Environmental factors influencing the distribution and salvage of young delta smelt: a comparison of factors occurring in 1996 and 1999

The delta smelt (Hypomesus transpacificus) is listed as a threatened species under both the Federal Endangered Species Act (FESA) and the California Endangered Species Act. Through formal consultation under Section 7 of the FESA, USBR and DWR received a Biological Opinion from the USFWS, which allows for the incidental take of delta smelt arising through operation of the Central Valley Project and the State Water Project. The incidental take of delta smelt is estimated as part of the ongoing CVP and SWP fish salvage operations. Salvage levels of young delta smelt have exceeded incidental take levels every spring and summer since 1994, except in the high spring outflow years of 1995 and 1998 (Nobriga and others 1999). These high salvage levels have resulted in changes to project operations, often leading to the curtailment of water exports. An extended period of high salvage and export curtailment in 1999 raised substantial concerns and numerous questions that remain unanswered.