Two oceanic manta rays have been tagged with tracking devices off Northland's coast in the first field study of the magnificent underwater species conducted in New Zealand.

A team of researchers were in the ocean off Northland last week in a bid to learn more about manta rays.

The team spent 27 hours over four days actively searching a large area between the Bay of Islands and Doubtless Bay.

Dr Mark Erdmann places an underwater camera on a reef to monitor manta ray activity off Northland. Photo / Irene Middleton
Dr Mark Erdmann places an underwater camera on a reef to monitor manta ray activity off Northland. Photo / Irene Middleton

Underwater cameras were set up on an offshore reef for 24 hours to see if any manta rays visited to have parasites removed by cleaner fish.

The team covered between 67km and 130km a day, and observed a total of 26 spinetailed devil rays, seven oceanic manta rays and a pair of Bryde's whales.

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Clinton Duffy, Department of Conservation technical marine adviser, said it was the first time oceanic manta rays had been tagged here.

Duffy said manta rays were giant oceanic relatives of the much smaller bottom-living eagle ray.

Two species commonly called manta rays occurred in New Zealand waters.

The largest is the oceanic or giant manta ray (Mobula birostris), which reaches a maximum reported size of 9m across.

The other species is the spinetailed devil ray (Mobula mobular), sometimes known as the giant devil ray or spinetailed mobula, which reach a wingspan of 5m.

However, the maximum reported size of spinetailed devil rays in New Zealand waters is 3.1m across. Manta and spinetailed devil rays feed mainly on krill.

Duffy said while both were protected species, almost nothing was known about their biology in New Zealand waters.

Being able to track the two rays for the next six months via the satellite tags would provide important information.

"We'll be able to collect data to see rays' positions in real time and diving behaviour. We'll also be able to see if the rays spend time swimming or basking at the surface," Duffy said.

"There are more rays in the area than people realise. Gamefishers have been reporting lots of them this summer."

The research project is a collaboration between DoC, Conservation International and the Tindale Marine Research Charitable Trust, which was formed to promote and encourage environmental education, conservation and research.

Team members were Dr Mark Erdmann, of Conservation International, Duffy, from DoC, Scott Tindale, Tindale Marine Research Charitable Trust and Irene Middleton from Massey University.