For fourth-year, CDFW finds zero Delta smelt in Fall Midwater Trawl Survey

Scientists at the University of California, Davis, Fish Conservation and Culture Laboratory work to prepare Delta smelt for experimental release in December 2021. Photo by Tien-Chieh Hung/UC Davis Fish Conservation and Culture Laboratory. | 

By Dan Bacher

2021 was a very bad year for Delta smelt and other declining fish populations on the Sacramento-San Joaquin River Delta.

For the fourth year in a row, the California Department of Fish and Wildlife has caught zero Delta smelt in its Fall Midwater Trawl (FMWT) survey on the Sacramento-San Joaquin River Delta.

The Delta smelt, once the most abundant fish in the entire Delta Estuary, numbered in the millions before state and federal projects started exporting massive quantities of water to San Joaquin Valley agribusiness and Southern California water agencies. 

Found only in the Delta, the 2 to 3 inch fish that smells like cucumber is considered an "indicator" species because it indicates the overall health of the Delta ecosystem. The FMWT 2021 sampling season began September 1 and was completed on December 16.  

The survey ended just after the U.S. Fish and Wildlife Service and the California Department of Fish and Wildlife, along with the California Department of Water Resources and the U.S. Bureau of Reclamation, experimentally released 12,800 captively produced Delta smelt on December 14 and 15. The fish were raised at the University of California, Davis, Fish Conservation and Culture Laboratory in Byron, California.

The purpose of this Delta smelt  project is “to benefit conservation of the species through studies of experimental release of captively produced fish into a portion of its current range,” according to the service:   

As the hatchery-raised smelt are released into the estuary, the dramatic collapse of Delta smelt and other pelagic (open water) species continues on the Delta, the largest estuary on the West Coast of Americas.  

In a December 21st memo summarizing the results of the survey, James White, CDFW environmental scientist wrote, “The 2021 abundance index for Delta Smelt was 0 and was tied with 2018 through 2020 for the lowest in FMWT history. This is a continuation of a pattern of low indices that occurred in recent years.”

“No Delta Smelt were collected from any stations during our survey months of September- December. An absence of Delta Smelt catch in the FMWT is consistent among other surveys in the estuary,” he wrote.

However, White noted that another survey, the Enhanced Delta Smelt Monitoring (EDSM) survey of the U.S. Fish and Wildlife Service (USFWS) caught 8 Delta Smelt, including 6 marked individuals — obviously from the experimental release — and 2 wild individuals, among 65 sampling days (between 9/1 and 12/17) comprised of 784 tows.

The federal survey’s catch occurred on December 16 and 17, 2021. “Delta Smelt numbers are very low and below the effective detection threshold by most sampling methods,” wrote White.  

The Delta smelt has declined to a point of virtual extinction in the wild due to several factors, including invasive species, drought and declining water quality, but none has a bigger impact than the changes in the Delta ecosystem caused by the export of massive amounts of water to corporate agribusiness interests in the San Joaquin Valley.  

The indexes for the other pelagic species, including striped bass, longfin smelt, threadfin shad, American shad, Sacramento splittail and Wakasagi, varied in the 2021 survey, but show a dramatic overall decline of the fish since the beginning of the survey in 1967.

The 2021 abundance index for Age-0 Striped Bass (Morone saxatilis), a popular introduced gamefish species, was 56, representing a 7% increase from last year’s index.  

“Striped Bass were collected every month during September-December. 49 age-0 Striped Bass were collected at index stations and 2 from non-index stations,” White stated. “Monthly catch was highest in November, with catch highest in Lower Sacramento River among months.”   

The 2021 abundance index for Longfin Smelt (Spirinchus thaleichthys), a native species that is a cousin of the Delta Smelt, was 323, representing a 91% increase from last year’s index, said White.

A total of 124 Longfin Smelt were collected at index stations and 0 from non-index stations. “Fish were distributed from San Pablo Bay through the confluence of the Sacramento and San Joaquin rivers. Monthly catch was highest in November, with catch highest in San Pablo Bay most months. Higher catch is usually expected in December as Longfin Smelt adults return to the estuary from the ocean to spawn as water temperatures drop in the late fall or winter,” he wrote.

The 2021 abundance index for Threadfin Shad (Dorosoma petenense), an introduced forage fish species, was 221, representing a 65% decrease from last year’s index.  

“A total of 190 Threadfin Shad were collected at index stations and 613 from non-index stations. The greatest monthly catch was in December, with catch highest in SRDWSC most months,” White noted. 

The 2021 abundance index for American Shad (Alosa sapidissima), an introduced gamefish species that is a member of the herring family, was 398, representing a 64% decrease from last year’s index. 

White said American Shad abundance indices have “fluctuated substantially” during the period 2017-2021, ranging from a low of 398 to a high of 3086.

