MYSTERY BEAST: Otago moose hunter Ken Tustin is unsure whether this photo captured a moose or a deer.

Is this a moose on the loose?

Otago moose hunter Ken Tustin thinks he may have snapped a photograph of a juvenile moose in southwestern Fiordland.

The hulking animals have not been officially spotted in New Zealand for more than 50 years.

The photograph was taken on March 7 in an area of Fiordland known as Herrick creek, Mr Tustin said.

It was snapped automatically by one of 13 cameras he had set up in the area.

When he retrieved the images a few days ago, he waded through thousands that showed only deer.

"But there was one photo that was strikingly different and it had me sitting back with my hair on end."

The first sign it was different was the "horse-shaped face", which contrasted with the dog-shaped face of a deer, he said.

But the photo did not show enough detail to be sure, and he suspected it might actually be a deer, he said.

"I think this will always be a 'maybe'."

It could not be a half-moose, half-deer because the two species did not interbreed, he said.

Most people regarded the last official sighting of a moose to have been from 1952, but he had documented several more sightings since then in his history of the species in New Zealand, he said.

Mr Tustin said his "absorbing, compelling interest" in all things moose had begun during a stint working as a scientist in Fiordland.

He estimated a population of 20 moose could be wandering around the area – though that was a "total guess".