FULL RESEARCH ARTICLE Predation impedes recovery of Sierra Nevada bighorn sheep DANIEL J. GAMMONS 1 *, JEFFERY L. DAVIS 2 , DAVID. W. GERMAN 1 , KRISTIN DENRYTER 3 , JOHN D. WEHAUSEN 4 AND THOMAS R. STEPHENSON 1 1 Sierra Nevada Bighorn Sheep Recovery Program, California Department of Fish and Wildlife, 787 North Main St., Suite 220, Bishop, CA 93514, USA 2 USDA APHIS Wildlife Services, 3419A Arden Way, Sacramento, CA 95825, USA 3 California Department of Fish and Wildlife, Wildlife Branch, 1010 Riverside Parkway, West Sacramento, CA 95605, USA 4 White Mountain Research Center, 3000 East Line St., University of California, Bishop, CA 93514, USA *Corresponding Author: daniel.gammons@wildlife.ca.gov Translocation of animals into formerly occupied habitat is a key element of the recovery plan for Sierra Nevada bighorn sheep (Ovis canadensis sierrae), which are state (California) and federally listed as endangered. However, implementing Sierra bighorn translocations is a signifcant conservation challenge because of the small size of the extant population and the limited number of herds available to donate transloca- tion stock. One such herd, the Mt. Langley herd, recently became unusable as a translocation source following a substantial population decline. At the time of listing in 1999, predation by mountain lions (Puma concolor; hereafter lion) was considered a primary threat to Sierra bighorn, and since then lion predation may have continued to limit the ability of source herds to provide translocation stock. We evaluated the relationship between lion predation and ewe survival rates within three source herds of the Southern Recovery Unit, compared lion abundance and ewe survival among years of varying predation levels, provided a range of estimated times for the Mt. Langley herd to recover to its former status as a translocation source, and determined if the rates lions have been removed to mitigate Sierra bighorn predation exceeded sustainable harvest guidelines. We found compelling evidence that lion predation has impeded the recovery of Sierra bighorn by reducing survival rates of adult ewes (and consequently, population growth) and by preying upon individuals that could have otherwise been translocated. Ewe survival was poor during years of extreme predation but even during years of typical predation, survival rates were below a level needed to ensure population growth, indicating that years with www.doi.org/10.51492/cfwj.cesasi.27 California Fish and Wildlife Special CESA Issue:444-470; 2021