Publications archive - Biodiversity
Key departmental publications, e.g. annual reports, budget papers and program guidelines are available in our online archive.
Much of the material listed on these archived web pages has been superseded, or served a particular purpose at a particular time. It may contain references to activities or policies that have no current application. Many archived documents may link to web pages that have moved or no longer exist, or may refer to other documents that are no longer available.
Biodiversity Group Environment Australia, 1999
ISBN 0 642 54634 7
Eradication of feral goats is an attractive prospect because, once achieved, it requires no further commitment of resources. To achieve eradication:
Complete removal of feral goats from Australia is well beyond the capacity of available techniques and resources because the species is well established across a vast area. Eradication from an island, or of a localised or newly introduced population, may be feasible provided a sufficiently coordinated, well-funded and persistent campaign can be mounted.
Parkes et. al. (1996) reviewed current knowledge on techniques for suppressing feral goat populations. The review concluded that the main deficiencies with control programs are associated with decisions on whether to attempt local eradication or strategic management and, if the latter, deciding on the frequency of control activities and the target densities required. In comments on the draft plan, Agriculture Western Australia noted that a lack of resolve on the part of landowners and land managers is the single greatest obstacle to effective management of feral goats.
Although mustering feral goats for slaughter or live sale is labour-intensive and limited to relatively flat terrain (Harrington, 1982), it is most efficient at high goat densities. The advantage of this technique in the context of harvesting is that the cost of control is either partly or fully offset by the sale of the goats. Two methods are used: aerial mustering, using helicopters or light aircraft to flush animals out of dense vegetation or inaccessible terrain, followed up by a ground team; and ground mustering on motor bikes or horseback usually with the help of dogs (Parkes et. al.1996).
The success of mustering in reducing the population can vary greatly from a low of 26 per cent reduction (Brill, pers. comm.) to a high of 80 per cent reduction (Henzell, 1984). In addition to density, effectiveness is also related to the value of a feral goat (Henzell, 1992a) with landholders intensifying efforts when goat prices are high. Parkes et. al. (1996) described a number of management strategies on pastoral land that involved mustering both alone and in combination with several other techniques. When mustering was combined with other techniques using higher levels of technology, progressively lower goat densities were achieved at an increasing cost.
Trapping groups of goats around watering points can be an effective and efficient control technique (Harrington, 1982). It involves the construction of goat proof fences around water points with a number of one way entrances or jump down ramps to allow the goats access to the water, but prevent their leaving (Parkes et al, 1996). This technique is most effective during dry times when goats are obliged to find water and there is limited access to alternative water sources. Once captured, the goats may be sold to offset the costs of capture or they may be humanely destroyed.
Agriculture Western Australia has designed trap yards to efficiently manage livestock at water points and these are particularly suitable for trapping goats. These trap yards are permanent installations that all animals become accustomed to using and are robust enough to contain goats effectively (Geoff Elliot, pers comm). Western Australia has proposed a general strategy to require the installation of such trap yards throughout the feral goat range in that State to ensure a level of control of both feral and domesticated goats.
Some concerns have been expressed about the use of traps at water points and the potential deleterious impacts on non-target species and animal welfare. Some of these concerns can be addressed by providing larger traps to minimise stress and allow for more effective handling of stock. Non-target species may also be trapped and these animals must be drafted out as quickly as possible to avoid undue stress. Trap yards at natural water holes pose special problems as they may severely restrict access by native species. One option suggested by Agriculture Western Australia, is to temporarily close the water source with a fence and provide an alternative water source in a permanent trap yard nearby. An alternative is to design fences that selectively exclude certain species from water points. Knowledge of other species that may be locally at risk from inappropriately designed traps could be used to identify the most suitable trap design and usage.
Fences will not permanently stop the movement of all goats and should, therefore, only be used as a tactical technique in a management program (Parkes, 1990). Fencing can:
Fencing can be expensive to establish. Lim et al, 1992 quoted a figure of $1500 per kilometre for upgrading an existing fence and $3000 per kilometre for construction of a new fence. Agriculture Western Australia have experimented with fence designs to enclose trained goats and these cost $670 per kilometre for material for a five wire electric fence plus approximately $800 per kilometre in construction costs. Six and seven wire fences have also been successfully used and these cost about $1600 per kilometre. Feral goats have been found to respect electric fences, particularly once they have encountered them. Where total exclusion of goats is required, adequate fences are likely to remain unacceptably expensive.
Points to be considered when deciding on fencing an area include the primary purpose of the fence, the area to be enclosed, cost and the position of watering points. To prevent animal welfare problems arising, due consideration must be given to the impact of goat proof fences on access to water by all animals as well as on the movement of native animals.
Ground based shooting is not commonly used as a control strategy for feral goats in the pastoral areas of Australia due to its labour intensity and its variable efficiency dependent upon climatic conditions. A shooting operation in South Australia during a dry period yielded 3400 goats (an unknown proportion of the population) in seven days over 1000 kilometre square at a cost of $3 per goat not including labour (Dodd and Hartwig, 1992). A separate shooting operation conducted following heavy rains yielded only 119 goats in nine days at $774 per goat including labour (Edwards et. al. 1994).
Regardless of the inclusion of labour costs in the second operation, the congregation of goats around water holes during the dry period and their dispersal after rain would undoubtedly have influenced the cost efficiencies of the two operations. It could also be argued that if goats are congregating around water points, cost efficiency would be maximised through trapping and sale rather than shooting, provided water points were accessible to heavy vehicles.
Volunteer shooters have been successfully used to conduct ground shooting as part of the control methods within Bounceback 2000. The success with volunteer shooters in this case has been achieved by having well defined objectives and an effective system of coordinating their activities to maximise the level of control achieved.
