Cathedral Sierra Nevada Bighorn Sheep Reintroductions
The National Park Service (NPS) and California Department of Fish and Wildlife (CDFW) will reintroduce up to 25 Sierra Nevada bighorn sheep, a federally endangered species, into the Cathedral Range of Yosemite National Park over a five year period from 2015-2019. Up to 20 of these animals will receive GPS and VHF tracking collars to monitor their movements throughout the range. In addition to collars, surveys will be conducted by NPS and CDFW personnel to monitor the herd.
In March 2015, contracted crews will capture up to 15 bighorn sheep (10 ewes and 5 rams) out of the Mt. Langley herd in Sequoia National Park. The crews will use net-guns operated from a helicopter. Net-gunning includes shooting individual sheep with a net, tying their feet together, and covering the bighorn's eyes with a mask. Research has shown net-gunning to be the safest alternative for bighorn captures with 2-3% accidental mortality. After sheep have been immobilized, they are harnessed and flown out of the capture site to a processing site on the east side of the Sierra Nevada. During processing, veterinarians and biologists will perform health assessments on each individual, take blood and hair samples for genetic analysis, and affix GPS and VHF collars for monitoring purposes. The sheep will then be loaded into large boxes and transported by truck north to a location close to the release site. Once there, biologists will transport all boxes of sheep to Washburn Lake via helicopter. Biologists will then release the sheep into the backcountry.
Field crews will conduct surveys throughout the following summer and fall to monitor the sheep and assess movement and mortality. Twice yearly surveys will continue for at least 7 years. The GPS collars will send out location fixes once per day and can last up to 3 years. Once the collar battery dies or nears depletion, collars may be replaced depending on monitoring needs for the herd. GPS collaring of multiple bighorns will continue for at least 7 years due to Endangered Species Act delisting requirements. VHF collars send out a short range radio signal that helps crews and air support locate the sheep. Batteries on the VHF collars have a much longer life and generally last throughout the lifetime of a sheep. Due to herd movements and dynamics, the park will attempt to collar all rams and multiple, but not all, ewes.
Additional population augmentations will occur in 2017 and 2019. Each of those years, up to 5 ewes or rams will be translocated to the Cathedral Herd. The source herd will likely be Mt. Langley, but could be from other herds if necessary. The maximum number of sheep reintroduced into the Cathedral Herd will be 25 animals (up to 15 ewes and up to 10 rams). Augmentations will be completed using the same methods as the original reintroductions in 2015. Monitoring methods and protocols will also be consistent with those identified in the Sierra Nevada Bighorn Sheep Recovery Plan.
Helicopter flights will be as short as possible (10 minutes or less) when transporting sheep and crewmembers. For the 2015 reintroductions, the release crew will be flown in on 1-2 flights. The sheep will then be delivered in a maximum of 8 trips. Up to 2 additional trips will be necessary to pick up the release crew. In 2017 and 2019, fewer trips will be required for fewer sheep. Over the five year duration of the project, a maximum of 30 landings over 6 days will be required for reintroductions.
The release site is located immediately southeast of Washburn Lake in the upper Merced River canyon. Habitat models and expert opinion predict winter range for the sheep will likely be the south-facing cliffs near Washburn Lake. Summer range will include extensive habitat throughout the Cathedral Range and in the headwaters of the Merced River. There is potential for rams from the Cathedral herd to migrate and breed with the existing Mt. Gibbs herd farther north.