Bighorn sheep dealing with fatal disease

Feb. 1—Wildlife officials from Idaho, Washington and Oregon are monitoring a new outbreak of pneumonia that is killing wild bighorn sheep in the northern end of Hells Canyon.

Preliminary data indicates the disease is most intense in Idaho’s Unit 11 between Cave Gulch Creek and the mouth of the Salmon River, where eight dead bighorn sheep have been found. The agencies have also collected one dead sheep each from Idaho units 13 and 18 and from the western side of the Snake River in Oregon and Washington.

“It’s very, very sad,” said Frances Cassirer, a biologist and wild sheep researcher for the Idaho Department of Fish and Game and Washington State University. “For like five to 8 years we had really healthy populations. I think you always kind of realize in the back of your mind there is a good chance of this happening, but we had such a good run we were hopeful we would keep it going.”

The disease is not new to the Snake River or its tributary canyons. Previous outbreaks have led to all-age die-offs of the iconic animals known for their social nature and impressive horns that make them a favorite of wildlife watchers and hunters alike. But Cassirer said initial tests indicate the strain of the Mycoplasma ovipneumoniae bacteria that causes the illness is new to the area. The strain was previously detected in Oregon’s Brownlee herd and in wild sheep on the Salmon River upstream of Riggins.

The bacteria, commonly called Movi for short, was originally introduced to wild sheep herds by their domestic cousins in outbreaks that date back decades. Cassirer said it is not known how this particular strain made it to the northern Hells Canyon herds, but it may have come from wild sheep moving between herds.

“It’s entirely possible it traveled by bighorn sheep to get here,” she said. “It’s also possible there are domestic sheep with that strain that moved up here. Right now we are probably more focussed on the bighorn sheep aspect of it but we can’t rule either out.”

The Idaho Department of Fish and Game and the fish and wildlife departments of Oregon and Washington routinely work together to manage bighorn sheep in Hells Canyon and adjacent areas. Cassirer said past experience has taught them there is little that can be done to slow or stop an active outbreak.

“Right now we are in a monitoring and information gathering stage and we are going to continue to do that over the next several months,” she said.

Wildlife managers now have decades of experience with the disease and know much more about it. Outbreaks can be as short as four or five months or last much longer. Some are mild and some can hammer populations. Once it has subsided, there are steps wildlife managers can take to help the herds recover.

“We will just have to see how bad it is,” said Cassirer. “We would like to think we know a lot more now and we can recover more quickly than maybe we could before.”

Cassirer said the agencies have had support from the National Wild Sheep Foundation and state chapters of the organization.

Barker may be contacted at or at (208) 848-2273. Follow him on Twitter @ezebarker.

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