Countdown to Extinction: Zero Delta Smelt Found in October Midwater Trawl Survey for Fourth Year

By Dan Bacher | @DanBacher

Time is running out for the Delta smelt, once the most abundant fish in the entire Sacramento-San Joaquin River Delta.

For the fourth October in a row, the California Department of Fish and Wildlife has caught zero Delta smelt in its Fall Midwater Trawl Survey of the Delta.

The smelt is now near extinction in the wild, although U.C. Davis continues to raise the fish in a captive breeding program.

The Delta smelt population has plummeted over the decades since the State Water Project began exporting Delta water to San Joaquin Valley growers in 1967.

There are several factors that scientists pinpoint for the ecosystem collapse, including toxic chemicals, decreasing water quality and invasive species, but no factor figures greater in the collapse than the export of massive quantities of state and federal project water from the Delta to San Joaquin Valley agribusiness interests like the Resnick family and the Westlands Water District.

The last year when Delta smelt were recorded in October was in 2017, when 2 were reported by state Fish and Wildlife biologists.

The last year when any Delta smelt were caught during the four-month survey was also 2017, when the two smelt reported in October were the only ones reported that year.  If no Delta smelt are caught in the remaining two months of the survey, this will be the fifth year that no smelt have been recorded. 

The abundance indices (a relative measure of abundance) for other Delta pelagic species, including longfin smelt, Sacramento splittail, striped bass, American shad and threadfin shad, also continue to be very low.

The CDFW this October reported an abundance index of 12 for longfin smelt, another native fish species that is a cousin of the Delta smelt, in its surveying stations throughout the Delta. The survey didn’t find any longfin smelt last October.

For the tenth October in a row, state scientists caught zero Sacramento splittail, a native member of the minnow family. The last time that any splittail were reported in the survey was in 2017, when 1 splittail was reported in December.

The index for striped bass, a gamefish from the Eastern Seaboard introduced to the Delta over 130 years ago, continued to be low, though not as low as last October. The CDFW reported an index of 10 young-of-the-year striped bass this October, compared with 2 last October.

The index for American shad, another introduced species, did about the same this October as last October. Biologists reported an abundance index of 103 for this member of the herring family, compared with 97 in October 2020.

Finally, CA Fish and Wildlife officials reported an index of 28 threadfin shad, an introduced forage fish, this October. That compares to 5 last October.

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, according to Bill Jennings, Executive Director of the California Sportfishing Protection Alliance (CSPA).

“Taken as five-year averages, 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.

The Delta smelt is an indicator species that demonstrates the health of the Delta, the largest estuary on the West Coast of the Americas. It is the proverbial “canary in a coal mine” for the Delta Estuary.

”Delta Smelt are the thread that ties the Delta together with the river system,” said Caleen Sisk, Chief of the Winnemem Wintu Tribe. “We all should understand how that affects all the water systems in the state. They are the irreplaceable thread that holds the Delta system together with Chinook salmon.”

“All signs point to the Delta smelt as disappearing from the wild this year, or, perhaps, 2022,” according to a California Water Blog analysis by Peter Moyle, Karrigan Börk, John Durand, T-C Hung and Andrew L. Rypel on January 10, 2021. “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.” 

I will be monitoring this survey every month and writing a brief report on the monthly results for each species. When the survey terminates in December and the final results are compiled for the four months, I will write a comprehensive report on the survey and its ecological implications.

Fall Midwater Trawl indices for age-0 striped bass (Morone saxatilis), delta smelt (Hypomesus transpacificus), longfin smelt (Spirinchus thaleichthys), American shad (Alosa sapidissima),splittail (Pogonichthys macrolepidotus), and threadfin shad (Dorosoma petenense) have been done every year from 1967-2021 except in 1974, 1979, and September and December 1976.

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