Ecosystems and impacts
Mana Island would have been a seabird-dominated ecosystem cloaked in dense coastal forest of kohekohe, milk tree, wharangi and kaikomako. However, early Maori settlement (from the 1400s) resulted in a cover of manuka/kanuka shrub-forest and bracken fern by the time European whalers and farmers settled on the island about 1830.
McGregor's skink
The island was farmed from 1832 until 1986, resulting in almost total loss of woody vegetation, apart from one steep-sided forested gully, and shrubs clinging to the steep coastal slopes. Other than farm stock, mice were the only mammals present on Mana until their eradication.
As a result of the 600 or more years of human presence, there are many wahi tapu (sacred sites) and archaeological sites on Mana. Measures are taken to ensure that these important features and their values are not compromised by the ecological restoration work.
Despite the almost total loss of native vegetation, Mana Island retained important relict populations of Cook Strait giant weta, McGregor's skink, goldstripe gecko and Cook's scurvy grass. A few seabirds and coastal birds persisted as breeding species, including:
- sooty shearwaters,
- blue penguins,
- red-billed gulls and southern black-backed gulls,
- white-fronted terns,
- variable oystercatchers
- reef herons
Mouse catch, 204 mice caught in one
bucket trap in a night
Following the removal of farm stock in 1986, the pasture grass grew rank and seeded prolifically, resulting in an explosion in mouse numbers, with estimates of total numbers ranging up to 15 million. The mouse plague had a severe effect on the resident threatened species, and it is likely that Cook Strait giant weta, McGregor's skink and goldstripe gecko would all have become locally extinct if the mice were not successfully eradicated in 1989-90.
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