R code to simulate effect of different culling regimes on feral pig populations on Kangaroo Island, South Australia
Accompanies joint Primary Industries and Regions South Australia (PIRSA) and Flinders University (Global Ecology) Report:
Page, B, CJA Bradshaw, M Korcz, M Tarran. 2021. "Eradication of pigs on Kangaroo Island: updated predictions to inform the probability of eradication. Biosecurity SA, Adelaide
Surveys in February 2021 indicated that feral pigs have recolonised watercourses in remote areas, which are not accessible for trapping and baiting. This report outlines three scenarios to inform the future of the pig eradication program, including two scenarios that require additional investment in thermal-assisted aerial culling. While the native vegetation remains sparse following the 2019–2020 bushfires, thermal-assisted aerial culling is expected to detect 90 per cent of pigs present in areas surveyed, all of which will be culled. This report updates predictions of pig abundance and distribution under three scenarios: (1) no further culling, which results in population recovery in approximately 20 years, (2) thermal-assisted aerial culling in 21,000 hectares of the high-quality pig habitat once per year for three years, and (3) thermal-assisted aerial culling in 145,000 hectares (total pig-infested area) once per year for three years. The models decisively indicate that an additional investment of $1.8 million into thermal-assisted aerial culling would eradicate pigs from Kangaroo Island, including one year of surveys to demonstrate proof of freedom. Accordingly, Scenario 3 is the preferred option, because it is the only one that is likely to achieve eradication. This scenario predicts eradication with 100 per cent probability after 2 years (as shown in light grey on the graph below, with confidence limits spanning 1.5 to 2.25 years). The additional cost of thermal-assisted helicopter culling for Scenario 3 is $1.8 million; with $600,000 of that used to confirm eradication in the third year (minimal or no culling is predicted to be required in the third year). Accordingly, between $1.2 and $1.8 million additional funding is required to eradicate pigs from the island.
Prof Corey J. A. Bradshaw
Global Ecology, Flinders University, Adelaide, Australia
March 2021
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