Yosemite Valley Restoring Native Frogs and Turtles
Yosemite National Park was once home to the federally threatened California red-legged frog (CRLF) and western pond turtle (WPT), a California species of special concern. Both species have disappeared from Yosemite Valley due in part to management actions that altered habitat suitability by impairing riparian function (e.g., removal of large woody debris) along the Merced River, artificially high populations of raccoons fed by previously abundant refuse, and the deliberate introduction of the invasive American bullfrog. The two species can be found in small strongholds elsewhere both inside (WPT) and outside (CRLF and WPT) of the park.
Factors leading to the disappearance of these species have been corrected. For example, bullfrogs have been eliminated in Yosemite Valley. However, the CRLF amd WPT have not recolonized Yosemite Valley all on their own. This collaborative project between the San Francisco Zoo and Yosemite National Park will reintroduce CRLF and WPT to Yosemite Valley. The goal is to reintroduce 1,000 adult CRLFs and 100 adult WPTs to establish self-sustaining breeding populations in Yosemite Valley by 2020.
California Red-Legged Frog
In 2016 and 2017, park biologists plan to collect 10% of donor source CRLF egg masses by hand from private land in El Dorado County. Egg masses will either go to the San Francisco Zoo for rearing (known as headstarting) or will be translocated immediately to Yosemite. Approximately 2,100 eggs per year (4,200 total) will be transferred directly to up to four sites in Yosemite Valley (see map). The eggs will be placed temporarily in predator protected pens (approximately the size of a laundry basket), reared onsite (approximately 10 - 20 weeks), checked daily and/or weekly, and then released once the tadpoles are large enough to avoid most predators. Tadpoles reared at the San Francisco Zoo will be released at the same points in Yosemite Valley. Should CRLF rearing and reintroduction goals not be met through the two initial CRLF phases, up to two additional phases of CRLF head-starting may occur, subject to the availability of funds.
Western Pond Turtle
Over the next 3 - 5 years, park biologists plan to collect and transfer a minimum of 30 WPT eggs and/or hatchlings per year from three or more donor sites in Mariposa and Tuolumne Counties. Identified source populations currently include the following sites: (1) North Fork Merced River, Bureau of Land Management; and (2) Stockton Creek Reservoir. Eggs and/or hatchling turtles will be transferred to the San Francisco Zoo to be reared to adult-sized turtles over an approximately 12 month period. WPT eggs would be collected by temporarily retaining adult females, locally performing x-rays, and hormonally inducing egg deposition at the San Francisco Zoo. After releasing eggs, turtles would be permanently marked (using a Passive Integrated Transponder tag and shell notched with a unique identifier using a hand file) and returned to the original site of capture.
While WPT are being head-started in the zoo, the NPS plans to introduce (below Stoneman Bridge and near the Amphitheatre) 6 - 10 WPTs collected from 3 or more donor sites that will be fitted with radio transmitters and tracked in Yosemite Valley during summer 2016 to ascertain habitat suitability and preference for releases of head-started WPT beginning in 2017 and beyond. Future release sites for captive reared turtles will be selected based on 2016 radio-tracking results for habitat preference.