Delta Smelt

Delta Smelt, Peter Johnson (More photos)

The delta smelt (Hypomesus transpacificus) was listed as threatened under the Endangered Species Act in 1993.

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.  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.

OCAP

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
Photo: USFWS

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.