Pacific Southwest Region
California, Nevada and Klamath Basin

Service Finds Uplisting of Delta Smelt From Threatened to Endangered Under Endangered Species Act "Warranted but Precluded"

Apr 02, 2010

April 2, 2010
Contact: Steve Martarano, (916) 930-5643,

Service Finds Uplisting of Delta Smelt From “Threatened” to “Endangered” Under Endangered Species Act “Warranted but Precluded”           

The U.S. Fish and Wildlife Service today announced that, based on accumulated scientific data, the delta smelt warrants uplisting from “threatened” to “endangered” under the Endangered Species Act but that uplisting at this time is precluded by the need to address higher priority species first.  The Service will develop a proposed rule to reclassify this species as priorities allow. The finding of “warranted but precluded” will have no practical effect on protections for the delta smelt, existing federal actions, or water flows in the delta smelt habitat.

Delta smelt are fish native and only found in the San Francisco Bay and Sacramento–San Joaquin Delta Estuary in California, found only from the San Pablo Bay upstream through the Delta in Contra Costa, Sacramento, San Joaquin, Solano, and Yolo counties. Their historical range is thought to have extended from San Pablo Bay upstream to at least the city of Sacramento on the Sacramento River and the city of Mossdale on the San Joaquin River. They were once one of the most common pelagic (living in open water away from the bottom) fish in the upper Sacramento–San Joaquin Estuary.

The delta smelt was first listed as threatened under the ESA in 1993 due to habitat loss, drought, introduced species, and reduction of food items. Critical habitat was designated for the species in 1994. The most recent estimate of delta smelt is the lowest ever recorded – about one-tenth the level it was in 2003. In addition, a 2005 population viability analysis calculated a 50 percent likelihood that the species could become extinct within the next 20 years.

There are several primary threats to delta smelt, including the direct entrainments by state and federal water export facilities, summer and fall increases in salinity and water clarity, and competition with introduced species. Additional threats are predation by striped and largemouth bass and inland silversides, entrainment into power plants, contaminants, and small population size. In addition, existing regulatory mechanisms are not adequate to halt the decline of delta smelt since the time of listing as a threatened species. 

The Service is still unable to determine with certainty which threats or combinations of threats are directly responsible for the decrease in delta smelt abundance. However, the apparent low abundance of delta smelt in concert with ongoing threats throughout its range indicates that the delta smelt is now in danger of extinction throughout its range. Therefore, based on a review of the best scientific and commercial information available, the Service finds that the delta smelt meets the definition of an endangered species under the Act, and that it warrants reclassification from threatened to endangered. However, the Service will not begin a formal rulemaking to reclassify delta smelt at this time.

Reclassification of delta smelt is considered a lower priority than other actions needing attention, because the species is currently listed as threatened, which receives certain protections under the Act. Service regulations prohibit take for threatened species in the same way as endangered species. Other protections include those under section 7(a)(2) of the Act whereby federal agencies must insure that any action they authorize, fund, or carry out is not likely to jeopardize the continued existence of any endangered or threatened species.

For the complete 12-month finding on the petition to reclassify the delta smelt from threatened to endangered, please visit . A copy of the Federal Register Notice is availabe at: For more information on the delta smelt provided by the Service, go to and open the Delta in the Spotlight box on the home page to begin.


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