State Searches for Answers as Bacteria Spreads Through Bighorn Herds

Posted

Capturing and collaring bighorn sheep, including some in the Yakima River Canyon, marked the next step in the state's ongoing efforts to limit the spread of a deadly bacteria.

The Washington Department of Fish and Wildlife used helicopters last week to conduct aerial captures of 20 bighorns in two northern herds and replace five collars in the Yakima River Canyon's Umtanum/Selah Butte herd. Meanwhile, the biggest threat to the sheep, the effects of a pathogen called Mycoplasa ovipneumoniae, or MOVI, appear to have taken their toll on the Cleman herd.

WDFW regional biologist Jeff Bernatowicz wrote in his 2021 hunting prospects that District 8 — comprised of Yakima and Kittitas counties — is home to more than 70 percent of Washington's bighorn sheep. Thanks to their proximity to domestic sheep, they all face a high risk of contracting MOVI, which can leave the sheep susceptible to fatal pneumonia and significantly reduce the number of lambs in a herd.

"Every bighorn herd in this area has been infected with MOVI," Bernatowicz said this week. "The canyon, twice. It is not if, but when a herd will become infected."

Putting collars on sheep gives the wildlife department a better idea of how bighorn sheep use their habitat, which can help guide management decisions. Bernatowicz said officials marked about 48 sheep from the Umtanum herd last February, but it's unclear exactly how many can still be monitored since some are visual collars and not all of the very high frequency collars are still working.

A mild initial outbreak more than a decade ago continues to cause a decreasing population for the Yakima River Canyon sheep, largely through fewer lambs and a higher number of aging adults. When officials caught and tested 80 sheep a year ago, none showed symptoms but seven adults came back positive and were euthanized in early April.

It's believed high antibody levels developed over time can largely suppress the pathogen after the initial outbreak, but after about three years "shedders" begin to emerge and wreak havoc on a herd. That can persist potentially for decades, so the long-term outlook for the Umtanum herd remains unclear.

"If you get lucky, the shedders die out before new ones are recruited," Bernatowicz said. "If unlucky, the population might get down to 10 animals and one is still a shedder."

Officials delayed the test and cull strategy for the Umtanum herd thanks to a new strain of MOVI , and Bernatowicz said that won't be tried for at least three years with the Cleman herd. But WDFW will offer more ewe permits to help bring down the population while determining whether it's another mild strain or stronger one like the pathogen that contributed to the decision to eliminate the Tieton herd after its population plummeted from almost 200 to fewer than 10 in about five years.

As expected, MOVI left its mark on lamb recruitment this year in the Cleman herd, where Bernatowicz said it's likely virtually all of the sheep were infected. Oak Creek Wildlife Area manager Greg Mackey said staff counted only two lambs out of nearly 151 sheep at the Cleman Mountain feeding site next to Old Naches Road.

In past years they've seen as many as 250 sheep, but Mackey said it's too early to tell what effect the MOVI outbreak's had on the total population. Garrison said the state put its test and cull program on pause in the region until more information can be determined regarding the severity of the recent outbreaks in the Cleman, Umtanum and Quilomene herds.

"It's a tough nut to crack," Garrison said. "There's lots of questions out there about the best management strategies to limit the spread."

Coordination with federal land managers and outreach to private landowners remains a key part of that approach to communicate the risks of wandering livestock coming into contact with bighorns. Sheep and goats appear to be impervious to MOVI, making them a common vector for spreading the pathogen.

Garrison said the state wants to find solutions to help people test their animals, and to remove them when they test positive. Bernatowicz said it's likely MOVI at least partially contributed to bighorns going extinct in Washington nearly a century ago, so perhaps it's no surprise the pathogen's proving to be the biggest obstacle to the state's reintroduction efforts.