An incursion response has been initiated after signs of a rat and mice were discovered on Mokoia Island recently.
Mokoia Island Trust announced the news on its Facebook page earlier today.
The island is a pest-free sanctuary which supports populations of threatened species such as kiwi, kokako and dactylanthus.
The trust stated, "Unfortunately during a routine biosecurity check late last week, multiple tracking tunnel on the Mokoia showed evidence of at least one large rat and multiple mice on the island."
Tracking tunnels work by encouraging predators into a tunnel using a lure, causing them to leave high-definition footprints. The predators are not trapped.
"The manu (bird) that we have on Mokoia are at real risk from rats and mice and we would hate for any let alone one kiwi or other manu to die as a result of this incursion."
The Department of Conservation has initiated an incursion response with the aim of restoring the pest-free status of the Wildlife Refuge as soon as possible.
Through the Facebook post, the trust asked for any support as the response would be a major operation due to the number of rodents on the island.
"We would also like to remind all boaties or people who want to visit Mokoia that permission to do so can only be granted by the Mokoia Island Trust and that the only commercial vessel which can land there is through Katoa Jets."
Department of Conservation community supervisor Carrie Abbott said an incursion response was designed to manage the presence of pests as quickly and efficiently as possible.
"As we're dealing with two different pest species we will need to use traps and baits that are specific to these species."
She said the current trap network extended around the island but focused on the shoreline, particularly around the areas which were closest to the mainland and areas where boats land.
"We're also planning on bringing in a conservation dog who is trained to pick up the scent of pests and indicate to its handler where they have recently been."
Abbott said it was known that rats could swim to the island from the mainland but believed it would be unlikely this was the cause for the pests.
"If a rat did decide to make the journey across Lake Rotorua, the existing trap network is designed to kill rats as soon as they get to the island.
"The mice are more likely to have been transported to the island on a boat or in luggage that has been taken to the island without the appropriate quarantine checks.
"Unfortunately the close proximity to the mainland leads to frequent unauthorised landings."