May 30, 2008

Is Captive Breeding in the Mountain Yellow-legged Frogs Future?

In last week's post, I wrote about the captive breeding of amphibians in general, and this week I'll focus specifically on the mountain yellow-legged frog. With the ongoing decline of this species, the topic of captive breeding seems to come up at every meeting in which population recovery efforts are discussed. Although the debate about what role captive breeding can realistically play in the global amphibian decline crisis is heated and will likely continue for many years, efforts to develop a captive breeding program for mountain yellow-legged frogs have already been underway for several years.

In April 2005, the Conservation and Research for Endangered Species (CRES) group at the San Diego Zoo began a captive breeding effort with southern mountain yellow-legged frogs (Rana muscosa) obtained from the last population hanging on in the San Bernardino Mountains. The goal of the effort was to create an "integrated program of captive propagation, headstarting, and release that will ensure the long-term viability of the species in the wild". These frogs were taken into captivity following a fire that swept across the area, creating the very real threat that these last frogs could be lost during winter floods and debris flows. Ultimately, seven frogs were captured and transferred to the San Diego Zoo. Unfortunately, all seven died due to an unspecified disease.

A second chance to develop a captive frog population came along a year later. In August 2006, a U.S. Forest Service biologist observed
R. muscosa tadpoles stranded in drying stream pools in the San Jacinto Mountains. No suitable habitat was present in the vicinity to which the stranded tadpoles could be transferred, so all 82 tadpoles were collected and brought to the San Diego Zoo. According to a short article published in yesterday's Los Angeles Times, 62 of the tadpoles have metamorphosed into froglets. If these animals survive into adulthood, the plan is to keep some at the zoo as part of a captive breeding program, and the remaining animals will be released back into their original habitat.

Successful reintroduction into the wild is only possible if the original cause of population decline has been mitigated. Unfortunately, for mountain yellow-legged frogs in southern California's Transverse Ranges, the cause of decline remains obscure. Introduced trout have likely played a role (see my post from May 16, 2008), but the relative importance of other factors is unknown. With fewer than 150 mountain yellow-legged frogs remaining in the Transverse Ranges, the only way find out what the population-limiting factors are may be to carefully follow the fate of frogs once they are released back into the wild.

Clearly, the path to recovering this species will be a slow and uncertain one.

Back to The Mountain Yellow-legged Frog Site.

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