Manta ray diving in New Zealand

Despite their impressive size, which can exceed 6m across, oceanic mantas are extremely elusive; they remain one of the most popular yet least understood species.

The little we do know is pretty impressive, and it turns out that these highly intelligent animals actually have a lot in common with us humans. We both share conservative life histories. We both reach sexual maturity in our teens, give birth to fully developed, functioning offspring after a year’s gestation and partake in complex social interactions with our kin.

Mantas even have the same brain size to body ratio as humans, and it also happens to have the largest brain of any fish! In-water encounters with these majestic, highly curious animals can be incredibly interactive and quite often, life changing.

Manta misconceptions

A common misconception is that manta rays are only found in the tropics and can’t handle cooler waters. This is only half true because there are two species of manta ray, and it’s the reef mantas found exclusively in the tropics.

Oceanic manta rays on the other hand grow much bigger and can live in both tropical and temperate waters, including here in Aotearoa New Zealand. In fact, oceanic manta rays can be found all around the North Island, from North Cape down to Gisborne on the East Coast, and to the west, as far south as Kapiti Island. They are known to associate closely with our offshore islands and have been sighted in both deep offshore waters, as well as in much shallower inshore waters a mere kilometre or two off the mainland.

Mantas are endangered

As of December 2020, oceanic manta rays were reclassified from Vulnerable to Endangered on the IUCN Red List. Globally, individuals in many populations continue to be captured or killed by targeted and bycatch fisheries and as a result have now become unstable and at serious risk of collapse.

Understanding the intricacies of Aotearoa’s population has never been more critical as it could prove to be one of the last remaining strongholds the species has left.

To date Manta Watch Aotearoa NZ has collated 350 verified sightings from 2001 through to 2021. Each sighting has a corresponding GPS position/coordinate which is then used to create Geo-referenced sightings maps. Areas of consistent activity (aka “manta hotspots”) are identified and become the focus of dedicated manta surveys.

Timing your encounter is vital

Timing is everything as manta rays don’t need to come to the surface, so when they choose to do so it’s for a time, which in turn is determined by their zooplankton prey. Manta rays have an in-built zooplankton super sense; they know exactly when prey densities are prime for feeding. Krill, a primary food source in New Zealand, forms dense swarms during the summer months and when conditions are just right can attract scores of manta rays to aggregate and feast.

In early January last year, MWANZ investigated a string of sighting reports focusing on the outer waters of Auckland’s Hauraki Gulf/Tikapa Moana. After several days of monitoring it became clear that we’d happened upon a significant feeding aggregation surpassing all our expectations. And from that moment on our team took every opportunity to hone in on the key variables that had fired up this very special hot spot.

Using a drone has become an essential means of collecting data, first to keep track of individuals once spotted from the boat, and second as a way to passively observe and document behaviours. Then we soon realized drone photogrammetry could be further utilised and applied to estimate manta disc width (the length between wing tips), cruising speed and even to take identification images.

Mantas have unique markings

All manta rays have unique markings on their belly or underside. By cataloguing these “photo-ID” images over time, we can estimate population size, determine an individual manta’s movements and life history including sexual maturity, injuries and pregnancies.

When surface feeding oceanic mantas somersault, which is essentially a series of energetic back flips to concentrate and entrain their prey before swallowing it, their entire belly breaks the surface. We found that hovering the drone over somersaulting mantas proved to be a very effective way of obtaining IDs!

Accurately measuring a manta ray’s size or disc width is also really important, as size directly relates to an animal’s age and sexual maturity. This when you’re in the water with it, as you have nothing to compare it to. Deploying something of a known length close by, (such as our trusty manta ruler) makes accurate measuring of an individual that much easier. To date we have observed a range of different sized mantas at the hotspot, the smallest a 2.8m male (likely sub adult or teen) all the way to some big pregnant females over 5.5m.

Getting our manta timing ‘spot on’ is still very much a work in progress. But so far we have been blown away by the progress and discoveries MWANZ has made this season. Every manta encountered is testament to the huge collective effort and collaboration that goes into the project.

About Manta Watch Aotearoa New Zealand

Manta Watch Aotearoa New Zealand (MWANZ) Charitable Trust was set up in 2017 to combine citizen science with targeted research to unravel the many mysteries associated with Aotearoa’s oceanic manta rays.

Our manta journey has just begun, and we are excited to see how the project develops. Public engagement and participation will continue to be an integral part of MWANZ and we look forward to broadening our nationwide manta community.

With such a massive search area, citizen science sightings, both recent and historic, are pivotal to the project’s success. Every sighting increases our collective understanding of manta ray distribution and how they are using specific habitats and locations up and down the country.

Ultimately the project’s aim is to determine whether New Zealand has our own distinct population, or if the mantas encountered here in our waters are connected to a larger South Pacific group.

Special thanks to our dedicated research partners, Conservation International Aotearoa, Auckland University, the Department of Conservation, the Manta Trust and Tindale Marine Research Charitable Trust for their continued support and guidance. Massive thanks too, to everyone who has submitted sightings so far!

For those keen to get involved and support the project, there are numerous ways you can get in touch/share your sightings with MWANZ.

Please check out our dedicated Manta Watch social accounts and/or email mantawatchnewzealand@gmail.com for an Electronic Manta Sightings Packs which contains all the links and information you’ll need to become an active citizen manta scientist!