“A total of 241 American Shad were collected at index stations and 107 from non-index stations. American Shad were collected mostly from the SRDWSC (Sacramento River Deepwater Shipping Channel) with the greatest monthly catch in October,” he wrote. 

The 2021 abundance index for Sacramento Splittail (Pogonichthys macrolepidotus), a native member of the minnow family found only in the Sacramento-San Joaquin River Delta, was 0, showing a continuing trend in recent years of “very little to no catch of Splittail in the survey.”

A total of 0 Sacramento Splittail were collected at index stations and 4 from non-index stations. Splittail catch was greatest in SRDWSC with the highest monthly catch occurring in December, according to White. 

“Splittail were collected 3 of the 4 months at non-index stations in the SRDWSC,” he noted. “The Splittail FMWT index tends to be low or zero except in relatively wet years, such as 2011, when age-0 fish tend to be abundant.”  

Finally, the abundance index for Wakasagi (Hypomesus nipponensis), or Japanese pondsmelt, was zero because Wakasagi were only caught at non-index stations. The California DFG first introduced this fish in northern California reservoirs in 1959 to provide forage for rainbow trout and other salmonids.

“A total of 0 Wakasagi were collected at index stations and 16 from non-index stations. Monthly catch was highest in October and December, with catch being highest in SRDWSC among months,” White concluded. 

The decline of Delta smelt and other pelagic fish species in recent years is part of the “Pelagic Organism Decline” (POD) that state and federal scientists first identified in 2005. The scientists attributed the decline to three major factors: changes in the Delta ecosystem spurred by water exports south of the Delta, the spread of invasive species and toxics in the water. 

Between 1967 and 2020, the state’s Fall Midwater Trawl abundance indices for striped bass, Delta smelt, longfin smelt, American shad, splittail and threadfin shad have declined by 99.7, 100, 99.96, 67.9, 100, and 95 percent, respectively, reported Bill Jennings, Executive Director of the California Sportfishing Protection Alliance.  

“Taken as five-year averages (1967-1971 vs. 2016-2020), the declines for striped bass, Delta smelt, longfin smelt, American shad, splittail and threadfin shad are 98.1, 99.8, 99.8, 26.2, 99.3 and 94.3 percent, respectively,” said Jennings.  

Last year, scientists forecasted the likely extinction of Delta smelt in the wild in 2021 or 2022. On January 10, Dr. Peter Moyle, Karrigan Börk, John Durand, T-C Hung, and Andrew L. Rypel, wrote on the California Water Blog a piece entitled, “ 2021: Is this the year that wild delta smelt become extinct? 

“All signs point to the Delta smelt as disappearing from the wild this year, or, perhaps, 2022,” said Moyle. “In case you had forgotten, the Delta smelt is an attractive, translucent little fish that eats plankton, has a one-year life cycle, and smells like cucumbers. It was listed as a threatened species in 1993 and has continued to decline since then.”

Then on November 14, California Sportfishing Protection Alliance (CSPA) fishery biologist Tom Cannon in his California Fisheries Blog revealed that two other surveys besides the Fall Midwater Trawl on the Delta had turned up similar results for the Delta smelt:

“The Enhanced Delta Smelt Monitoring (EDSM) caught only 1 Delta smelt in 2200 smelt-targeted net tows in 2021,” wrote Cannon. “This compares to 49 captured in 2020 and hundreds in prior years.  None were captured in the Spring Kodiak Trawl 2021 survey.”

“This year’s results indicate that Delta smelt are likely virtually extinct in the wild,” concluded Cannon.

I will be following the progress of the experimental reintroduction of hatchery-raised Delta smelt into the wild.

I am not optimistic about its success because of the dramatic changes in the Delta ecosystem that have been caused by water exports south of the Delta by the State Water Project and the Central Valley Project over the decades — combined with the impacts of invasive species, toxics, declining water quality and other factors — and the apparent unwillingness of the state and federal governments to make the necessary changes in their water export and dam operations needed to save the Delta smelt and other fish populations.

Background from CDFW:

“The California Department of Fish and Wildlife (CDFW) has conducted the Fall Midwater Trawl Survey (FMWT) to index the fall abundance of pelagic — open water fishes annually since 1967 (except 1974 and 1979). FMWT equipment and methods have remained consistent since the survey’s inception, allowing the indices to be compared across time. These relative abundance indices are not intended to approximate population sizes. However, we expect that our indices reflect general patterns in population change (Polansky et al. 2019).  

In September, October, November, and December, 121, 122, 122, and 122 fish tows were conducted as well as 32 zooplankton tows, respectively. Here we report catch from index and non-index stations, species distributions by region, and annual abundance indices for seven pelagic fish species; Delta Smelt (native), Striped Bass (introduced), Longfin Smelt (native), American Shad (introduced), Threadfin Shad (introduced), Splittail (native), and Wakasagi (introduced).”  

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