Delta smelt were once one of the most abundant fish in the Delta. They could also be found year-round in Suisun Marsh, in Napa River and in the waterways of the south and central Delta.
In the late 1950s the first of two large water export facilities began pumping water out of the Delta, and then in 1967 the second large facility started up, pumping even more water. Pesticides and herbicides began showing up with more frequency, which led to increased contamination of the Delta. And ships from China and elsewhere came to San Francisco and dumped their ballast water, which infected the Delta with invasive organisms, exotic species of zooplankton and a voracious plankton eating clam.
From that point, the ecological environment of the Delta was radically changed and damaged, and Delta Smelt numbers began declining in the 1970s, plunging in the early 1980s to worrisome levels. Delta Smelt was listed under the Endangered Species Act in 1993, and have declined to the edge of extinction today.
June 23, 2016 Mathematician Uses Big Data to Save Tiny Smelt
For more than 30 years, Ken Newman has used his statistical methods to help endangered fish and wildlife species in some of the most complex ecosystems across the U.S. and Scotland. Yet, his work with the Delta smelt may be his most daunting task.
There are four significant threats to the species:
direct entrainments by State and Federal water export facilities;
summer and fall increases in salinity,
summer and fall increases in water clarity,
and effects from introduced species.
Ammonia in the form of ammonium may also constitute a significant threat to the delta smelt. Additional potential threats include predation, entrainment into power plants, contaminants and small population size.
Existing regulatory mechanisms have not proven adequate to halt the decline of delta smelt since the time of listing as a threatened species.
We are unable to determine with certainty which threats or combinations of threats are directly responsible for the decrease in delta smelt abundance.Â 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.
On December 15, 2008, the Sacramento FWO issued a biological opinion (BO) on the Long-Term Operational Criteria and Plan (OCAP) for coordination of the Central Valley Project and State Water Project. The Service determined that the continued operation of these two water projects, as described in the plan, was likely to jeopardize the continued existence of the delta smelt and adversely modify its critical habitat. See OCAP page for more information.
Delta smelt by metric ruler
Smelt Working Group
The Smelt Working Group (formerly known as the Delta Smelt Working Group) consists of experts in delta smelt biology from the U.S. Fish and Wildlife Service, U.S. Bureau of Reclamation, U.S. Environmental Protection Agency, California Department of Water Resources and California Dept. of Fish and Wildlife. See bottom of OCAP page for SWG minutes.
Reclassification from threatened to endangered warranted but precluded by other
higher priority listing actions. Federal Register 75:17667
April 7, 2010 (PDF 193 KB) Five Year Review (PDF 368 KB)
Completed September 13, 2010