Bighorn Sheep Study Underway

Fish and Game biologists recently spent some time examining bighorn sheep in several areas of the Salmon region. A total of thirty-four sheep were captured using net-gunning methods in Morgan Creek, the East Fork of the Salmon River, and the Little Lost River Valley and the Pahsimeroi Valley. Each sheep was checked for overall general health and external parasites. Blood samples were drawn and swabs taken from the ears and throat. Fecal samples were also collected. The five bighorns captured in the Little Lost River Valley received radio collars. Biologists hope to track this group of animals to get information on their distribution and movement patterns. The overall purpose of this study is to attempt to understand why bighorn sheep populations in these areas remain depressed. Approximately 8 -10 years ago, the sheep experienced a major die-off due to pneumonia caused by the Pasteurella bacteria. Twenty-five to fifty percent of the population died. Since then, some of the herds have been slowly increasing, but lamb production in other herds remains exceptionally low. Pasteurella is a fairly large group of bacteria that has been found in birds, livestock (where it is called "shipping fever"), and some wild animals. Found worldwide, it was first recognized in western Europe as a severe epidemic in deer. Here in the United States, bighorn sheep seem to be very susceptible to the bacteria. In some cases, the infection can be so acute that no symptoms are seen several days before the animal dies. It is thought that some forms of the bacteria are carried by adult bighorn, but remain latent until the animal becomes stressed due to a primary infection, poor forage conditions, bad weather, or excessive disturbance. Once these conditions trigger the latent bacteria, it can spread causing severe pneumonia or generalized infection and death. Occasionally, the bacteria are more virulent, rapidly killing native bighorn when introduced to populations that have not been previously exposed. Pasteurella can be detected in the throats and upper respiratory tracts of healthy animals. Throat swabs taken from the captured bighorns will show biologists if the bacteria are still present in these populations. If adult bighorn still harbor the bacteria, it is possible that lambs, which lose their immunity to the disease shortly after weaning, may be contracting the disease and dying. If so, this could be part of the reason that lamb production is remaining low in these herds. Analysis of the samples collected will be done through the Caine Veterinary Teaching Center and the results forwarded to Fish and Game biologists. As part of this same study, 30 sheep were sampled earlier this winter along the main Salmon River as well as in the Selway in areas where they could be easily approached and darted on the ground. In addition, sheep hunters were asked to collect biological samples to add to the sample size. At this time, approximately 80 bighorn sheep scattered across Central Idaho have been sampled as part of this ongoing study.