Design of aerial surveys for population estimation and the management of macropods in the Northern Tablelands of New South Wales, Australia

As part of a kangaroo management program, eastern grey kangaroos (Macropus giganteus) and common wallaroos (M. robustus robustus) are harvested from three kangaroo management zones in north-eastern New South Wales, Australia. To set sustainable harvest quotas, it is necessary to obtain reasonably accurate estimates of the sizes of the populations of these two species of macropod. Recently, this has been done on two occasions using helicopter line-transect surveys. For the most recent of these surveys, conducted in 2004, each management zone was subdivided into three strata of increasing kangaroo density and the surveys were designed in relation to this stratification using an automated survey design algorithm. The results of the surveys were that eastern grey kangaroo densities were estimated as 8.11 +/- 1.81 km(-2) in the Glen Innes zone, 10.23 +/- 2.41 km(-2) in the Armidale zone and 4.82 +/- 0.87 km(-2) in the Upper Hunter zone. Wallaroo densities for these three zones were 3.06 +/- 0.73 km(-2), 5.68 +/- 3.45 km(-2) and 4.40 +/- 1.01 km(-2) respectively. The wallaroo densities were determined by multiplying the initial estimated densities by a correction factor of 1.85. Across the three kangaroo management zones, eastern grey kangaroo densities did not change in any significant way between the two surveys. This was also the case for wallaroos in the Glen Innes and Armidale zones. Wallaroo density in the Upper Hunter zone, however, increased significantly between the two surveys. Over a decade before these surveys were conducted, a series of ground surveys using walked line-transect sampling were undertaken. The density estimates derived from the helicopter surveys proved to be broadly comparable to those derived from the ground surveys, suggesting that conducting helicopter line-transect surveys designed using the method deployed here is effective in producing population estimates for the purpose of kangaroo management.