Feeding Stripers Again

Oroville hatchery steelhead smolts being released into the lower Feather River near Boyd’s Pump in early February. CDFW photo.

State and federal agencies have begun stocking over a million steelhead smolts from Central Valley hatcheries into the Sacramento River and its tributaries.1 Fishing reports in the SacBee and other sources note that the annual stocking provokes a strong striper bite in the river, one of the more popular fisheries in the Central Valley.  The yearling smolts are the perfect food for stripers.

Shasta, Oroville, and Folsom reservoir releases are each at about 3000 cfs, low for mid-winter.  As a result, along with the record warm weather, river and Delta water temperatures (Figures 1-4) have been in the preferred range for striped bass feeding (55-65°F).

The federal Coleman hatchery near Redding released its steelhead smolts in January during high flows, before the warm weather arrived and stripers began feeding in earnest.  But at Thermalito Afterbay on the Feather River, the state is stocking a quarter of a million steelhead and feeding bass. And the feds are will be stocking a half-million endangered winter-run salmon hatchery smolts near Redding in February and March.

The striped bass will soon decimate the Feather River steelhead and will be well positioned for the annual April hatchery salmon smolt stocking season in April.  In the meantime, the stripers attracted by massive chumming will be knocking off the wild juvenile salmon and steelhead heading for the ocean.

Why do hatcheries continue to waste so many of the over 20 million salmonid smolts raised each year to mitigate for all the dams on Central Valley rivers?  Smolts cost more than $1 each to raise.

Hatchery managers and their partners need to barge hatchery steelhead and fall-run salmon smolts to the Bay.  Barging smolts would likely increase adult returns sharply in coming years.  Both steelhead and salmon populations are relatively homogeneous genetically, which reduces concerns about the effects of straying.  Coleman smolts should be barged from near Hamilton City.  Oroville smolts should be barged from Verona.  Nimbus smolts should be barged from Discovery Park.

If releases of hatchery smolts into the rivers are to continue, water managers need to at least provide pulsed flows from Shasta Reservoir to help the fish succeed in reaching the Bay and ocean.  Shasta storage is 106% of average.  A 5% allocation to pulsed flows would amount to approximately 140,000 acre-feet, enough for seven days of an 10,000 cfs extra flow to the Sacramento River.  Pulsed flows would also reduce water temperatures.  Hatchery managers should also not  release smolts into the rivers during warm spells that stimulate striper feeding.

State hatcheries plan some trucking of salmon smolts to the Bay-Delta this year, as they have done in past years.  Trucked fish should also be barged or at least taken to the Golden Gate, not just to Rio Vista.

In addition to barging and trucking, and pulsed flows, hatchery managers need to accelerate a pilot program to stock hatchery salmon fry into lower river and Delta floodplain habitats for rearing closer to the Bay.  In these habitats, fry would grow faster than their hatchery counterparts and get to the ocean quicker.

Anglers should take advantage of the great striper fishery.  But let‘s at minimum give the salmonid smolts some chance of reaching the ocean, so we can also once again have great salmon and steelhead fisheries.


Figure 1.  Water temperature in early February 2018 in the Sacramento River at the mouth of the Feather River

Figure 2.  Water temperature in early February 2018 in the Sacramento River below the mouth of the American River near Sacramento.

Figure 3.  Water temperature in the lower Sacramento River upstream of the mouth of the Feather River at Wilkins Slough

Figure 4.  Water temperature in the lower Sacramento River in the Delta near Rio Vista.

WaterFix will devastate more than just Salmon

Dave Vogel and I are contributing a series of posts on the potential effects of the WaterFix Twin Tunnels Project on Delta fishes. Our focus to date has been on salmon. In this post, I focus on the “other” fishes of the Bay-Delta that will be harmed by WaterFix.

