SIOUX FALLS, S.D. - A pneumonia outbreak may have killed 150 of the 200 bighorn sheep in Custer State Park and likely will force cancellation of at least one bighorn hunting season there.
The 75 percent mortality rate is an estimate based on the number of live animals seen in the park because many of the dead sheep are in remote areas and never will be found, park wildlife biologist Gary Brundige said March 8.
Laboratory tests on two animals confirmed a bacterial pneumonia - likely a type that domestic sheep can carry without developing health problems, Brundige said.
Lab workers never could positively identify it as that bacteria, which would confirm what game biologists suspected - that one or more of the park's bighorn sheep picked up the disease by coming in contact with domestic sheep.
"There was a lot of circumstantial evidence. It came post-rut, a time when the rams that are out come back to the herd, and there have been a couple incidents of bighorns in domestic herds around here in the hills," he said.
The Game, Fish and Parks Department's policy is to kill any bighorns known to mingle with domestic herds to prevent the spread of disease to the park herd, Brundige said.
Twenty-five to 30 dead animals were found in the first few weeks after bighorn sheep began showing signs of the disease, but only 40 to 50 live sheep have been seen in the park since, Brundige said.
He said there's no indication the disease has spread to the estimated 250 sheep in several other bighorn herds elsewhere in the Black Hills. One ewe, equipped with a radio collar and known to travel between Custer State Park and another herd in the Hill City area, was killed to keep her from spreading the disease, he said.
The 75 percent die off, seen with such outbreaks in other states, likely will mean transplanting sheep from other herds to rebuild the park herd.
"Normally, we see some limited lamb production and survival following the disease for some years, and we're anticipating that. We will look at supplementing the herd here in the future. The exact source of that still remains open," Brundige said.
The GF&P issues three hunting licenses for bighorn rams in Custer State Park.
"Our recommendation is that we close the season this fall because we don't know the extent of the disease. We'll monitor the ram population next fall with the rut and then decide where to go from there," Brundige said.
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