Bighorn sheep

Assessment of Bighorn Population Ongoing

Authors and Contributors
Ron Wilson

North Dakota Game and Fish Department officials cancelled the 2015 bighorn sheep hunting season in order to better understand the severity of a bacterial pneumonia outbreak on the population.

Up until that point, the state’s bighorn sheep hunting season in western North Dakota had run without pause for many years.

After continued review of the population, including data collected from this summer’s population survey, Game and Fish allocated eight bighorn sheep licenses for 2016. More than 10,300 people applied for a bighorn sheep license this year.

Game and Fish announced in February that the status of the bighorn sheep hunting season would be determined after completion of the summer population survey. Typically, the license drawing is held in spring, but with the chance of even more sheep dying in summer, the drawing was held in September.

Brett Wiedmann, Department big game management biologist in Dickinson, said there is a lot of uncertainty when bacterial pneumonia invades a bighorn population.

“The common theme when you have these pneumonia-related die-offs is that you don’t know exactly what is going to happen,” Wiedmann said. “Are you going to lose 90 percent of the population? Are you going to lose 50 percent? Are you going to lose 20 percent? You just don’t know.”

In 2014, Wiedmann said sheep were dying at such a significant rate that having a hunting season in 2015 wasn’t an option.

“So, we had to take a year and step back to really assess the status of the population,” he said. “Fortunately, in 2015 our counts came in better than what we were expecting.”

License numbers are determined by assessing the age structure and total number of rams in the population. The July-August survey in 2016 showed a minimum of 103 rams in the badlands, an increase of 18 percent from 2015.

Wiedmann said that, overall, Department wildlife officials are encouraged by the results of the summer survey. “In fact, the ram count was the highest on record,” he said.

Jeb Williams, Game and Fish wildlife division chief, said the last time the Department made eight bighorn licenses available to hunters was in 1998.

“There are currently good numbers of mature rams on the landscape, and we are going to take advantage of providing as much hunter opportunity as possible with the situation that we have,” Williams said. “We feel good that we are able to provide this opportunity as impacts from the die-off have lessened substantially since 2014, but it is also very unpredictable.”

Knowing that pathogens are in the population, and the number of males on the landscape is good, Wiedmann said now is not the time to restrict harvest of males.

“Use them or lose them,” Wiedmann said. “We have big, healthy rams out there that are in wonderful shape and we don’t want them to die of pneumonia.”

And secondly, considering there are few bighorn populations northeast of the North Unit of Theodore Roosevelt National Park that have yet to be influenced by pneumonia, it’s good to trim the number of rams.

“Rams wander during the rut and they can potentially spread these pathogens into unaffected herds,” Wiedmann said. “What you want to do is bring the male to female ratio to a more manageable level where rams kind of stay home during the rut as much as possible. While you can’t prevent this totally, you don’t want rams, typically young rams, running all over the place looking for females.”

This is just the second pneumonia outbreak in North Dakota’s bighorn sheep population, the first coming in 1997 when about 100 sheep died south of Interstate 94.

Wiedmann said bighorns continue to die of pneumonia in western North Dakota, but at a much slower rate. He said there are examples in other states where bighorn populations recovered nicely after being hit with pneumonia.

“You see these populations recover and then they crash again,” he said. “It’s just that you don’t know when that is going to happen.”