TADPOLE RELEASE INTENDED TO BOLSTER ENDANGERED POPULATION

University of California, San Diego Zoo, State and Federal Agencies Work to Increase Mountain Yellow-Legged Frog Population in So. Calif.

Endangered tadpoles were released into a stream near Idyllwild, Calif., today (Nov. 23, 2010) with hopes that the Southern California population of the mountain yellow-legged frog Rana muscosa will thrive again.

This is the second release of tadpoles into the same stream at the University of California James San Jacinto Mountains Reserve in Riverside County, which is part of the University of California Natural Reserve System. 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, and the San Diego Zoo Institute for Conservation Research.

The initial reintroduction effort of this species occurred in April 2010 when about 500 eggs were released into the stream in hopes of successful hatching. The tadpoles from that release of eggs are so small that it has been difficult for scientists to determine how many survived.

The first-ever tadpole reintroduction for the species occurred in August. By “head starting” the tadpoles, partners hoped to increase survival in the wild. The release was conducted using both caged and free-swimming tadpoles. Eighteen tadpoles were released immediately into the stream while another 18 were put into a cage in the stream; the cage protected the tadpoles from predators and also allowed researchers to feed them. Each grouping was tagged with a different color marker. All 18 tadpoles in the cage survived the three-month period of reintroduction into the stream and were about 50 to 60 millimeters long (1 to 2½ inches) when they were released from the cage today. In the spring, scientists will go back to the stream and count the tadpoles to determine which of the release methods was most successful.

 “The experiments will help us to determine the most successful way to re-populate Southern California creeks with the highly endangered mountain yellow-legged frog,” said Frank Santana, research technician for the San Diego Zoo Institute for Conservation Research, where the tadpoles were bred. “The initial success that we have had with tadpole survival is very encouraging, but the real test will be how many tadpoles survived through the harsh winter.”

The creek is frequently monitored and some of the free-swimming tadpoles from the August release have been spotted during these efforts.

“When I survey the creek I am constantly on the lookout for the tadpoles,” said Becca Fenwick, director of the James San Jacinto Mountains Reserve. “I am excited for the day when I come upon my first full-grown mountain yellow-legged frog, a species that once thrived throughout Southern California.”

Globally, amphibians are on the decline because of habitat loss, effects of climate change, pesticide residue, introduction of nonnative species, 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 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 laboratories. 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 an even higher fertility rate.

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’s salvage effort started the next day. Recovered tadpoles were taken to the San Diego Zoo Institute for Conservation Research, where they metamorphosed into frogs.