NSW Scientific Committee - final determination
The Scientific Committee found that:
1. The Stuttering Frog Mixophyes balbus, is a large myobatrachid amphibian. The species is yellow-grey above and the limbs have narrow dark cross-bars that may be incomplete or indistinct (Cogger 2000). Individuals grow to a length of approximately 80mm. The Stuttering Frog is currently listed as a Vulnerable species under the Act.
2. The historical distribution of the Stuttering Frog was from east of the Great Divide and extended from Gippsland in north-eastern Victoria to the upper northern catchment of the Clarence River north-east of Tenterfield, NSW. In the north of its range the species occurs only at high altitude while in the south both upland and lowland populations have been recorded.
3. The Stuttering Frog inhabits rainforest, Antarctic beech and wet sclerophyll forests (Cogger 2000). The species depends on freshwater streams and riparian vegetation for breeding and habitation. No records are known from riparian habitat that has been disturbed (Mahony et al. 1996).
4. The southern portion of the Stuttering Frog's range appears to be separated from the northern portion by the Hunter Valley. Intensive surveys of 35 historical locations south of the Hunter River found only 12 locations where the frogs were still extant, in addition to two new sites (A. White, pers. comm.). Of these 14 sites, 13 were clustered between Gosford and the Watagan Mountains with the next closest locations to the north of the Hunter Valley being Barrington Tops and Myall River State Forest near Bulahdelah.
5. Within the southern portion of its range, the Stuttering Frog appears to have declined dramatically in recent times. Targeted surveys by Daly et al. (2000) from south of Sydney to Victoria found only two locations where frogs remain: around Narooma on the south coast and near Macquarie Pass. No frogs were found at altitudes above 300m. The only known upland population of Stuttering Frog south of the Hunter Valley is near Mount Werong in Blue Mountains National Park (R. Mjadwesch, pers. comm.). The local extinction of these populations would represent a 50% reduction in the range of this species in the past decade.
6. The Stuttering Frog is threatened by habitat fragmentation and degradation. Fragmentation of Stuttering Frog habitat, as a result of urban development and agricultural landuse, isolates sub-populations and increases their vulnerability to local extinction via such stochastic events as drought or epidemic disease. Degradation of riparian vegetation and siltation or pollution of watercourses reduces the availability of habitat and further exacerbates the impact of other threats.
7. The Stuttering Frog is likely to be threatened by the amphibian disease chytridiomycosis. Chytridiomycosis is caused by a waterborne chytrid fungus and is potentially virulent to all amphibians (Berger et al. 1999). There are no known records of chytridiomycosis infection in Stuttering Frog populations however it has been reported in congener populations including Fleay's Barred Frog, M. fleayi, and the Giant Barred Frog, M. iteratus (Speare and Berger 2000). In general, upland frog populations that depend on flowing streams are most susceptible to the disease. Therefore, the loss of upland populations south of Sydney may at least in part be attributed to the disease.
8. The Stuttering Frog is potentially threatened by predation of eggs and tadpoles by the exotic Plague Minnow, Gambusia holbrooki. Predation by the Plague Minnow is listed as a Key Threatening Process under the Act.
In view of the above the Scientific Committee is of the opinion that Mixophyes balbus Straughan, 1968 is likely to become extinct in nature in NSW unless the circumstances and factors threatening its survival or evolutionary development cease to operate.
Proposed Gazettal date: 13/12/02
Exhibition period: 13/12/02 - 31/01/03
Berger, L., Speare, R. and Hyatt, A. (1999). Chytrid fungi and amphibian declines: overview, implications and future directions. In 'Declines and Disappearances of Australian Frogs'. (Ed. A. Campbell.) pp. 23-33. (Environment Australia: Canberra).
Cogger, H.G. (2000). Reptiles and Amphibians of Australia. Reed Books: Chatswood.
Daly, G., Pennay, M. and Coombes, D. (2000). Targeted surveys for the Stuttering Frog Mixophyes balbus on the south coast of New South Wales. Report to New South Wales NPWS.
Mahony, M., Knowles, R. and Pattinson, L. (1996). Stuttering Barred Frog. In 'Threatened Frogs of New South Wales: Habitats, Status and Conservation'. (Ed. H. Ehmann.) pp. 65-71. (Frog and Tadpole Study Group of NSW Inc: Sydney).
Speare, R. and Berger, L. (2000). Chytridiomycosis in amphibians in Australia. November 2011.