ISSUE 1 JUNE 2003 Feral Pig Impacts and Control Issues in Tropical Forest Landscapes Feral pigs pose ecological, economic and disease threats to around 40% of the Australian mainland, with population estimates ranging from 3.5 to 23.7 million. In the Wet Tropics bioregion population density ranges from 3.1 pigs per sqkm in the World Heritage Area to 2 per sqkm outside the listed area. These feral pigs are a possible host for foot and mouth disease – a potential disaster for Australia’s $14 billion agricultural industry. It is estimated an outbreak would have an immediate $6 billion impact and cost $8 million a day. It may be extremely difficult to eradicate this disease if it were to establish in a feral pig population, particularly in inaccessible terrain. This issues paper looks at the current state of knowledge of feral pigs, principally in the Wet Tropics bioregion, the effectiveness of current control methods, management problems and the possibilities of emerging biotechnology solutions. Feral pigs were Feral Pig Impacts Introduced into Australia by early and flexible activity patterns allow listed as a European settlers, the feral pig is feral pigs to range widely across a mobile, social animal with very habitats. These include subalpine high reproductive potential that grasslands and forests, dry threatening prospers in response to woodlands, tropical rainforests, environmental opportunities and semi-arid and monsoonal a lack of natural constraints such floodplains, swamps and other process under as disease and predators. Human wetlands. attitudes to this animal vary from Research suggests that digging the Environment regarding them as a resource, activity decreases seedling such as a sport animal or meat survival rates in moist microhabitats export, to considering them a by as much as 36 %. Rooting by Protection and serious pest animal threat or pigs in soil along roadsides and potential agent of disease. streams, and the sight of pigs Biodiversity Feral pigs prey on and compete themselves, is a significant with a range of native plant and aesthetic impact in pristine and Conservation Act 1999 largely because of their role in modifying habitat across as much as 38% of the Australian continent. Evidence of the rooting damage caused by feral pigs. (photo: Jim Mitchell DNRM) animal species, and almost beautiful environments like the certainly contribute to the spread Wet Tropics World Heritage Area. of weeds and exotic fungi. The Feral pigs use their powerful snouts most obvious ecological impacts to root up moist areas, selectively are in the area of habitat feeding near roads and tracks degradation, predation and looking for fruit and seeds, leaves disturbance. Signs of pig activity and stems, bulbs, tubers, fungi, include patches of grassland or soil invertebrates and insects. Such forest litter rooted up in the search disturbance can damage soil for food along drainage lines, in structure resulting in erosion, affect depressions, and around grassy plant succession or play a role in flats. Disturbance of soil in these dispersing exotic plant seeds. habitats may affect ecosystem Studies are needed on the effects processes and water quality. of pigs on the demography of potentially vulnerable species A large robust body, a snout such as cassowaries, ground- specifically developed for rooting nesting birds, endemic up the ground, omnivorous diet Researcher Jim Mitchell using radio tracking equipment to find feral pigs regions. While group sizes range and endangered animal and from 1-12 up to 40-50, depending plant species. Current stomach on the season and location, it is and faecal sampling found plant not unknown for groups of 100 material in 100% of subjects. individuals to gather around Earthworms are the most waterholes in the dry season. common source of animal protein in the Wet Tropics region. Essential requirements for The pig diet has been found to permanent populations include include: centipedes, beetles and A captured male feral pig. water, shelter, and suitable food. other insects, snails, frogs, lizards, Pigs are opportunist omnivores, the eggs of the freshwater preferring a diet of carrion, earthworms, or stream-dwelling crocodile, Crocodylus johnstoni, earthworms, a wide variety of frogs. There is also some evidence turtles and their eggs. animals, succulent green that pigs cause the spread of feral earthworms. Perceptions of “the pig problem” vary. Pig hunting is a significant recreational activity, generating economic benefits. Hunting feral pigs for human consumption by Indigenous communities helps to maintain rainforest traditions and connection to country. To date pig control has been expensive. While pigs are responsible for crop damage, there is some industry acceptance that they play a role in controlling fruit fly in banana plantations. It is conceivable that a cost-effective population threshold exists below which the impacts could be tolerated and their services accepted. Discovering this threshold and evaluating the cost of holding a population below it could only be achieved by large-scale experiments. Pigs on the move. (photo: Jim Mitchell DNRM) Ecology vegetation, fruit and grain. The Movement patterns energy requirements of pigs are Contrary to general community Populations also relatively high, particularly in perceptions research has sows in the last month of Pigs have the capacity for rapid produced no evidence of large- pregnancy and lactation. Feral population increase. Female pigs scale seasonal movements of pig population growth in Australia breed all year round with birth feral pigs in the Wet Tropics is most commonly limited by numbers peaking in January, or bioregion. Surveys suggest periodic protein shortages like at the start of the wet season. On landholders believe feral pigs those found in the dry season. average, pigs have 1.64 migrate from highlands to pregnancies a year, with litters Diet averaging 6.4 individuals. The first litter is likely when a sow reaches Research is underway to quantify a weight of 20kg if the