North Dakota bighorn sheep population stable
The North Dakota Game and Fish Department’s spring bighorn sheep survey revealed a minimum of 296 bighorn sheep in western North Dakota, up slightly from last year and 3 percent above the five-year average.
Altogether, biologists counted 104 rams, 170 ewes and 22 lambs. Not included are approximately 20 bighorns in the North Unit of Theodore Roosevelt National Park.
Big game biologist Brett Wiedmann said the survey revealed both good and bad news after a sheep die-off that began in 2014.
“This year’s count of adult bighorn was encouraging given the ongoing effects of bacterial pneumonia throughout most of the badlands, but the lamb count was discouraging,” Wiedmann said.
The northern badlands population, which was hit the hardest from the die-off, increased 2 percent from last year. However, the southern badlands population was down 3 percent.
“The total count of adult rams and ewes was the highest on record, but the total count, recruitment rate and winter survival rate for lambs were all the lowest on record,” Wiedmann said. “The recruitment rate of lambs per adult ewes was 15 percent, well below the long-term average.”
Wiedmann noted that one year isn’t necessarily a trend, but poor lamb survival is typical in populations exposed to Mycoplasma ovipneumoniae, the pathogen responsible for most die-offs of bighorn sheep, and those effects can last many years.
Game and Fish Department biologists count and classify all bighorn sheep in late summer, and then recount lambs the following March, as they approach one year of age, to determine recruitment.
“Adult mortality was low in 2016, and we had a good number of lambs survive in 2014 and 2015 to compensate for most of the adult losses in 2014,” Wiedmann said. “However, many bighorns are still showing signs of pneumonia and lamb recruitment was poor in 2016, so next year’s survey will be important in determining if the state’s population continues to recover from the disease outbreak, or if the pathogens are likely to persist and cause a long-term population decline.”
Dr. Dan Grove, Department veterinarian, said that 19 adult bighorn were tested for deadly pathogens last winter, but results are still pending. He said animals continue to succumb to pneumonia, albeit at a much slower rate.
A bighorn sheep hunting season is tentatively scheduled to open in 2017, unless there is a recurrence of significant adult mortality from bacterial pneumonia. The status of the bighorn sheep season will be determined Sept. 1, after the summer population survey is completed.
Game and Fish issued eight licenses in 2016 and all hunters were successful harvesting a ram.