Introduction Of Pigs Into Australia

Published Date: 02 Nov 2017

Introduced species are the greatest threat facing agriculture in Australia. Many organisms have been introduced to the Australian Land and many of these introduced plants and animals harm or have negative effects on the environment and on the native species. Feral Pigs (Sus Scrofa) will be the basis of this essay. Feral pigs have been in Australia for over 200 years now and continue to be a national pest. The Australian environment was unfamiliar to early Europeans who didn't know what was safe to eat, so pigs were brought to Australia as a food source in the 1800's. Feral pigs are descendants of a variety of introduced species of pig that became feral. There is now an estimated population of around 23 million individuals Australia wide. They are mainly located across the top of the Northern Territory and throughout Queensland. Many Australian ecosystems are complex and can be easily damaged and affected by feral pigs. Pigs, being omnivores, can eat an extensive array of different food sources including such things as crocodile eggs, roots and even ground nesting birds. The damage feral pigs cause is not limited only to the wildlife, pigs destroy vegetation by rooting and wallowing around swamps and watercourses which causes native habitat destruction and erosion. Feral pigs also spread weeds and transmit disease such as leptospirosis and foot and mouth. This essay will answer the questions of; what science is doing to help reduce this species, how the native organisms of Australia are being affected by the feral pig population, whether the treatments are affective and how they are impacting the environment.

History and Distributionhttp://www.feral.org.au/wp-content/gallery/feral-pig-distribution-national-map-200607/FeralPig_Nat0607.png

The Australian feral pig is a descendant from various breeds of Sus Scrofa, the domesticated pig (reference). There is some indication in the north of Australia that a number of other pig species were also brought here including Sus Celebenis and Sus Papuenis(reference). According to records, European settlers aboard the First Fleet brought domesticated pigs to Australia as a food source in the 1800's (reference). Pigs were transported around the country quickly by the 19th century settlers and were kept in unrestrained and semi feral conditions. Individuals could easily wander and escape and quickly established wild populations. Truly feral colonies eventually became established by the 1880's, their spread mainly along watercourses and flood plains reached such numbers that they became considered a pest in parts of New South Wales. Feral Pigs can now be found across 38 percent of the Australian continent. They are now widely distributed across Queensland, the Northern Territory, the Australian Capital Territory and the western parts of New South Wales (as shown in the diagram). There are also some isolated populations that occur in Western Australia and Victoria. Between years the abundance and distribution of feral pigs fluctuates depending on environmental conditions and the availability of sufficient food and water.

Environmental Impacts

The environmental impact of feral pigs takes one of two forms: direct damage to animal species or damage to habitat. The degree of environmental damage that feral pigs cause can be hard to measure. The most obvious form of damage by feral pigs is environmental degradation. It is well known that feral pigs have a negative impact on the native ecological systems in Australia. These include changing species composition, disrupting species succession and by the alteration of nutrient and water cycles. The impacts may be periodic or constant, direct or indirect depending on the seasonal conditions. The digging and rooting behaviour associated with feral pigs effectively uproots and destroys riparian vegetation and native ecosystems. This type of behaviour leaves these areas susceptible to the establishment of weeds, soil loss and the spread of diseases such as dieback (Phytophthora cinnamomi) through native vegetation. The congregation of feral pigs is usually in accordance with the presence of water as pigs are highly susceptible to heat. The foraging and rooting behaviours of feral pigs has been closely linked to areas of high soil moisture. Rooting and wallowing around the fringes of swamps and water basins destroys the vegetation that helps to prevent erosion and provides a food and nesting source for native Australian wildlife. The regeneration of plants can also be disrupted by rooting. Feral pigs also contribute to vegetation destruction by the way in which they find their food, being an ungulate they trample the vegetation while foraging. Pigs are known for the ability to feed on most parts of a wide array of exotic and native plants. Softer higher energy parts, fruits and tubers are usually preferred when feeding. The feral pig population also aides in the dispersal of weeds through the passing of seeds in dung. The non selective feeding behaviour of feral pigs also affects the biodiversity of native vegetation and adds to the competition for food resources for native organisms. Although the competition with other native animal species has not yet been proven there is mounting evidence suggesting that pig populations may be competing directly with specialist feeders such as Magpie geese (Anseranas semipalmata), cassowary (Casuarius casuarius) and the Brolga (Grus rubicundus). It is not only native vegetation that the feral pig populations have a negative effect on. Feral pigs being opportunistic and omnivorous will scavenge and prey on birds eggs, amphibians, invertebrates as well as reptiles and small mammals. Some areas where pigs are found have seen the disappearance of many bird species including the endemic woodhen. Due to degradation, competition, predation, habitat loss and disease transmission feral pigs have been listed as a Key Threatening Process under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC).

