Document ID: chunk:federal_register_of_legislation:F2024L00270:body:0:p16
Version: federal_register_of_legislation:F2024L00270
Segment Type: other
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Character Range: 43534–46538

censuses of all individuals have been undertaken since 1996 (Harley 2015a) – its subpopulation in 2023 was reliably estimated to be 34 individuals (D. Harley pers. comm.).
The TSSC (2019) estimated that the population of possums may have exceeded 10,000 mature individuals, but was more likely in the range 2,500–10,000. However, that estimate used a conservative value of three possums per colony and was based on the earlier estimate of approximately 200,000 ha of potential habitat. Given that potential habitat is now estimated to be approximately 300,000 ha, and new records continue to accumulate, the previous estimate is likely lower than the actual population size.
It is useful to attempt to derive an accurate estimate of population size, to better resolve population viability modelling and assessment of conservation status but the actual population size is a less important parameter for conservation management than the population trend, in particular the current and projected rate of population decline.

Priority research needs to enhance management
    * Further investigations to provide a robust and reliable estimate of current total population size, and that of discrete subpopulations.

3.3.2             Rates of current and projected population decline
Population trends are largely influenced by changes in the extent, quality and connectivity of suitable habitat, and such changes are considered in more detail in Section 3.4 Habitat.
Population trends have been described based on population monitoring at some sites, and – more broadly – on population projections based on models of the variation over time in the extent of suitable habitat.
Regular, detailed monitoring of the subpopulation at Yellingbo since 2001 has demonstrated a largely continuous downward trajectory, with total decline over this period of approximately 80% (Harley 2015a, 2023; Figure 3). In 2023, the total subpopulation size was estimated to be 34 individuals (Zoos Victoria, unpublished data). Despite evidence of inbreeding depression in the lowland subpopulation (Zilko et al. 2020), reproductive rates in the wild remain within an acceptable range, with at least 54 young produced at Yellingbo Conservation Area during the past 5 years (since 2018) indicating that the population retains the capacity to increase in size. However, the critically small size of this subpopulation, places it at extremely high risk of local extinction.
Figure 3: Leadbeater's possum subpopulation trend based on estimates of 'Known to be Alive' (KTBA) from long-term nest box monitoring and camera trapping at Yellingbo Nature Conservation Area (lowland habitat)
Source: Harley (2023)
Population counts were made at several sub-alpine woodland sites prior to the 2009 bushfires, and repeated after those fires. For the Lake Mountain area, an estimated subpopulation of 200–300 individuals, based on survey results prior to the fire, was reduced to just six individuals following the bushfire, indicating that the