Longfin Smelt End of 2018 A Case for Higher Delta Outflow Standards in June

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.

Figure 1. Longfin Recruits (Fall Midwater Trawl Index) vs Spawners (Index from two years prior) in Log10 scale. Wet years in blue. Dry years in red. Note the progressive decline in recruits in the last three wet years (06, 11, 17). The relationship is very strong and highly statistically significant. Taking into account Delta outflow in winter-spring makes the relationship even stronger. Recruits per spawner are dramatically lower in drier, low-outflow years (red years). Source: http://calsport.org/fisheriesblog/?p=1360.

Figure 2. Fall midwater trawl index for longfin smelt versus average June outflow (cfs) 2008-2017. Wet years in blue. Normal years in green. Dry years in red. Source of data: http://www.dfg.ca.gov/delta/data/fmwt/indices.asp?view=single.


Summer Delta Salinity Standards: 2018 Example

In a July 2016 post I recommended a 500 EC (electroconductivity) salinity standard from July-to-mid-August for the western Delta. The longstanding Water Rights Decision 1641 standard includes this only in Wet years. It should apply in all year types unless south Delta exports are at minimum levels.

In summer 2018, a Below Normal, subnormal snowmelt year, Jersey Point salinity was kept near 500 EC through early August (Figure 1) instead of the allowed 740 EC. Was this an adaptive management experiment? If so what benefits were derived from the experiment?

Figure 1. Jersey Point salinity (EC) remained near 500 EC in early summer 2018. The applicable standard was 740 EC 14-day average through August 15.

Benefit #1:
The water temperature in the west Delta in 2018 was kept near 73°F or below (Figure 2), a good thing. In 2016, the previous Below Normal year, EC was allowed above 500 EC (Figure 3) per the existing standard. Water temperature exceeded 73°F to near 75°F (Figure 4), a bad thing, when EC exceeded 500. The reason for the higher early summer 2016 EC and warmer water temperatures was low Delta outflow (Figure 5). Outflow in 2016 was about 7000 cfs, but needed to be near 8000-9000 cfs. In 2018, outflow in late June was 7500-7900 cfs (Figure 6), in part due to relatively low early summer Delta exports (Figure 7) compared with 2016 (Figure 8).

Other Benefits:
It is really too bad that we can no longer look to Delta smelt for response to adaptive management. But I suspect positive response to the 2018 “experiment” occurred in survival of other juvenile Delta fish (e.g., striped bass), shrimp, zooplankton, and phytoplankton. When 2018 data become available, the comparison with 2016 and prior years can be made.

The salinity standard for the west Delta at Jersey Point and Emmaton should be 500 EC daily average unless south Delta exports are restricted to minimum health and safety levels. The standard should be year-round in all year types. Delta exports should be restricted to the minimum unless the salinity standard is met.

Figure 2. Water temperature at Jersey Point in west Delta summer 2018.

Figure 3. Jersey Point salinity EC summer 2016. Standard was 740 EC 14-day average through August 15.

Figure 4. Water temperature at Jersey Point in west Delta summer 2016.

Figure 5. Delta outflow in summer 2016.

Figure 6. Delta outflow in summer 2018.

Figure 7. State exports from south Delta summer 2018.

Figure 8. State exports from south Delta summer 2016.


No Delta Smelt Fall 2018

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.

Fall mid-water trawl survey catch for September and October 2008-2018. Data source: http://www.dfg.ca.gov/delta/data/fmwt/indices.asp

Solving the Delta’s Invasive Aquatic Vegetation Problem

A recent science paper reminded me about the benefits of aquatic vegetation to lake fish species like largemouth bass. It also reminded me that invasive aquatic vegetation has ruined lake-like salmon habitats of the west coast, such as Seattle’s Lake Washington and portions of the Columbia River and California’s Bay-Delta estuaries. Instead of rearing salmon and smelt, these waters now rear non-native bass and sunfish (centrarchids). These once-turbid waters conducive to rearing juvenile salmon and smelt are now best suited for sight-feeding centrarchids, competitors and predators of salmon that love clear water and abundant cover. The non-native aquatic vegetation (Egeria, hyacinth, and milfoils) in the Bay-Delta provides abundant cover, uses all the aquatic plant nutrients, and collects the suspended sediment – all bad for the Bay-Delta’s pelagic/planktonic habitat.

