Reestablishing desert bighorn sheep (Ovis canadensis mexicana), sustainable conservation and infectious disease management

The Arizona Game and Fish Department (AGFD) translocates bighorn sheep to reestablish locally extinct populations. One population in the Santa Catalina Mountains once numbered >200 animals, but died out in the late 1990s,... [ view full abstract ]

The Arizona Game and Fish Department (AGFD) translocates bighorn sheep to reestablish locally extinct populations. One population in the Santa Catalina Mountains once numbered >200 animals, but died out in the late 1990s, possibly as a result of declining habitat quality, disease, predation, or human disturbance. Between 2013-2015, AGFD reintroduced desert bighorn sheep to the Santa Catalina Mountains with 3 translocations of roughly 30 bighorn sheep each from 3 populations in Arizona. Source populations were selected based primarily on their recent population trends, though their current disease status, relative habitat conditions, and density of mountain lions (Puma concolor) within each area were known. Of 91 total translocated bighorn sheep, 77 came from ranges with fewer mountain lions and were positive for Mycoplasma ovipneumoniae, while 14 came from a range with more mountain lions and no exposure to M. ovipneumoniae. All adult bighorn sheep were equipped with GPS collars, and mortalities were investigated within 24 hours. From the 2013 release of mountain lion-naïve bighorn, 16 died from predation 6 months of release. One early post-translocation death was attributed to acute capture myopathy. Two mortalities, months after translocation, were undetermined. From the 2014 release, 5 lion-naïve bighorn died from predation. Beginning 9 months after translocation, 6 bighorns with no prior exposure to Mycoplasma ovipneumoniae succumbed to acute bacterial pneumonia with a strain type matched to the bighorn from the other source population. There have been 11 mortalities in the 2015 lion-naïve cohort: 7 from predation, 1 to a fall, 2 to pneumonia, and 1 undetermined. Translocation success occurs when early mortality is minimized and reproduction is maximized. Translocation planning should assess the probable impact of factors such as disease status for both the source and receiving populations, exposure to predators, and habitat conditions in order to achieve species conservation goals.