A dead shark found on a beach by a well-known Northland doctor has proved invaluable for research into the elusive great white.

Earlier this year Kaitaia GP and New Zealander of the Year 2014 Lance O'Sullivan took the shark home from Great Exhibition Bay and put it in his freezer after a call to the Department of Conservation (DoC).

The 1.8m shark spent three months in the freezer, until it was taken to the Auckland Museum and then dissected at Massey University's Albany campus. The necropsy was performed by DoC marine scientist Clinton Duffy, Auckland Museum's head of natural sciences Tom Trnski and marine technician Emma Betty.

Duffy said it was very rare to find great white specimens on the beach, although they are occasionally found tangled in fishing nets.

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"It's probably the first time I've seen one someone's found on the beach," he said.

Duffy has done necropsies on many sharks of various species, including about a dozen great whites. This was one of the smaller ones, he said. It was also a young shark, at only one year old. Sharks can live for around 70 years.

He said the shark's cause of death was obvious, as it had a fishing hook still in its mouth.

Duffy said anyone finding a great white shark on the beach needed to report the find to DoC as it is a protected species.

"People aren't meant to just pick them up on the beach and hang on to them."

In this case, DoC asked O'Sullivan to keep the shark when he reported it so it could be used for research purposes. The shark was used to find out more about the species - "all the things we can't tell just by looking at them".

"We don't get to see too many a year, so while an individual doesn't tell us very much, we're able to build up a picture over time," Duffy said.

Massey University lecturer Dr Adam Smith said there is still relatively little known about sharks.

"Some fairly fundamental knowledge is still unknown or only partially known for many marine species, particularly elusive sharks," he said.

"Since it is so rare to have actual specimens of sharks, a wealth of information is gathered whenever we can get our hands on one."

It is only the second dissection of a great white Smith has seen - the last took place 10 years ago.

Despite the low numbers, great whites have been spotted in Houhora Harbour recently, with about half a dozen sightings in April and early May, leading to a warning from the harbourmaster.