Mr Tustin and his wife Margie have just finished installing a dozen digital cameras in the bush between Wet Jacket Arm and Dusky Sound, where 10 moose were released in 1910.
The last confirmed contact with moose was in 1952, when one was shot.
Despite finding many signs of moose browsing in the area since, and getting positive DNA results from the analysis of hairs, Mr Tustin has struggled to convince people that the species survives in Fiordland.
"We've been mocked for decades; even when the DNA came out," Mr Tustin said from his Bull Creek home this week.
His search for indisputable, visual moose proof over more than 30 years led him to use remote film cameras strapped to trees and triggered by animal movement.
Over the last three and a-half years, the film cameras have produced 850 photos of deer and 160 of possums, but none of moose.
Mr Tustin is not deterred and expects his new American, Moultrie digital trail cameras will overcome the limitations of film, with longer battery life and the ability to take more photos between checks.
He says selecting camera positions has become more difficult because more red deer in the Fiordland National Park are creating many more trails.
"In a closed forest, with just a few trails, it's quite easy, but in an open forest, animals are more inclined to wander."
He also considers the increase in red deer numbers - doubling every four years - threatens the existence of moose because of the competition for food.
"The main influence on moose in this country is the status of the red deer."
Mr Tustin plans to check his cameras again in the autumn and, in the meantime, is waiting for the results of more DNA testing being done in Canada.
He also has droppings in the refrigerator, waiting to be sent away for analysis.
Each of his new cameras is sponsored by groups or individuals and Mr Tustin believes conclusive moose evidence could emerge at at any time.
"It could quite easily happen that someone could shoot one tomorrow."
