June 19, 2013

Diseased bighorn sheep might have to be killed in Mojave National Preserve

Desert bighorn sheep gather at night on June 6 at a guzzler set up to provide water for the herd. A virus that is killing sheep in the largest herd at the Mojave National Preserve is described as "a grim situation" by spokeswoman Linda Slater.


Wildlife officials in California might resort to killing desert bighorn sheep in an effort to contain an outbreak of a deadly disease now spreading through the largest herd in Mojave National Preserve, 100 miles southwest of Las Vegas.

At least 20 dead sheep have been found in the past month on Old Dad Mountain, about 15 miles southeast of Baker, Calif. Tests have confirmed that at least some of the animals died from a strain of pneumonia generally transmitted by domestic sheep and goats and usually fatal to bighorn.

“It’s really kind of a grim situation to be perfectly honest with you,” said Linda Slater, spokeswoman for the 1.6 million-acre preserve.

Officials from the National Park Service and the California Department of Fish and Wildlife are now considering whether to hunt down sheep showing signs of sickness. But even that might not be enough to halt the spread.

“To really get rid of the disease, you have to kill every animal, but that’s not practical or likely to happen,” Slater said. “There are no good management options.”

Wildlife officials in Nevada are watching the situation anxiously, hoping the sick animals can be contained somehow before they come into contact with sheep in the Silver State.

The diseased herd is “only a 45-mile trip as the crow flies” from mountains that harbor desert bighorn at the southern edge of Clark County, said Doug Nielsen, spokesman for the Nevada Department of Wildlife.

“We do have some right down there close to the state line. So it’s a concern, and it’s something that needs to be monitored.”

Slater said the afflicted animals are part of what she called “the biggest and healthiest herd” in Southern California. Transplants from the group have been used in the past to bolster struggling herds elsewhere in California, she said.

Bighorn have no natural resistance to pneumonia and tend to die at a high rate. Those that survive become carriers, infecting newborn lambs in a cycle that can ravage the herd for up to a decade.

Biologists may never know for certain how the isolated herd of 200 to 300 sheep was exposed to the disease, but they have their suspicions.

Slater said a domestic goat turned up in the area about six months ago — a rare and unexplained find — but the animal showed no signs of pneumonia. However, tests for the disease are not always reliable, she said.

Biologists and veterinarians “seem really pessimistic that anything can be done” to keep the entire herd from being exposed, Slater said. The worry now is that the disease will spread to one of four other herds in the preserve, possibly by a ram sent wandering when rutting season gets underway in the coming weeks.

Volunteers from the Sierra Club and the Society for the Conservation of Bighorn Sheep assisted with the initial search for sick and dead animals. A lack of resources and the remote, rugged location of the herd have hampered efforts so far to address the outbreak, Slater said.

Back in Nevada, wildlife officials are hoping that hot, dry weather this summer will keep the affected herd close to the water sources in its home range and away from other herds. Beyond that, Nielsen said, there isn’t much that can be done from the Nevada side of the state line but to wait and watch what happens.

Bighorn sheep once roamed nearly every mountain range in Nevada, but their numbers began to decline in the mid-1800s, as settlers and prospectors swept into the region, mostly in the north.

By 1960, disease, unregulated hunting and habitat loss had reduced Nevada’s bighorn population to about 1,200 animals in a handful of ranges, none of them north of Ely or west of Hawthorne.

Wildlife officials launched the Bighorn Sheep Release Program in 1967 to return the official state animal to its former glory.

Today, Nevada is home to more bighorn sheep than any other state — better than 10,000 adult animals in at least 60 different mountain ranges.

But disease always looms as a threat to those gains.

In 2010, pneumonia nearly wiped out a herd of Rocky Mountain bighorn sheep in the Ruby Mountains near Elko.

The most recent outbreak in Southern Nevada struck in 2002 in the Specter Range, along U.S. Highway 95 about 75 miles northwest of Las Vegas.

After several years of what Nielsen called “very low lamb survival,” the herd’s numbers finally began to rebound in 2009.