The North Dakota Game and Fish Department’s 2017 bighorn sheep survey, completed by recounting lambs in March, revealed a minimum of 265 bighorn sheep in western North Dakota, down 11 percent from 2016 and 9 percent below the five-year average.
Altogether, biologists counted 91 rams, 149 ewes and 25 lambs. Not included are approximately 20 bighorns in the North Unit of Theodore Roosevelt National Park.
Big game biologist Brett Wiedmann said the survey count was the lowest since 2006.
“The decline in the 2017 count reflects the spread of bacterial pneumonia to three previously unaffected herds and consequently the adult and lamb mortalities that followed,” Wiedmann said.
The northern badlands population declined 10 percent from 2016, and the southern badlands population was down 21 percent.
“The total count of adult rams and ewes was much lower than the record high counts in 2016, but the lamb count and recruitment rate improved slightly in 2017, albeit still much below the long-term averages,” Wiedmann said.
Wiedmann noted that 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.
“Fortunately, adult mortality was low in previously affected herds, and lamb survival improved as well, which could indicate those herds initially exposed to the deadly pathogens in 2014 are beginning to recover,” Wiedmann said. “The next few years will be important in determining if the state’s population shows signs of recovering 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 20 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 2018, 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 five licenses in 2017 and all hunters were successful harvesting a ram.