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Bighorn sheep pneumonia lingers
Game and Fish swabs animals' tonsils to test for deadly disease.

By Rebecca Huntington

The Jackson bighorn sheep herd is still suffering setbacks from a pneumonia outbreak first detected three years ago, according to Wyoming Game and Fish.

In December, a ewe was struck and killed by a car. Her carcass was sent to a lab for testing, and results showed some pneumonia in her system, said Doug Brimeyer, Game and Fish biologist.

Meanwhile, fewer lambs are surviving to adulthood to bolster the population, which was cut in half by the outbreak, he said Monday.

The herd now numbers about 300, down from the state's goal of 500. Before the pneumonia outbreak in 2001, the herd numbered 560 to 600 animals, Brimeyer said. Since pneumonia halved the herd's numbers, Game and Fish has cut bighorn hunting permits to four, down from 28 in 2001.

"We may still be seeing some of the effects from the outbreak three years ago," he said. "We're just trying to monitor the population."

Game and Fish darted 10 sheep with tranquilizers, drew blood samples and swabbed their tonsils last month as part of an ongoing effort to monitor the herd's health.

Fortunately, none of the 10 sheep showed signs of pnuemonia, said Hank Edwards, a wildlife disease specialist at the Wyoming State Veterinary Laboratory in Laramie. But lab tests are ongoing to determine the general health of those animals, he said.

Game and Fish tested four sheep at Russold Hill, east of lower Slide Lake; four sheep on the hills above Camp Creek Inn, south of Jackson; and two sheep on Miller Butte, on the National Elk Refuge. On the refuge, tested sheep were marked with ear tags. Sheep at the other two sites were given other visual markers, including pink blazes on their horns.

Game and Fish has designated the Jackson bighorn sheep herd a "core" native herd because it is naturally occurring and was not reintroduced to the area. Preserving "core" bighorn herds is a top priority for the wildlife agency, Brimeyer said.

The Jackson herd ranges from north of the Gros Ventre River south to Clause Peak and Beaver Mountain, which are south of Hoback Junction.

Prior to the outbreak, the herd was doing so well, Game and Fish was considering transplanting some wild sheep to supplement other herds.

One herd that could have been a recipient of the transplants was the Targhee bighorn herd, which occupies the Teton Range and Targhee National Forest. That herd numbers in the low hundreds, though a firm census is not available, Brimeyer said. The herd is isolated at high elevations, where many sheep die in avalanches each winter. Grand Teton National Park officials expanded bighorn sheep closures last winter to include popular ski terrain, such as Mount Hunt, to give the beleaguered herd a break by limiting disturbances. Wildlife are particularly vulnerable in winter when food is less available and the animals depend on limited fat reserves to survive.

In 2001, Game and Fish began testing the Jackson herd to ensure those wild sheep were healthy and fit for transplant. But those tests turned up pneumonia, which squelched any plans of transplanting.

Although wildlife officials are convinced pneumonia killed the sheep, they have been unable to pinpoint the primary agent causing the outbreak. The prime suspect remains the bacteria Mannheimia haemolytica.

Mannheimia is a primary invader that weakens the sheep's immune system. Once the tissues are compromised, a secondary invader comes in and causes abscesses on the lungs, which ultimately kills the sheep. The secondary invader masks the original cause of pneumonia, according to Edwards. Domestic sheep may carry strains of pneumonia that are fatal to wild sheep. But that has not been proven the cause in this case.

"We're still unable to determine the initial agent," Brimeyer said. "We're not going to say it was domestic sheep."

Even so, Game and Fish officials have been urging the Bridger-Teton National Forest to move a domestic sheep grazing allotment that overlaps with the Jackson herd to the south to give the "core" wild herd a buffer from domestic sheep. So far, Bridger-Teton officials have rejected requests to move domestic sheep grazing in the Wyoming Range farther south, though a final decision has not yet been made.

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