RARE TADPOLES RELEASED FOR FIRST TIME INTO WILD STREAM

University of California, San Diego Zoo, State and Federal Agencies Celebrate
Historic Moment for the Mountain Yellow-Legged Frog

Scientists and researchers released 36 endangered tadpoles into a stream near Idyllwild, Calif. today (Aug. 24, 2010) with hopes that the Southern California population of the mountain yellow-legged frog (Rana muscosa) has a chance of thriving in the wild again.

The tadpoles were bred at the San Diego Zoo Institute for Conservation Research and carefully transported to the University of California James San Jacinto Mountains Reserve in Riverside County, which is part of the University of California Natural Reserve System. There the tadpoles were gently released into a quiet stream where researchers can monitor them regularly. This release of tadpoles follows a release of mountain yellow-legged frog eggs in the same area four months ago.

The release was done in collaboration with partners including the U.S. Geological Survey, U.S. Forest Service, U.S. Fish and Wildlife Service, the California Department of Fish and Game, the California Department of Transportation and the San Diego Zoo.

“This is a very exciting day for everyone involved in this important effort to save this frog,” said Becca Fenwick, director of the James San Jacinto Mountains Reserve. “We are proud to be part of the effort to save this species that once thrived throughout Southern California.

“We will be monitoring carefully in hopes these tadpoles will be the beginning of the species’ resurgence.”

Globally, amphibians are on the decline because of habitat loss, effects of climate change, pesticide drift, introduction of nonnative species in the past, and the spread of a deadly pathogen called the chytrid fungus. The mountain yellow-legged frog is one of three frogs or toads on the federal Endangered Species List in Southern California and has recently been proposed for listing under the California Endangered Species Act. Today, only a small wild population of less than 200 adult mountain yellow-legged frogs can be found in the San Gabriel, San Bernardino, and San Jacinto mountains.

The same team of researchers who released the tadpoles into the creek today, released about 500 mountain yellow-legged frog eggs into the creek in April. The eggs also were the result of breeding at the San Diego Zoo Institute for Conservation Research. Scientists believe about 40 of those eggs morphed into 5-millimeter-long tadpoles.  The tadpoles from that first release are so small that it has been difficult for scientists to determine how many survived. The tadpoles released today were about 40 to 50 millimeters long (1½ to 2 inches), which gives them a better chance of survival.

“This is the first time we have reintroduced captive-bred offspring of this species into the wild,” said Adam Backlin, a USGS scientist. “This tadpole release will refine our methodology for future releases and help us find the most effective and successful strategy.”

The San Diego Zoo Institute for Conservation Research was the first to breed the mountain yellow-legged frog outside of its native habitat.  Historically, scientists have had great difficulty breeding frogs in the lab. This year, Zoo scientists discovered that the frogs’ breeding behaviors increased in the lab after the frogs were chilled to temperatures that resembled their high mountain stream environment.  Scientists hope the second year of breeding will result in a higher fertility rate.

“Reproduction in the lab and the subsequent release is a small first step, but it is a great one,” said Jeff Lemm, an animal research coordinator for the San Diego Zoo. “We hope to have many more tadpoles to release in years to come and look forward to helping in the recovery of this frog.”

The Zoo’s breeding program, in conjunction with its partners, began after a wildlife biologist with the San Bernardino National Forest noticed declining creek water levels in Dark Canyon in Riverside County in 2006. The Fish and Wildlife Service salvage effort started the next day. Recovered tadpoles were taken to the San Diego Zoo Institute for Conservation Research, where they metamorphosed into frogs.