Striped Bass (non-native gamefish)

Striped bass will be devastated by WaterFix tunnel intakes located on the lower Sacramento River. The main spawning run of striped bass is in spring in the lower Sacramento River from near Colusa down to the tidal Delta. Eggs and larvae are buoyant and are carried by currents to the tidal Delta and Bay. Nearly all the eggs and larvae must pass the tunnel intakes. The original Peripheral Canal (circa 1980) had a provision to limit diversions during the striped bass spring spawn. The Vernalis Adaptive Management Program (VAMP) from the late 1990s to the late 2000s protected striped bass in spring with higher Delta inflows and reduced exports (generally a limit of 1500 cfs from mid-April to mid-May). The D-1485 Delta standards had a limit on exports through June (6000 cfs). The proposed WaterFix would have spring exports up to 15,000 cfs (9000 from tunnels and 6000 from existing South Delta pumps). Those eggs and larvae that pass the tunnel intakes would be subject to the pull of south Delta exports without the benefit of the extra flow taken at the tunnel intakes.

Longfin Smelt (native)

Longfin smelt will suffer from reduced flows in the winters of drier years. The WaterFix will take a quarter to a third of sporadic uncontrolled winter flow pulses that support the spawn of longfin smelt in drier years. The lower flows will force longfin to spawn further upstream in the Delta where they are vulnerable to central and south Delta exports. The longfin population declines in drier year sequences; the WaterFix will add to downward population pressure.

Delta Smelt (native)

A recent post by Moyle and Hobbs at UC Davis suggests Delta smelt will be better off under WaterFix:

“The status quo is not sustainable; managing the Delta to optimize freshwater exports for agricultural and urban use while minimizing entrainment of delta smelt in diversions has not been an effective policy for either water users or fish.” Comment: So allowing the water projects to take more water will help? Delta inflow and outflow are the key factors in Delta smelt population dynamics – both will be negatively affected by WaterFix.

Moyle and Hobbes point out “reasons to be optimistic about Waterfix,” as follows:

  • “Entrainment of smelt into the export pumps in the south Delta should be reduced because intakes for the tunnels would be upstream (of) current habitat for delta smelt and would be screened if smelt should occur there.” Comment: The existing south Delta intakes will continue to take spring-summer water (and smelt) from the Delta in similar amounts as in the past. However, smelt in the south Delta will not have the benefit of the inflow taken by the proposed tunnels. Smelt will also be more likely to spawn near or upstream of the tunnel intakes. Screens on the tunnel intakes would not help save larval smelt and would be minimally effective for adult smelt.

  • “Flows should be managed to reduce the North-South cross-Delta movement of water to create a more East-West estuarine-like gradient of habitat, especially in the north Delta.” Comment: If outflow remains low or becomes even lower, the low salinity zone will more frequently move further into the Delta. The north Delta already has a strong gradient – allowing the gradient to move further upstream into the Delta will have adverse effects. Circulation in the south Delta will remain poor, and the south Delta will continue to experience reverse flows, because south Delta exports will continue. The south Delta will lose the benefit of inflow taken by the tunnels.

  • “Large investments should be made in habitat restoration projects (EcoRestore) to benefit native fishes, including delta smelt.” Comment: Delta smelt are totally dependent on pelagic (open-water) habitats, but few EcoRestore projects will improve such habitats. Salinity, water temperature, turbidity, tidal-flow dynamics, water quality, and nutrients are by far the most important factors controlling smelt population dynamics.

Steelhead (native)

Steelhead, much like salmon, are affected by ancillary changes in reservoir storage and releases, river flows, Delta inflow and outflow, water temperatures, and turbidities. But the greatest threat to steelhead, as for salmon, is from the three large intakes and their screen systems, which will adversely affect young steelhead passing on their way to the ocean.

