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Debra Hughson, Science Advisor, Mojave National Preserve
BY JOAN WHITELY -- It’s a grim prospect, but resource managers at the Mojave National Preserve in California likely will have to kill sick bighorn sheep in order to protect other bighorn herds, including some in Southern Nevada that are barely 50 miles away. It’s just a question of how many to kill, one scientist says.
The preserve’s science advisor, Debra Hughson, says federal and California wildlife experts are weighing three options for a controlled kill in order to contain an epidemic of pneumonia in a herd not far from Baker, Calif. About 20 dead sheep have been found there in the last month, according to the Las Vegas Review-Journal.
The options are to kill a few, kill the sick, or kill them all. Each strategy has different drawbacks and supporters, even among experts.
“Really, it’s what’s the least bad option,” Hughson says. As science advisor, her job is to serve as liaison between Park Service, the California Department of Fish and Wildlife and outside scientists, to ensure that decisions about resources within the preserve are based on the best science, using the best techniques.
The only non-kill way to stop this pneumonia – which comes from domestic sheep or goats but is deadly in bighorn – is impractical, she added. That would entail medicating each sheep in the herd with an injection every 28 days. “These are wild animals in very remote areas. It’s not feasible to catch them every month,” Hughson said.
Once symptoms appear, a sheep sickens rapidly. Its lungs fill with fluid, there’s nasal discharge. “Eventually it’s unable to stand or walk,” she explained. “Quite often then, the animal falls and kills itself … They basically fall off a ledge and break their neck.”
The degrees to a controlled-kill approach, according to Hughson are to first, kill only the rams, so they don’t spread the disease if they migrate to other herds during mating season. The second option is to kill sick sheep, but not all infected sheep are symptomatic. Last, resource managers could decide to kill all members of the infected herd, for a fresh start. The Nelson’s bighorn is not on the endangered list.
If the pneumonia is not halted, this particular strain is known to cause die-offs among bighorn that range from 10 percent to 100 percent of herd population, Hughson said. The disease leaves a legacy, too. Female bighorn that don’t die from the disease are apt to still carry the pathogen, which then infects their young, who generally die at about 3 months old. The result is a herd that ages without replenishing itself, and eventually disappears.