Rodent Eradication

Project Objectives
To remove all rats and mice from Pomona Island.
To remove all mice from Rona Island.

Rats and mice were present on Pomona Island for many years. A total of 312 rats were caught in the stoat traps between August 2006 and July 2007. In addition, live rats were often seen running around the island by volunteers as they checked the stoat traps. Mice were known to eat the meat bait in traps on both Pomona and Rona Islands.

Method Used
Best practice for eradicating rodents from islands is to use an aerial application of brodifacoum  - an second generation anti-coagulant poison. A resource consent was needed to carry out such an operation on the islands. An Assessment of Environmental Effects (AEE) was prepared by volunteer Megan Willans. In addition, a Social Impact Assessment, funded by the Lottery Grants Board, was completed in order to gain the views of the local community on the restoration of the islands in general and in particular on the planned use of an aerial poison operation to eradicate the rats and mice. The resource consent application was submitted to Environment Southland in January 2007. Seven submissions were received, five in support and two against. Careful negotiation by Murray Willans (the Trust's DOC advisory Trustee at the time) with the NZ Deerstalkers Association enabled the Trust to avoid a costly hearing process. Consent for the operation was granted in May 2007.

In July and August 2007, two aerial applications of brodifacoum were undertaken on Pomona and Rona Islands. South West Helicopters was contracted to fly the missions, with Chief Pilot, Peter Garden, donating his flying time to the Trust. Nick Torr volunteered his knowledge and expertise as Operations Manager and ground handling was carried out by a number of volunteers with assistance from DOC staff. In total, 7.1 tonnes of bait were dropped on the islands over two separate days (8 July and 18 August 2007).

Current Status
In 2010 a rat's paw prints were found in a tracking tunnel on Pomona. A dead rat was found in a trap shortly afterwards. Since 2011, small numbers of rats have been found on Pomona. DNA testing suggests that a breeding population has established. In late 2012 an extensive bait station network was set-up on Pomona and the trap network was extended further in August 2013. The aim is to keep rats down to very low numbers on Pomona.

No evidence of rats on Rona Island has been found since the aerial operation.

A single mouse was found in a trap in a rodent motel on each of Pomona and Rona in June/July 2009. An extensive trap network, targeting mice, has been placed on both islands since then. It is looking increasingly likely that this was a re-invasion probably from a boat or by swimming, rather than evidence of a remnant mouse population on either island. In March 2010, a further single mouse was trapped on Rona. Sadly a mouse population re-established on Pomona during 2010, and then on Rona in 2012.

Thanks to:
Donald Riley for funding the majority of the costs associated with the initial rodent eradication programme in 2006-2007, and to Community Trust of Southland for making up the shortfall.
Gary Chisholm Family Trust for funding the extensive bait station and trap network during 2012-2013.
Pomona Island Charitable Trust
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Pomona Island Charitable Trust
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Photo: T. Tibbles
Photo: T. Tibbles
Photo: T. Tibbles
Photo: T. Tibbles