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Environmental Assessment

Analysis of the Causes of a Decline in the San Joaquin Kit Fox Population on the Elk Hills, Naval Petroleum Reserve #1, California

Notice

EPA is announcing the availability of the final report, Analysis of the Causes of a Decline in the San Joaquin Kit Fox Population on the Elk Hills, Naval Petroleum Reserve #1, California.

Report Information

This report describes a causal assessment of the decline in the abundance of San Joaquin kit foxes on an oil field. The EPA CADDIS system was used to perform the causal inference.

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Glenn W. Suter
  • by phone at:   513-569-7808
  • by fax at:   513-569-7475
  • by email at:  suter.glenn@epa.gov

Background

Cover of the Elk Hills Kit Fox Population Decline ReportThis report demonstrates the utility of the Causal Analysis/Diagnosis Decision Information System (CADDIS) for determining the cause of biological impairments on contaminated sites. The case is a decline in the abundance of a population of the endangered San Joaquin kit fox on the Elk Hills Naval Petroleum Reserve, California, between 1981 and 1986. This precipitous decline was a cause for concern at the time because of its magnitude and because it was associated with an increase in oil production on the site. Although multiple potential causes were investigated at the time, the cause of the decline was not determined. This investigation proposed and analyzed six candidate causes: prey abundance, habitat quality, predation, toxicants, accidents and diseases.

Evidence for each of these potential causes was analyzed using the CADDIS scoring system and 15 types of evidence. The conclusion is that predation by coyotes was the proximate cause of the decline. Road kills contributed to the high mortality of foxes, but were much less common. The decline in prey probably contributed to mortality by making the foxes more susceptible to predation. As a model for causal analysis at contaminated sites, this study was successful. Contaminants were eliminated as the cause and an alternative was strongly supported by the evidence. In addition, this study demonstrated the great utility of some types of evidence that had not previously been used in CADDIS: mathematical modeling (a kit fox demographic model) and the analysis of tissues (i.e., fur and blood analyses to eliminate toxicants and diseases, respectively).

The assessment demonstrates the applicability of CADDIS to terrestrial systems and in particular to a wildlife population. It also demonstrates the use of demographic modeling to identify causes and the importance of using the right spatial and temporal scale.

History/Chronology

Oct 2008An external peer review was conducted by an independent contractor.
Nov 2008Revised final report based on peer review comments.
May 2009EPA released the final report.

Next Steps

This is the final report.

Citation

U.S. EPA. Analysis of the Causes of a Decline in the San Joaquin Kit Fox Population on the Elk Hills, Naval Petroleum Reserve #1, California. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-08/130, 2008.

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