NSW Scientific Committee - final determination
The Scientific Committee has found that:
1. Pseudophryne australis (Gray 1835) the Red-crowned Toadlet is a brown to black frog with a bright red or orange triangle on the head and a red or orange coccygeal stripe (Cogger 2000). Individuals attain a length of approximately 30mm.
2. Pseudophryne australis (Gray 1835) the Red-crowned Toadlet is currently listed as a vulnerable species on Schedule 2 of the Act. This status was assigned following a threat assessment of all vertebrate species in New South Wales (NSW) by Lunney et al. (2000). The species was considered vulnerable due to its low population size, low fecundity, habitat specialisation, low habitat availability, and that a large proportion of its range is affected by threatening processes.
3. The Red-crowned Toadlet's range coincides with the Hawkesbury Sandstone geology of the Sydney Basin Bioregion (Thumm and Mahony 1999) including densely populated urban areas of Sydney. Known records are distributed in a belt around, but not on the Cumberland Plain. The range limits of the species have not been extended significantly despite intensive surveys in recent years.
4. The Red-crowned Toadlet shows considerable ecological specialisation. Suitable habitat follows the interface of Hawkesbury Sandstone and shale e.g. the Wianamatta and Narrabeen Shales, with individuals found below sandstone ridges, generally where shale lenses are weathering at the base of cliff lines. The species deposits eggs in terrestrial nests beneath rocks and logs or in leaf litter. The Toadlet relies on rainfall to wash the partially developed tadpoles into ephemeral creeks for completion of the reproductive cycle (Thumm and Mahony 1999).
5. The Red-crowned Toadlet is relatively long-lived (8-10 years). It is a non-seasonal, iteroparous breeder and fecundity is relatively low, with clutch sizes averaging 24 eggs. Reproductive success is very low, as demonstrated by a local population at Hornsby Heights where 1,368 eggs were laid over three years and only 11 tadpoles reached metamorphosis (Thumm and Mahony 1999).
6. The Red-crowned Toadlet is threatened by urban development. Urbanisation results directly in habitat clearance and fragmentation and indirectly, urban development degrades Red-crowned Toadlet habitat through disruption of catchment hydrology and alteration of soil pH and plant species composition. The intensification of urbanisation within the Sydney Basin within recent years has seen habitat for the species subject to development and its consequences. Thumm and Mahony (1997) recorded 47 breeding locations, of which two had been directly destroyed by development, 12 were threatened by housing, 10 were potentially exposed to storm water pollution and six were totally isolated with no possibility of interaction with other populations.
7. Red-crowned Toadlets (and Brown Toadlets, P. bibronii) have apparently become locally extinct at four sites (reported by Woodruff 1978, K. Thumm pers. comm.). Moreover, a recent study demonstrated significant genetic differences between northern and southern populations of the species (Stauber 1999), suggesting that some historical separation of populations has occurred.
8. Red-crowned Toadlets are susceptible to infection by amphibian chytrid fungus, Batrachochytrium species. Batrachochytrium is a water-borne pathogen virulent to adults of all frog species and causes the fatal disease chytridiomycosis (Berger et al. 1999). Chytridiomycosis epidemics are responsible for the decline of many frog species from the east coast and Great Dividing Range, particularly upland populations in cooler environments. There has been no specific study of the impact of chytridiomycosis on Red-crowned Toadlets. However, both wild and captive populations of the species are known to have been infected (K. Thumm, pers. comm.), and the disease is now considered endemic in congener populations of the endangered Corroboree Frog, P. corroboree, and the vulnerable Northern Corroboree Frog, P. pengilleyi (Speare and Berger 2000). Despite the largely terrestrial nature of the species, Red-crowned Toadlets are exposed to pathogens via seepage areas in which they live and through infection as tadpoles. Moreover, aggregation of local populations at breeding sites may actually increase the potential impact of a chytridiomycosis epidemic on this species.
9. Arson and repeated burning to protect assets has had a deleterious effect on the habitat of the Red-crowned Toadlet and caused changes to the hydrology of the catchments feeding the ephemeral streams.
10. The removal of bushrock, a Key Threatening Process, destroys Red-crowned Toadlet shelter and nests. The Final Determination for 'Bushrock Removal' listed Red-crowned Toadlets as a threatened species that is detrimentally affected by this process.
11. In view of the above, the Scientific Committee is of the opinion that Pseudophryne australis (Gray 1835) the Red-crowned Toadlet is likely to become endangered unless the circumstances and factors threatening its survival or evolutionary development cease to operate, and is therefore eligible to remain listed as a Vulnerable Species.
Proposed Gazettal date: 19/07/02
Exhibition period: 19/07/02 - 23/08/02
References
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 New Holland: Sydney.
Lunney, D., Curtin, A.L., Ayers, D., Cogger, H.G., Dickman, C.R., Maitz, W. Law, B. and Fisher, D. (2000). The threatened and non-threatened native vertebrate fauna of New South Wales: status and ecological attributes. Environmental & Heritage Monograph Series No. 4. NPWS: Sydney.
Speare, R. and Berger, L. (2000) Chytridiomycosis in amphibians in Australia. 9 October 2000.
Stauber, A. (1999). Geographic variation in Pseudophryne australis: morphological and genetic differences. B. Sc. Honours Thesis, University of Technology: Sydney.
Thumm, K. and Mahony, M. (1997). Red-crowned Toadlet. In 'Threatened Frogs of New South Wales: Habitats, Status and Conservation'. (Ed. H. Ehmann.) pp. 126-36. Frog and Tadpole Study Group of NSW Inc: Sydney.
Thumm, K. and Mahony, M. (1999). Loss and degradation of red-crowned toadlet habitat in the Sydney region. In 'Declines and Disappearances of Australian Frogs'. (Ed. A. Campbell.) pp. 99-108. Environment Australia: Canberra.
Woodruff, D.S. (1978). Hybridization between two species of Pseudophryne (Anura: Leptodactylidae) in the Sydney Basin, Australia. Proceedings of the Linnean Society of New South Wales 102, 131-47.