Modelling African swine fever introduction in diverse Australian feral pig populations

African swine fever (ASF) is a viral disease that affects domestic and feral pigs. While not currently present in Australia, ASF outbreaks have been reported nearby in Indonesia, Timor-Leste, and Papua New Guinea. Feral pigs are found in all Australian states and territories and are distributed in a variety of habitats. To investigate the impacts of an ASF introduction event in Australia, we used a stochastic network-based metapopulation feral pig model to simulate ASF outbreaks in different regions of Australia. Outbreak intensity and persistence in feral pig populations was governed by local pig recruitment rates, population size, carcass decay period, and, if applicable, metapopulation topology. In Northern Australia, the carcass decay period was too short for prolonged persistence, while endemic transmission could possibly occur in cooler southern areas. Populations in Macquarie Marshes in New South Wales and in Namadgi National Park in the Australian Capital Territory had the highest rates of persistence. The regions had different modes of transmission that led to long-term persistence. Endemic Macquarie Marshes simulations were characterised by rapid transmission caused by high population density that required a fragmented metapopulation to act as a bottleneck to slow transmission. Endemic simulations in Namadgi, with low density and relatively slow transmission, relied on large, well-connected populations coupled with long carcass decay times. Despite the potential for endemic transmission, both settings required potentially unlikely population sizes and dynamics for prolonged disease survival.

How many feral pigs in Australia? An update

The abundance of feral pigs in Australia has been estimated previously and been a topic of some debate. This study aims to update a previous estimate of abundance (13.5 million, 95% CI: 3.5 million to 23.5 million) of feral pigs in Australia. Abundance estimates for the 1970s, 1980s, 1990s, 2000s and 2010s were collated from published literature. Mean abundances in the middle decades were estimated using the ratio method. The average abundance of feral pigs varied from 4.4 million (95% CI: 2.4 million to 6.3 million) in the 1980s, to 3.0 million (95% CI: 2.3 million to 3.7 million) in the 1990s, to 3.2 million (95% CI: 2.4 million to 4.0 million) in the 2000s. Mean density across all 142 studies was 1.03 pigs km–2. The average abundance of feral pigs in Australia during the 1980s to 2000s was much lower and more precise than estimated previously, so scientists and managers should update their use of abundance estimates. Density estimates are above, and below, estimates of threshold host densities for infectious exotic disease establishment.

Public attitudes to animal welfare and landholder resource limitations: implications for total grazing pressure management in the southern rangelands of Australia

Sustainable grazing in the nationally iconic southern rangelands of Australia requires landholders to actively manage the grazing pressure from both domestic livestock and non-domestic herbivores. Landholders have primary responsibility for controlling the non-domestic herbivores. In doing so, they must meet the Australian public’s expectations for resource conservation (mainly a public good) and animal welfare. Governments are also involved in the management of non-domestic herbivores via native and feral animal legislation and control programs. The Australian public will not accept cruelty to animals, perceived or otherwise. In this paper we explore the challenges faced by landholders in their attempts to manage the grazing pressure from native herbivores, particularly kangaroos, feral goats and feral pigs, while meeting the Australian public’s expectations for animal welfare. Landholders typically live on extensive properties and their capacity to manage these is influenced by high climate variability, low labour availability, commodity price fluctuations and limited capital available for investment in new technologies. The additional requirement to reduce the grazing pressure from kangaroos, feral goats and feral pigs is a significant burden on already time-poor landholders. Hence, there is a critical disparity between landholders’ capacity and their responsibility to effectively manage the non-domestic herbivores on their properties. We suggest that current expectations of landholders to deliver public benefits by publicly acceptable practices are unreasonable. Further, we suggest that governments should accept more responsibility for managing non-domestic grazing pressure. The concept of duty of care to land management provides a means by which a more appropriate division of responsibilities between landholders and government could be achieved to ensure that valued attributes of this iconic Australian landscape are retained.