Management of Invasive Species in Christmas Island, Australia

8/13/20232 min read

Christmas Island, located just south of Java (Indonesia) between Singapore and Perth (Western Australia), is a protected area under the Environment Protection and Biodiversity Conservation Act 1999 (DCCEEW a). Its fascinating biodiversity, including “red crabs, sea birds, whale sharks, and spectacular coral reefs”, has earned it the sobriquet of the ‘Galapagos of the Indian Ocean’ (Tourism Australia), and more than two thirds of its 85 square kilometre area constitutes the Christmas Island National Park (DCCEEW b).

The core biosecurity challenges currently being encountered in Christmas Island with regard to invasive alien species (“IAS”) are those posed by the yellow crazy ant (Anoplolepis gracilipes) (“YCA”), feral cats (Felis catus) (Willacy et al 2023) and black rats (Rattus rattus) (Willacy et al 2023) (DCCEEW c).

Super-colonies of YCA present the greatest threat to Christmas Island's red crabs and robber crabs, of which they have destroyed tens of millions to date (DCCEEW c; Invasives Species Council 2017). The cats on Christmas Island are predators of endemic reptiles, seabirds who nest on land, flying foxes, and forest birds, while rats feed on the eggs of native wild birds (DCCEEW c).

In response to these aforementioned challenges, the key biosecurity strategies and polices have been put in place in relation to the YCA include period surveillance and mapping of the spread of YCA colonies; aerial baiting wherever topographically possible; and management of the scale insect population, being YCA's primary food source (DCCEEW c).

As for cats, there have been ongoing baiting, trapping, de-sexing, and prohibition of entry of new domestic cats (DCCEEW 2014). Feral cats have also been removed from the island (DCCEEW 2011). However, despite these and other multi-stakeholder efforts, the management of cats and rats continues to plague Christmas Island and its authorities (DCCEEW c).

The above strategies could be enhanced, as regard the YCA, by deeper pathway and risk analysis, more stringent biosecurity measures before and at the Australian border, risk-based surveillance, and a full evaluation of all YCA colonies (Invasive Species Council).

It could also be prudent to formulate a more detailed and broader ecosystem management strategy which considers the complex network of relationships between black rats and all native species, so as to track eradication milestones, determine appropriate triggers for action by authorities, and optimise monitoring costs (Willacy et al 2023).

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