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NATURAL HISTORY

LONGFIN SMELT } Spirinchus thaleichthys
FAMILY: Osmeridae

DESCRIPTION: The longfin smelt is a medium-sized fish, usually growing to about 10 centimeters as an adult. It is translucent silver on the sides and olive to iridescent pink on the back. Its most distinctive characteristic is its long pectoral fins, which give the species its common name.

HABITAT: Primary habitat is the open water of estuaries, both in seawater and freshwater areas, typically in the middle or deeper areas of the water column.

RANGE: The longfin smelt inhabits estuaries along the Pacific  Coast, from San Francisco Bay to Alaska.

MIGRATION: Longfin smelt migrate to suitable spawning habitat in estuaries between January and March. They migrate throughout the estuary over the course of their life cycle.

BREEDING: Longfin smelt spawn in estuaries in fresh or slightly brackish water over sandy or gravel substrates, with most spawning occurring between January and March. Males arrive on the spawning grounds before females, which carry between 5,000 and 24,000 eggs.

LIFE CYCLE: After hatching, longfin smelt larvae disperse widely throughout the estuary. Larval longfin smelt appear to move up and down in the water column, synchronizing with tides to adjust or maintain their geographic position in the estuary. Larvae metamorphose into juveniles about 30 to 60 days after hatching, depending on water temperature. The smelt generally mature at the end of their second year, at which point they migrate to spawn.

FEEDING: The favored food of longfin smelt is opossum shrimp, but they will eat a variety of small crustaceans.

THREATS: Longfin smelt have declined due to degraded environmental conditions in the Bay-Delta Estuary caused by massive water diversions that reduce freshwater inflow; 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.

POPULATION TREND: Longfin smelt may already be extinct in some smaller estuaries in northern California, and the San Francisco Bay-Delta population has experienced two catastrophic population declines in two decades. So far, throughout the 2000s, the Bay-Delta longfin smelt population has been at just 3 percent of levels measured less than 20 years ago, and numbers in this estuary dropped to record lows from 2004 to 2007.

 

Photo courtesy of NOAA