Spotted tree frog (Litoria spenceri) - critically endangered species listing
The Scientific Committee, established by the Threatened Species Conservation Act, has made a Final Determination to list the Spotted Tree Frog Litoria spenceri Dubois, 1984, as a CRITICALLY ENDANGERED SPECIES in Part 1 of Schedule 1A of the Act, and as a consequence, to omit reference to the Spotted Frog Litoria spenceri Dubois, 1984 from Part 1 of Schedule 1 (Endangered species) of the Act. Listing of Critically Endangered species is provided for by Part 2 of the Act.
NSW Scientific Committee - final determination
The Scientific Committee has found that:
1. The Spotted Tree Frog Litoria spenceri Dubois, 1984 (family Hylidae) is an endemic Australian frog described by Cogger (2000) as follows: ‘Grey to olive-green above, with irregular darker mottling or marbling, the latter often forming irregular cross-bands on the limbs. Ventral surface white or yellow. Lower and concealed surface of limbs yellowish. Skin shagreened, with a few tiny whitish tubercles on the back becoming numerous on the sides. Skin granular below. Small but prominent vomerine teeth, mostly behind choanae. A slight pectoral fold. Finger and toe discs moderate, only a little wider than digits. Fingers with distinct basal webbing; toes fully webbed. A small but prominent inner metatarsal tubercle, no outer. Tympanum indistinct. Second finger larger than first, 45 mm’.
2. The warty back of the Spotted Tree Frog distinguishes this species from the similar species, Leaf Green Tree Frog, Litoria nudidigitus and its lack of a distinct tympanum distinguishes it from Blue Mountains Tree Frog, Litoria citropa .
3. The Spotted Tree Frog is restricted predominantly to the western side of the Great Dividing Range, from Lake Eildon in the Central Highlands of Victoria to Mount Kosciuszko, NSW (Gillespie and Hollis 1996). The species has an extremely limited range, and has only been recorded from three sites along streams within Kosciuszko National Park (NSW NPWS 2001).
4. The Spotted Tree Frogs occurs in swift-flowing remote mountain streams, with a preference for rapid-flowing sections of stream with loose rock and steep banks (Gillespie and Hollis 1996; NSW NPWS 2001).
5. The breeding season of the Spotted Tree Frog begins in suitable weather between late October and early December. Egg laying has been recorded between late November and the end of December (NSW NPWS 2001). Clutch sizes range from about 50 to nearly 1000, averaging around 500 (Gillespie 1997). Larval development occurs during summer and autumn, and between mid-February and late March they undergo metamorphosis (NSW NPWS 2001).
6. The area of occupancy in New South Wales is estimated to be no more than 4 km2, based on 2 x 2 km grids cells, the scale recommended for assessing area of occupancy by IUCN (2008), indicating a very highly restricted geographic distribution. The population experienced a very large reduction in the number of individuals from 700–1000 adults in the mid 1990s to only one individual in 1999. In addition, breeding activity had not occurred at the site for the two years prior to this decline (Gillespie 1999). The number of mature individuals in the wild population is estimated to be extremely low, based on the most recent estimate that the total population of the Spotted Tree Frog comprises a single mature individual. Given that this individual was male, that the record dates from 10 years ago (1999) and that the individual was removed from the wild, there is a possibility that the species may already be extinct in the wild in NSW. There is also a possibility that some individuals of L. spenceri persist and remain undetected, although a substantial search effort of suitable habitat has not yielded any evidence of extant populations. The number of mature individuals of the species is therefore almost certainly less than 50 and possibly zero.
7. A captive breeding program has been undertaken and a batch of individuals has been released into the wild each year since 2006. The estimated number of individuals currently surviving in the wild from this release is between 130 and 210 (D. Hunter pers. comm. June 2008). Translocated individuals are considered part of wild populations when they produce viable offspring (IUCN 2008). There is no evidence that introduced individuals of the Spotted Tree Frog have yet produced viable offspring.