Splittail (native)

Splittail were once on the endangered species list. Today, splittail numbers, especially for recruitment of juveniles, are way down, well below the numbers occurring at the time of their listing. Splittail from the Bay-Delta migrate upstream into river floodplains upstream of the Delta to spawn in spring. The three largest floodplain areas are in the Yolo Bypass, Sutter Bypass, and the lower San Joaquin River wildlife areas. The Sutter group will be at high risk to fry-stage entrainment/impingement at the tunnel intakes. The San Joaquin group will have a continued risk to south Delta exports, a risk made worse by the diversion of inflow from the Sacramento River into the tunnels.

American shad (non-native gamefish)

American shad migrate from the ocean to Valley rivers to spawn in the spring. Eggs, larvae, and fry from the major spawning rivers of the Sacramento Valley must pass the tunnel intakes in the north Delta. Like the striped bass, these lifestages of American shad will be devastated by entrainment and impingement at the tunnel intakes.

Pacific Lamprey

Like salmon and steelhead, Pacific lamprey migrate from the ocean to spawn in Valley rivers during the spring. Young larval lamprey would pass the tunnel intakes on their migration back to the ocean. Because they are weak swimmers they would be highly vulnerable to impingement or predation at the screens.

Native Minnows and Suckers

Many species of native minnows and suckers migrate upstream from the Delta to Valley rivers to spawn in spring and summer. Their young must pass the tunnel intakes on their return to the Delta, and thus will be at risk to entrainment/impingement at the tunnel screens.

The Delta smelt Summer Townet Index is at record low numbers in recent years including the wet year 2017 index.

The striped bass Summer Townet Index remains near record low in 2017.


The Twin-Tunnels Project: A Disaster for Salmon Part 4 of a Series

Ring the Dinner Bell!

Despite the extraordinary hazards facing salmon as described in the previous Parts 1, 2 and 3, the greatest source of mortality at the Twin Tunnels’ water intakes will very likely be caused by artificially-induced predation. This topic in the fourth part of this series is probably the most complex and, arguably, most controversial. Here is where all bets are off and we enter the realm of diverse scientific opinions among experienced fishery biologists.

The high level of concern about predation at proposed massive water intakes on the lower Sacramento River is not new. It boiled to the surface during planning for the infamous “Peripheral Canal” that was roundly rejected by California voters in 1982. Based on an extensive literature review, veteran fishery biologists Odenweller and Brown1 (1982) summarized the need for minimizing predation associated with the proposed Peripheral Canal fish facilities:

“The literature offers some assistance for minimizing and discouraging predation at the intakes and fish facilities. Piers, pilings, other supportive structures, and corners or other irregularities in a channel are referred to as structural complexities. Such structures may cause uneven flows and can create shadows and turbulent conditions. A structurally complex environment should be avoided.”

Unfortunately for salmon, the planning documents for WaterFix reveal that such artificial structures for the Twin Tunnels’ intakes will provide a vast detrimentally complex environment favoring predatory fish habitats. The documents provide no credible details on how that crucial problem will be solved.

The 2017 National Marine Fisheries Service Biological Opinion (BiOp) for WaterFix states that 32 – 40 vertical pilings will be placed directly in front of each of the three water intakes (or more than 100 total pilings!). The alignment of the pilings will be positioned just off the face of the fish screens and parallel to the migration pathway for salmon, greatly adding to the formidable gauntlet of waiting predators. Furthermore, an enormously-long floating boom (also parallel to the screens) will be supported by the pilings, accumulating and exacerbating the structural complexity Odenweller and Brown (1982) warned against 35 years ago. Even the BiOp openly admits that “These structures create habitat that provides holding and cover for predators.” I have heard it said, “We learn from history that we do not learn from history.”2 And so it goes with the Twin-Tunnels Project.

Based on research I have conducted since 1981, salmon predators are highly opportunistic and quickly adapt to habitats where salmon can easily be preyed upon. Remember the giant “toothbrush” wiper blades mentioned in Part 2 of this series? Using a high-tech sonar camera, I have observed predators hiding behind such wiper blades, darting out and eating unsuspecting salmon that have no protective cover. This clear predation predicament will be greatly intensified due to the very low sweeping velocities at the proposed WaterFix fish screens (discussed in Part 1 of this series). Predatory fish (e.g., striped bass and pikeminnow) can easily swim back and forth in front of the screens with minimal expenditure of energy, gobbling up highly-vulnerable, fatigued salmon like popcorn.

