By Steve Gorman
LOS ANGELES (Reuters) - A pneumonia outbreak is threatening hundreds of bighorn sheep in California's Mojave National Preserve, and wildlife officials said Monday they see no promising options for saving the state's biggest herd or protecting a nearby population in Nevada.
The disease is believed to have killed 20 bighorn sheep during the past month in the 1.6-million-acre (650,000-hectare) desert preserve, which lies 50 miles southwest of Las Vegas, National Park Service spokeswoman Linda Slater said.
"I suspect that many more are infected," Slater said, adding that the entire herd, numbering as many as 300 animals, is in danger. "The biologists seem to be very pessimistic."
Potential options under consideration include shooting some or all of the remaining members of the herd in a bid to prevent further spread of the disease, or continuing to monitor the situation and essentially let nature run its course, wildlife officials said.
"There really are no good options," Slater said.
Episodic waves of disease have thinned bighorn herds for years. Fewer than 100,000 sheep are believed to roam the rugged mountain slopes of the West today, compared with an estimated 1.2 million head that inhabited the region at one time.
A series of nine separate outbreaks across five western states, including Nevada, in the winter of 2009-2010 claimed roughly 1,000 bighorn sheep, prized as game animals for the prominent curled horns of the adult males, or rams.
The current outbreak is the most severe ever to hit the desert species of bighorn sheep in California, home to 5,200 head in roughly 60 herds across the state, said Steve Torres, a supervisor for the California Fish and Wildlife Department's investigations lab.
It was also the first to hit the Mojave National Preserve since it was established in 1994.
The infected bighorn herd, one of five groups in the Mojave preserve, is a "foundation" herd and one of California's healthiest, used to re-establish the species in other parts of the state, officials said. It also is the state's largest.
Tests have confirmed that at least five of the animals on Old Dad Mountain died from a strain of pneumonia carried by domestic sheep and goats that is usually fatal when transmitted to bighorn sheep, which have no natural defenses to the disease.
Nevada wildlife officials worry the disease could spread to their state's nearest herd, just 45 miles to the northeast, especially now that rutting season is beginning and males are known to wander as far as 100 miles from home.
But Nevada officials are hoping that an extreme hot spell in the forecast will tend to keep young rams close to their familiar water sources.
California's wildlife investigator Torres said another big jump in infections within the herd could come with the start of mating season next month.
(Additional reporting by Laila Kearney; Editing by Lisa Shumaker)