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Feral Pig Impacts and Control

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					                                   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 rainforestcrc@jcu.gov.edu.au




                                                                                          Pest Animal Control CRC
                                                                                          Telephone (02) 6242 1724
                                                                                          Facsimile (02) 6242 1511
                                                                                          Email office@pestanimal.crc.org.au




    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 wtma.reception@epa.qld.gov.au
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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