Mr Tustin has been chasing moose in Fiordland since the early 1970s and has now put 12 new cameras in a specially selected area which drains into Dusky Sound.
He said the evidence he had that moose were still roaming Fiordland was compelling, but "everyone demands a photograph", so that is what he is doing and has been doing for decades.
Moose were first introduced into the area in 1910, with plans for them to be hunted. However, it had limited success and the last known sighting was in 1952.
But Mr Tustin has always been certain the largest member of the deer family was still in Fiordland.
"We’ve been really encouraged. We’ve had, of course, those two live animal sightings last March, astonishingly by North American hikers who know their stuff.
"In 2020, we had another live sighting just north of Doubtful Sound. So, we’ve put them together, and then the site that we’re monitoring ... We’ve got at least four or five different moose known to be alive at the moment in Fiordland. So, it’s all pretty encouraging," he said.
He said a sighting of a moose last year was missed by a camera, but he knew it had been in the area at least four years in a row.
"I work with the biology of the animal to get the sort of stuff that I need to tell a moose story, but everyone is demanding a photograph. So, we’ll do our best this year to see if we can pick one up.
"They have a very distinctive method of feeding. It’s what I call sort of a reach, grasp, break, strip," he said.
"It’s difficult country. But the characteristic feeding sign is very distinctive and easily separated from red deer."
Mr Tustin, who flew helicopters for years in Fiordland, said feeding conditions were tough at the moment for moose as an overpopulation of red deer had stripped the forest of food for both species.
"Moose has one advantage — they have reach. They can outreach a red deer because they’re a bigger animal. But the disadvantage for them is that they cannot graze; they can only browse. They can’t even handle the digestion of grasses."
With the boom in red deer numbers, moose may be starving their way into extinction.
It had happened before as red deer numbers swelled, but moose had survived.
"The moose have hung on. Amazingly they’ve hung on. And we’ve had 115 years and they’re still hanging on, but just by a thread. So it makes quite a nice story.
"I’ve been confident we’ll get a photo for many decades. But put together right now, we’re in the best position we’ve been for a long time, for decades."
Now 80, Mr Tustin has just about finished his third book on the elusive moose, and said it was something worth continuing.
"We’ve camped out there a heck of a lot. Literally years if you add it all up.
"But we’re still on the case."
