Late last summer, on August 29th, 2024, the United States Fish and Wildlife Service listed the San Francisco Bay-Delta distinct population segment of longfin smelt (Spirinchus thaleichthys) as ‘endangered’ under the federal Endangered Species Act (ESA). With this decision, the Longfin Smelt joins the Delta Smelt (Hypomesus transpacificus) , the longfin’s infamous cousin species, as a list species under the ESA. Longfin smelt had already been listed as ‘threatened’ under the California Endangered Species Act (CESA), but the new federal listing is a sign of the challenges that smelt and the broader Delta ecosystem face. The listing brings additional protections and new regulatory requirements that may further complicate water management in the Delta. This blog post provides an overview of this population of Longfin Smelt, explains what listing means, and then discusses ongoing work at UC Davis and beyond to recover Longfin Smelt populations.
About the Longfin Smelt
The Longfin Smelt is a small (~10 cm) migratory forage fish within the true smelt family Osmeridae that occurs in coastal habitats from Central California to Alaska. Spawning, hatching, and larval rearing occur in tidal fresh and low-salinity estuarine habitats, with juveniles migrating to higher-salinity bay and coastal marine habitats where they forage on mesozooplankton until returning to estuaries to spawn at 2-3 years of age. The San Francisco Estuary (SFE) Longfin Smelt population represents the southernmost spawning population of the species. This population may have been an important component of SFE food webs, from freshwater to marine habitats, given its former abundance (Nobriga and Rosenfield 2016). Because the SFE population has declined to < 1% of its 1970s abundance levels, the listing reflects concerns that it could be rapidly heading toward extinction (Hobbs et al. 2017; USFWS 2022).
Regulatory Impact…