Spencer’s River Tree Frog

Population and DistributionLitoria spenceri is restricted predominantly to the w. fall of the Great Divide, from L. Eildon in the Central Highlands of Vic. to Mount Kosciuszko NSW, at altitudes of 200-1100 m (Gillespie & Hollis 1996; Victorian Wildlife atlas unpublished data). The extent of occurrence of the species is about 15000 km2 (map in Gillespie & Hines 1999). Despite extensive systematic surveys throughout e. Vic. and s. NSW (Watson et al. 1991; Gillespie 1992; Gillespie & Hollis 1996; Hunter & Gillespie 1999) Litoria spenceri has only ever been found in 19 streams, and has always been considered rare (Watson et al. 1991). The species is now believed to be extinct in four of these streams, and has declined substantially in distribution and abundance along most others (Gillespie & Hollis 1996). The remaining streams comprise 12 discrete isolated populations (Gillespie & Hollis 1996; Hunter & Gillespie 1999). Monitoring has been conducted at eight populations since 1994 and has recently been expanded to include 15 streams (G. Gillespie pers. comm.). With the exception of the historic site on Buffalo Creek, Mt Buffalo National Park, monitoring of extinction sites ceased in 1998 (G. Gillespie pers. comm.). Most extant adult populations have remained relatively stable since 1993, however, a population at Bogong Ck, Mt Kosciuszko NP suffered a precipitous decline in 1996 (Gillespie 1997). It is the highest elevation population and was the only high density population known prior to the decline (Gillespie & Hollis 1996). Gillespie & Hines (1999) estimates the largest population to contain approximately 1000-1500 adults in the Upper Goulburn R. with the sizes of all other populations comprising less than 1000 adults. Litoria spenceri is wholly distributed on public land from Kosciuszko NP in NSW and Alpine NP, Eildon NP and Buffalo NP, and several unnamed state forests in Vic. (Tyler 1997). HabitatLitoria spenceri is associated with a range of vegetation communities from montane forest at high altitudes to wet and dry forest at moderate to low altitudes respectively (Gillespie & Hollis 1996). The extent of riparian forest at known localities ranges from virtually non-existent, with scattered riparian tree or shrub species, to a dense canopy of Leptospermum spp. shading the stream (Gillespie & Hollis 1996). The species is found almost exclusively in association with rock habitats along streams and occurs along sections of streams with steep banks, invariably in steeply dissected country or gorges with numerous rapids and waterfalls (Gillespie & Hollis 1996). Litoria spenceri is restricted to riffle and cascade stream sections with exposed rock banks, resulting in a highly patchy distribution along most streams (Gillespie & Hollis 1996). Adults and juveniles most likely remain in the vicinity of the stream, rarely venturing far from riparian zone (Gillespie 1997). Tadpoles occur predominantly in slow-flowing sections of streams, usually associated with the shallow margins of water courses (Gillespie 1997). Tadpoles have rarely been found in isolated stream-side pools (Hero et al. 1995; Gillespie 1997)

ReproductionLitoria spenceri has been found between Sept. and May., and calling males have been heard in Oct., Nov. and early Dec. (Hero 1990, 1991; Watson et al. 1991; Gillespie 1993) and Feb. (G. Gillespie in Hero et al. 1995). Clutches consist of 200-1000 eggs (Gillespie 1997). Oviposition sites are in narrow spaces beneath large river stones within the stream and eggs are hidden as they adhere to the underside of the rock (Gillespie 2001a). The seasonal distribution of size classes of frogs and breeding activity (Watson et al. 1991; Gillespie 1993) suggest that eggs are laid in late spring/early summer and tadpoles reach metamorphosis in late summer/autumn (Hero et al. 1995). The tadpole has been described by Hero et al. (1995). At lower altitudes, sexual maturity is reached 18 months and 3.5 years after metamorphosis by males and females respectively (Gillespie 2001a). At higher altitudes, sexual maturity is reached at least 3.5 and 4.5 years by males and females respectively (Gillespie 1997)FeedingAdults appear to be generalist insectivores, feeding on a variety of flying insects (Ehmann et al. 1992; Gillespie pers. obs). Tadpoles are benthic browsers, and appear to graze on filamentous algae, scraping periphyton from rocks, and benthic detritus (Gillespie in press).Invasive speciesTwo exotic fish species, Rainbow Trout Oncorhynchus mykiss and Brown Trout Salmo trutta occur throughout the distribution of L. spenceri and are able to exert significant predation pressure on larvae (Gillespie 2001). Trout are believed to be a major cause of population declines of this species. (Gillespie & Hero 1999; Gillespie 2001). MovementsIndividuals are highly sedentary, not venturing away from the stream, and most adults appear to move less than 80 m over several years (Gillespie 1997).

Declines occurred in the 1970’s and early 1980’s (Watson et al. 1991). Gillespie and Hollis (1996) suggest that, based upon the known demography of the species, this species probably suffered population declines over a wider area earlier in the 20th century, and possibly late in the 19th century. Human disturbances to streams, such as gold dredging, forest roads and recreational pressures are correlated with the general pattern of decline of this species (Gillespie & Hollis 1996). Trout species occur throughout the distribution of L. spenceri and are able to exert significant predation pressure on larvae (Gillespie 2001). Trout are believed to be a major cause of population declines of this species (Gillespie 2001). Several moribund frogs have been located from four populations (Gillespie & Hines 1999) and recently identified as being infected with the chytrid fungus (Berger et al. 1998; Gillespie & Hines 1999). However, the role of the fungus in the population dynamics of this species remains to be resolved (Gillespie & Hines 1999).