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Hitting the target for eradicating feral pigs on Kangaroo Island

The Black Summer bushfires of 2019–20, that razed more than half of the landscape on Kangaroo Island in South Australia, left an indelible mark on the island's unique native biodiversity, which is still struggling to recover.

However, one big bonus for the environment's recovery is the likely eradication of feral pigs, say ecology and biosecurity experts from Flinders University and the State Government Department of Primary Industries and Regions South Australia (PIRSA).

Invasive feral pigs (Sus scrofa) cause a wide range of environmental, economic and social damages. In Australia, feral pigs occupy about 40% of the mainland and offshore islands, with a total, yet highly uncertain, population estimated at around 13.5 million.

Feral pigs are recognized as a key threatening process under the Environment Protection and Biodiversity Conservation Act 1999, with impacts on at least 148 nationally threatened species and eight threatened ecological communities (Commonwealth of Australia 2017). They are a declared invasive species and are subject to control programs in all Australian jurisdictions.

In a new article in journal Ecosphere, scientists from the Flinders University Global Ecology Lab and PIRSA give optimal strategies for culling feral pigs.

This could be helpful in Australia and wherever feral pigs are a major environmental problem, says lead author Peter Hamnett, a Ph.D. at Flinders University.

"Globally, feral pigs cause extensive damage to biodiversity and agricultural land and infrastructure, so successes like this one are extremely important," he says.

"As well as likely having eradicated pigs entirely, the success of the program was even more astounding when you consider its rough terrain and large size—as Kangaroo Island is Australia's third-largest island at 4,430 square kilometers."

Despite an estimated cost up to $40 billion a year for global management and economic losses of invasive species, reduction and eradication campaigns are often ad hoc, researchers say.

First introduced to the island in 1803, the feral pig population grew exponentially, mainly on the western end of the island where native flora and fauna attracts tourists from around the world. Despite sporadic eradication efforts, the annual cost to farming and the economy has run about $1 million.

Co-author Corey Bradshaw, Professor of Global Ecology at Flinders University and the Australian Research Council Center of Excellence for Australian Biodiversity and Heritage, says, "This is an important result, particularly when many attempted eradications of invasive species are prone to fail. It also was well-timed after the fires on Kangaroo Island already reduced the pig population by about 90%."

The program managed to kill 900 pigs in total, using the most advanced technology, including trapping and thermal imaging from helicopters. Follow-up monitoring is checking whether any pigs remain.

Major investment from the State, Commonwealth and other partners, totaling about $7 million, was another reason the Kangaroo Island program has been successful.

"The paper assesses the costs and techniques that led to success, which will help land managers to select the most cost-effective control methods in the future," says Hamnett.

"The method we applied will support decision-making in future feral animal eradication programs, allowing pest managers to identify the best control methods and estimate expenditure to achieve eradication in a realistic timeframe.

"More effective eradication strategies will give project investors, partners and local communities more confidence and, in turn, attract more support and help."