Hells Canyon bighorn sheep test positive for lethal bacteria

YAKIMA – The Washington Department of Fish and Wildlife (WDFW) and its management partners detected pneumonia in the Northern Hells Canyon bighorn sheep population in December 2023. The disease is confirmed in Washington, Idaho, and Oregon and potentially affected bighorn sheep populations are located along the Snake River and tributaries in Idaho, Oregon, and Washington.

The Idaho Department of Fish and Game (IDFG), WDFW, and Oregon Department of Fish and Wildlife (ODFW) are working together to monitor and address this disease outbreak.

Bighorn pneumonia is caused by the bacteria Mycoplasma ovipneumoniae, referred to as “Movi.” The disease can cause all age die-offs in affected populations and can reduce lamb survival for many years after the initial outbreak. There is no treatment or preventative vaccine for bighorn sheep pneumonia.

This is one of several pneumonia outbreaks in bighorn sheep that have occurred over the past century in the Hells Canyon area. More information is being gathered to understand the severity of die-off associated with this pneumonia outbreak.

“It will take some time before we know the magnitude of this outbreak,” said Kyle Garrison, WDFW ungulate section manager. “Biologists in all three states are in the field working to get a better understanding of the impacts.”

“Unfortunately, there is no way to treat animals to slow the spread of disease or reduce deaths,” said Frances Cassirer, Idaho Department of Fish and Game. “Our best option is to let the disease run its course over the next several months and then reassess the situation. At that point our objectives are to restore the health of those populations that are affected and prevent further spread among the interconnected populations throughout Hells Canyon and the surrounding area.”

To report dead or sick bighorn sheep in Washington, use WDFW’s reporting tool.

The Idaho, Oregon, and Washington chapters of the Wild Sheep Foundation and the national Wild Sheep Foundation are providing support for the states’ efforts. The state agencies and the Wild Sheep Foundation, along with other participants of the Hells Canyon Bighorn Sheep Initiative that include the U.S. Forest Service, Bureau of Land Management, the Nez Perce Tribe, and the Confederated Tribes of the Umatilla Reservation will continue to work together on Hells Canyon bighorn sheep management and conservation. 

The Washington Department of Fish and Wildlife works to preserve, protect, and perpetuate fish, wildlife and ecosystems while providing sustainable fish, wildlife, and recreational and commercial opportunities.