfin smelt were susceptible to being drawn into the central and south Delta, away from their low salinity zone nursery area in eastern Suisun Bay.

Spring

With low spring Delta outflows of 3000-6000 cfs, similar to critical drought years 2014 and 2015 (Figure 3), longfin juveniles were concentrated in the low salinity zone in the western Delta (Figure 4). In that location, they are more vulnerable to Delta exports than in the prior winter, and are also subjected to warmer water temperatures (Figure 5) detrimental to their survival (Jeffries et al. 2016).1

Summer

The prognosis for the summer is grim, given expected water temperatures over 68ºF under low flows allowed under the Temporary Urgency Change Petition (Figure 5).

Population Response

The combination of low outflow (poor habitat), vulnerability of larval and juvenile longfin smelt to export, and reduced numbers of adult spawners that have survived in recent years leads to low population recruitment (Figure 3).2

Summary and Conclusions

In a critically dry year like 2014, 2015, or 2021, Delta outflows should not fall below 6,000-8,000 cfs on a daily or tidally filtered basis (Figure 3). Such outflows keep the low salinity zone west of the Delta in Suisun Bay, where water would be cooler and longfin would be less likely to be drawn into the central and south Delta. State recovery planning for longfin smelt should also proceed as has been recommended.3

Figure 1. Catch distribution of larval longfin smelt in the mid-January 2021 larval fish survey. Red area is approximate location of low salinity zone. Red arrow is net direction of west Delta flow toward south Delta export pumps. Data Source: CDFW survey online report.

Figure 2. Catch distribution of larval longfin smelt in the February 2021 larval fish survey. Red area is approximate location of low salinity zone. Red arrow is net direction of west Delta flow toward south Delta export pumps. Data Source: CDFW survey online report.

Figure 3. Delta outflow in spring and early summer 2014, 2015, and 2021. Note the sharp decline in late May 2021 (blue line) following approval of Temporary Urgency Change Petition (TUCP).

Figure 4. Catch distribution of larval longfin smelt in the May 2021 20-mm fish survey #5. Red area is approximate location of low salinity zone (2-4 EC). Blue areas are higher salinity zones in Bay. Red line is approximate location of X2. Data Source: CDFW survey online report.

Figure 5. Longfin Recruits (Fall Midwater Trawl Index) vs Spawners (Index from two years prior) in Log10 scale by water year. The relationship is very strong and highly statistically significant. Adding Delta outflow in winter-spring as a factor makes the relationship even stronger. The 2019 brood year index was lower than expected, given the potential number of spawners (from the relatively high 2017 index) and 2019 having been a wet year. The 2020 index is as expected for a dry year, with low spawner numbers.

Longfin Smelt – 2020

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In a February 2020 post on the status of longfin smelt, I lamented the poor 2019 population index (Figure 1) and thus made a grim prediction for the future of the Bay-Delta sub-population of this state-listed endangered species.  The index in wet year 2019 should have been 10 times higher (one higher in log number).  Preliminary survey results suggest that the 2020 population index for longfin smelt will likely be as poor as those in 2018 and 2019.

In Figure 1 below, the 2020 index will likely show as a red 20 just above the red 14.  Most of the 2020 spawners came from the 2018 spawners (green 18 in Figure 1).  Like the 2018 spawn, the 2020 year class grew up in a drier year, upstream in Suisun Bay and the western Delta (Figure 2), as compared to a more western Bay distribution like wet year 2019 (Figure 3).

I am very concerned what will happen if winter 2021 stays dry and there are thus two dry water years in a row (2020 and 2021).  This would drive the 2021 production index down to 2015-16 levels.  Coupled with the absence of Fall-X2 flows in 2020 and the unusually low 2019 longfin index, a second straight dry year presents a serious threat to the population index in 2021 and future years.

Figure 2. Longfin smelt catch distribution in 2020 Survey 1 of 20-mm Survey. Delta outflow was 8,000-20,000 cfs. Source.

Figure 3. Longfin smelt catch distribution in 2019 Survey 1 of 20-mm Survey. Delta outflow was 160,000-180,000 cfs. Source.

 

Delta Smelt – 2020 Status

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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.