A global breakthrough in recording information about the endangered manta ray has been made by an Auckland University PhD candidate.
In a study titled ‘How Big Is That Manta Ray?’ published in Drones, Edy Setyawan outlines how a drone camera, with the addition of a PVC pipe in the ocean, can be used to accurately measure the endangered giant of the sea.
The technique includes throwing the manta measure pipe in the vicinity of the fish when they are feeding on the surface of the ocean, which is later used as a size reference when recording measurements from the drone footage.
"I could see that from the drone there was some size variation, some mantas, they are bigger than the others," Setyawan said.
"It’s quite cheap using a small drone, but it can give us a big impact on manta ray conservation."
He said fellow manta ray researchers in several locations around the world are interested in using the method.
The technique was first trialled in Raja Ampat, Indonesia with reef manta rays and then in the Hauraki Gulf near Auckland with oceanic manta rays.
Age indicating details such as the claspers of mature males and scarring from mating on the left wings of mature female mantas are also clear when filmed with a drone.
Usually researchers estimate the size of manta rays by being near them in the water, but that method is often unreliable.
"That often disturbs the manta rays and the manta rays just swim away – ‘yep, I don't need to be with you… that's too close!’" Setyawan said.
Manta Watch Aotearoa New Zealand founder Lydia Green has been involved in the New Zealand part of the study.
"It's exponentially grown our understanding, as well as the means of being able to collect data on these animals," she said.
Green said New Zealand’s manta rays may be the only population to not be showing conservation impacts as a result of overfishing and other human marine activity so gathering as much information as possible through the drone technique as quickly as possible is important.
"Mantas are fully protected in New Zealand waters but they’re currently data deficient so if we give the Department of Conservation and other decision makers a lot more information, then they can make better informed decisions and then if our mantas go overseas then the protections are different so it’s just getting prepared for that and having that data there ready as and when we need it."
She’s calling for the public’s help, saying citizen science is the driver of the group’s research.
"It also helps target our research… it can be a bit of a frustrating game of hide and seek and so just to have the low down of where mantas were recently seen, what they were doing, it just gives us a bit more insight."
Green said the information needed from the public is the date, time, GPS location and photos or video of the manta ray.
Capturing the spots on their underside is particularly useful as each animal has a unique marking which is used by researchers for identification.
"When you're in the water, they'll want to look at you and if you're in a good position they'll actually turn onto their bellies so they can get a better look and that’s the perfect opportunity for getting a nice ID shot of that belly," Green said.
The oceanic manta ray found in New Zealand is the largest ray in the world, weighing up to 2000kgs and with a wingspan of up to seven metres.
Manta Watch is launching a website in the coming days, where people can upload photos of manta rays and view reported sightings on an interactive map.
People can also report sightings to @mantawatchnewzealand on Instagram and Facebook.
Department of Conservation marine scientist Clinton Duffy said while there are no rules on how far away from manta rays people should stay, people are advised not to harass them or attempt to ride them.
"Divers should follow best international practice and stay at least 3m away from them if possible and should not get in the water with courting rays as this can break-up male-female pairs and interfere with mating," he said in an email.
Prosecutions under the Wildlife Act for harassment are possible.
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