Longfin smelt
The longfin smelt (Spirinchus thaleichthys) is a medium sized fish associated with estuaries along the Pacific Coast, from San Francisco Bay to Alaska. The abundance of longfin smelt in all major estuaries in California, the southern extent of the species’ range, has declined severely in the past two decades. In the San Francisco Bay-Delta Estuary, which supports the largest and southernmost longfin smelt population, abundance has reached record low levels. In some smaller estuaries in northern California the species may already be extinct. The San Francisco Bay-Delta longfin smelt population has experienced two catastrophic population declines in the past 20 years and has dropped to record low population numbers for the past four consecutive years.

Longfin smelt

In August 2007 the Center for Biological Diversity, along with the The Bay Institute, and Natural Resources Defense Council, petitioned for state and federal endangered species protection for the longfin smelt. 

Longfin smelt were once one of the most abundant open-water fishes in the Bay-Delta and a central component of the food web that sustained other commercially important species. Throughout the 2000s, the Bay-Delta longfin smelt population has been just three percent of levels measured less than 20 years ago; for the past four years, longfin smelt numbers have been at record lows. Longfin smelt have declined due to many of the same degraded environmental conditions in the Bay-Delta Estuary that also caused the collapse of the Delta smelt: reduced freshwater inflow to the estuary as a result of massive water diversions; loss of fish at agricultural, urban, and industrial water diversions; direct and indirect impacts of nonnative species on food supply and habitat; and lethal and sub-lethal effects of pesticides and toxic chemicals. 

Other Bay-Delta fish species, such as the delta smelt, a species already listed under state and federal Endangered Species Acts, recently plummeted to the lowest population levels ever recorded, and the southern population of green sturgeon was federally listed as threatened in 2006. 

Read the federal listing petition for the S.F. Bay-Delta population of longfin smelt 

Read the California state listing petition for longfin smelt 

Map of longfin smelt range and distribution

Read the August 8, 2007 press release on the listing petitions

Population Dynamics and Distribution Patterns of Longfin Smelt in the San Francisco Estuary


August 7, 2007
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