New Spawning Grounds Still Don’t Spell Relief for Delta Smelt
Researcher:
James A. Hobbs
Researcher Scientist
Interdisciplinary Center for Inductively Coupled Plasma Mass Spectrometry
UC Davis
E.: jahobbs@ucdavis.edu
T.: (707) 480-0188
Relevant Links:
- UC Davis/Interdisciplinary Center for Plasma Mass Spectrometry
- U.S. Fish & Wildlife Service's Delta Smelt Recovery
Tools:
Revised:
March 16, 2010
A Delta smelt. Credit: J. Hobbs/UC Davis
March 16, 2010
Contact: Christina S. Johnson, csjohnson@ucsd.edu, 858-822-5334
DAVIS - The state and federally protected Delta smelt is no longer spawning in the interior of the San Francisco Bay-Delta, a UC Davis researcher says. Instead, the small fish, which is unable to swim against the currents created by the state’s massive water pumping system, is seeking refuge in the Cache Slough Region of the lower Sacramento River.
The shift in spawning habitat, the scientist reports, occurred after water exports rose by 30 percent between 2002-04. During this same period, the Bay-Delta witnessed declines in several other pelagic fish species, besides the Delta smelt.
CAP: A slice through an otolith about 1.2 mm in diameter. The spots and lines are scars from the laser. Credit: J. Hobbs/UC Davis
Many scientists theorize that the cause of the decline in pelagic organisms is due to a lack of food (such as copepods) in the Bay-Delta, says James Hobbs, a former CALFED Science Fellow, now a researcher at the Interdisciplinary Center for Inductively Coupled Plasma Mass Spectrometry at UC Davis. Consistent with this, Hobbs has documented a slowing of Delta smelt growth rates since 2002-04.
Sophisticated lasers can extract material from otolith rings for chemical analysis. Credit: J. Hobbs/UC Davis
As if there can’t be any good news for the fish, which is listed on both state and federal endangered species lists, Hobbs has also found that water diversions can entrain and kill smelt residing in Cache Slough, more than 30 miles from the intake system.
Hobbs’ findings, presented at several science conferences, are based on growth rates and isotope analyses of more than 1,000 Delta smelt otoliths (ear bones) collected by the California Department of Fish and Game between 1999 and 2007.
A summary of his project’s findings, as well as references to scientific presentations, can be downloaded at no-charge from the CA Sea Grant website at http://www.csgc.ucsd.edu/ BOOKSTORE/project_profiles_10.html.
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