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Survey of Ungulate Abundance on Santa Rosa Island, Channel Islands National Park, CA.


non native elk in CALying off the coast of southern California, Santa Rosa Island was purchased by the National Park Service (NPS) in 1986. A court-sanctioned settlement agreement requires a phased reduction of non-native deer (Odocoileus hemionus) and non-native elk (Cervus elaphus) numbers from 2008 through removal of all cervids from Santa Rosa Island by the end of December 2011. The settlement agreement has a mandated maximum number of animals of each species that are permitted to be present on the island each December. The National Park Service is required to determine the number of deer and elk on the island and to ensure that numbers do not exceed the limits specified in the settlement agreement. Elk and deer have been counted annually by the animals’ owner and the NPS as part of the settlement agreement. The USGS conducted aerial surveys in March and July to enumerate deer and elk on Santa Rosa Island and to assess the detection probability, and thereby potential counting bias, of both species on the Island. The counts were completed as a cooperative effort between USGS-NOROCK, USGS-FRESC and USGS-FORT along with Colorado State University.

A total of 461 elk were detected by observers during the March 2009 survey. Two models were developed to analyze the data. Modeling approach 1 led to an estimate of 483 elk in the survey zone, (95% C.I. 479 to 524 elk. Modeling approach 2 led to an estimate of 489 elk in the survey zone, (95% C. I. 471 to 535 elk). The July counts of elk and deer are being analyzed at this time. Analyses of the March 2009 elk count reveals that approximately 5% of the animals present were not detected during the aerial survey. This has led biologists at Channel Islands National Park to insist on implementation of aerial counts designed to permit calculation of sightability probabilities and thereby estimate the number of animals missed during the survey.

coverAssociated Reference
Griffin, P.C., Schoenecker, K.A., Gogan, P.J.P., and Lubow, B.C. 2009. Survey of ungulate abundance on Santa Rosa Island, Channel Islands National Park, California, March 2009: U.S. Geological Survey Open-File Report 2009–1243, 23 p.

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