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A bighorn sheep die-off is occurring on the Stansbury Mountains in north-central Utah. Even though sheep are dying from pneumonia, biologists with the Division of Wildlife Resources anticipate mature rams will still be available this fall for the limited number of hunters who draw a permit to hunt the area.

Bighorn sheep were first transplanted to the Stansbury Mountains in 2005 and 2006. A total of 56 sheep were released. In 2008, an additional 36 bighorns were added to the herd.

When biologists transplant bighorn sheep to a new area, they keep the number of hunting permits low. They want to give the newly transplanted sheep time to establish themselves in their new area. They also want to give rams time to mature. And that's exactly what's happened on the Stansbury Mountains: in 2015, the sheep population on the mountain was estimated at 230 animals. Roughly 100 of those animals were rams, 53 percent of which were mature animals.

In 2015, a total of three bighorn sheep hunting permits were offered for the unit. DWR biologists were considering a substantial increase in permits for 2016, but the die-off has caused them to reconsider. For fall 2016, biologists will again recommend three permits for the unit.

Number of sheep lost

In 2015, biologists placed radio collars on 20 bighorn sheep on the mountain. The collars allow the biologists to track the movement of the bighorns and assess their survival. Based on data from the radio collars, biologists estimate that 50 percent of the estimated 230 bighorns on the unit were dead by mid-March 2016. The beginning of March was an especially bad time, as the rate of bighorns dying increased in frequency then.

Even though half of the population is gone, biologists anticipate that mature rams will still be available for hunters to pursue this fall. Bighorn sheep hunt success in Utah is close to 100 percent, so — with the limited number of permits that will be offered — the hunters who draw the permits should have a successful hunt.

Pneumonia and bighorn sheep

Biologists collected biological samples from some of the bighorn sheep that died. Laboratory results show the bighorns died from pneumonia. The dead bighorns tested positive for Mycoplasma ovipneumoniae, a key pathogen that can wreak havoc among bighorn sheep.

Bighorn sheep are highly susceptible to infection from respiratory pathogens. They usually become infected through contact with domestic sheep or goats. These domestic animals carry the disease but aren't affected by it.

If respiratory pathogens enter a bighorn sheep herd that's never been exposed to them, the pathogens can spread quickly. Frequently, between 30 and 70 percent of the herd is lost. And lambs born into the herd can continue to die for years after an outbreak. That's why biologists do everything possible to maintain distance between wild bighorns and domestic sheep.

Next steps

In addition to monitoring sheep that are wearing collars, biologists will conduct on-the-ground and aerial surveys to assess the overall impact of the pneumonia outbreak. They'll continue to monitor the situation closely. If needed, they'll make changes to the hunt.

If you're one of the hunters who draw a permit to hunt the unit this fall — and you're not satisfied with what you see during your pre-season scouting trips — you can surrender your permit before the hunting season starts. If you surrender your permit, you'll get your bonus points back, you'll earn a bonus point for 2016 and your waiting period will be waived.

If you surrender your permit at least 30 days before the season starts, you'll also receive all of your money back except the $25 handling fee.

Several of Utah's bighorn sheep herds have experienced similar disease challenges and continue to provide great hunting and viewing opportunities. Biologists expect the population on the Stansburys will do the same.