Category Archives: Bay-Delta

American Shad – It is time to manage their populations

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I have studied American shad, a popular sportfish and anadromous herring native to the East Coast, in the Hudson, Columbia, Sacramento, American, Feather, Yuba, and Stanislaus rivers. I have also fished for them for 50 years.  They are the most abundant anadromous fish in the Bay-Delta and Columbia River watersheds.  Millions run up the Sacramento and Columbia rivers every spring to spawn.  The 1-to-6-pound adults arrive in spring and spawn from late spring into summer as waters warm.  After spawning, some die, but many adults return to the ocean.   The eggs are large like those of salmon, but. unlike salmon eggs, shad eggs float and hatch as they drift downstream toward tidewater in the Delta through late spring and summer.  Young shad then rear in the tidal estuary through the summer before heading to the ocean.

Shad interact with our native fish in various ways, most of which are detrimental.  Whether they and other nonnative fish like striped bass contribute to population declines of native species like salmon, steelhead, smelt, and sturgeon is open to debate.  I believe that coupled with changes in climate and water management, the effects of nonnative fish on native species are getting worse.

A 2017 review of the ecological role of American shad in the Columbia River (Haskell 2017) provided three hypotheses regarding the Shad’s effect on Columbia River food webs:

  1. Juvenile shad are an abundant and highly energetic food that increase the growth rate of major salmon predators [e.g. Northern Pikeminnow, Walleye, Smallmouth Bass, and Channel Catfish) – viewed as negative by supporting production of salmon predators.
  2. Juvenile shad are planktivores that compete with juvenile salmon, particularly later migrating sub-yearling Chinook Salmon in the lower Columbia River – viewed as negative by reducing food for salmon thus reducing growth and survival.
  3. Large numbers of adult shad could influence nutrient balances given their capacity to convey marine-derived nutrients – another source of marine carbon input viewed as positive.

I would add four further hypotheses/issues on the role played by American shad:

  1. Adult shad migrate from the ocean into the Bay-Delta estuary in spring on their way to spawning rivers. They number in the millions, feeding on plankton including larval fish such as newly hatched Longfin and Delta smelt, and fry salmon that frequent the estuary and lower rivers.
  2. Adult shad spend late spring and most of the summer spawning in major in the mainstem rivers and their larger tributaries, during which they feed on aquatic invertebrates and juvenile salmonids. Their spawning run in the spring coincides with the rearing of juvenile fall-run salmon and steelhead.  Shad adults can be extremely abundant during the spring emergence of fry steelhead, especially in tailwaters below dams that block shad migrations.  The American, Feather, Yuba, and Mokelumne Rivers have such conditions.  Historical anecdotes of adult shad feeding on young salmonids below the Red Bluff Diversion Dam in the upper Sacramento River are available from CDFW predator survey reports.  In my own experience, I commonly use small spoons representing salmonid fry and parr size (2-3 inches long) that are readily swallowed by feeding adult shad.
  3. Adult shad may spawn through the summer in some tributary tailwaters where cold water releases (<65ºF) are prescribed for over-summering salmonids. Cold water can extend the period of shad spawning and the period in the tidal estuary when juvenile shad compete with smelt and other fishes for zooplankton prey.
  4. Juvenile American shad rear in freshwater and low-salinity tidal zones of the Bay-Delta estuary from late spring through summer (Figures 1-6), where they feed on zooplankton of the same types as Delta smelt and other native fishes.

As is the case with many native fish species, American shad populations suffer during periods of drought.  This has been especially true in the past two decades in the San Francisco Bay-Delta Estuary (Figure 7), commonly referred to as the period of the Pelagic Organism Decline.  It is an open question whether the American shad are simply experiencing the decline like the native fish, or contributing to the native declines, or both.

The likely answer is both.  All the fish suffer in drought.  All the fish do not recover completely after droughts.  All the fish populations exhibit a long-term downward population spiral.  For some, it is a spiral toward extinction.  Even in decline, some nonnatives like American shad and striped bass can have increasing effects on the natives facing extinction.  If that is the case, then we should do everything possible to at least provide habitat conditions that favor native fish over nonnative fish.  The fact is that, in many cases, nonnative fish, including shad and striped bass, are more resilient than the native fish.  That is because the physical habitat and water management increasingly are less favorable to the native species.  We need to reverse this trend.

For more recent discussion on Central Valley American shad see:

https://calwatercenter.org/american-shad-the-deltas-most-abundant-and-least-considered-anadromous-fish/

Figure 1. Wet year 2019 American shad juvenile catch-size distribution in Bay-Delta spring 20-mm Survey.

Figure 2. Wet year 2019 American shad juvenile catch-size distribution in Bay-Delta Summer Townet Survey.

Figure 2. Wet year 2019 American shad juvenile catch-size distribution in Bay-Delta Summer Townet Survey.

Figure 3. Wet year 2019 salvage and export rates of juvenile American shad at south Delta export facilities.

