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FILE — A bighorn sheep is pictured near the Cleman Mountain feeding site on Saturday, Nov. 14, 2020, in Naches, Wash.

The Washington Department of Fish and Wildlife will try a new approach to address diseased bighorn sheep in the Yakima River Canyon.

Experimental efforts to capture and test as many of the herd’s 100 sheep as possible will continue through the rest of February, dependent on weather. Regional Director Mike Livingston said they hope to identify sheep infected with a pathogen responsible for a declining population since it appeared in 2009.

The disease negatively affects lamb survival.

“The adults don’t seem to be affected,” Livingston said.

Mycoplasma ovipneumoniae, a type of pneumonia, is believed to persist through asymptomatic carriers. Their prevalence could be better understood through testing, potentially allowing wildlife department staff to protect healthy sheep from those that carry the pathogen.

Livingston expects this to be a long-term effort and it’s unclear what exactly the next steps would be for an approach never before tried in Washington. Staff spoke with partners from the Wild Sheep Foundation as well as in Idaho and Oregon to learn more about the experimental method.

Aerial captures will help the Wildlife Department identify and isolate healthy sheep while eliminating those infected. Biologists tried to euthanize sick lambs in the winter of 2009-10 and saw some early success, but those efforts ultimately failed.

When the bacteria reached the Tieton Herd in 2012, it quickly wiped out most of the sheep and the Wildlife Department eliminated the rest to protect the nearby Cleman Herd.

At one point, the Yakima River Canyon Herd numbered close to 300, and they’ve managed to hang on better than many populations infected by the deadly disease. As the sheep keep fighting for survival, Livingston said it’s critical to take the next step in trying to save them.

Biologists don’t anticipate any scenario in which they would need to eliminate the Umtanum Herd, since a sheep from the nearby Cleman Herd tested positive for the bacteria last year.

Reach Luke Thompson at luthompson@yakimaherald.com and on Twitter: @luketscribe