On Friday morning it was one kilometre off Tauroa (Reef Point).
Mr Duffy said even a juvenile great white could be dangerous, so people should exercise common sense about where they swam, surfed and dived, but given how common they were around the upper North Island attacks on people were very rare.
Aucklanders Hamish Don and Ben Brooks, who were enjoying themselves at Te Kohanga on Friday before attending a wedding next day, certainly weren't too concerned about potentially sharing the water with a great white.
Mr Don said sharks were incredible animals, adding that there was said to be a resident shark at Henderson Bay that didn't bother people.
"They're probably too well fed up here to be a worry," he said.
Muriwai, where the last fatal great white attack occurred (in 2013), was his local beach, and no one there seemed to worry too much either. (Film-maker Adam Strange, who was taken about 200 metres off the beach, was believed to have been swimming through a school of fish, in an area where people had recently been fishing, when he was attacked).
Meanwhile, on the same day that Mr Duffy saw eight great whites, Kerikeri electrician Barry Jordan was on a family fishing trip when he hooked something big in 90 metres of water off Nine Pin Rock in the Bay of Islands.
An experienced game fisher, he was live-baiting for marlin when a tagged shark took the bait and "went airborne." It took half an hour to bring it alongside the boat, where it broke free.
"I had my hands a bit full to take a photo but I got a pretty good look at it. It was definitely a great white," he said.
Mr Jordan put its length at 3.5-4 metres and its weight at 400kg. The same week a spearfisher had told him he had been forced out of the water near Hole in the Rock by a great white with the same kind of tag attached to its flank.
Mr Jordan said he had caught plenty of sharks before, "but nothing like this".
Mr Duffy said Mr Jordan's description of the tag had allowed him to trace it to the Neptune Islands, off the South Australian coast, where it had been tagged in the course of research into the effects of cage diving operations in 2011.
Great whites were known to travel frequently between New Zealand and Australia's east coast, but not from South Australia, which made the Kerikeri sparkie's catch unusual.
The only other New Zealand sighting of a great white from South Australia was in 2002, when one was caught in a gill net at Ahipara.
Last month's sighting of so many juveniles in the Kaipara Harbour lends weight to the theory that the upper North Island is a great white breeding area and nursery. The Kaipara sharks measured 1.8 to 3.4 metres; adult males grow to a maximum of about 5.5 metres and females possibly as long as seven metres.
The distinctive markings on great whites mean that individual animals can be easily identified from sightings or photos.
Anyone with photos of great whites, even if taken years ago, is welcome to send them to cduffy@doc.govt.nz to aid Mr Duffy's research.
Other sightings last month include a 4.5-metre great white in the Waitemata Harbour, and one "as big as a tractor" leaping from the water at Leigh.
