The Global Seven-gill Shark Project is a scientific collaboration studying genetic diversity in the shark species.
Seven-gills found in California and South America were so different from Tasmanian samples that they could be a sub-species, said New Zealand project co-ordinator Craig Thorburn, who is the director of Ocean Zoo in Auckland.
"Research DNA samples show they may be, genetically speaking, two different species of sharks. Further samples from New Zealand, Argentina and South Africa will be key to assessing whether this is the case," he said this week.
"We're trying to learn whether the worldwide populations are related or, in fact, separate species that may become locally extinct."
Scientists hope to source 50 samples from New Zealand, Australia, South Africa, South America and California.
Dunedin fisherman Peter Scott and his brother, Stuart, have already taken DNA samples from eight seven-gill sharks this week.
Only 20 samples have so far been taken around New Zealand for the project.
"We just trim a small piece the size of a fingernail off and put it in a jar and send it to Ocean Zoo in Auckland," Mr Scott explained.
"There are a lot more sharks in the harbour than people think.
"We've had some big great whites caught out there. They're always around, but there's probably a few more around at the moment as they move south with the warm water."
Mr Scott planned to get samples from 12 more sharks.
"But we'll wait a day or two till we've got a bit of our skin back. We were out from 4.30am till 9pm the other day, and you lose quite a bit of skin catching them."
Mr Thorburn said the shark was found in temperate seas worldwide, in waters ranging from shallow harbours and bays to deeper than 500m offshore.
"The seven-gill has remained unchanged for 140 million years, making it one of the oldest and most successful species," he said.
"It's a very interesting shark and very underrated. Hopefully, we'll uncover something new about a really old shark."
The DNA samples would be collected over summer and ultimately sent to the Guy Harvey Research Institute in Florida for analysis early next year, Mr Thorburn said.
The World Conservation Union lists the seven-gill shark as "near threatened" in the eastern Pacific Ocean.
The seven-gill shark (Notorynchus cepedianus) grows up to 3m long and is one of the few species of shark with seven gill slits on each side, rather than the usual five slits.
While they have occasionally attacked people in New Zealand, it is very rare for them to cause severe injury.
The International Shark Attack File has records of only five unprovoked attacks on humans by seven-gill sharks since the 16th century.
They are the most commonly caught fish in Dunedin's shark nets at St Kilda, St Clair and Brighton beaches.