Figure 4. Wet year 2019 catch distribution of juvenile American shad in September Fall Midwater Trawl Survey.

Figure 5. Wet year 2019 American shad catch distribution versus salinity (EC) for September Fall Midwater Trawl Survey. Red line indicates shad concentrate in low-salinity zone (5-15k EC).

Figure 6. Wet year 2011 Delta smelt catch distribution versus salinity (EC) for September Fall Midwater Trawl Survey. Red line indicates smelt concentrate in low-salinity zone (5-15k EC).

Figure 7. Catch index of American shad juveniles in Fall Midwater Trawl Surveys 1967-2021. Recent drought periods noted.

A Ridiculous Premise

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A recent post from the Center for California Water Resources Policy and Management (Center) discusses the extinction of the Delta smelt.  The post starts by saying, “To be sure, the delta smelt’s numbers are in decline.”  That is a real understatement, but it contains some acknowledgement of the facts.

The author goes on to say, “It might fairly be argued that prime contributors to the delta smelt’s distressed status are California’s resource agencies.”  The ostensible rationale for this attribution is, first, that the resource agencies don’t look for smelt in the right places in the right way.  Second, because the agencies can’t find the smelt, “they have resisted managing the species ‘adaptively’” based on the monitoring that they don’t do.

This ridiculous premise suggests the decline has not been caused by excessive exports of water from the Bay-Delta watershed over the past five decades, but by the resource agencies who don’t know where to find and thus protect the smelt.

The author argues: “The agencies persist in mobilizing trawler-based open-water fish surveys, originally intended to census juvenile striped bass, as their primary means of monitoring delta smelt and the Delta’s other protected fish species.”  This statement is simply untrue.  To provide better coverage of “open-water” pelagic smelt, the Interagency Ecological Program (IEP) in recent decades added the Larval Survey, the 20-mm Survey, the Kodiak Trawl Survey, and most recently the Enhanced Delta Smelt Monitoring Program (EDSM).   All of these surveys, plus the historic Fall Midwater Trawl and Summer Townet Surveys (and 50 years of Delta Export Fish Salvage Surveys), show the smelt’s catastrophic decline and march toward extinction.

But the author insists that the smelt are out there somewhere.  “The surveys sample neither the relevant habitat strata used by those fishes nor the extent of their ‘closed’ populations, which would allow for estimates of the sizes of their populations.”  If the smelt are out there in “closed populations” whose numbers would change the conclusions about the smelt’s catastrophic downward trend, then surely the author and the water purveyors who have a vested interest in finding those populations can muster some evidence and show the agencies and the rest of the world where to look.

Basic review and analyses of the available information show the decline of Delta smelt is highly associated with increasing exports and associated factors (see my many posts on this subject).  The partial truth in the notion that the resource agencies have been complicit in the decline of Delta smelt stems from agency inaction to cut back those exports consistent with biological sustainability.  Agency managers don’t lack information and scientific method.  They lack the political courage to deploy them.

More on the Delta Threat to Winter-Run Salmon – Fall 2021

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During early November, juvenile winter-run salmon were moving into the Delta after two short fall rainfall pulses (Figure 1). The allowed export of 65% of Delta inflow is not protective of these wild young winter-run salmon, which are in short supply this year. My October 30 post, in which I warned about the threat of rising Delta exports on this year’s production of juvenile winter-run salmon entering the Delta, is being borne out.

From November 9-12, south Delta exports exceeded 70% of Delta inflow,1 with about 2000 cfs of calculated Delta outflow. The USGS measurement of Delta outflow on November 8-9 was as low as -3000 cfs. Delta exports were simply drawing from the Delta’s freshwater reservoir supplied by the recent rains. The cries of San Joaquin Valley farmers for the capture of the runoff before it was “wasted” into the Bay and Ocean were indeed being answered. The Delta export pumps were shipping 15,000-20,000 acre-feet of water south each day.

Up at the Delta Cross Channel (open) and Georgianna Slough, over half the daily flow was being diverted into the central Delta. With the False River Barrier installed, most of the diverted water (and young salmon) flowed south toward the export pumps. Since no young salmon were showing up in the export fish salvage collections, it is likely that few successfully made the 50-mile journey from the northern Delta through the predator-laden central Delta corridor.

Hopefully, the several hundred thousand winter-run hatchery smolts will have better circumstances when they are released this winter near Redding for their 300-mile migration to the ocean.

Figure 1. Capture of juvenile winter run salmon in the lower Sacramento River in 2021.

Delta Smelt Status 2021

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The Enhanced Delta Smelt Monitoring (EDSM) caught only 1 Delta smelt in 2200 smelt-targeted net tows in 2021.  This compares to 49 captured in 2020 and hundreds in prior years.  None were captured in the Spring Kodiak Trawl 2021 survey (Figure 1).  This year’s results indicate that Delta smelt are likely virtually extinct in the wild.

Figure 1. Spring Kodiak Trawl survey index of Delta smelt (2004-2021), in which none were caught in 2021. Only one was captured in 2020. (source)

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.