individual what effect feral pigs have on is under 18 months, and at 25-30 threatened species. kg if older. Mean litter mortality in Measurements of length and the first year is 50%, rising as high weight and biological data as 81%. Research suggests feral collected from stomach and pigs in the Wet Tropics rainforest faecal analyses will be used to environments have faster growth produce a detailed picture of rates and are, on average, feral pig dietary preference. There heavier than pigs in dry tropical is a perception pigs threaten rare Signage in the Wet Tropics World Heritage Area. lowlands in the dry season to costing $141 for every pig caught. Disease forage in ripening sugar cane Contract trapping cost $209 per and banana crops, returning in pig capture, dogging cost $257 Feral pigs carry a range of the wet season after harvesting. per pig and shooting $1,048 per diseases of high importance to Home range studies have animal. public health and are potential revealed most pig populations hosts of exotic animal disease are located in transitional areas plagues like foot and mouth and such as the rainforest-crop Indigenous perspectives swine flu. Exotic diseases carried boundary. Males have a larger by feral pigs include screw worm A Central Land Council study on mean home range (8.95sqkm) fly, Japanese Encephalitis, the perspectives of Indigenous than females (2.35 sqkm) and Cysticercosis and Trichinosis. people on feral animals found a both have a larger mean home marked difference between the Endemic diseases include range in the dry season (9.94 Aboriginal and non-Aboriginal Tuberculosis, Brucellosis, sqkm) than the wet season (3.1 views on animals such as feral Leptospirosis, Meliodosis and sqkm). There is some evidence pigs. Feral pigs are highly Sparganosis. pigs are not territorial and do not regarded as a food source for defend an area, preferring groups Aboriginal people and provide of up to 30 individuals, based on an outlet for the maintenance of Phytophthora cinnamomi a matriarchal structure of related aspects of traditional culture. The There is growing evidence feral females and young at foot in a question of “what should be done pigs may help spread the root home range that overlaps other about pigs”, creates one of the fungus Phytophthora cinnamomi, groups and individuals. points of difference between which is responsible for dieback Indigenous and non-Indigenous disease in native vegetation. Economic Landholders regard pigs as a significant agricultural pest, controlling numbers according to the perception of negative economic impacts. Recently completed work for Queensland Department of Natural Resources and Mines found that in the Wet Tropics pig damage costs $300 for every 1000 cartons of bananas and $813 for every 1000 tonnes of harvested cane. This research used an average yearly figure estimated from harvest returns, finding $828 worth of damage per banana farm and 3.5% or $5,352, rising to 5.6% Wallowing is typically how feral pigs pick up diseases and infected plant and soil material. or $8,515 per farm in the sugar (photo: Jim Mitchell DNRM) cane industry. Sugar cane in the Wet Tropics is perspectives. Because Aboriginal There is no evidence pigs spread predominately grown close to communities regard feral pigs as this fungus by eating infected feral pig habitat. Damage, such a resource, they have difficulty material, but there is growing as trampling of young cane and with any management options evidence the organism is carried physical destruction to paddocks, that favour eradication. For some in soil on hooves. Pigs could also is severe in some locations, Aboriginal peoples the effect of carry infected material on other ranking third after cane grub and pigs on bush tucker – digging up parts of their body, particularly rat damage. of turtle eggs, yams, bulbs, water after wallowing during warmer lilies – is an issue. Further research conditions when the fungus Total on farm pig damage and into the impacts of feral pigs on produces spores. The spread of management costs were $4,099 Aboriginal economic and the fungus has also been for each banana farm and ecological life is needed if new associated with soil disturbance $10,632 for each cane farm control programs are to be and reduction of litter cover. Pigs annually. Landholder trapping properly assessed. also chew or tusk the bark on was found to be the most buttress roots and lower trunks of effective control technique, trees, which might allow the entry of fungi. Management landholders. Friction exists • Poison baiting is regarded as Considerations between some sectors of the the most effective method of community and government quickly reducing feral pig Unless pig populations are over the efficiency of current numbers. However, baits may reduced by 70% or more, control measures. Wet Tropics be taken by other species and recovery to pre-control levels is Management Authority research are therefore not a preferred likely within two years. Rates of indicates adjacent land holders method of pig control in the increase can vary according to demand government agencies region. the availability of protein sources take responsibility for pig control, • Fencing can be effective for and are generally dependent on because they regard areas small, critical areas but the rates of first-year mortality and protected in the 1988 World most successful pig-proof mortality in the weaning phase. Heritage listing as breeding fences are the most expensive grounds safe from outside with high maintenance costs. disturbance. Control Programs The Community Based Feral Pig Current options for reducing pig Trapping program is an example The capacity to produce populations in the Wet Tropics are of land managers and primary maximum population reduction limited. Many control methods producers working together to over a short period of time is have been attempted: deal with a mutual problem. clearly fundamental to effective • Advances in trap design and Funding for the program came control. Currently, reductions to