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The eradication of ungulates (sheep and goats) from Dirk Hartog Island, Shark Bay World Heritage Area, Australia

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Abstract

The eradication of ungulates from offshore islands has now become achievable for island managers, with the size and complexity of an island no longer a major impediment to the desired outcome. Here, we report on a whole-of-island eradication campaign of ungulates (sheep Ovis aries and goats Capra hircus) from the semi-arid Dirk Hartog Island (63,300 ha) off the western Australian coast. The motive behind this campaign was to contribute towards the ecological restoration of this former grazing lease. From 2005, a concerted effort to remove ungulates began with regular destocking, and from 2010 a methodical aerial and ground shooting campaign was undertaken. Long-term commitments of funding and departmental support, staff with diverse skills, and an advisory network of professional people, have been critical components to this large-scale exercise. From 2005 to 2017 a total of 16,318 ungulates (5185 sheep and 11,133 goats) were removed from Dirk Hartog Island: 6839 by mustering, 2422 by ground shooting, 7040 by aerial shooting, and finally 17 by follow-up aerial monitoring and ground shooting. The island was declared free of ungulates in November 2017. To determine the success of the whole-of-island eradication campaign, multiple methods were adopted to locate remaining animals: use of ‘Judas’ goats, monitoring by motion-sensor cameras at water sources and across the island, and recording of tracks and fresh scats to locate any remaining animals. We estimated the likelihood that sheep and goats have been successfully eradicated from the island is 99.9% and 96.9%, respectively. The total cost (AUS$) of the aerial component of the eradication was $1,055,184, an average of $150/goat or $16/ha. The monitoring phase of the campaign (aerial detection and ground shoot) cost the least in terms of actual expenses (approximately $187,000) but the most is terms of cost per remaining goat (approximately $14,400). Ecosystem recovery following the eradication is already apparent with increased vegetation cover and reduced erosion. We conclude with some shared lessons that may assist similar large-scale eradication campaigns of islands. To date, Dirk Hartog Island is the largest island in the world where whole-of-island goat (and sheep) eradication has been achieved.

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Acknowledgements

On behalf of the Department of Biodiversity, Conservation and Attractions, the authors thank Geoff Wardle, former lessee of Dirk Hartog Island, for commencing sheep and goat removal in expectation of Dirk Hartog Island becoming a national park and in allowing the Department early access to his grazing lease to commence ground shooting. We also thank Jock Clough and the Wardle family for allowing their private land on Dirk Hartog Island to be included in the whole-of-island eradication program, and Tory and Kieran Wardle for their hospitality during the aerial shooting operations. We thank Butch Maher for his piloting expertise, and skills in aerial shooting and animal tracking from a helicopter. Aerial shooting was initially made possible through funding from the Australian Government’s Caring for Our Country Program. Ongoing funding was available from the Gorgon Barrow Island Net Conservation Benefits Fund which enabled these eradications to be achieved. The Net Conservation Benefits Advisory Board, Shark Bay District staff and the Dirk Hartog Island Management Committee are thanked for their continued support of this Project. Two anonymous referees provided helpful comments to improve this manuscript, and we thank John Parkes for access to his unpublished database on global island goats and sheep eradications. Finally, we thank Ricky van Dongen for production of the flight path map and access to remote sensing unpublished data related to vegetation recovery.

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Authors and Affiliations

  1. Department of Biodiversity, Conservation and Attractions, 61 Knight Terrace, Denham, WA, 6537, Australia

    Shane Heriot

  2. Department of Biodiversity, Conservation and Attractions, P.O. Box 1693, Bunbury, WA, 6231, Australia

    John Asher

  3. Department of Biodiversity, Conservation and Attractions, Kensington, WA, 6151, Australia

    Matthew R. Williams & Dorian Moro

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  1. Shane Heriot
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Correspondence to John Asher.

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Heriot, S., Asher, J., Williams, M.R. et al. The eradication of ungulates (sheep and goats) from Dirk Hartog Island, Shark Bay World Heritage Area, Australia. Biol Invasions 21, 1789–1805 (2019). https://doi.org/10.1007/s10530-019-01937-7

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