By Lydia Green
During the summer months, in various hotspots along the North Island’s east coast including the Hauraki Gulf Marine Park/Ko te Pātaka kai o Tīkapa, majestic oceanic manta rays can often be seen exploiting our planktonic-rich waters. Oceanic manta rays (Mobula birostris) are a fascinating species, possessing the largest brain of any fish species, and an incredible wingspan of up to 7 metres. Amazingly, they can never stop moving, as they must keep water flowing over their gills to breath.
Little is known about these rays in New Zealand. Thankfully, marine scientist Lydia Green is trying to fix this through Manta Watch New Zealand (MWNZ) – a central data collection platform for sightings – and to learn more about this elusive and highly intelligent species. We caught up with Lydia at the beginning of the year. We began by asking her what drew her to the ocean and the career of a marine biologist.
I’m originally from the UK and grew up in the East Midlands, two and a half hours drive away from the nearest beach. Despite this, I was obsessed with the ocean from a very early age. As I got older, I got my fishy-fix by having an aquarium, investigating our garden pond and by watching a lot of National Geographic and David Attenborough. When I was old enough to know what a marine biologist was, I wanted to be one. I completed my Marine Biology BSc (Hons) at Swansea University and started my ocean journey.
Sharks and rays have always been my favourite marine species. I saw my first manta ray in 2011 whilst volunteering for the Thresher Shark Research Project in the Philippines. We were conducting dive surveys on a sea mount (underwater mountains that rise hundreds or thousands of feet from the seafloor) when suddenly the light from above dimmed and a huge manta hovered above us. The experience was so cool that manta rays became firmly lodged on my radar.
Manta rays are highly intelligent and, depending on their personality and/or mood at the time, you can have some incredible in-water encounters with them – similar to interactions you get swimming with dolphins. It’s easy to get hooked on mantas!
I’ve been really lucky so far to work with reef mantas in Fiji and the Maldives, oceanic mantas here in Aotearoa, and a special subspecies in the Mexican Caribbean that act like a combination between the two.
One of my most memorable experiences with manta rays occurred in the Maldives when I joined a phenomenon known as ‘manta soup’. With 5,000+ individuals, the Maldives has the world’s largest known population of reef manta rays, which reach a wingspan of 3.5 metres. During the Maldivian monsoon, large numbers of mantas aggregate to feed when their zooplankton prey become densely concentrated. ‘Manta soup’ is the best way to describe the occurrence of up to 200+ mantas feeding together in a relatively small area. Being in the water with so many mantas all at once and trying to take ID shots is both truly incredible and pretty tricky, but definitely the kind of work problem you don’t mind having!
New Zealand’s elusive oceanic manta ray population
I was aware many people had seen oceanic manta rays in New Zealand waters (including myself). Clinton Duffy from the Department of Conservation (DOC) had published a paper in 2003 confirming their presence, but very little data had been collected on their population size, distribution and movements. I established Manta Watch New Zealand (MWNZ) to start answering those key questions, and to build a better picture of the location and behaviour of manta rays in local waters. Ultimately our aim is to determine whether we have our own distinct population of manta rays, or if the mantas we see in our waters are connected to a larger South Pacific population. Moving forward, this information will dramatically influence future conservation management of this population.
In late December 2020 oceanic manta rays were reclassified from vulnerable to endangered on the IUCN Red List, which means globally, the majority of populations have become unstable and are at serious risk of extinction. The more we can learn about the connectivity of populations, the more we can understand the specific threats these manta rays face and work toward providing greater protections for them.
You can help!
MWNZ rely heavily on ‘citizen scientists’, aka the public, recording encounters with manta rays. Our outreach work involves encouraging people to provide the date, time and GPS position of sighted mantas along with a verification photo or video if possible, as well as a description of their behaviour. The position-based data enables us to identify seasonal manta ray hotspots, while the behavioural data helps us to determine how mantas are using these areas, giving us clues as to whether they might be feeding or breeding grounds for example.
On occasion, citizen scientists are able to take ID photos, also known as a ‘belly shot’. Mantas have unique markings on their bellies, much like a human fingerprint. By cataloguing these images over time, we get population size estimates and determine an individual manta’s movements and life history, including sexual maturity and pregnancies.
Once we confirm a manta hotspot, we then go about intensely monitoring that area to learn all about the locals, get ID photos and record their behaviours, the associated marine life and environmental variables. Currently we are using that data in a collaborative research paper, but overall, the project has incredible scope to develop numerous more in-depth projects focusing on specific locations and behaviours, so watch this space!
Medicine and mantas – a global threat
Globally, the primary threat to manta rays are from both targeted and bycatch (accidentally caught) fishing industries. Manta and devil ray (mobulid) gill plates are considered by some cultures to contain medicinal properties. There is no scientific backing to support these health claims, but despite this, mobulid gill plates are worth big money which, in turn, drives the gill plate industry.
Currently 30 countries actively fish manta and devil rays, and non-target fisheries often retain accidentally caught rays due to the value of their gill plates. This equates to hundreds of thousands of these animals being killed annually. The problem is that both species have conservative life strategies, much like humans, in that they are long lived (oceanic manta rays are thought to live over 40 years), take a relatively long time to research sexual maturity, and once mature give birth to a single, fully formed pup after 12.5 months gestation. Any targeted exploitation results in rapid population decline, as manta and devil rays simply can’t reproduce at the rate at which they are being removed from the ocean.
A very special species
I find manta rays fascinating, exciting and incredibly beautiful. There is still so much that we don’t know about them, especially the mantas here in Aotearoa. This makes every encounter so exciting and everything we are learning, either directly or through citizen science, is brand new to science!
Here are my top 5 things you should know about oceanic manta rays. They are:
2. Highly intelligent
You can help Lydia and Manta Watch New Zealand by recording sightings of manta rays. Simply:
1) Fill out MWNZ’s Online Sightings Form
2) Fill out the Online Data Sheet
3) Send MWNZ an email at firstname.lastname@example.org
4) Or DM MWNZ on their Facebook Sighting Group
Lydia would like to thank all the lovely citizen scientists that have submitted their manta ray sightings to MWNZ, and the Manta Trust, the global charity of which MWNZ is affiliated. Check out their website to learn all about manta and devil rays on a global scale, as well as the research, education and collaboration efforts that have been set up to conserve these amazing animals.
Close relatives of all sharks and rays, manta rays belong to the mobulid family which includes oceanic manta rays, reef manta rays and devil rays. They are cartilaginous, filter-feeding fish found throughout the tropical and sub-tropical oceans of the world. They have specially modified gill plates which they use to strain zooplankton from the water column. Their large brains, intelligence and curiosity set them apart from other fish species, but as they have only been scientifically studied in detail for around a decade, much of their life history remains a mystery. They visit the Hauraki Gulf Marine Park – New Zealand’s only national park of the sea.
Love it, Restore it, Protect it.
This was a fascinating read, especially their reproductive biology. 12.5 months!