WDFW to Survey Bighorn Sheep Populations Amid Deadly Disease Outbreak

The Washington Department of Fish and Wildlife biologists are set to conduct helicopter surveys of bighorn sheep populations in southeastern Washington this week. Slated for Thursday, Dec. 12, and Friday, Dec. 13, 2024, weather permitting, the surveys will focus on the Joseph Creek and Grande Ronde River areas, particularly the Black Butte and Mountain View sub-herds. 

Purpose of the Surveys 

The surveys are intended to gauge the health and size of the bighorn sheep populations, which have been decimated by a deadly outbreak of Mycoplasma ovipneumoniae ("Movi") since late 2023. Movi is a bacterial pathogen that causes pneumonia and has resulted in severe mortality rates, with over 60% of radio-collared sheep dying from the disease. The outbreak has spread along the Snake and Grande Ronde Rivers and into Asotin Creek, further threatening these herds. 

These surveys provide an opportunity to get a look at the bighorns in this area and determine the magnitude of the die-off compared to population estimates from last year," said Mark Vekasy, Acting District Wildlife Biologist for WDFW. 

Survey Details 

WDFW biologists will fly low in helicopters to maximize visibility across the rugged, remote terrain. This is especially crucial for areas like the Black Butte herd's roadless habitat. During the flights, biologists will classify sheep by age and sex as quickly as possible to minimize stress on the animals. Notably, no sheep will be captured during the operation. 

The information will: 

• Establish a baseline population estimate. 

• Confirm mortality data and herd composition. 

• Assist in assessing the severity of the population decline compared with the 2023 estimates. 

Context and Background 

There are 1,690 wild bighorn sheep that exist in the state, divided among 17 different herds spread between east and central Washington. A currently active outbreak of Movi has raised serious concerns about the long-term viability of those populations. The disease has taken the worst toll along river corridors-the very habitats that harbor concentrations of the sheep.  

It is the WDFW mission to conserve and support wildlife and their ecosystems while promoting sustainable use and recreational opportunities. This survey effort reflects the commitment to better understand and alleviate the challenges facing Washington's wildlife. 

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Looking Ahead 

These surveys will, in turn, inform future management actions to stabilize and restore affected herds. As WDFW continues to monitor the situation, biologists hope to build a clearer picture of the extent of the outbreak and develop measures to protect the state's bighorn sheep population. 

Residents in the survey areas could see low-flying helicopters over the two-day period as biologists work to gather crucial data about these iconic animals.