Concern Over Arizona's Kofa Sheep Herd Elevated

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Biologists recently presented the Arizona Game and Fish Commission with compelling data indicating that recovering the critically important Kofa desert bighorn sheep herd from near record-low population levels will be challenging due to additive mountain lion predation.

Game and Fish Department biologists informed the commission at its Aug. 7 meeting that the monitoring of one radio-collared mountain lion revealed it had killed 14 bighorn sheep since February, an average of one bighorn sheep about every 10 days. At this rate, this one lion is on pace to kill an estimated 37 bighorn sheep annually.

By comparison, the estimated annual yearling recruitment from the Kofa National Wildlife Refuge bighorn sheep herd is only 39 animals.

Additionally, biologists reported last week that the same radio-collared lion has made a 15th kill. The animal killed was a bighorn lamb within the Kofa Predation Management Area near the Little Horn Mountains.

"The rate at which this lion is preying on bighorn sheep is of grave concern," said Game and Fish Yuma Regional Supervisor Pat Barber.

Eleven of the bighorn sheep killed were within the department's Kofa Mountains Complex Predation Management Area. This management area includes all of the Kofa National Wildlife Refuge (NWR) and three key areas that extend slightly beyond the refuge to encompass contiguous mountain ranges not captured by the Refuge boundaries. These areas contain habitats used by Kofa NWR bighorn sheep population.

Barber added, "The Kofa NWR bighorn sheep population provides 76 percent of all bighorn sheep recruitment in a greater isolated metapopulation in southwestern Arizona and is a critical core in sheep restoration for Arizona and the southwestern U.S."

This isolated metapopulation is comprised of several smaller subpopulations between Interstates 8 and 10 and State Routes 85 and 95. Due to human development, fragmentation, and changes in landscapes active management is required.

Although managers are working to address several issues that might limit sheep recovery, such as water availability, disease and human disturbance, predation at this level remains a significant concern.

Past surveys indicate that, historically, mountain lions were virtually non-existent or only transient guests around the Kofa region. However, in recent years, a number of lions have become residents on and around the Kofa NWR and are having a significant impact on the bighorn sheep population.

Furthermore, officials estimate there are three to five other mountain lions in the Kofa Mountains Complex Predation Management Area. Conservative modeling of four mountain lions (three males and one female) suggests predation could exceed the annual bighorn sheep recruitment by more than 150 percent.

"Once a localized wildlife population has zero recruitment or less, meaning it's not replacing lost animals from standard mortalities, it's just a matter of time before that population is extirpated." said Game and Fish Wildlife Specialist John Hervert.

"We want to remind the public, our goal is not lion eradication," said Barber. "“When the Kofa bighorn sheep populations return to their historic levels, normal depredation is typically not a concern and in fact is healthy. However, with the herd at record lows, it is inhibiting critical recovery efforts of this valuable resource."

The mountain lion population in Arizona is neither threatened, endangered, or at risk, and they are the most broadly distributed large mammal species in North America.

The concern over declining bighorn sheep populations is not unique to Arizona. There are a number of distinct bighorn sheep populations that have required federal listing through the Endangered Species Act, in part or exclusively due to mountain lion depredation, including the Peninsular, Sierra Nevada and the San Gabriel Mountain bighorn sheep populations. Recovery efforts for those populations will cost millions of dollars.

The department's second self-imposed moratorium of lethally removing offending mountain lions when off the Refuge, that have been captured and collared on the refuge, ended July 31. In accordance with the May 2007 "Kofa Mountains Complex Predation Management Plan," an offending lion – defined as one that kills more than one bighorn sheep within a six-month period – may be lethally removed when off of the Refuge.

No mountain lion has been removed from the Kofa National Wildlife Refuge. Prior to the moratorium, two offending lions were removed from the Kofa Mountains Complex Predation Management Area, but they were outside of the Refuge.

The department agreed to delay implementing of some portions of the Kofa Mountains Complex Predation Management Plan (i.e., instituted the moratorium) to accommodate the U.S. Fish and Wildlife Service's desire to complete an environmental assessment (EA). However, the EA was originally estimated to be completed in October 2008. The date was extended to April 2009, then October 2009. The current estimated completion date is now March 2010. Data of lion predation and bighorn sheep populations makes it evident that further delays will continue to reduce this seriously depressed population.

The U.S. Fish and Wildlife Service's draft environmental assessment (EA) proposing management options for limiting mountain lion predation on bighorn sheep within the Kofa NWR is now open for public comment. The proposed alternative will provide the Refuge with added management tools to help restore and preserve the bighorn sheep herd – one of the principal reasons for the refuge's creation in 1939. The comment period is open until Oct. 2 and a public meeting is scheduled for Wednesday, Sept. 16 in Yuma. The anticipated completion date is March 2010. To learn more or comment on the draft EA, visit www.fws.gov/southwest/refuges/arizona/kofa,.

The EA is not required for the Arizona Game and Fish Department to manage resident wildlife (including mountain lions and bighorn sheep) off the Refuge.

The Kofa NWR bighorn sheep herd was once one of the most robust herds in the nation. Prior surveys estimate population levels ranging from 600 to more than 800 animals. However, in 2006 the survey revealed a historic low of 391 animals. The last two surveys showed an estimated 460 in 2007 and 436 in 2008. The 2009 survey is scheduled for October.

For history on the struggling Kofa bighorn sheep population, visit www.azgfd.gov/kofa.