Another bighorn dies in Catalinas — apparently of pneumonia

The number of collared sheep known to be alive in the range north of Tucson has dropped to 35.

“At this point, the pneumonia is limited” in the bighorn population, said Mark Hart, spokesman for the Arizona Game and Fish Department. “We’re continuing to monitor the situation closely, but the progress of the disease will be slow if we have additional cases.”

SOURCE OF DISEASE

Game and Fish officials are trying to determine the origin of pneumonia in the bighorns, which were brought to the Catalinas from three source populations in 2013 and 2014 in an effort to rebuild a herd that disappeared from the range in the 1990s.

One possibility, according to a new report from the department, is that animals from one of the groups might have encountered the disease and developed resistance to it — and subsequently passed it on to a group with less resistance.

Bighorn sheep reintroduced to the Catalinas have come from the Plomosa and Trigo mountains in the Yuma area and the Superstition Mountains in the Tonto National Forest east of Phoenix, the report says.

Blood work on animals from the Tonto Forest showed no indication of Mycoplasma ovipneumoniae, a common source of bighorn pneumonia — meaning that they likely had no recent exposure to the pathogen. But, the report notes, “Blood work on bighorn sheep from the Yuma region has shown that the animals had more recent exposure to Mycoplasma, and thus have developed some degree of immunity to this pathogen.”

Contact between animals from the groups could have led to transmission of the disease from resistant to vulnerable animals.

“Some animals succumb to disease while others develop a resistance to it,” the report says. “All five of the recent mortalities have been ewes from the Tonto National Forest, which may not have been previously exposed to Mycoplasma, likely lacked antibodies, and were therefore more vulnerable.”

ADDITIONAL BIGHORNS

“We’re still planning for a November release” of additional bighorns in the Catalinas from a source population elsewhere in the state, Hart said. “We have to do that planning because it’s not something you can stand up and do at the last minute.

“We’re looking at capturing from a herd that had prior exposure (to pneumonia) because that would give some resistance,” he said. “Those animals would be less likely to contract it than others that have never been exposed.”

Plans are going forward for bringing more bighorns to the Catalinas in November, but it’s not a certainty.

“Something new may come up that we haven’t anticipated,” Hart said.