Assessment of re-introduction methods for the Southern Corroboree Frog in the Snowy Mountains region of Australia

Summary

The southern corroboree frog (Pseudophryne corroboree), Critically Endangered and reduced to fewer than 40 wild males by 2010 primarily due to chytridiomycosis, is the focus of a NSW Department of Environment and Taronga Zoo program in Kosciuszko National Park comparing two experimental reintroduction methods after an earlier egg-augmentation approach boosted recruitment to metamorphosis but failed to slow the species' overall decline. The first method released wild-collected eggs into specially designed 400-liter artificial pools elevated above ground to exclude the disease-reservoir common eastern froglet, achieving 35% survival to metamorphosis in 2008 and 66% in 2009, comparable to or better than natural-pool augmentation, with only one of eleven successful 2008 pools showing chytrid infection versus 60% infection typically found in natural pools. The second method released 196 four-year-old captive-reared frogs plus 15 five-year-olds across two sites in January 2006, individually measured and photographed for identification; breeding males were absent in the first survey year but confirmed at one site in 2008 and both sites in 2009-2010, with survivorship to breeding estimated at just 1-17%, though a severe drought immediately following release likely worsened outcomes. Major difficulties included the multi-year (minimum seven years) timeline needed to properly assess the artificial-pool method, drought reducing survivorship of released older frogs, and the relatively small number of four-year-old frogs available for release limiting statistical power. The project rates itself Partially Successful, noting that reintroducing older frogs can help maintain wild populations but only at substantial resource cost, given the very low survivorship observed.