Eradication of feral cats from Tasman Island
Tasman Island off the coast of Tasmania. Image - Grant Norbury.
Tasman Island forms part of Tasman National Park off the coast of Tasmania. The island comprises 120 hectares of plateau and very steep cliffs and boulder fields. It is home to Australia’s largest population of fairy prions. Despite such status, Tasman Island was, until very recently, also home to an estimated population of 32–50 feral cats that colonised the island about 70 years ago. It has been suggested by Tasmanian Parkes and Wildlife Service staff that the cats may have killed approximately 50,000 fairy prions and other seabirds each year.
To remedy this situation and to restore the island’s natural values, Grant Norbury and Alan Saunders were contracted through Invasive Species International and in association with Tasmanian colleagues, to draft a plan to eradicate the cats. The eradication project was subsequently undertaken by the Tasmanian Parks and Wildlife Service. The plan was developed following a visit by the ISI team to the island. It proposed a mix of toxic baiting, trapping, and shooting in and around the boulder fields below the cliffs where many of the cats resided (see photo).
Hand and aerial baiting using the toxin para-aminopropiophenone (PAPP) in meat sausage baits began on 3 May 2010. Unfortunately, there were technical problems with the encapsulation of the toxin (some toxin was lost from the bait) so only 5 of 15 cats radio-collared before the control died from poisoning. Bait take by cats, however, was very good. Baits also contained the marker rhodamine B and 89% of the carcasses of cats retrieved by other means contained the marker, illustrating that the palatability, timing, and distribution of the bait was good. Baiting was followed by trapping with cage traps and padded leg-hold traps, which removed another 27 cats. The final control phase involved skilled rifle marksmen searching for surviving cats. No cats were seen, indicating that the population estimate for the cats at the start of the eradication programme was accurate. The last (supposedly) of the island’s feral cats was trapped 12 days after baiting began. Field teams have visited the island each month since the control operation. They used permanently positioned remote cameras and cat-detecting dogs to look for live cats or for evidence of their presence from fresh bird kills, scats and footprints.
After 12 intensive searches between June 2010 and May 2011 Tasmanian Parks and Wildlife staffare confident that no cats remain on Tasman Island, although ongoing vigilance will be required. Recent surveys of shearwater breeding indicate that hatching success has jumped from fewer than 8% before the eradication to over 40% following eradication. The number of prions recorded by the remote cameras has also increased. The situation is looking very promising for the rapid recovery of seabird populations on Tasman Island.
One of the Parks and Wildlife objectives for this project was to develop expertise and capacity within the organisation to undertake further eradications. In addition to the more recent rodent and rabbit eradication programme on Macquarie Island, which involved several stafffrom the Tasman Island project, consideration is being given to further eradications of invasive species from other islands near Tasmania.
The Tasman Island cat eradication project, including preparation of the plan, was funded by the Tasmanian Parks and Wildlife Service.