Predation, habitat degradation, competition and disease transmission by feral pigs
Advice to the Minister for Environment and Heritage from the Threatened Species Scientific Committee on a public nomination of a Key Threatening Process under the Environment Protection and Biodiversity Conservation Act 1999
1. Name and description of the key threatening process
The nomination is titled 'Recognition of feral pigs as a Threatening Process: Predation, habitat loss and competition'. Information on the impacts of predation, habitat loss, competition and disease transmission by feral pigs is included.
The nominator believes the title 'Feral pigs' is adequate.
To date the list of key threatening processes has included the whole process attributable to a feral species, rather than just the species name eg. 'Predation by feral cats', 'Competition and land degradation by feral goats'.
TSSC therefore recommends this threatening process be titled: 'Predation, habitat degradation, competition and disease transmission by feral pigs'
The following description is based on that provided in the nomination:
'Predation, habitat loss, competition and disease transmission by feral pigs' includes the impacts on native ecosystems, flora and fauna due to the presence of feral pigs (Sus scrofa), their movement, rooting, wallowing, trampling, tusking or rubbing trees, and consumption of water, animals, plants and soil organisms. Feral pigs are found in all states of Australia, particularly in association with wetlands and riparian ecosystems. Ecological parameters affected include species composition, succession, and nutrient and water cycles. Impact can be direct or indirect, acute or chronic, periodic or constant, and may be seasonally influenced.
Feral pigs consume bird chicks, reptiles, reptile and bird eggs, frogs, soil organisms, earthworms and other invertebrates, carrion, fruit, seeds, roots, tubers, bulbs and plant foliage. Habitat changes due to feral pigs include: destruction of plants; changed floristic composition; reduced regeneration of plants; alteration of soil structure; increased invasion and spread of weeds; increased access for other predator species; reduced amount and quality of water available; spread of exotic earthworms; and creation of habitat suitable for disease vectors. They provide reservoirs for endemic diseases, can be vectors of exotic diseases, spread the root-rot fungus Phytophthora cinnamomi, and physically damage plants, providing entry points for infection.
2. How judged by TSSC in relation to the Environment Protection and Biodiversity Conservation Act 1999 criteria
A. Could the threatening process cause a native species or an ecological community to become eligible for listing as Extinct, Extinct in the Wild, Critically Endangered, Endangered or Vulnerable?
B. Could the threatening process cause a native species or an ecological community to become eligible to be listed in another category representing a higher degree of endangerment?
The nomination and additional information recognise both that the effects of feral pigs on native species and natural ecosystems are not clearly defined or easily measured, and that there are few quantitative data on actual impacts. The nomination and expert opinion contains information on known and potential adverse effects on a range of species, but no information on the potential for any native species (listed or unlisted) to be listed in a category representing a higher degree of endangerment.
C. Does the threatening process adversely affect 2 or more listed threatened species (other than conservation dependent species) or 2 or more listed threatened ecological communities?
Feral pigs have been identified, in the relevant recovery plans, as known or perceived threats to sixteen listed species. Of these species:
- thirteen are Endangered - Red-finned Blue-eye (Scaturiginichthys vermeilipinnis), White-bellied Frog (Geocrinia alba), Southern Corroboree Frog (Pseudophryne corroboree), Southern Cassowary (Casuarius casuarius johnsonii), Northern Bettong (Bettongia tropica), Long-footed Potoroo (Potorous longipes), Caladenia elegans, Caladenia winfieldii, Eriocaulon carsonii, Phaius australis, Phaius tankervilleae, Pterostylis sp. Northampton, and Ptychosperma bleeseri; and
- three are Vulnerable - Orange-bellied Frog (Geocrinia vitellina), Hawksbill Turtle (Eretmochelys imbricata) and Black-breasted Button-quail (Turnix melanogaster).
In addition, feral pigs adversely affect two of the threatened species included in the nomination: the Eastern Bristlebird (Dasyornis brachypterus), listed as Endangered; and the Flatback Turtle (Natator depressus), listed as Vulnerable. Habitat damage and possible disturbance to breeding are primary threats to the northern subspecies of the Eastern Bristlebird. Egg loss due to feral pig predation is a source of impact to the Flatback Turtle.
Conclusion: Based on the evidence provided and summarised above TSSC considers that the threatening process adversely affects at least eighteen listed threatened species, including: two mammals (Northern Bettong and Long-footed Potoroo), three frogs (White-bellied Frog, Orange-bellied Frog and Corroboree Frog); three birds (Southern Cassowary, Black-breasted Button-quail and Eastern Bristlebird); one fish (Red-finned Blue-Eye); two turtles (Hawksbill Turtle and Flatback Turtle); and seven plants (Caladenia elegans, Eriocaulon carsonii, Phaius australis, Phaius tankervilleae, Pterostylis sp. Northampton, Ptychosperma bleeseri and Caladenia winfieldii) and is therefore eligible under this criterion.
Conclusion: The threatening process meets s188(4)(c) of the EPBC Act. Predation, habitat degradation, competition and disease transmission by feral pigs adversely affects at least eighteen listed threatened species.
3. Threat Abatement Plan
The nomination recognises that the total eradication of feral pigs throughout Australia is impossible with the control techniques currently available, and that resources will never be sufficient to deal with all feral pig problems. However, the nomination suggests that a national Threat Abatement Plan could: ensure the strategic allocation of resources; coordinate and integrate existing work; target threatened species management; allow implementation of control techniques at high conservation value sites; and collect information to improve our understanding of feral pigs and their impacts.
Expert opinion indicates that a national Threat Abatement Plan for feral pigs is desirable, and that the plan should consider the following issues:
- socio-political concerns due to the commercial market;
- the likely significant cost of threat abatement;
- general difficulties with control methods due to conflicts with commercial values; and
- new pig colonisations and the spread of Phytophthora cinnamomi infestations.
Conclusion: A Threat Abatement Plan is considered to be a feasible, effective and efficient way to abate the process.
The TSSC recommends that:
- the list referred to in section 183 of the EPBC Act be amended by including in the list as a key threatening process 'Predation, habitat degradation, competition and disease transmission by feral pigs', as described in this advice.
- a Threat Abatement Plan is a feasible, effective and efficient way to abate the threatening process.