Diving with Manta Rays: Studying Mantas on Lady Elliot Island

Are you as obsessed with manta rays as we are? If so, we’ve caught up with freediving instructor and marine scientist, Michelle Ooi, to talk about her time freediving with manta rays on Lady Elliot Island in Queensland, Australia.

Hey Michelle! Thanks for chatting with us. Could you please tell us a little about who you are and where you’re based?

Hi! I’m a freediving instructor currently based in Singapore, where I teach at a freediving school, Zen Freediving. Besides freediving, I have many other interests, like surfing, skating, health and wellness, and marine conservation.

You spent some time studying manta rays on Lady Elliot Island with Project Manta. What brought you there and what was your goal?

Ever since I learnt how to dive, diving with mantas was on high on my priority list. I’m also very interested in wildlife biology and conservation, so when I learnt about Earthwatch’s expedition with Project Manta, I signed up. After that, I was hooked and wanted to do more to help with manta research and conservation.

At that time, I had an opportunity to do a research project as part of a university course, so I got in touch with Kathy, the lead scientist on Project Manta. Together we decided on the research project to look at the levels of certain metals in manta and mobula ray (rays that are related to mantas) gill and muscle tissue, because mantas and mobulas are increasingly fished for their gills, which are consumed in Chinese Medicine. Lady Elliot Island was my field site. It’s an amazing place so I was really lucky to have been able to do that!  

To most people, manta rays all look the same. How could you tell each one of them apart? Do they have different personalities from one another?

You can tell them apart by the pattern on their underbellies, which are unique, like human fingerprints. They definitely have different personalities; some are shy and swim away when they see you, others are curious and watch you, and some will come up close and interact with you.

How did you take samples for heavy metals and what did you find?

We obtained tissue samples from mobula rays from two locations – Sri Lanka and Lady Elliot Island. With the help of a researcher in Sri Lanka, we managed to get gill and muscle tissue from the actual fish markets that land and sell mobula rays. From the mantas at Lady Elliot Island, we took muscle biopsies while freediving or scuba diving at the cleaning stations. We then processed these samples in the laboratory and analysed them for lead, arsenic, cadmium and mercury.

We compared what we found to international food standards set by regulatory bodies such as the World Health Organisation and found that levels of metals in some of the individual samples indeed exceeded the maximum limits in those standards. Another interesting find was that lead was the only metal which was found at higher levels in the Lady Elliot Island samples compared to the Sri Lanka samples.

For the complete findings and analyses you can access my paper, Levels of arsenic, cadmium, lead and mercury in the branchial plate and muscle tissue of mobulid rays.

What did a typical day look like as a researcher in the field?

Pretty awesome! We would wake up and have breakfast, then go freediving or scuba diving to take photo IDs of the mantas and get a biopsy if possible. Sometimes we would tag the mantas as well with satellite tags to track their movements. After the session, we would have to make sure the samples were properly labeled and stored. Then we would have lunch and do it again. In between the dives, we would catch up on data entry or identify some mantas from the footage we got.  

Why are manta rays so under threat?

Unfortunately there are quite a few reasons. The first is targeted fishing for the gill raker trade, where fishermen actively hunt for manta and mobula rays. After they have been caught, the fishermen cut out the gill rakers and sell them to traders for the Chinese medicine market. The rest of the ray is considered poor quality meat. The demand for their use in Chinese medicine has increased only in recent years and is not backed by scientific evidence.  

Along with other marine life, mantas are caught by accident as fishing by-catch and get entangled in marine debris such as discarded fishing nets and drift nets. I’m not aware of any cases of mantas ingesting plastic and dying like the many examples of whales, dolphins and turtles we see on the internet, but given that they are filter feeders and there’s plastic pretty much everywhere in the sea, I’m sure that this is a threat to them.

What was it like living on Lady Elliot Island? Is it somewhere you’d enjoy going back to?

I’ve only lived there for about a week at a time for each field trip, but have been there seven times. It’s an amazing place and the marine life around the island is spectacular. I’ve never seen so many sharks, turtles, fish and of course, mantas, in one area. I really looked forward to waking up each day to dive. The eco resort on the island is very well run as well, and there are lots of educational tours for visitors. I definitely would love to go back, and have plans to.

Manta rays are so majestic. Is there anything we can do help protect manta rays for the future?

Spread the word about the gill raker trade. I doubt anyone reading this consumes manta rays, but if more people who know and talk about it, maybe it will spread to people who do consume it.

Pick up trash! Pollution is a big problem for our seas and the amount of trash already in the ocean might seem overwhelming and disheartening, but every little bit you pick up could be one less piece ingested by some poor marine creature.

When you go diving with mantas, choose to go with responsible operators so that they will keep doing what they are doing. Diving with mantas will also inject tourism dollars into the economy and countries that benefit from this will be more likely to want to conserve the rays for that reason.

Thank you, Michelle! You hear more stories in person during a freediving course with her at Zen Freediving in Singapore.

If you want to learn more about freediving, check out our interview with Michelle where we talk about all the things your freediving instructor wishes you knew.