Although problems facing salmon will be worse when the intakes are in operation, the in-river structures alone will remain a serious hazard for salmon even when no water is diverted. For example, if those facilities were in place during the recent four-year drought, little or no water would have been diverted into the Twin Tunnels. Nevertheless, the salmon would still have had to migrate past the non-operating intakes where predation would likely remain high. I have already observed large numbers of striped bass concentrated near an artificial structure just upstream of the proposed intakes locations (see: Striped Bass). The WaterFix structures will be permanent fixtures in the river, forever tipping the scales in favor of predatory fish habitats over salmon habitats.

Unfortunately for the salmon, there is not just one, but three intakes for WaterFix. In the worst-possible scenario for salmon, all three water intakes are to be located on the same side of the river and in relative close proximity. Water (and therefore fish) will be driven toward the east riverbank, particularly when all intakes are operating in unison. Up to 3,000 cfs will be removed from the river at each of the three intakes with many baby salmon undoubtedly drawn to the east riverbank. What this means is that the increasingly fatigued and exposed downstream-migrating juvenile salmon will become more and more consolidated along the east bank of the river as the fish traverse the long length of each individual screen structure and arrive (if the fish have not already perished) at the downstream end (Figure 1). This sequence of events will culminate in a very undesirable concentration of salmon, but a perfect environment for the predators as well. Predatory fish will unquestionably become accustomed to these ideal “feeding stations” at the lower end of each fish screen. These highly-adaptable predators simply have to wait for dinner to be delivered at the downstream end of the fish screens. The resultant impacts on juvenile salmon could well be catastrophic. WaterFix does not describe tangible solutions for how this grave predation dilemma can be avoided other than employing the use of “adaptive management” (discussed next in this series).

Figure 1. Conceptual plan-view schematic (not-to-scale) of the three proposed WaterFix intakes on the Sacramento River and the concentrating effect on downstream migrating salmon toward the east or left bank (facing downstream).


Odenweller, D.B. and R.L. Brown.  1982.  Delta fish facilities program report through June 30, 1982.  FF/BIO 4ATR/82-6.  IESP Technical Report 6.  December 1982.  90 p.

Next in the Series:  Adaptive Management – Salmon Salvation?

  1.  Ironically, Odenweller’s and Brown’s employers (California Department of Fish and Game and California Department of Water Resources, respectively) supported the Peripheral Canal.
  2.  Quote attributed to Georg Wilhelm Friedrich Hegel.

Striped Bass Status – End of 2016

The prognosis for stripers was not good in 20151 after four years of drought. The normal water year in 2016 brought only minor improvement in recruitment of juveniles into the population, but recruitment remains near record lows (Figures 1-3). The wetter 2016 started with higher juvenile production, but that stalled by late spring. Striped bass salvage at south Delta export facilities showed typical patterns, with about 10% of the numbers salvaged in year 2000 and two primary peaks in salvage – late spring/early summer and late fall (Figure 4).

The Fall Recruitment Index of juveniles into the population as derived from the Fall Midwater Trawl Survey (Figure 2) compared with the prior Summer Townet Survey (Figure 1) indicates a strong positive relationship (Figure 5). The year class strength is very much dependent on the number of young starting the summer, which in turn is likely related to the number of eggs laid in spring and subsequent survival of larvae hatched to the early summer juvenile stage as measured in the Summer Townet Survey. Subsequent survival to the fall appears related to summer habitat conditions, for which a good indicator is Delta outflow. High relative survival to fall in 1998 and 2006 (labeled blue in Figure 5) is likely due to these summers’ higher Delta outflow (Figure 6) and related Delta conditions including export levels (Figure 4). The 2010 and 2016 fall indices were likely suppressed by low outflow, high exports, and resulting poor in-Delta survival, indicated by high salvage numbers. Likewise summer and fall indices in drought years 2007, 2014, and 2015 were likely depressed (Figure 5) by these same factors.