Other than gripe about the obvious problem over the past several decades, what has anyone done about it? Boating and Waterways has tried spraying herbicides, but that has been costly, ineffective, messy, and organically/chemically polluting. Flushing the Delta all year with more-and-more clear reservoir water to south-Delta export pumps has not helped. The proliferation of non-native clams has also contributed to the problem.

There are no easy solutions, but there are options that should be implemented. Though costly and with their own environmental problems, these options can potentially lead toward recovery of the most important Delta habitats. The best option is an aggressive (and expensive) long-term program of manual cutting and harvesting using boat‐mounted cutters, harvesting barges, and suction dredges to remove the rooted and floating aquatic plants. A longer-term option is to increase turbidity from inorganic and organic sources by adding silts or reducing silt “sinks;” this would help cut sunlight and nutrients to rooted aquatic plants. Direct application of aquatic fertilizers has recently been considered by resource agencies; this could also help. Finally, reducing exports from the south Delta could help because it would reduce the proportion of low-turbidity reservoir water in the Delta and lessen the direct loss of millions of tons of silt.

Shifting the Bay-Delta habitat away from centrarchids by increasing Delta turbidity will measurably improve salmon and smelt recovery.

Central Valley Spring Run Salmon – Record Low Run

In a 10/31/17 post, I described record low spring-run Chinook salmon runs in Sacramento Valley rivers in 2017, with emphasis on the Feather River, the largest component of the Central Valley spring-run population. In this post, I update information on Central Valley spring-run. The combined Central Valley runs of spring Chinook salmon were indeed at record low levels in 2017 (Figure 1). The run total includes escapement to all Central Valley streams that host spring-run salmon, including Battle Creek, Clear Creek, Butte Creek, Antelope Creek, Big Chico Creek, Cottonwood Creek, Mill Creek, Deer Creek, Antelope Creek, Feather River-Yuba River, and the mainstem Sacramento River.1

I plotted these numbers in a spawner-recruit relationship, with spawners being recruits three years earlier (Figure 2). The water year type during the first winter-spring following spawning is shown in Figure 2 by color. Winter-spring conditions reflect early rearing and emigration conditions in spawning rivers, as well as conditions in rivers downstream an in the Bay-Delta.

Factors contributing to poor recruitment in the eight critically dry years in the observed period include low river flows, high water temperatures, excessive predation, loss at water diversions, and low turbidity, all factors that are inter-related. Poor ocean conditions and hatchery operations also were likely factors, which may also be related directly or indirectly to river flows.

Most recent recovery efforts and planning have focused on habitat restoration.2 My own focus has been on poor river conditions (low flows and high water temperatures) and related predation.3 My reasoning is based on escapement trends over the past decade that indicate sharply dropping escapement during dry year low-flow conditions in most of the spawning rivers (Figures 3-5).

Figure 1. Spring run salmon in-river escapement (spawning run size) in the Central Valley from 1975 to 2017.

Figure 2. Spawner-recruit relationship for Central Valley river escapement of spring-run Chinook salmon. Recruits represent spawner escapement for that year. Spawners are recruits from three years prior. Numbers are log10 of escapement minus three. Red represents dry years during winter-spring after fall spawn. Blue represents wet years. Green represents normal years. Blue dotted line is statistical trend line. Yellow line is replacement level. Note eight points in bottom-right quadrant represent winter-springs of critically dry drought years (77, 89-91, 07-08, 13, and 15).

Figure 3. Battle Creek spring run salmon escapement from 1989 to 2017.

Figure 4. Deer Creek spring run salmon escapement from 1975 to 2017.

Figure 5. Mill Creek spring run salmon escapement from 1975 to 2017.