Organism ID'd that may be killing sheep

< Prev | 1 | 2

More tests are being done to confirm whether mycoplasma is leaving bighorns open to pneumonia. One test involves infecting captive bighorn lambs at Washington State University to see how they react.

Biologists say about 2 million bighorns once inhabited the West, but they disappeared over most of their range in the 1800s and early 1900s due to unregulated hunting and disease believed to have been carried by domestic animals.

Repopulating projects and added protection in the last 50 years have now boosted bighorn numbers to about 50,000, Cassirer said.

Story continues below ↓

advertisement | your ad here

But sweeping epidemics of a mystery illness have wiped out thousands of Rocky Mountain bighorns, California bighorns, Sierra Nevada bighorns, and desert bighorns since reintroductions began. Cassirer said precise numbers of deaths are not known.

Vic Coggins, a biologist with the Oregon Department of Fish and Wildlife, said pneumonia likely was the main reason, even more than unregulated hunting, for the bighorns' decline from 2 million. He said habitat loss also factored in, but there is enough habitat available now across the West to support far more than the current population.

"Easily," he said. "We estimate that in Hells Canyon we could have over 10,000." Currently, the area has a population of about 900, he said.

Building resistance
Cassirer said biologists aren't finding that infected herds can build up a resistance with successive generations.

"If it's happening, it's not obvious to us," she said. "That's why we're looking for another solution because the sheep might not be able to deal with it on their own."

She said she didn't know how bighorn herds already infected with mycoplasma — if that's a crucial factor in what's killing them — could be helped.

She said attempts to find mycoplasma vaccines for domestic sheep have failed, and even if one existed it would be difficult to administer to bighorns in the wild.

Besser said mycoplasma is found in domestic sheep, but they typically survive. He said he didn't know if domestic sheep were transmitting the bacteria to wild sheep.

But Greg Dyson, executive director of the Hells Canyon Preservation Council, is convinced domestic sheep are making bighorns sick.

"All indications are that the domestics are passing diseases and killing off the bighorns," said Dyson. "And the bighorns just can't get a foothold to become re-established. There have been entire herds that have died off."

Federal lawsuit
In May the U.S. Forest Service, facing a lawsuit from Dyson's group and two other environmental groups that share his concerns, announced that it was restricting domestic sheep grazing in some areas of the Payette National Forest this summer. The forest borders Hells Canyon.

In a federal court lawsuit filed in late June against the U.S. Department of Agriculture over sheep grazing on land near Yellowstone National Park, the Western Watersheds Project and the Center for Biological Diversity claim that allowing domestic sheep to graze in the greater Yellowstone region of Idaho and Montana puts wild bighorn sheep herds at risk of catching diseases from the domesticated animals.

< Prev | 1 | 2