Agricultural

There are 3 types of economic impacts caused by pigs;

1. The price of the direct losses to agricultural production.

2. The continuing cost of pig control.

3. Value of lost opportunities to make profit from alternative investment of these costs.

Feral pigs have a significant and detrimental effect on the agricultural industry. There are numerous types of agricultural damage that feral pigs are responsible for. Feral pigs can prey on newborn lambs which poses a significant problem for a lot of sheep graziers. Losses of between 15% - 38% have been reported. Lamb production in Australia is critical to the overall viability of the wool growing enterprise because almost all flocks are self replacing. A broad genetic flock is relied upon by most graziers in order to supply commercially important wool traits. Also an important source of cash flow is obtained through the sale of excess lambs. Goat and lamb predation has become so serious that large areas of land infested with pigs have become unsuitable for sheep farming. Lamb production is not the only source of agricultural damage caused by feral pigs. The feral pig population also has a large impact on the grain industry. Pigs consume grain and trample plants to gain access to the centre of crops. Tisdell (1995) had an estimate that the impact overall of feral pigs on grain crops 1990-91 was approximately $105 million. The wheat industry had the greatest impact, $86 million worth from New South Wales and Queensland alone. It also saw significant losses in sorghum crops of up to 5%. Pigs ,being omnivorous, also pose as competition to domestic livestock. Pigs root up and eat pasture which could also be used by stock to grow wool or meat. There are numerous indirect effects that pigs have on livestock productivity by changing the composition of pastures ultimately degrading quality. On average on introduced pastures rooted areas had green feed reductions by as much as 74% and dry matter reductions by as much as 34%. This also coincided with an increase in weed species. At present there are no reliable estimates to attribute the costs of feral pig damage to agricultural production in Australia, but it is likely that it is around $100 million annually but it may be considerably more depending on seasonal variations. The constant control of feral pigs also adds to the cost for landholders.

Disease

The feral pig poses a serious threat to human health and Australia's livestock industries through the potential of being either a carrier or amplifier of many exotic and endemic diseases. The threat of an exotic disease outbreak, for example Foot and Mouth Disease, has led to increased management to control feral pigs. If such a disease entered the feral pig population it could prove costly and difficult to remove. Some diseases that pose the greatest threats are in a table below.

Potential Diseases carried by Sus Scrofa (feral pig)

Endemic

Exotic

Murray Valley Encephalitis

Rabies

Brucellosis (Brucella suis)

Swine Vesicular Disease

Leptospirosis (Leptospira spp)

Trichinosis

Melioidosis (Pseudomonas

pseudomallei)

Foot and Mouth Disease

(FMD)

Tuberculosis (Mycobacterium spp.)

Screw-worm Fly infestations

Porcine Parvovirus

Classical Swine Fever

Sparganosis (Spirometra erinacei)

Japanese Encephalitis

Of the above mentioned diseases, the greatest threat posed to Australia's economy is Foot and Mouth Disease (FMD). According to research conducted by Dr Jonathon Lee (1996) an outbreak of Foot and Mouth Disease would cost more than $3 billion nationally and if it were to persist it could cost between $0.3 - 4 billion annually. Foot and Mouth Disease would have devastating effects on the live stock industries throughout Australia in particular if it was introduced through Cape York, where eradication and early detection would be near on impossible. The Australian Veterinary Emergency Plan(AUSVETPLAN) is a national approach to exotic disease management formulated by the Commonwealth and The Department of Primary Industries .

Control/Regulation

The responsibility of the reduction of feral pig densities on properties rests with the land owner/manager, whether this is a private land holder, indigenous group or park ranger. In order to suppress the growth potential of feral pigs the population must be knocked down by 70 % or more. In Australia there are numerous techniques available for the control of feral pigs. There are 4 main techniques used to control feral pigs; trapping, fencing, recreational hunting and the main one baiting. Baiting is considered to be the most cost effective and efficient way of controlling feral pigs in Australia. The poison of choice, 1080 (Sodium Monofluroacetate), is one of two products registered for use in Australia to control feral pig populations. 1080 poison is found in many native plant species therefore some native animals have somewhat of an inbuilt tolerance to it, it also degrades readily in soil. It is these attributes that make 1080 poison suitable for general use. 1080 poison has its draw backs as well, it is highly toxic to dogs and has no known antidote, secondary poisoning can occur via animals consuming carcasses. 1080 poison can be used with meat, grain, pellets or vegetables as bait material. The rates of success for baiting vary, with population reductions ranging from 99.4% to 58%. Baiting success also varies with operator experience and the incidence of feral pigs vomiting after the ingestion of 1080. Feral pig vomiting behaviour may reduce the effectiveness of the current poisoning campaigns and could eventually lead to bait shyness for the future campaigns.

Conclusion