Maori supremacists say that colonisation caused a decline in the Maori population but this is aptly disputed as follows by Mike Butler.

Some assert without evidence that the Maori population in 1839 was 150,000.

The earliest census in NZ was in 1858, when there were 56,000 Maori.

The proportion of young in that population was 20 percent, which is low.

This low proportion of young indicates a low birth rate and poor health in preceding years.

The proportion of young in the Maori population in the 1881 census was around 35 percent.

This higher proportion of young 30 years later shows a recovering population.

The evidence shows that the Maori population sustained trauma before colonisation.

Colonisation brought recovery.

The Maori population was probably around 70,000 in 1840, and probably around 120,000 in 1800.

Inter-tribal fighting from 1800 to 1840 appears to be the main cause of the decline of the Maori population.

Inter-tribal wars occurred in the first half of the 19th century.

The 2013 census counted 598,605 Maori. -- no demise there.