Management methods under pest institutions

Table 5.2 cites several management methods that are employed in different situations. The main methods used to cull goats for non-commercial purposes under the pest paradigm are briefly presented below. Appendix 3 details goat control methods used for both commercial and non-commercial purposes.

5.2.2.1Shooting

Aerial shooting has been successfully used to control pest species in Australia, including goats (Mahood, 1985; Pople et al., 1996), with an estimated effectiveness of 45–99 per cent in arid and semi-arid areas, especially with the assistance of ground spotters (Bayne

et al., 2000; Parkes et al., 1996). Ground shooting is less commonly used in pastoral areas, as it is labour- and time-intensive and highly dependent on favourable climatic conditions (DEWHA, 2008a).

5.2.2.2Judas goat

A goat fitted with a radio or global positioning system (GPS) collar is released to join a mob of wild goats, as the animals are known for their strong social instincts (Taylor and Katahira, 1988). Like shooting, this method is often used to detect goats at low densities following other wide-range control methods (Parkes et al., 1996; Kimball and Chuk, 2011). It is mostly efficient in difficult terrain or on islands but is not normally used in semi-arid pastoral areas.

5.2.2.3Biological control

Theoretically, the use of microbiological organisms to control goats could be possible. However, so far there is no recognised pathogen that is humane, virulent and specific to goats (Kimball and Chuk, 2011). The other option is the use of vertebrate predators for the control of goat populations, namely dingoes. However, this could be a dangerous approach on pastoral areas and requires careful consideration of its economic and social implications (DEWHA, 2008a).

Other less commonly used methods include poisoning, fertility control, habitat manipulation and sedation followed by removal or shooting. These methods are often not feasible on large-scale operations, and some have never been implemented or developed.

The aims and purposes of institutional control programs, and consequently the control methods used, differ among landscapes and land uses. Often the best results are achieved via integrated approaches that consider local or regional circumstances, the best available options, and, if feasible, the economic interests of primary producers that might be interested in harvesting goats (DEWHA, 2008a). For example, trapping and mustering are the most widely used methods of commercial harvesting (Parkes et al., 1996; Fisher

et al., 2004; DEWHA, 2008a), but is often not enough to reduce goat numbers to desired

levels. Shooting becomes more economical, especially if the goats’ density is low, or they are in rough and densely vegetated areas. For example, in a pilot study in a Mulga woodland landscape within Currawinya National Park, Queensland, Edwards et al. (1997) confirmed that the combination of mustering of the animals followed by aerial shooting to reach target density was the best control strategy. This control strategy effectively reduced the goat population inside the reserve by about 60 per cent.

Solid recommendations regarding rates of harvest or culling are difficult to determine, given the dynamic variability of the goat population, the state of resources, climatic conditions and other factors that might affect the number of goats in the wild. Also, most natural mortality rates and population increases of rangeland goats are confounded with commercial harvesting or culling (Parkes et al., 1996; Kimball and Chuk, 2011). Some reports proposed that goat population can double every 1.6 years without human intervention, and that there is a need for a harvest offtake of around 35 per cent per year (Parkes et al., 1996; Fisher et al., 2004; Kimball and Chuk, 2011) to prevent the growth of the population and keep it within maximum sustainable yield levels—the point at

which the population is maintained (Pickles, 1992). However, this figure was contested in several other reports. For example, Freudenberger and Barber (1999) suggested an 80 per cent reduction level on property level, in a semi-arid woodland in WNSW to effectively keep goat numbers under check. Mahood (1985) suggested that in WNSW, an annual offtake of 42 per cent is required to prevent an increase in goat population. Another notable example is a study by Pickles (1992) in WA. The author indicated that to effectively reduce the numbers of goats, 50–70 per cent of the population must be removed annually. This figure was obtained after the failure to control a feral goat population in WA in the 20 years up to the early 1990s. The study discovered that removal of around 2.5 million head over this period by harvesting for commercial purposes or simply culling and leaving by culling, did not stop an increase in the population. Pickles (1992) argued that a commercialisation policy in the long term preserves rather than eradicates goat populations.

Regardless of the recommended rates of uptake to control goats Australia-wide, there is evidence that the population has increased over the last two to three decades, despite the continuous commercial harvest and non-commercial control efforts. This suggests that the offtake is below the rate of increase (Ballard et al., 2011). Some participants confirmed these findings:

The numbers are still going up. So, the numbers were going up massively even before we weren’t taking large numbers out. We’re taking large numbers out but those numbers are nowhere near the numbers that need to be taken out to even stabilise the population, let alone slow it down. (P25, conservationist/government)

This could be attributed to many factors. Perhaps the most important two are that control measures, including commercial harvesting, are sporadic and opportunistic, rather than continuous, and that non-commercial control methods become inefficient and less cost- effective as numbers decline. Further, because goats often hide in rugged terrain, like rocky cliffs and densely forested areas, it is impossible to fully exterminate their numbers in terrains that are either inaccessible or too dense for successful aerial shooting (Parkes, 1990; Forsyth and Parkes, 2004). Follow-up with ground shooting can be very expensive in these cases, which means that a mob of goats will survive and begin reproducing again.