For the seventh consecutive September, a Zero Delta smelt was encountered in the Midwater Trawl Survey

Delta Smelt, Adult (side view), UC Davis Fish Conservation and Culture Laboratory, Byron, California

For the seventh consecutive September, the California Department of Fish and Wildlife (CDFW) caught zero Delta smelt during a fall midwater trawl survey in the Sacramento-San Joaquin River Delta.

Delta smelt, an indicator species that demonstrates the relative health of the San Francisco Bay-Delta Estuary, were found last September when 5 individuals were caught by CDFW biologists in 2015.

The last year any Delta melts were captured during the four-month study was 2016, when a total of 8 Delta melts were reported.

Final results from the four-month survey of pelagic (open water) fish species from September to mid-December will not be available from CDFW until late December or early January. A report is usually issued at that time by the Department summarizing the results of abundance indices (a relative measure of abundance) for various fish species.

Data for September 2022 is available on the annual state surveys webpage here.

Once the most abundant fish in the entire estuary, Delta smelt are now extinct in the wild, although UC Davis continues to breed the fish in a captive breeding program. In an experiment late last year and early this year, thousands of these hatchery-raised smelt were released into the Delta.

On December 14 and 15, 2022, the US Fish and Wildlife Service and CDFW, along with the California Department of Water Resources and the US Bureau of Reclamation, experimentally released 12,800 hatchery-raised Delta smelt into the Delta for the first time. The agencies released another cargo meltdown in January and three more in early February.

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

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

While there are several factors that scientists have identified for the ecosystem’s collapse, including toxic chemicals, declining water quality, and invasive species, none is a bigger factor in the collapse than the diversion of water from Central Valley rivers and the export of large amounts of state and federal project water. From the Delta to the San Joaquin Valley, agribusiness interests such as Stewart and Lynda Resnick, owners of the Wonderful Company and Westlands Water District.

“Delta Smelt is the thread that connects the Delta to the river system,” said Winnemem Wintu Chief Caleen Sisk. “We all need to understand how this affects all water systems in the state. They are the indispensable thread that holds the Delta system together with Chinook salmon.”

The department also found 7 longbill smelt, a cousin of the Delta smelt, at research stations throughout the Delta this September. This is compared to September 1 last year.

The US Fish and Wildlife Service proposed on October 6 that a distinct population segment of the San Francisco Bay-Delta be listed as a “threatened” species under the Endangered Species Act (ESA).

“Scientific analyzes indicate that the Bay-Delta longfin smelt is threatened with extinction throughout its range,” the service said in a statement. The Service is now seeking public comment within 60 days of publication of the proposed rule in the Federal Register.

In response to the proposed listing, Jon Rosenfield, chief scientist at San Francisco Baykeeper and a noted expert on longfin smelt ecology, said, “Our local longfin smelt population is particularly sensitive to changes in the volume of inflowing freshwater. to San Francisco Bay. The catastrophic decline in longfin smelt is another sign that the flow of water from the rivers feeding the bay is unsustainable.

Eel smelt were once one of the most abundant fish in San Francisco Bay, which spans the Sacramento-San Joaquin River delta, Rosenfield said.

“However, annual state surveys show that longline smelt in San Francisco Bay have been at or near record lows nearly every year since 2007 — and the species is virtually undetectable in other Northern California estuaries,” Rosenfield said.

For the eleventh consecutive September, state scientists have caught zero Sacramento splittails, a native member of the minnow family found only in the Delta Estuary and Central Valley rivers. The last time the survey reported any splits was in 2017, when 1 splittail was reported in December.

Eastern Seaboard striped bass, imported to the Delta for more than 130 years, continue to score poorly, but the index was better than last year. Caught the CDFW index 10 young of the year striped bass this September compared to last September 1.

Although the index is down sharply from historical levels, another introduced species, American shad, was better than last September. Biologists reported an index 110 for this herring family member this September, compared to 24 in September 2021.

Finally, CDFW officials announced a September 2022 forage fish index of 7 shad. This is even lower than the index of 11 reported last September.

Since the State Water Project was launched in 1967, the decline of the Delta’s pelagic species has been catastrophic. Between 1967 and 2020, the state’s Fall Midwater Trawl abundance indices for striped bass, Delta smelt, longfin smelt, American shad, splittail and threadfinsmelt were 99, respectively, according to Bill Jennings, executive director of the California Sport Fisheries Conservation Alliance (CSPA). 7, 100, 99.96, 67.9, 100 and 95 percent decreased.

“Taking a five-year average, 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,” Jennings said.

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