A mega manta ray which washed up at a Northland beach on Wednesday is the first-ever recorded to strand on the New Zealand shore.

The 4.3m ray has invited fascination from marine scientists, who have travelled to remote Rarawa Beach on the Far North's east coast to study it.

Manta Watch New Zealand project leader Lydia Green made the trip with Department of Conservation marine scientist Clinton Duffy to examine the carcass yesterday.

"This is a really important sighting for us because it's the first time ever this has happened," Green said.

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"Looking at the manta ray, we saw no obvious sign of external trauma.

"We then opened the body and found no microplastics or internal trauma either," Green explained.

The bellies of manta rays are unique for each individual - just like a fingerprint.
The bellies of manta rays are unique for each individual - just like a fingerprint.

There is a large manta ray population living in New Zealand waters; however, they usually stay about 100m off-shore feeding on microscopic plankton, small fish and crustaceans.

The manta ray is called a "cartilaginous" fish, meaning – like sharks – it doesn't have bones but is made up of cartilage. The species is most commonly found in the tropics, where it is called the reef manta ray.

The specimen which stranded on Rarawa Beach is an oceanic manta ray, the largest type of ray and one of the largest fish in the world.

They can get up to 9m across – with an average size of 4-5m – and weigh up to 2000kg.

Scientists only recently discovered the difference between oceanic and reef manta rays which "completely changed the way we think about the animal," DoC's Duffy said.

Duffy explained that previously it was assumed that the manta rays found around New Zealand were migrating down from the tropics.

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"We now believe, that there is a New Zealand population living permanently off the coast," he said.

Duffy and Green collected several tissue samples from the Rarawa carcass - a unique opportunity, as Duffy describes it - as manta rays are protected in New Zealand and dead manta rays usually float to the ocean floor.

Another fact that makes the Rarawa ray special is its dark colouring.

"They are called black moths. It's a very unique colour variation with only a few populations around the world," Green said.

November marks the start of the manta ray season, with the majority being sighted December to March, from Cape Reinga, along the east coast – prominently around the Poor Knights and other Hauraki Gulf islands – down to the Bay of Plenty.

"The furthest south a manta ray has been spotted was around Kāpiti Island," Green said.

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Manta Watch NZ together with DoC, Conservation International, Tindale Marine Research Charitable Trust have collaborated on a two-year project collecting manta ray data from 1994 until today and will release their research paper early next year.

Green said there was still a lot to learn about the rays and that they relied on the public to collect further data.

The carcass was found 200m north of the Rarawa Beach car park.
The carcass was found 200m north of the Rarawa Beach car park.

"When feeding, manta rays tend to roll on their bellies, which are quite white," she explained.

"Their bellies are unique to each individual, much like a fingerprint."

Green said if people find manta rays washed up at the beach, it would be helpful to take photos, including pictures of the belly, and record GPS data of where the fish has been seen.

To support Manta Watch NZ research, send information and photos manta ray sightings to mantawatchnewzealand@gmail.com.