trapping techniques have principally from Wet Tropics population numbers of between proven to be the most Management Authority, Natural 60% and 80% are most common. effective method of catching Resources and Mines, Natural Failure to control pig populations large numbers of pigs in the Heritage Trust and Queensland below 30% allows pre-control region, and trapping is Parks and Wildlife Service, with numbers to return within two years. Poisoning, trapping, shooting from the ground or from helicopters and dogging are the most common techniques used in Australia to manipulate feral pig populations. Reductions of up to 100% have been recorded in favourable environments. Controlling pigs in the Wet Tropics World Heritage Area Feral pigs have become established and wide-ranging in the Wet Tropics World Heritage Area, presenting a major management question for the region. Community perception is that pigs have a negative impact on the conservation values of the (photo: Jim Mitchell DNRM) World Heritage Area, but very little quantitative information on their ecological impact is available. A becoming more widely minor funding from a range of significant relationship between accepted. A pig specific gate other sources. The pig trapping pig diggings and rainfall has been trip mechanism has been program has caught over 15,000 established and while only a small developed to minimise the risk pigs, but this count may not area of the region is affected, of trapping non-target native include trapping done by some those microhabitats experience species such as cassowaries private land owners. Trapping by intense disturbance, particularly and wallabies. landholders themselves was the as the soil dries at the end of the • Shooting and hunting with cheapest trapping option. While wet season. dogs have been commonly the trapping program has had used to control pigs. While minimal effect on pig populations The Queensland Parks and they may be effective in dry in the region, it has been Wildlife service is the government seasons when pigs are successful at reducing pig land manager responsible for the congregated at available damage in local areas and has Wet Tropics World Heritage Area, waterholes, there are strict been a benefit to farmers. Cairns controlling over 76% of the region controls over the use of City Council has also had some as either state forest, timber firearms in protected areas success with baiting of pigs in the reserve or national park. The and shooting is ineffective in Copperlode Dam area. burden of responsibility on private rainforest areas. land rests with individual CONTACTS CRC Research Telephone (07) 4042 1246 Facsimile (07) 4042 1247 Email firstname.lastname@example.org Pest Animal Control CRC Telephone (02) 6242 1724 Facsimile (02) 6242 1511 Email email@example.com A palm seedling uprooted by feral pigs looking for food. (photo: Jim Mitchell DNRM) Wet Tropics Management Authority Telephone (07) 4052 0555 particularly one that may have Facsimile (07) 4031 1364 Biotechnology market ramifications. Economic Email firstname.lastname@example.org Biotechnology may increase the consequences such as effectiveness of existing compensation would make REFERENCES management programs by genetic modification less Blinkhorn, R. (2002) Department of Natural providing researchers with an attractive. Resources and Mines Feral Pig Management understanding of the chemical Strategy Workshop, 19-20 June 2002. signals that influence pig Operations support, Parks Division, QPWS. Achilles Heel Choquenot, D., McIlroy, J.C. and Korn, T. (1996) behaviour. An Achilles Heel is a small but fatal Managing Vertebrate Pests: Feral Pigs. Bureau The Pest Animal Control CRC of Resource Sciences. Australian Government weakness. Research into an Publishing Services, Canberra. estimates that it would cost in the Achilles Heel solution in feral pig order of $12 to $20 million to take Cooperative Research Centre for Biological physiology is underway and may Control of Pest Animals (2002) Cooperative a biotechnology solution to pig be found among particular Research Centres Program 2002 Selection control from proof-of-product metabolic responses to drugs, Round. Pest Animal Control CRC, Canberra. stage to an on-the-ground pesticides or carcinogens and Hone, J., Pech, R.P., Robinson, A. and Tidemann, solution. These figures suggest their toxicity or within its blood, C. (2000). The management of wildlife diseases shorter-term research and hormone or digestive system by vaccines: objectives, strategies and development and control research needs. University of Canberra, CSIRO responses. and ANU. Canberra, June 2000, 10 pp. programs may provide a more secure investment than either Johnson, C.N. (Ed.) (2001) Feral Pigs: Pest Status and prospects for Control: Proceedings of a virally-vectored or bait delivered feral pig workshop, James Cook University, immunocontraception. Cairns, March 1999. Cooperative Research Centre for Tropical Rainforest Ecology and Fertility Controls Management. Cairns. Mitchell, J.L. and Dorney. W. (2002) Monitoring Research has established a virally Systems for Feral Pigs: Monitoring the Economic vectored anti-fertility vaccine is Damage to Agricultural Industries and the technically possible. Population Dynamics of Feral pigs in the Wet Tropics of Queensland. Final Report to Bureau More community consultation is of Resource Science National Feral Animal needed to establish whether Control Program. Department of Natural genetic modification is Resources and Mines. Queensland. acceptable. The domestic pig Peacock, A. J. (2003) Virally Vectored Immunocontraception is not a viable option industry may need to take for Feral Pig Control. Pest Animal Control CRC. protective action but is unlikely Canberra. to accept added cost, Pech, R.P. and Hone, J. (1988). A model of the Researchers weigh a captured feral pig. dynamics and control of an outbreak of foot and mouth disease in feral pigs in Australia. Journal of Applied Ecology, 25: 63-77.
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