The Delta smelt (Hypomesus transpacificus), a 2 to 3 inch native fish listed under both federal and state Endangered Species Acts, is found only in the Delta estuary. It is regarded as an indicator species, a fish that demonstrates the health of the entire Delta ecosystem.
Once the most abundant fish in the entire estuary, the population has collapsed to the point where not one fish was found in the 2018 Fall Midwater Trawl survey. The 2018 abundance index (0), a relative measure of abundance, is the lowest in FMWT history.
“No Delta Smelt were collected from any station during our survey months of September- December,” wrote James White, environmental scientist for the CDFW’s Bay Delta Region.
This is not the only survey of Delta smelt populations that the CDFW conducts — and the other assessments have found smelt, although in alarmingly low numbers.
“While this survey did not catch any Delta Smelt, it does not mean they are not present. Spring Kodiak Trawl (SKT) survey caught 5 Delta Smelt in December,” White noted.
White also said another survey, the Enhanced Delta Smelt Monitoring (EDSM) survey, caught 13 Delta Smelt during December. (https://fileshare.fws.gov/?linkid=KZi4zr6VWWXpAmKqe8kAlLwMpNbkSIFi8YDODS6 ncAGbVD1eD7Lrjg).
While decades of water exports and environmental degradation under previous governors and federal administrations have brought the smelt, once the most abundant fish in the Delta, to the edge of extinction, Governor Jerry Brown and his administration did nothing to reverse the trend, according to fishermen and environmentalists.
Before this fall, the 2017 abundance index (2) was lowest in FMWT history. Only 2 Delta smelt were collected at index stations in the survey during the fall of 2017.
The Delta smelt is not the only fish not found during the fall 2018 survey. The CDFW didn’t observe any Sacramento splittail, a native minnow species that was formerly listed under the Endangered Species Act until Bush administration delisted the species and the Obama administration agreed with the delisting, in the 2018 fall survey either.
The striped bass, a popular gamefish that migrates from the ocean, San Francisco Bay and Delta into the Sacramento and San Joaquin rivers every spring to spawn, also showed an alarming drop in abundance during the survey.
The 2018 abundance index (42) for striped bass was the lowest in FMWT history, slightly less than the previous low value (43) in 2010. Thirty-one age-0 striped bass were collected at index stations, noted White.
The longfin smelt, a cousin of the Delta smelt, isn’t faring very well either in the estuary. “The 2018 abundance index (52) was the 5th lowest value in FMWT history, a 63% reduction from the previous year. Thirty-one Longfin Smelt were collected at index stations,” said White.
The number of threadfin shad, an introduced forage fish species, continued to decline. The 2018 abundance index (198) was the 4th lowest in survey history, a 32% reduction from the previous year. The CDFW found 150 threadfin shad at index stations.
The abundance of American shad in the trawl is also disappointing. The 2018 abundance index (1064) was the 21st lowest value on record, a 66% reduction from the previous year. Seven-hundred and two American shad were collected at index stations.
The January 2 memo summarizing the Fall Midwater Trawl results is available here: nrm.dfg.ca.gov/…
The link to the Fall Midwater Trawl monthly abundance indices is available here: www.dfg.ca.gov/…
Bill Jennings, Executive Director of the California Sportfishing Protection Alliance (CSPA), commented on the disastrous decline of Delta smelt and other fish species in the Fall Midwater Trawl.
“The abundance of both Delta smelt and striped bass is the lowest in the trawl’s history,” said Jennings. “Longfin is the fifth lowest, threadfin shad is the fourth lowest, American shad is a 66 percent reduction from the previous year and the splittail is zero. This is a very comprehensive trawl and the results were a disaster for Delta fisheries.”
“Not only is the Delta smelt on the brink of extinction but there are several species lined up behind it,” noted Jennings. “Governor Brown’s legacy is likely to be several extinctions of fish that flourished in this estuary for millennia.”
“We know what fish need. Fish prosper when they have adequate flows and quality water. They suffer when they don’t. The question is how do we get them to survive on less water of poorer quality than they evolved with for thousands of years. The answer appears to be they can’t,” Jennings concluded.
Dr. Jonathan Rosenfield, the Lead Scientist for The Bay Institute, emphasized in a tweet that Delta smelt are “not extinct,” since other sampling programs still catching them.
“Extinction is not imminent (if agencies take action),” he noted. “‘Flexible”, ‘adaptive’ implementation of the ESA (Endangered Species Act) has not worked. It’s time to enforce protections.”
Scientists don’t have any easy answer for the precipitous decline of Delta smelt over the past couple of years, particularly in 2017, a record water year when biologists would have expected a rebound.
“The answer is that we really don’t know,” said Dr. Peter B Moyle, Distinguished Professor, Emeritus, at the Department of Wildlife, Fish, and Conservation Biology, Center for Watershed Sciences, UC Davis, in December 2017. “The best explanation I can think of is that numbers are so low that an increase (or decrease) in the index would not be detectable with the FMT sampling.”
“Another is that there was so much water last winter (2017) that smelt were more dispersed than usual and had a hard time finding mates; this would keep numbers low. When numbers are as low, as they clearly are for smelt, random factors in sampling, in distribution, in spawning success etc can make a big difference to the total population or the index,” said Moyle.
“Note that Delta smelt are still abundant enough in places so that focused sampling can find them. For example, Tien-Chieh Hung had no problem collecting a 100 smelt in one day for his smelt culture program,” he noted.
A number of factors have resulted in the decline of Delta smelt and the other pelagic species, including increases in toxics and invasive species, but no factor has helped precipitate the collapse of Delta fish species more than the export of big quantities of water to agribusiness and Southern California water agencies from the state and federal pumping facilities in the South Delta over the past 50 years, according to fish advocates.
The record total for water exports, including water diverted by the Contra Costa Canal and North Bay Aqueduct, was 6,633,000 acre-feet in 2011 under the Brown administration. That was 163,000 acre-feet more than the previous record of 6,470,000 acre-feet set in 2005 under the Schwarzenegger administration, according to DWR data.
Found only in the Sacramento-San Joaquin River Delta, the Delta smelt mainly inhabits the freshwater-saltwater mixing zone of the estuary, except during its spawning season. That’s when it migrates upstream to freshwater following winter “first flush” flow events, around March to May.
The smelt is very susceptible to changes in the environmental conditions of its habitat due to its one-year lifecycle and relatively low fecundity. Because of this, the fish is regarded as an “indicator species” that demonstrates the health of the Delta, the largest estuary on the West Coast of the Americas.
Background from CDFW: The California Department of Fish and Wildlife has conducted the Fall Midwater Trawl Survey (FMWT) to index the fall abundance of pelagic fishes nearly annually since1967. FMWT equipment and methods have remained consistent since the survey’sinception, which allows 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.
The FMWT conducts monthly surveys from September through December. The annual abundance index is the sum of the September through December monthly survey indices. During each monthly survey, one 12-minute oblique midwater trawl tow is conducted at each of 100 index stations used for index calculation and at an additional 22 non-index stations that provide enhanced distribution information.
The 2018 sampling season completed on December 18. Field crews successfully conducted tows at all index and non-index stations during the first three survey months. Two non-index stations in Cache Slough (stations 713 and 721) were not sampled in December due to heavy vegetation damaging sampling gear.
