In my last update on the status of longfin smelt (February 2018), I decried the continuing decline of the Bay-Delta population of longfin, which are listed under the California Endangered Species Act. The fall index for 2018 indicates continued low population levels (Figures 1 and 2), with 10 to 100 times higher production in wetter years than dry years. After the very poor recruitment in 2015 and 2016, there was some recovery in wetter years 2017 and 2018. Despite record low spawner numbers in 2015 and 2016, recruits increased with wetter years 2017 and 2018, which in turn could lead to improvement in 2019 and beyond with indices above 100 (log 2.0 in figure 2) or perhaps even near 1000 (log 3.0 in figure 2). If drought returns, bets are off.
In a February 2018 post I last updated the status of longfin smelt in the Bay-Delta. I showed that longfin smelt have a strong spawner-recruit or stock-recruitment relationship wherein new recruits into the population depend on the abundance of spawning parents (Figure 1). The relationship also indicated a strong influence of water–year type.
What is it in wetter years that improves survival? What is it about wet years that is important to longfin survival? My analysis is it is the spring Delta outflow, with June likely being important. The fall longfin index is significantly correlated with June outflow (Figure 2). It requires Delta outflows in the 8000-10,000 cfs range to keep the low salinity zone and young longfin in the Bay, west of the Delta and away from the south Delta export pumps and warm low-productivity pelagic habitats.
Present standards (see link, pdf pages 26-27) for June require outflow of 7100 cfs on a 30-day running average. This contrasts sharply with previous June standards under Water Rights Decision 1485 (see link, pdf page 43) which required an average monthly flow of 9500 cfs in some below normal years, 10,700 cfs in Above Normal years, and 14,000 cfs in Wet years. In its ongoing update of the Bay-Delta Plan, the State Water Resources Control Board must account for the importance of the outflow standard for June in protecting Bay-Delta ecological resources.
Though I hate to “beat a dead horse” or perhaps more appropriately “put another nail in the coffin,” I’m sad to report that the California Department of Fish and Wildlife’s first two fall trawl surveys for 2018 collected no Delta Smelt. This is consistent with this past summer’s townet survey results. Let’s get on with implementing the smelt hatchery program.
A summer pulse flow through the Yolo Bypass via the Colusa Basin Drain (Figure 1) was implemented in September per the Delta Smelt Resilience Strategy’s North Delta Food Web Action (Figure 2). I reviewed the initial application of the action in July 2016, concluding then there was no evidence that the action would meet its overall goals, but that the approach had potential.
The basic concept is this:
– By routing agricultural drain water through Yolo Bypass instead of the Sacramento River, DWR scientists predicted that a flush of plankton-rich water would provide a “seed” for the downstream Delta, enhancing food resources for Smelt. (Note: Historically, summer drain water from Colusa Basin rice fields was discharged into the Sacramento River at Knights Landing.)
– A similar managed flow pulse was generated in July 2016 with the help of Sacramento Valley water users, which helped transport plankton to the Delta. (Note: additional Sacramento River water was diverted near Red Bluff to the Colusa Basin Drain to supplement rice field drainage. There was no evidence that plankton blooms in the Yolo Bypass reach the Delta in meaningful amounts.)
– The action is designed to maximize the environmental benefits of water. Water isn’t “consumed” by the action–it is directed down a different and more productive path to the Delta. (Note: The basic concept is simple. The nutrient-laden drain water stimulates Yolo Bypass productivity, and the added river water flushes it through to the north Delta. Taking some of the Sacramento River at Red Bluff and routing it through the Colusa Basin irrigation and drainage system, then on to the Yolo Bypass tidal channels, should stimulate biological productivity and flush it, along with excess nutrients and organic debris from rice fields into the Delta at the end of the Bypass (Cache Slough – Rio Vista area). The Delta (and smelt) would benefit from the added biological productivity (phyto-zoo plankton) and nutrients (nitrogen, phosphorous, and organic carbon).
Does the concept work, and does it come without complications?
- During implementation in 2018, there was an 60% uptick in aquatic plant productivity in the lower Yolo Bypass (Figure 3).
- There was no increase in productivity as of early October in the north Delta at Rio Vista (Figure 4).
- The water routed through the Bypass was initially warm (>70oF, Figure 5), high in salts (Figure 6), lower in turbidity (Figure 7), and low in dissolved oxygen (Figure 8).
- Warm water and the high organic load resulted in poor dissolved oxygen levels (3-5 milligrams-per-liter) that violate state standards and are potentially lethal to salmon migrating through the Bypass1.
On a positive note, routing drain water to the Bypass does keep the poor quality drain water out of the Sacramento River below Knights Landing.
In sum, the benefits of the action remain questionable. Waiting to conduct the action until fall when waters are cooler could alleviate high water temperatures and low dissolved oxygen in the water. It might also create more Delta benefits by delaying nutrient use until nutrients reach the Delta. Further research is warranted into the water quality of the drain water, especially its oxygen-depriving, high-organic load and its chemical constituents (salts, herbicides, and pesticides). Otherwise, it may be that the action is little more than an augmentation of the current practice of dumping what might be described as polluted agricultural drain water into Central Valley rivers and the Delta.
- Migrating adult salmon are common in the Bypass in September, possibly being attracted to rice drainage flows with the chemical signal of the upper Sacramento River. ↩
After catching over 800 Delta smelt in 2011 (Figure 1) and near 30 in 2017 (Figure 2), the Summer Townet Survey captured only 3 in 2018 (Figure 3). The pattern is consistent with the spring 20-mm Survey collections
The only option now other than extinction is stocking hatchery smelt in large numbers in their primary summer-fall habitat, the Low Salinity Zone of the Bay-Delta. Release should be near the 2 ppt (3800 EC) location, commonly referred to as X2, which recently has been moving tidally back and forth between Collinsville and Sherman Island in the Sacramento River channel just downstream of the Emmaton gage (Figures 4 and 5). The X2 location has optimum salinity, water temperatures (<70oF), turbidity, and food for Delta smelt.