Does it take ANU 150 years to publish a paper ?

But seriously, everything about this paper is flawed, Assuming building sites correlates to population is in no way a proxy. Look at current villages anywhere in the Pacific and you find a range of building/person ratios. This really depends on cultural practices. For example, look at Pitcairn Island and figure how many people live there.

Then there is the assumption that the variance is caused by disease. A huge human toll was due to tribal warfare when natives acquired guns after 1800. Some other stuff also happened in this period, and then there is emigration, as crew (Melville describes this).