|2007 survey results released for bighorn sheep on the Kofa National Wildlife Refuge |
Dec 27, 2007
Arizona Game and Fish Department and U.S. Fish and Wildlife Service
2007 survey results released for bighorn sheep on the Kofa National Wildlife Refuge
YUMA, Ariz. — The recently completed survey of desert bighorn sheep populations in southwestern Arizona estimated the population on the U.S. Fish and Wildlife Service’s Kofa National Wildlife Refuge at 460 sheep. The number is up from the 2006 survey estimate of 390 sheep, the lowest level recorded since aerial surveys began in 1981. Surveys conducted earlier this decade have tracked a significant decline in sheep numbers on the refuge. Calculations for the 2003 survey, which followed a very severe 2002 drought year, estimated a population of 620 sheep, down from 812 computed after the 2000 survey. Although this most recent survey indicates a slight increase in sheep numbers, wildlife management agencies remain concerned with the historically low population levels on the refuge.
Kofa surveys have been jointly conducted since 1981 by the U.S. Fish and Wildlife Service (USFWS) and Arizona Game and Fish Department (AGFD) as part of AGFD’s overall survey of desert bighorn sheep populations throughout southwestern Arizona. Prior to 1992, surveys were conducted annually. In 1992, funding constraints reduced the survey schedule to once every three years. As a result of the 2006 survey, AGFD organized funding using sportsman-generated Department dollars and USFWS monies to temporarily reinstitute annual surveys starting in 2007.
The size, location, and unfragmented nature of 1,038 square miles that make up the Kofa NWR, have long been recognized as a unique combination that has made its 435 square miles of sheep habitat especially productive. With the passage of the 1990 Arizona Desert Wilderness Act, 856 square miles of the refuge have been designated as wilderness.
For the past 50 years, the Kofa has been an important source of desert bighorn sheep for the reestablishment and maintenance of bighorn populations across Arizona and throughout the southwestern United States, to include New Mexico, Colorado, and Texas. The most recent translocation of sheep from the Kofa was in 2005 when 30 sheep were captured and transported to the San Andres Wildlife Refuge in New Mexico. As a result of the findings of the 2006 survey, no new translocations from the Kofa herd are scheduled.
While severe drought is a significant limiting factor for bighorn sheep and other desert species, the decline in the face of somewhat improved rainfall conditions since the 2003 survey is concerning and is the subject of ongoing study by both the USFWS and AGFD. In November, 30 bighorn sheep ewes were captured and fitted with tracking devices in order to monitor nutrition, movements, and mortality, and assist in making management decisions in keeping with the findings and recommendations of the joint USFWS-AZGFD investigative report published earlier this year. The research component of this effort marks the beginning of a five-year collaborative effort on the Kofa bighorn herd by the U.S. Geological Survey-Biological Resources Division (USGS-BRD), the USFWS, and AGFD. As part of the processing of the captured animals, blood samples were drawn for disease analysis and measurements taken to determine body condition. Results of the disease analysis are still pending.
Predation, permanent water availability, disease and public recreation impact on lambing areas are among the other factors being studied for their possible contributions to population decline. These ongoing research and management efforts are currently being funded by the USFWS, AGFD, and the Arizona Desert Bighorn Sheep Society, the Foundation for North American Wild Sheep, and the Yuma Valley Rod and Gun Club.
The ongoing investigation and management of mountain lion predation includes the use of waterhole cameras; searches for lion tracks, scats or kills; the capture, collaring and tracking of lions; and recording of all reported lion sightings. Newly arrived on the Kofa as a resident component of the ecosystem, it is thought that lions may be adding significant additional mortality to prey populations already heavily stressed by drought or disease.
Survey data also will continue to be used to adjust hunting and translocation activities so as to minimize any additive downward pressure on the bighorn population.
The USFWS and AGFD continue their combined research and active management strategy in the pursuit of a desert bighorn sheep herd that can once again sustain a translocation program.
For additional information about the management and research activities related to the Kofa desert bighorn sheep population, see the AGFD website at: http://www.azgfd.gov/kofa