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Western pond turtles and California red-legged frogs, described by Mark Twain in his 1865 story “The Celebrated Jumping Frog of Calaveras County,” are being raised for a return to Yosemite Valley this summer and next summer after a half-century absence.
Scientists with the National Park Service, San Francisco Zoo & Gardens, federal Fish & Wildlife Service and state Department of Fish & Wildlife are working together to make it happen.
“We’re not breeding them, we are rearing them,” Jessie Bushell, a biologist and director of conservation with San Francisco Zoo & Gardens, said Friday in a phone interview. “The turtles are from a number of sites inside the park but outside Yosemite Valley, the far corners of the park. The frogs are from right around the Yosemite National Park area, private land near the park.”
Bushell said some turtles may be released in Yosemite Valley as early as next week. Scientists at a rearing facility at the zoo are raising California red-legged frog tadpoles, and they will be ready for release in Yosemite Valley next summer, Bushell said.
Western pond turtles are a candidate species for designation as endangered or threatened, and California red-legged frogs are considered threatened, Bushell said.
The National Wildlife Federation describes the California red-legged frog as “a rare species of frog found almost exclusively in the state of California.” Biologists and conservationists agree the species is the same one Twain wrote about 150 years ago.
Human decisions, like putting American Bullfrogs in the Ahwahnee Hotel reflection pond in the 1950s, played a big role in wiping out California red-legged frogs that used to be in Yosemite Valley, according to Yosemite National Park staff, who described imported bullfrogs as “non-native, highly invasive and predatory.”
According to Jenny Loda, amphibian and reptile staff attorney and a biologist with the Center for Biological Diversity, bullfrogs were not native species when they were brought to Yosemite.
“They are larger and their tadpoles stay in water for up to a year,” Loda said. “They can eat the tadpoles and larvae and the baby frogs of the red-legged frogs, and adult bullfrogs will eat adult red-legged frogs.”
An adult American Bullfrog can grow up to 8 inches long and weigh up to 2 pounds, much larger than California red-legged frogs, Loda said.
In addition, open trash and refuse dumps in the 1970s drew raccoons to artificially high elevations, including Yosemite Valley, where raccoons hunted turtles and frogs with severe impacts on their populations, park scientists say. Western pond turtle habitat was also impacted by removal of large woody debris along the Merced River.
Those conditions in Yosemite Valley are now reversed, according to park staff. In recent decades, bullfrogs have been eradicated, open refuse sites are closed, and naturally-occurring river and stream bank habitat have been left in place, allowing for reintroduction of native turtles and frogs.
According to a 2005 UCLA faculty study, “Range-Wide Molecular Analysis of the Western Pond Turtle,” the species is the only freshwater turtle restricted to western North America.
The Western pond turtle is highly aquatic, inhabiting ponds, streams, rivers, and marshes from Washington and Oregon through California, from the Pacific coast to the west slope of the Sierra, with an isolated population in the Mojave Desert in southern California, and south to Baja California Norte, Mexico.
In Yosemite, the Western pond turtle has been absent from Yosemite Valley for about 50 years but is still found in the Hetch Hetchy area, according to park staff.
Federal fish and wildlife scientists are working on determining if Western pond turtles will be listed and if so, whether as endangered or threatened, Bushell said.
California red-legged frogs are not to be confused with Sierra Nevada yellow-legged frogs and other mountain yellow-legged frogs, which are found in alpine meadow ponds, springs and lakes at higher altitudes, Bushell said.
“Red-legged frogs are more lowland species, not high alpine,” Bushell said. “They are bigger than the mountain yellow-legged frogs found in the Sierra Nevada. The yellow-legged frogs do really well in high-elevation lakes. Red-legged frogs are more coastal to lower elevations of the Sierra Nevada.”
Miners ate frogs
California red-legged frogs can get up to 5 inches long and yellow-legged frogs are shorter, they get to about 3 inches, Bushell said. Generally speaking, red-legged frogs can get up to twice the size of the higher-altitude yellow-leggeds.
Yellow-legged frogs are considered endangered because they’ve lost 95 percent of their population over the past couple decades, due to introductions of non-native trout and a fungal disease affecting amphibians, Bushell said.
California red-legged frogs are considered threatened, Bushell said. They’ve had population declines of about 70 percent in their natural range. Most of that decline has been in the Sierra Nevada and southern California.
The California red-legged frog was designated the official state amphibian in June 2014, a move championed by southern California elementary school children who went to Sacramento and testified on the frog’s behalf at the state capitol.
According to the text of Assembly Bill No. 2364, the California red-legged frog’s place in state history extends to the Gold Rush era, when miners ate close to 80,000 frogs a year, nearly eating the species into extinction.
The Western pond turtle and the California red-legged frog will be reintroduced to suitable lake, river or meadow habitats in Yosemite Valley beginning this summer and next summer, according to park staff.
Over the next eight years, 100 adult Western pond turtles will be reintroduced to establish self-sustaining breeding populations, scientists say. The first 10 turtles released this June will be fitted with radio-transmitters so researchers can track and identify preferred turtle habitats in Yosemite Valley.
For the California red-legged frogs, a goal over the next three years is to reintroduce 4,000 of their tadpoles and 500 adult red-legged frogs.
A permanent frog and turtle rearing facility at San Francisco Zoo is known as the “San Francisco Zoological Society and Yosemite National Park Conservation and Recovery Facility.” It was dedicated Wednesday May 25.
The quarantined facility is right now raising 14 Western pond turtles and more than 500 California red-legged frog tadpoles.
Small animals like frogs and turtles are indicators of environmental health and an important part of the food chain, Tanya M. Peterson, San Francisco Zoo & Gardens president, said in prepared remarks.
“We have to save them in order to conserve all wildlife,” Peterson said. “We are grateful to Yosemite National Park and Yosemite Conservancy for asking us to partner on this significant collaboration, which will have an immediate impact right in our own backyard.”
Yosemite Conservancy donors contributed $185,000 for research and habitat restoration to restore turtles and frogs in Yosemite. According to park staff, the conservancy has provided $540,000 to protect aquatic species in Yosemite over the past decade.
“Maintaining the natural balance of biodiversity in the park is important to its long-term well-being and to sustaining opportunities for visitors to experience the park as nature intended,” said Frank Dean, conservancy president.
People from NatureBridge, a program that offers hands-on environmental science for children and teens, will take part in releasing turtles and frogs in Yosemite Valley, according to park staff.
Scientists say Western pond turtles generally measure 4 inches to 7 inches long. They are olive, dark brown or blackish in color, with undersides that are yellow with irregular color patches. They’re found in streams, pools and vegetated banks, and they like to bask on logs and rocks.
California red-legged frogs are reddish in color on the underside of their legs and belly. They communicate with a series of short, soft grunts. They’re found in ponds, pools and streams and wet meadows.