Tusked frog (Adelotus brevis) population, Nandewar and New England Tablelands bioregions - endangered population listing

The Scientific Committee, established by the Threatened Species Conservation Act, has made a Final Determination to list the Tusked Frog, Adelotus brevis (Gunther 1863), population in the Nandewar and New England Tablelands Bioregions as an ENDANGERED POPULATION in Part 2 of Schedule 1 of the Threatened Species Conservation Act. Listing of Endangered Populations is provided for by Part 2 of the Act.

NSW Scientific Committee - final determination

The Scientific Committee has found that:

1. The Tusked Frog is not listed as an Endangered Species on Part 1 of Schedule 1 of the Threatened Species Conservation Act, and thus populations of Tusked Frog are eligible for listing on Part 2 of Schedule 1 of the Act.

2. The Tusked Frog is a small flattened frog, readily distinguished by its ventral colouring and call, a single 'cluck' repeated several times per minute. The species is sexually dimorphic with males being larger than females (50mm compared with 40mm); males have a large head that is wider than their body, whereas females have a small head; and the dentary pseudo-teeth (tusks) are much larger in males than females (Barker & Grigg 1977).

3. The Tusked Frog is distributed along the coastal plain and adjacent Great Dividing Range from central Queensland to southern New South Wales (Cogger 1994). It occurs in a wide range of habitats including rainforest, wet sclerophyll forest and flooded pasture. The Tusked Frog occupies a broad range of minimum temperature and annual rainfall zones and is found at altitudes of up to 1400m (Heatwole et al. 1995).

4. Historically, Tusked Frogs were recorded in most parts of the New England Tablelands Bioregion (Heatwole et al. 1995) and west in the adjacent Nandewar Bioregion. Despite considerable survey effort in the past decade, no records are known from either Bioregion since 1976, with the exception of one record from 1992 at Riamukka to the extreme south of the New England Tablelands. Two records from 1997 are known from just outside the New England Tablelands, approximately 25km south-east of Dundee.

5. The New England Tablelands and Nandewar population of Tusked Frog represents a distinct and disjunct high-elevation population that is at the western limit of the species' range in NSW. Given the apparent lack of records from this population in the last 25 years, its numbers are likely to be reduced to a critical level, if it is not already extinct.

6. The decline in this Tusked Frog population may result from the impact of chytrid fungi, to which the Tusked Frog is susceptible (Berger et al. 1999). Such fungal pathogens were suggested as the cause of death following post-mortem examinations of ill and dead Tusked Frogs in Queensland (L. Berger, unpublished data), and studies of north Queensland frog species show that a chytrid fungus was the proximal cause of death (Berger et al. 1998). High altitude populations of frogs are those most affected by this pathogen.

7. Other likely threatening processes that may have caused decline in this population include extensive clearing and modification of Tusked Frog habitat for pastoralism, and predation by introduced fish such as the Plague Minnow Gambusia holbrooki.

8. In view of the above points, the Scientific Committee is of the opinion that the Tusked Frog, Adelotus brevis (Gunther 1863), population in the Nandewar and New England Tablelands Bioregions is eligible for listing as an endangered population because its numbers have been reduced to such a critical level that it is in immediate danger of extinction, and it is disjunct and at or near the limit of its geographic range and the population is of significant conservation value.

Proposed Gazettal date: 15/12/00
Exhibition period: 15/12/00 - 25/01/01

References

Barker, J. & Grigg, G. (1977). A Field Guide to Australian Frogs. (Rigby, Sydney).

Berger, L., Speare, R., Daszak, P., Earl Green, D., Cunningham, A.A., Goggin, C.L., Slocomb, R., Ragan, M.A., Hyatt, A.D., McDonald, K.R., Hines, H.B., Lips, K.R., Marrantelli, G. and Parkes, H. (1998). Chytridiomycosis causes amphibian mortality associated with population declines in the rainforests of Australia and Central America. Proceedings of the National Academy of Science 95, 9031-6.

Berger, L., Speare, R. and Hyatt, A.D. (1999). Chytrid fungi and amphibian declines: overview, implications and future directions. (In) A. Campbell (ed.). Declines and Disappearances of Australian Frogs. (Environment Australian, Canberra).

Cogger, H.G. (1994). Reptiles and Amphibians of Australia. (Reed Books, Chatswood).

Heatwole, H., de Bavay, J., Webber, P. and Webb, G. (1995). Faunal survey of New England. IV. The Frogs. Memoirs of the Queensland Museum 38, 229-49.