Delta smelt

Delta smelt
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii
Order: Osmeriformes
Family: Osmeridae
Genus: Hypomesus
Species:
H. transpacificus
Binomial name
Hypomesus transpacificus

The delta smelt (Hypomesus transpacificus) is an endangered[1] slender-bodied smelt, about 5 to 7 cm (2.0 to 2.8 in) long, in the family Osmeridae. Endemic to the upper Sacramento-San Joaquin Estuary of California, it mainly inhabits the freshwater-saltwater mixing zone of the estuary, except during its spawning season, when it migrates upstream to fresh water following winter "first flush" flow events (around March to May).[4] It functions as an indicator species for the overall health of the Delta's ecosystem.[5]Delta Smelt are usually found at temperatures of less than 25°C and prefer temperatures of around 20°C. They are euryhaline but occur mostly at salinities of 0–7 practical salinity units.[6]

Because of its one-year lifecycle and relatively low fecundity, it is very susceptible to changes in the environmental conditions of its native habitat.[7] It is listed as a federally threatened species under the Endangered Species Act of 1973.[2][3][8] Efforts to protect the fish from further decline and extinction have focused on limiting or modifying the large-scale pumping activities of state and federal water projects at the southern end of the estuary, thereby limiting water available to farming. However, these efforts have not prevented the species from becoming functionally extinct in the wild.[9]

Delta smelt is easily to be confused with longfin smelt. They are both small, pelagic fish species native to the estuarine and coastal waters of the Pacific coast, but they exhibit distinct ecological, morphological, and behavioral characteristics. The delta smelt, a key indicator species, is endemic to the San Francisco Bay-Delta and has a slender body averaging 5–7 cm in length, with a translucent appearance and a faint, blue lateral line. It primarily inhabits low-salinity waters and is critically endangered due to habitat loss and water management practices. In contrast, the longfin smelt is slightly larger, typically reaching up to 15 cm, and is distinguished by its long pectoral fins that extend beyond the base of the pelvic fins.

  1. ^ a b NatureServe (2020) [errata version of 2014 assessment]. "Hypomesus transpacificus". IUCN Red List of Threatened Species. 2014: e.T10722A174778740. doi:10.2305/IUCN.UK.2014-3.RLTS.T10722A174778740.en. Retrieved 7 May 2023.
  2. ^ a b "Delta smelt (Hypomesus transpacificus)". Environmental Conservation Online System. U.S. Fish & Wildlife Service. Retrieved 7 May 2023.
  3. ^ a b 58 FR 12854
  4. ^ Sommer, T. et al. 2011. The spawning migration of delta smelt in the Upper San Francisco Estuary. San Francisco Estuary and Watershed Science: 9(2).
  5. ^ "Delta Smelt". Center for Biological Diversity. Retrieved 10 May 2015.
  6. ^ Cite error: The named reference :3 was invoked but never defined (see the help page).
  7. ^ Moyle, PB. 2002. Inland fishes of California. University of California Press, Berkeley.
  8. ^ Cite error: The named reference USFWS was invoked but never defined (see the help page).
  9. ^ Cite error: The named reference Krieger was invoked but never defined (see the help page).