8. The major decline in the number of individuals in the only extant population is believed to be due to the introduction of the Chytrid fungus, Batrachochytrium, into a previously disease-free population (D. Hunter pers. comm. June 2008). ‘Infection of frogs by amphibian chytrid causing the disease chytridiomycosis’ is listed as a Key Threatening Process under the Threatened Species Conservation Act 1995.
9. Other key threats to the species may include predation on larvae by trout, alteration of natural flow regimes and increased sedimentation of streams (NSW NPWS 2001). Minor threats may include invasion by Blackberry (Rubus spp.) and atypical climatic events (NSW NPWS 2001). ‘Alteration to the natural flow regimes of rivers and streams and their floodplains and wetlands’ is listed as a Key Threatening Process under the Threatened Species Conservation Act 1995.
10. The very highly restricted distribution and small population size make this species highly prone to reduction as a result of stochastic environmental events, disturbances and demographic variability.
11. The Spotted Tree Frog Litoria spenceri Dubois, 1984 is eligible to be listed as a Critically Endangered species as, in the opinion of the Scientific Committee, it is facing an extremely high risk of extinction in New South Wales in the immediate future, as determined in accordance with the following criteria as prescribed by the Threatened Species Conservation Regulation 2002:
Clause 14
The species has undergone, is observed, estimated, inferred or reasonably suspected to have undergone or is likely to undergo within a time frame appropriate to the life cycle and habitat characteristics of the taxon:
(a) a very large reduction in population size
based on:
(d) an index of abundance appropriate to the taxon.
Clause 15
The geographic distribution of the species is estimated or inferred to be:
(a) very highly restricted
and:
(d) a projected or continuing decline is observed, estimated or inferred in:
(i) an index of abundance appropriate to the taxon
(ii) geographic distribution, habitat quality or diversity, or genetic diversity
(e) the following conditions apply:
(i) the population or habitat is observed or inferred to be severely fragmented,
(ii) all or nearly all mature individuals are observed or inferred to occur within a small number of populations or locations.
Clause 16
The estimated total number of mature individuals of the species is:
(a) very low
and:
(d) a projected or continuing decline is observed, estimated or inferred in either:
(i) an index of abundance appropriate to the taxon,
(ii) geographic distribution, habitat quality or diversity, or genetic diversity;
(e) the following conditions apply:
(i) the population or habitat is observed or inferred to be severely fragmented,
(ii) all or nearly all mature individuals are observed or inferred to occur within a small number of populations or locations.
Clause 17
The total number of mature individuals of the species is observed, estimated or inferred to be:
(a) extremely low.
Dr Richard Major
Chairperson
Scientific Committee
Proposed Gazettal date: 04/12/09
Exhibition period: 04/12/09 – 29/01/10References:
Cogger HG (2000) Reptiles and Amphibians of Australia. 6th ed. Reed New Holland, Sydney.
Gillespie GR (1997) The biology of the Spotted Tree Frog (Litoria spenceri) and examination of factors responsible for population declines. Final Report of the Recovery Plan (Research Phase). Unpublished report to the Biodiversity Group, Environment Australia, Canberra.
Gillespie GR (1999) Population Monitoring and Survey for the Spotted Tree Frog Litoria spenceri in Bogong Creek, Kosciuszko National Park, 1999. Unpublished report to New South Wales National Parks & Wildlife Service. Arthur Rylah Institute, Department of Natural Resources & Environment, Heidelberg, Victoria.
Gillespie GR, Hollis GJ (1996) Distribution and habitat of the Spotted Tree Frog Litoria spenceri Dubois (Anura: Hylidae) and an assessment of potential causes of decline. Wildlife Research 23, 49-75.
IUCN (2008) ‘Guidelines for using the IUCN Red List Categories and Criteria. Version 7.0.’ (Standards and Petitions Working Group of the IUCN Species Survival Commission Biodiversity Assessments Sub-committee: Switzerland).
NSW National Parks and Wildlife Service (2001) Approved Spotted Tree Frog (Litoria spenceri) Recovery Plan. NSW NPWS, Hurstville NSW.