Delta smelt
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 Delta smelt, Hypomesus transpacificus
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| Hypomesus transpacificus |
Delta smelt, Hypomesus transpacificus, are slender-bodied smelts, about 5 to 7 cm long, of the Osmeridae family. They have a steely blue sheen on the sides and seem almost translucent. Smelts live together in schools and feed on zooplankton (small fishes and invertebrates). One female may lay from 1,400 to 1,800 eggs. Mature unfertilized eggs are about 1 mm.
[edit] Habitat
Delta smelt are endemic to the Sacramento Delta, California, where it is distributed from the Suisun Bay upstream through the Delta in Contra Costa, Sacramento, San Joaquin, Solano and Yolo counties. The delta smelt is a pelagic (live in the open water column away from the bottom) and euryhaline species (tolerant of a wide salinity range). They have been collected from estuarine waters up to 14 ppt (parts per thousand) salinity.
[edit] Life cycle
Most delta smelt live one year and die after their first spawning (semelparous). Delta smelt spawning occurs in spring in river channels and tidally influenced backwater sloughs upstream of the mixing zone (saltwater-freshwater interface). The Sacramento and San Joaquin rivers then transport the delta smelt larvae downstream to the mixing zone, normally located in the Suisun Bay. Young delta smelt then feed and grow in the mixing zone before starting their upstream spawning migration in late fall or early winter.
Delta smelt used to be a common fish in the Sacramento - San Joaquin rivers estuary. As at 2006, however, the population is much smaller than historically and the species is now listed as threatened under the Federal Endangered Species Act (Federal Register 58:12863; March 5, 1993). Critical habitat was listed for delta smelt on December 19, 1994 (Federal Register 59:65256).
[edit] References
- Gimenez Dixon (1996). Hypomesus transpacificus. 2006 IUCN Red List of Threatened Species. IUCN 2006. Retrieved on 11 May 2006. Listed as Endangered (EN B1+2cd v2.3)
