CSPA’s fisheries biologist Tom Cannon gave a presentation entitled “Contributing Cause of Smelt Decline: Water Exports” at a symposium on March 29, 2016 at UC Davis. The theme of the conference, sponsored by the Delta Stewardship Council, was: “Delta and Longfin Smelt: Is Extinction Inevitable?”

In his presentation, Tom put forth the hypothesis that the cause of the probable extinction of Delta smelt was the commencement of operation of the State Water Project’s Banks Pumping Plant in the mid-1970s. When Banks came on line, South Delta exports tripled, going from 2 million acre-feet to 6 million acre-feet per year. Tom’s hypothesis is that the mechanism of likely extinction was entrainment of Delta Smelt into the inflow to State and Federal South Delta pumping plants: exports.

The presentation’s first slide shows the familiar long-term Fall Midwater Trawl Index (Figure 1). Tom emphasized the sharp drop in the Index in 1981 (red circle in Figure 1), the first dry year of operations under the 1978 Delta Plan (water quality standards limiting operations of the Delta pumping plants). He noted that the decline likely started in the mid-1970s, but was most severe in 1981. There were recovery periods in the non-drought years of the 1990’s and 2010-2011. However, in 2001-2005, smelt and other Delta species crashed, a period now known as the “Pelagic Organism Decline,” or POD. Following a mild recovery in the wet year 2011, Delta smelt collapsed to record low indices in 2014 and 2015 (indices of 9 and 7, respectively, not shown in Figure 1).

Other slides depict (1) the huge losses of adult smelt as indexed by January¹ salvage numbers in 1981 (Figure 2), and (2) the salvage counts of juvenile Delta smelt in spring 1981 (Figure 3). The total salvage for January 1981 alone was over 10,000 adult Delta smelt, which compares to a total of 56 in January 2015 and 12 in January 2016. The total juvenile Delta smelt salvage in spring 1981 exceeded 100,000; in 2015, it was 4.

An example of salvage during the 2001-2005 POD is winter-spring salvage in 2003 (Figure 4). Tom attributes the POD decline to the tens of thousands of Delta smelt lost to entrainment in winter and spring, including a likely large number of non-detected larvae under conditions of maximum exports.

According to Tom, export entrainment is the primary causal factor for the death spiral of Delta smelt, not low outflow. There were relatively high or improved smelt abundance indices in 1972, 1990, and 1991 (see Figure 1), which were all years with low outflows but also low exports. This is not to say, however, that low outflows are not also factors that contribute to high entrainment (Figures 2 and 3).

Tom concludes that Delta smelt are virtually extinct because their adult spawning numbers are insufficient to provide recovery even under 2016’s good (wet) conditions. Adult numbers are simply too low to produce sufficient offspring (Figure 5). The proof will come this spring, summer, and fall when indices of Delta smelt juveniles will likely remain critically low and not reach 2010 or 2011 levels, the last years when habitat conditions were favorable.

Tom Cannon Presentation – Contributing Cause of Smelt Decline: Water Exports

Figure 1. Fall Midwater Trawl Index for Delta smelt 1967-2013. (Source: CDFW.)

Figure 2. January salvage of adult Delta smelt at South Delta export pumps in 1981. Also shown is export rate (cfs) and Delta outflow (cfs). The maximum allowed export rate is 11,400 cfs. (Data Source: CDFW.)

Figure 3. Spring salvage of juvenile Delta smelt at South Delta export pumps in 1981. Delta smelt juveniles begin reaching salvageable size (>20 mm) in early May. Also shown is export rate (cfs) and Delta outflow (cfs). The maximum allowed exportsrate is 11,400 cfs. (Data Source: CDFW)

Figure 4. Winter-spring salvage of Delta smelt at south Delta export pumps in 2003. Delta smelt young begin reaching salvageable size (>20 mm) in early May. Also shown is export rate (acre-feet per day) by pumping plant. The maximum allowed export rate is 11,400 cfs (about 23,000 acre-feet per day). (Data Source: CDFW). Winter salvage is primarily adult smelt. Spring salvage is predominantly juvenile smelt (>20 mm). April entrainment of 5-15 mm larval smelt is not accounted for at salvage facilities, because they pass undetected through salvage screens.

Figure 5. Index of adult Delta smelt spawner abundance from winter Kodiak Trawl Survey 2002-2016.

Since the last update, Delta and longfin smelt have continued their trends of record low numbers, as shown in the most recent Smelt Larvae Survey and 20-mm Survey. They are not yet gone, but close. It remains to be seen whether the good conditions provided so far in this wet winter 2016 can lead to some form of recovery for these two endangered species.

