RVERS Project: Captive Delta Smelt

Based on IEP monitoring data, the species is nearing extinction in wild. Causes for declines are multi-factorial and include environmental conditions, food web alterations, entrainment in export pumps, and contaminant exposure. A refuge population was established by the UC Davis Fish Conservation and Culture Laboratory (FCCL) in 2007 to provide an “insurance policy” against extinction in the wild.

Use of Captive Delta Smelt to Support Species Recovery


Wild populations may not recover without supplementation from the captive refuge population. DWR and others organized a workshop in 2017 focused on using captive Delta Smelt more broadly to support species recovery. Regional and national experts identified key knowledge gaps of highest priority (Lessard et al. 2018): 

  • Response of Delta Smelt to enclosures
  • Creation of a Hatchery and Genetic Management Plan (HGMP)
  • Understanding hatchery domestication effects
  • Others related to outreach, disease, physical tags, and early life stage release methods.

Enclosure Studies

Studies are currently in place to test the effectiveness of Delta Smelt enclosures.

  • Studies are highly collaborative, involving DWR, UC Davis, USFWS, CDFW, USGS, and USBR. 
  • Deployments occurred in 2019 winter and spring in Rio Vista and the Deep Water Ship Channel, and 2019 summer and fall in Rio Vista, Suisun Marsh, and the Yolo Bypass.
  • Directly test Delta Smelt’s response to management actions and restoration efforts.
  • Success of the study is opening the door for future use of captive Delta Smelt in the wild.

Next Steps

  • Create an HGMP guide for conservation hatchery for hatchery operations and preservation of genetic diversity.
  • Conduct further testing of enclosures.
  • Optimize methods and conduct testing in other habitats (e.g. restored wetlands).
  • Design new enclosures for earlier life stages.
  • Examine hatchery domestication effects and initiate studies to examine behavioral and genetic effects of increased domestication and potential for thermal adaptation.

bar chart of delta smelt indices, via the Spring Kodiak Trawl samples, 2005-2020, showing peak of 130.2 in 2012, with a steady decline to 0.3 in 2020 - link opens image in new window
Adult Delta Smelt Annual Index from 2004-2020 (CDFW Spring Kodiak Trawl Survey)
click to enlarge in new window

aerial view of UC Davis's Fish Culture Lab
UC Davis Fish Conservation and Culture Laboratory

small silver fish
Delta Smelt (UCD FCCL)