November 12, 2013

Bighorn sheep numbers way down

These bighorn sheep were photographed in 2009 on Old Dad Mountain, the same area of the eastern Mojave Desert where a deadly disease has spread among at least two herds. Biologists have started an effort to monitor the health of the elusive animals.

Press Enterprise

Only a fraction of the bighorn sheep typically seen in a Mojave Desert mountain range was spotted during a recent helicopter survey, a sign that a deadly pneumonia outbreak has taken a significant toll on the population, a scientist said Tuesday, Nov. 12.

Crews found no obviously sick animals in many of the other mountain ranges the sheep inhabit in the eastern Mojave. Blood test results will show whether those sheep are carrying the bacteria that causes the disease.

In the hardest-hit area, around Old Dad Mountain and Kelso Peak 15 miles southeast of Baker, the helicopter crew saw 6.4 sheep per hour. Data from the past 18 years show the previous lowest encounter rate there was 8.2 sheep per hour and the average is 14.5, said Deborah Hughson, science adviser for the Mojave National Preserve.

Two animals were accidentally killed during the four-day survey last week, Hughson said.

One ewe, after collaring, became startled and jumped a short distance off a hillside, Hughson said. Her leg broke on landing, and she had to be euthanized.

The second sheep died when a capture net was discharged from the helicopter in windy conditions. The net caught the sheep’s horn and spun her abruptly around; a veterinarian who conducted a field autopsy determined the animal died instantly. It did not have pneumonia.

During the survey, 73 bighorn were fitted with locator collars that will help experts track them — and the disease — for the next four to six years.

In addition to the herd around Old Dad Mountain, which has a population of 200 to 300, the outbreak has affected a second group in the Marble Mountains, 35 miles south.

Hughson said she was surprised that there were no sick sheep beyond a few in the Marble Mountains. Crews also surveyed the Bristol, Clipper, Soda, Providence, Granite, Hackberry and Woods ranges.

“We now are pretty clear the disease is centered in the Old Dad Peak area. There has been a substantial population decline that could be as much as half of the population,” Hughson said.
In that area, crews saw four carcasses and no lambs, she said.

The disease, which can have an incubation period of months, is easily transmitted to bighorn that come in contact with domestic goats and sheep. Authorities do not know how the Mojave herds contracted it, she said.

Healthy looking sheep can carry the bacteria, then suddenly show symptoms and die soon after, Hughson said.

Scientists should have the results of blood and fecal samples and nasal swabs taken in the field by early December, and will know then which animals are infected, Hughson said.

The results will help determine the next step in dealing with the outbreak. Experts may cull sick animals from the herd to stop the disease from spreading or manipulate water sources next summer to keep the infected sheep from interacting with other herds, Hughson said.

The federal and state governments have spent more than $100,000 on the helicopter survey, collars and database, she said. The survey of more than 80,000 acres was a joint operation of the National Park Service, Mojave National Preserve and California Department of Fish and Wildlife.