Longfin Smelt

With the high winter flows, the young from this year’s spawn are now distributed well to the west, although some remain in the north Delta (Figure 1). Their numbers continue at record low levels (Figure 2) despite a wet winter.

Figure 1. Longfin smelt catch in mid-March in Survey #1 of 20-mm Survey.

Figure 2. Average catch-per-unit-effort of young longfin smelt in mid-March 20-mm surveys from 2008-2016.

Delta Smelt

Delta smelt have yet to grow into the size range captured in the 20-mm Survey, but remain present in the last Smelt Larvae Survey (Figure 3). High winter through-Delta flows have resulted in a slightly more westward distribution than in recent drought years such as 2013 (Figure 4). Although numbers collected are very low, it is too early to determine relative production for 2016 compared to previous years in the Smelt Larvae Survey or the 20-mm Survey. Under similar wet winter-spring conditions in 2010 and 2011, Delta smelt had modest population improvements. It remains to be seen if the very low adult spawning population this year (in comparison to the populations in 2010 and 2011) can lead to some form of recovery in the population under this year’s relatively wet conditions.

Figure 3. Delta smelt larvae catch distribution in mid-March 2016 Smelt Larvae Survey.

Figure 4. Delta smelt larvae catch distribution in mid-March 2013 Smelt Larvae Survey.

In my March 12 post, I related that Senator Feinstein’s request for higher Delta exports would put the Delta Smelt population in the Delta at further risk of extinction. Well, she received her wish, and exports increased from 6000 cfs to 8000 cfs (11,400 cfs is maximum pumping capacity) in the week after her request when storms brought more inflow to Delta from the San Joaquin River.

However, the higher exports were short–lived, because the 3/14-3/17 Smelt Larvae Survey picked up larval smelt for the first time this year (Figure 1 – green dots). Exports dropped below 5000 cfs again. Though only two newly hatched larvae were collected in the central Delta, their presence is a concern. The presence of larval smelt shows that smelt are spawning in the lower San Joaquin River in the central Delta. According to the Smelt Working Group the net negative flows shown in red in Figure 1 for late March indicate a “medium” risk to smelt and a likelihood that larval smelt will be drawn toward the south Delta export pumps.¹ The -5000 cfs Old and Middle River (OMR) reverse flows are the maximum allowed under the Smelt Biological Opinion.

In its review of the results of particle tracking model runs, the Smelt Working Group concluded: “Members stressed the importance of weighing more heavily the results from inserting (particles) at Prisoner’s Point, given the consistent catch of adults there this year and the hydrologic proximity of that location to the south Delta (as compared to Jersey Point). For OMR flow of -5000 cfs, approximately 20% of the particles inserted at Prisoners Point were entrained into the South Delta. For an OMR flow of -2500 cfs, approximately 10% of particles inserted at Prisoners Point were entrained into the South Delta. For an OMR flow of – 1250 cfs, less than 10% of particles inserted at Prisoners Point were entrained into the South Delta.” Prisoners Point is the green dot from the right on the Figure 1 map. In all likelihood, larval smelt are now being drawn or will soon be drawn into the south Delta. It is too early to determine what portion of the population is subject to this risk. But given the unprecedented depressed condition of the smelt population after four years of drought, the risk is significant.

On March 24, after review of “Smelt Working Group’s March 21 recommendations,² the U.S. Fish and Wildlife Service “determined”³ that the OMR should be no more negative than -2500 cfs on a 14-day average, and no more negative than -3150 cfs on a five-day average. Reclamation took a slightly more liberal interpretation in the subsequent week’s operations (Figure 2), staying nearer -3500 cfs most of the week with no apparent interest in reaching a -2500 cfs 14-day average. It could be that the Service meant to recommend a -3500 cfs OMR limit. Or maybe the Service got a call from Senator Feinstein’s office. We shall see what this week’s meetings and determinations offer.

In any event, the risk to Delta Smelt remains “medium” at combined exports of about 3500-4000 cfs. With an export capacity of 11,400 cfs, Delta outflow still exceeding 50,000 cfs, reservoirs continuing to release snowmelt, and San Luis Reservoir in the San Joaquin Valley only half full, there will be continued cry for more exports and for approval of the Tunnels. In the meantime, it appears from Figure 1 that some smelt larvae and a good amount of snowmelt are escaping west to Suisun Bay, while some larval smelt remain at risk in the central Delta.

Figure 1. Net daily flow in Delta in late-March 2016. (Gage data source: USGS). Green dots are location of seven Delta Smelt larvae collected in Survey 6 of Smelt Larvae Survey (http://www.dfg.ca.gov/delta/data/sls/CPUE_Map.asp ).

Figure 2. OMR March 23 to March 28. (Source: CDEC)