Aerial shooting has been successfully used to control different pest animal species in Australia, including pigs (Saunders and Bryant, 1988; Hone, 1990), donkeys (Choquenot, 1988), water buffalo (Bayliss and Yeomans, 1989) and goats (Mahood, 1985; Naismith, 1992; Maas and Choquenot, 1995; Pople et. al. 1996). In pastoral areas this method is mostly used to control inaccessible populations, manage low density populations or remove survivors from other control campaigns (Parkes et al, 1996). It may also be the only technique to achieve broad scale reductions when goat prices are low (Clancy and Pople, pers. comm.). It generally involves using helicopters as a shooting platform with light aircraft occasionally acting as 'spotters'. This method is costly, but allows difficult terrain to be covered quickly and gives culling rates far in excess of other control methods (Lim et. al. 1992). The costs of this technique vary greatly, but tend to rise exponentially with decreasing goat density (Parkes, 1993b; Maas and Choquenot, 1995).
This technique involves attaching a radio collar to a feral goat and releasing it in the expectation that it will join up with other goats. The goat is then tracked down and the herd which it has joined is killed. Judas goats are generally used where there is a low density population; to locate survivors of other control campaigns (Parkes et. al. 1996); and to monitor areas thought to be free of goats (Taylor and Katahira, 1988).
The threat abatement plan for feral goats in Tasmania (developed by the Tasmanian Parks and Wildlife Service) advocates this technique since feral goats in Tasmania occur in small isolated groups in difficult terrain (Gaffney and Atkinson, 1995). However, this technique is expensive as it requires costly equipment and skilled staff. It may be warranted only in areas where extremely low goat densities are identified as being necessary to protect conservation values or where eradication of goats is a feasible option.
Fertility control of wild animals is still at an experimental development stage. In practice, fertility control of wild vertebrates has been achieved on only a very limited scale using expensive, labour-intensive methods (Bomford, 1990). It has not been successfully applied to a free-ranging population of wild vertebrates over a large area. Nor has it been attempted as a method of reducing the impacts of land degradation or competition on an endangered or vulnerable species or ecological community.
Fertility control methods include hormone treatment and the use of abortifacients. The use of contraceptive control through hormone treatment is not considered a viable option for managing feral goat populations as there are no practical methods of ensuring effective treatment of unrestrained animals.
An alternative technique based on developing sterility through an auto-immune response to reproductive proteins or hormones (immunocontraception) has been proposed. This technique has the potential to provide a target specific form of fertility control which can be used on wild populations. Tyndale-Biscoe (1994) argued that if the immunocontraceptive technology can be made to work, it may provide a cheap, easily disseminated method for reducing fertility and populations of some pest species on a continental scale. Some scientists and wildlife managers remain sceptical about the likely success and effectiveness of this approach (Carter, 1995). The obstacles to achieving a workable method are formidable and include:
Major benefits of the development of immunocontraceptive techniques are that they can be made species specific and are humane. Broad scale control of goats using an immunocontraceptive vaccine, if one were developed, would depend on developing a suitable delivery mechanism for the vaccine and obtaining appropriate approvals to release the vaccine into the wild.
In those situations on pastoral properties where feral goats can be effectively trapped and mustered regularly, normal livestock management procedures involving mechanical and surgical sterilisation may be viable options to regulate breeding. Every effort should be taken to convert unmanaged feral herds into managed livestock and to remove animals from refuge areas where they are uncontrollable.
The only poison that has been trialed for feral goat control in Australia is 1080 (sodium monofluoroacetate). The main risk with this technique is consumption of baits by non-target species. Eliminating the risk to native species relies on exploiting differences in the behaviour, ecology and tolerance of this poison between goats and other species (Daly and Goriup, 1987).
Three baiting techniques have been reported: pelletised grain bait (Forsyth and Parkes, 1995); foliage baiting (Parkes 1983); and poisoning of a water supply (Norbury, 1993). Pelletised baits are ineffective, due to feral goats' aversion to eating food off the ground (Forsyth and Parkes, 1995). Foliage baiting works well if only preferred food plants which are baited are accessible (Parkes, 1983). However, it is unsuitable in Australian conditions due to the lack of a highly preferred food plant and the high risk to non-target species (Parkes et. al. 1996). For these reasons it is illegal in all Australian States and Territories. The addition of 1080 to water supplies has been successful in trials conducted in Western Australia. The risk to non-target species was reduced by designing the trough to exclude birds and livestock, and poisoning between 8:00am and 12:00pm to circumvent consumption by macropods (Norbury, 1993). This technique is being used in experimental trials only in Western Australia by certified Agricultural Protection Board Officers under strict regulation.
Control of feral goats using a pathogen may be theoretically possible, but currently none is known to be virulent, humane, specific to goats and not transferable to other species. The potential risks to both the domestic goat industry and other livestock industries from using a pathogen are too high to warrant any research on this approach. Another disadvantage is that animals are likely to develop resistance to the pathogen and such resistance will eventually spread through the species.
Feral goats do not generally occur where there are uncontrolled populations of dingoes (Parkes et. al. 1996). One feral goat population on an offshore island was successfully controlled by releasing dingoes onto the island (Allen and Lee, 1995). It is unlikely that dingoes would be acceptable as a 'biological control' in pastoral areas where most feral goats occur, as predation by dingoes is not a target specific control measure and other livestock would be at risk.
Under the Income Tax Assessment Act 1997 expenditure on preventing and treating land degradation is eligible for a rebate or a deduction. Subdivision 387-A allows for: