More than 25 percent of all wild sheep in North America live in Alaska. Dall sheep are highly valued by countless sportsmen, photographers, nature lovers, subsistence users, and scientists. Weather patterns and predators have influenced Dall sheep populations through the millennia but now there is a relatively new threat on the scene.
Wild sheep are susceptible to diseases carried by domestic sheep and goats that can affect herd survivability. The most significant diseases affecting our wild sheep are respiratory infections that result in pneumonia. Pneumonia in North American wild sheep has been documented in numerous scientific studies resulting in more than 70 technical publications. Pneumonia most often results in death across all age groups of wild sheep, and is typically followed by years of depressed lamb survival.
Many scientists and biologists believe that thinhorn sheep, Dall and Stone's, may be particularly susceptible to these respiratory pathogens. This is due to their relative isolation and lack of previous exposure to domestic sheep and goats. Although the threat is real, there is no evidence that the current reduction in Alaska's Dall sheep population is due to widespread pneumonia. Only a very small percentage of the wild sheep in Alaska have been tested for these pathogens, but testing is ongoing despite limited resources.
Respiratory bacteria carried and expelled by domestic sheep and goats don't significantly impact those domestic animals because of thousands of years of adaptation. However, when introduced to North American wild sheep, these airborne respiratory bacteria pose a highly significant threat to their survival. This is a similar response to the millions of native peoples around the world that lost their lives when exposed to introduced diseases like smallpox for which they had no natural immunity. Not all pneumonia outbreaks in wild sheep have occurred following documented contact with domestic sheep and goats. The preponderance of scientific evidence, however, shows that interaction between domestic sheep and goats with wild sheep frequently results in the death of wild sheep.
Should a transmission event occur from domestic sheep or goats, the disease would be spread by Dall sheep themselves. First within their herd, and then from one herd to another, most often carried by rams traveling in search of a mate. The disease could spread long distances from one mountain range to another because young rams often travel surprising distances. Unchecked, this could result in significant die-off of Alaska's Dall sheep that might take several lifetimes from which to recover. The spread and effects of pneumonia may also be heightened by stress from adverse weather and predation.
Management options to prevent a significant die-off of wild sheep caused by respiratory disease are limited. To date, there are no effective vaccines or treatments for pneumonia outbreaks in wild sheep. Collectively, 20 western state, provincial, and territorial fish and game agencies have recognized this risk and recommend steps be taken to manage for effective separation between domestic sheep and goats and wild sheep as the only viable method of prevention.
We support multiple-use resource management and are in no way against agriculture and the raising of domestic sheep and goats, either commercially or as a hobby. This is a traditional occupation and pastime done by fine people with no intended malice. We are, however, also strong advocates of science-based wildlife management in general, and for Dall sheep in particular.
Alaskans now have the opportunity to exercise science-based management to avoid risking potential loss of their incredible Dall sheep resource while still maintaining a traditional agricultural business or hobby. Whether via regulatory mechanisms through the Alaska Board of Game or legislative means via Alaska's Legislature, we recommend a proactive, collaborative effort to address this important challenge before it becomes a crisis.
Kevin Kehoe is president of the Alaska Wild Sheep Foundation, based in Anchorage. Also contributing to this commentary were Kevin Hurley, conservation director for the Wild Sheep Foundation in Bozeman, Montana; Dr. Peregrine Wolff, president of the American Association of Wildlife Veterinarians in Reno, Nevada; and the Alaska Chapter of the Wildlife Society.
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