A large hole that appears to be the start of a cave has been dug on the tiny sandstone Motungaegnae, or Watchman, Island in the Waitemata Harbour, 600m off Herne Bay.
Herne Bay resident and regular kayaker Mike van Niekerk said he had watched with surprise in the past few weeks as the cave or hole was dug.
"It appeared about a month ago but I think they've stopped digging now because the cliffs above were crumbling," he said.
Van Niekerk took a series of photographs to show the extent of the excavations, which he said had destabilised a cliff face of the tiny motu. The photos also show extensive graffiti on the sandstone face beside the new cave and he asked what was being done to ensure the entire maunga did not collapse.
The Herald has reported that the island, once known as Sentinel Rock, has special or undefined legal status. As it was never given Crown ownership in the 19th century, neither the Auckland Council nor Ports of Auckland can claim it. But some iwi are considered to have customary rights over it as an ancestral site.
Ngarimu Blair of Ngati Whatua's Whai Rawa, said: "It's called Motungaengae."
Told of the new cave, he said: "That is concerning. I have no idea who or why someone would do that. I believe there should be an archaeological assessment undertaken to see what is left of the archaeological sites there and what can be done, if anything, to protect what is left.
"Ngati Whatua Orakei is happy to work with council or the Department of Conservation on protection and understanding its historic value. I intend making contact with them both today to see what we can do," Blair said.
Auckland councillor Mike Lee said he was disappointed to hear of the cave.
"The culprit should be found. The physical damage needs to be rectified. It may be opportune to remove weeds and place rat bait stations as part of this," Lee said.
Auckland War Memorial Museum botany curator Ewen Cameron said he had undertaken a botanical survey of the island in 1987 and had re-visited in 2006.
"The island is mainly weedy and eroding but there's a threatened New Zealand native species of geranium, Geranium retrorsum, just managing to hold on there. I'd be disappointed if the cave excavations had threatened the geranium but it's impossible to say without visiting," he said.
"The island is eroding naturally so someone digging a cave would possibly speed up that erosion," Cameron said.