Searching for manta rays

– By Clinton Duffy, DOC Technical Marine Advisor

Last week a team of researchers were searching the waters off Northland to try and learn more about our manta rays.

Manta rays are giant oceanic relatives of the much smaller bottom-living eagle ray. Two species commonly called ‘manta rays’ occur in New Zealand waters.  The largest is the oceanic or giant manta ray (Mobula birostris), which reaches a maximum reported size of 9 m across.

3.6 m disc width female oceanic manta ray inspecting the divers. 📷: Irene Middleton

The other species is the spinetailed devil ray (Mobula mobular), sometimes known as the giant devil ray or spinetailed mobula. They’re reported to reach 5 m across, however the maximum reported size of spinetailed devil rays in New Zealand waters is 3.1 m across. Manta and spinetailed devil rays feed mainly on krill. Although both are protected species, almost nothing is known about their biology in New Zealand waters.

Swimming past three spinetailed devil rays. 📷: Irene Middleton

The research project is a collaboration between DOC, Conservation International and the Tindale Marine Research Charitable Trust. Team members are Dr Mark Erdmann, Conservation International, Clinton Duffy, DOC, Scott Tindale, Tindale Marine Research Charitable Trust, and Irene Middleton, Massey University.

The team set up underwater cameras on an offshore reef for 24 hrs to see if any manta rays visited it to have parasites removed by cleaner fishes, and were able to deploy satellite tags on two oceanic mantas to track their movements over the next six months. 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.

Dr Mark Erdmann, CI, placing underwater cameras on a reef to monitoring manta ray activity. 📷: Irene Middleton

This is the first field study of manta rays in New Zealand waters and the first time that oceanic manta rays have been tagged here.

The team spent a total of 27 hrs over four days actively searching a large area between the Bay of Islands and Doubtless Bay. They covered between 67 km and 130 km a day, and observed a total of 26 spinetailed devil rays, 7 oceanic manta rays and a pair of Bryde’s whales.