"He was over the Louisville Seamount chain, northeast of New Zealand, so he's on his way home again." Grim had visited Fiji, Tonga and Niue.
Duffy believed the shark was about 9 years old, some way off raising a family.
Duffy, from the Department of Conservation, said Grim may stop by Auckland. "It's possible he could end up here. But it looks like he's heading for Stewart Island."
He thought Grim would probably gather with other great whites in the deep south.
"I wouldn't exactly describe them as best friends, but certainly at the aggregate sites they interact a lot."
According to new research, every living shark could add more than $2.5 million to the economy over its lifetime.
University of Otago marine ecologist Stephen Wing said shark-based tourism was a potential pot of gold for the economy.
He said the latest figures on sharks, collated by scientists for a UN conference on migratory species this week, mirrored previous studies.
"Ecologists have made some of these calculations about the value of ecosystem services and the value of clean natural environments," Wing said. "When you put them in dollar terms, they're huge."
Duffy said savvy eco-tourism operators had sprung up in Gisborne and the Poor Knights Islands to give people shark experiences, including free-diving with sharks.
"It's increasingly popular in New Zealand. It doesn't have to be in a cage." Duffy said overseas research showed that when big shark numbers dropped, smaller sharks thrived, feeding on some fish popular with recreational fishers.
In New Zealand, overfishing of the gummy shark - the "fish and chips shark" - was blamed as the reason for paddle crabs overrunning swimming beaches.
