Evaluation of line-transect sampling for estimating koala abundance in the Pine Rivers Shire, south-east Queensland
Dique, DS, de Villiers, DL & Preece, HJ 2003, Wildlife Research, vol. 30, pp. 127-133.
Using line-transect sampling to estimate koala density, this study quantifies the abundance of koalas in Pine Rivers Shire, Queensland. Initially, line- and strip-transect sampling were compared in a pilot survey, with both methods providing similar density estimates. Following this result, line transects were established in bushland sites throughout the Shire and 82 koalas were identified. After integrating total count data from urban areas, koala abundance was estimated at 4584.
Pilot survey results demonstrated that estimated koala density was similar for both sampling methods. Using strip-transect sampling, density (koalas/ha) was calculated at 0.76 and 0.73 for line-transect sampling. Strip transects required more than twice the number of person-hours of searching, thus line-transect sampling is the preferred method here. It is acknowledged that accurate density estimates can only be obtained where a large proportion of all individuals are detected during the survey. As a number of koalas are likely to have remained undetected, this unknown proportion was calculated using pooled distance data. Using ArcView GIS, koala distribution and abundance was estimated by extrapolating the density for each survey site across areas of remnant eucalypt vegetation. Eighty-two koalas were identified in bushland surveys, with detection probability shown to decrease evenly across distance classes ranging from 0 to 60 metres. Density estimates ranged from 0 to 0.79 koalas/ha. Fifty-eight koalas were detected during urban site surveys and density ranged from 0.06 to 0.42 koalas/ha. The estimate of 4584 koalas in Pine Rivers Shire is likely to be conservative given that a large area of dispersed food trees in rural/semi-rural areas were not included as areas of remnant bushland.
Accurate estimates of koala abundance are important for conservation and management of the species. These survey findings suggest that, compared to strip-transect sampling, the line-transect method can provide reliable estimates of koala density, with significantly less sampling effort required.
Summarised by Julian Radford-Smith
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