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The Collapse of Pelagic Fishes in the Upper San Francisco Estuary: El Colapso de los Peces Pelagicos en La Cabecera Del Estuario San Francisco

Ted Sommer, Charles Armor, Randall Baxter, Richard Breuer, Larry Brown, Michael Chotkowski, Steven Culberson, Frederick Feyrer, Marty Gingras, Bruce Herbold, Wim Kimmerer, Anke Mueller-Solger, Matthew Nobriga, Kelly Souza | January 9th, 2007

Although the pelagic fish community of the upper San Francisco Estuary historically has shown substantial variability, a recent collapse has captured the attention of resource managers, scientists, legislators, and the general public. The ecological and management consequences of the decline are most serious for delta smelt (Hypomesus transpacificus), a threatened species whose narrow range overlaps with large water diversions that supply water to over 25 million people. The decline occurred despite recent moderate hydrology, which typically results in at least modest recruitment, and investments of hundreds of millions of dollars in habitat restoration and environmental water allocations to support native fishes. In response to the pelagic fish collapse, an ambitious multi-agency research team has been working since 2005 to evaluate the causes of the decline, which likely include a combination of factors: stock-recruitment effects, a decline in habitat quality, increased mortality rates, and reduced food availability due to invasive species.


endangered species, fisheries, invasive species, native fish, planning and management, Sacramento–San Joaquin Delta, water project operations, water quality