The above patterns and observations are very important because the striped bass remain an important indicator of Bay-Delta Estuary ecological health.

Figure 1.  Striped bass Summer Townet Survey Index 1959-2016.  (Data Source )

Figure 1. Striped bass Summer Townet Survey Index 1959-2016. (Data Source2)

Figure 2.  Striped bass Fall Midwater Trawl Survey Index 1967-2016.  (Data Source )

Figure 2. Striped bass Fall Midwater Trawl Survey Index 1967-2016. (Data Source3)

Figure 3.  Striped bass Fall Midwater Trawl Survey Index 2000-2016. (Same source as Figure 2)

Figure 3. Striped bass Fall Midwater Trawl Survey Index 2000-2016. (Same source as Figure 2)

Figure 4.  Striped bass salvage at south Delta fish facilities in 2016.  Export rate is shown as acre-feet (~2 times rate in cfs).  (Data Source )

Figure 4. Striped bass salvage at south Delta fish facilities in 2016. Export rate is shown as acre-feet (~2 times rate in cfs). (Data Source4)

Figure 5. Striped bass Fall Midwater Trawl Survey Index (log10[index+1]) versus prior Summer Townet Index (log10).  Select years labeled, with color of number showing year type: blue=wet, green=normal, and red=critically dry.

Figure 5. Striped bass Fall Midwater Trawl Survey Index (log10[index+1]) versus prior Summer Townet Index (log10). Select years labeled, with color of number showing year type: blue=wet, green=normal, and red=critically dry.

Figure 6.  June through August Delta outflow in 1998, 2006, and 2010.

Figure 6. June through August Delta outflow in 1998, 2006, and 2010.

Does the Central Valley Need a Predator Removal Program?

The Columbia River Pikeminnow Sport Reward Program just finished another year.  A near-record 200,000 adult pikeminnow were harvested and $1.7 million rewards paid.  The goal of the program is to harvest 10-20% of the population each year to reduce the population about 50%.  Harvest rates in recent years reached as high as 17% as compared to this year’s 11%.

So why after 25 years is the program still harvesting near-record numbers of pikeminnow?  The likely reason is that the program is not based on sound science.  The Columbia pikeminnow population dynamics likely are best described with a standard Ricker-Type Population Model (see chart below), with reduced recruitment of young at high adult population levels because of competition and cannibalism.  The introduction of a light harvest can actual increase recruitment of young by reducing competition and cannibalism, with the increased recruitment replacing the harvest, even providing a constant harvest or yield.  This is how fishery quotas may be sustained year after year, such as in Alaska’s Bristol Bay Sockeye salmon fishery.

This same dynamic likely applies to pikeminnow and some other predators in the Central Valley.  Pikeminnow are likely near their saturation level in the Central Valley.  Any light harvest such as from a sport-reward or removal program would likely have little or no effect.  Increasing harvest on non-native predators like largemouth bass by reducing sport-fishing harvest regulations would likely also have a limited benefit.  However, striped bass, the most popular sport fish in the Delta, has a population that is already seriously depressed by long-term loss of juveniles to water diversions.  Striped bass may respond more directly to increased harvest, further reducing recruitment and further depressing the population.

Thus the species composition of fish that eat other fish could change, satisfying those who vilify stripers and infuriating those who fish for them.  But the potential for reduced overall loss of juvenile salmon or other native species that might follow from “predator removal” is far more complex and questionable than its proponents maintain.

Ricker-type stock-recruitment population dynamics model that likely applies to Columbia River and Sacramento River pikeminnow populations

Ricker-type stock-recruitment population dynamics model that likely applies to Columbia River and Sacramento River pikeminnow populations