Although a wildlife sanctuary, and thus with no permanent human population, the island is officially defined as a suburb of Porirua City.

Mariano Vella bought one remaining keeper's cottage, dismantled it and rebuilt it close to an existing store shed on the eastern side of the island.

In 1894 he visited Dalmatia and on 3 September that year married Elizabetta Caterina Tarabochia at Lussinpiccolo on the small island of Lussin (Lošinj) in the Adriatic Sea.

The ship was wrecked on Great Barrier Island on 29 October 1894 with the loss of 121 lives; Mariano and Elizabetta reached the shore but all their possessions were lost.

He and Elizabetta (known in New Zealand as Elizabeth) raised a family of two girls, Mattea and Antonia (Anne), and two boys, Giovanni (Jack) and Mariano junior.

[4] In 1973 the government purchased the lease from the Gault family in order to allow the Ministry of Agriculture and Fisheries (MAF) to establish a branch of the Ruakura research station on the island.

More than $2 million dollars was invested in the construction of a research laboratory, a new woolshed, hay barns, a mating shed, equipment buildings, accommodation and diesel generators to provide electricity, while two windmills were installed to pump ground up the surface.

Following a land-use study a proposal was made in 1986 by the Lands and Survey Department for the island to be reverted for conservation purposes to bush and forest.

[4] Following a proposal by the Wellington branch of the Forest & Bird Society a seven month long eradication program (which began in July 1989) removed all mice from the island.

Subsequently, a wetland on the island was restored and several threatened bird, lizard and plant species translocated to Mana.

[7] A ranger from DOC lives on the island, which has its own native plant nursery, electric generator and boat shed.

The restoration program has been characterised by a high level of community involvement, led by groups such as the Royal Forest and Bird Protection Society of New Zealand, the Friends of Mana Island, tramping clubs and school children.

[9] The Department of Conservation and the Friends group also collaborated on a five-year program to establish the threatened tūturuatu / shore plover on the island.

The birds, of which only about 200 remain in the wild, were sourced from a captive population at the Pūkaha / Mount Bruce National Wildlife Centre.

Notable amongst these will be the tuatara, the little spotted kiwi, a subspecies of the carnivorous Powelliphanta snail, and a range of threatened plants endemic to the Wellington Region.

These species are an important part of the restoration of the island because of their nutrient inflows (free fertiliser) and the habitats their burrows provide for reptiles and invertebrates.

[14][15] The same combination of techniques is showing good results in a similar project at Young Nick's Head, near Gisborne.

The plateau slopes gently to the south-east, with deeply-incised valleys on the eastern half and cliffs on the north and west sides.