The Giant Manta Rays of Revillagigedo

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Steph photographing manta - Doug Keim.jpg

For 28 hours we saw nothing but blue. Sure, there were a few white caps and the occasional seabird, but the majority of the time was spent trying to decide where the sky ended and the sea began. On the second morning, I woke to the feeling of the boat swaying back and forth and walked onto the deck to be greeted by the sight of a huge volcanic island looming on the port side – we had arrived at San Benedicto, and it felt like we were anchored at the edge of the world.

People travel for a variety of reasons, some to adventure, some to relax, some to experience new cultures. Me? I travel for manta rays, and at times this takes me to places I can’t even pronounce. 

The Revillagigedo Archipelago (revi-ya-he-hair-doh) lies 250 nautical miles (approximately 400 kilometres) southwest of Baja California, in Mexican waters. These four volcanic islands emerge from the waters of the eastern Pacific Ocean and are commonly referred to as Socorro, after the largest island in the chain. They were declared a UNESCO world heritage site in 2016 and a marine reserve and national park in 2017. 

The archipelago is known for its unique ecosystem and the waters are bursting with life, making it a world-class scuba diving location. Divers are drawn here by epic encounters with larger, pelagic species (predatory fish like tuna, barracuda and wahoo), numerous species of shark (Galapagos and silky sharks, tiger sharks, hammerheads, and whale sharks), along with humpback whales, bottlenose dolphins and most importantly for me, giant manta rays.

As a marine scientist and manta ray researcher, I have been lucky enough to dive with these incredible creatures in a number of different countries. For the past five years, I’ve worked with the Marine Megafauna Foundation, a not-for-profit organization focused on the research and conservation of large marine species. Joined by my best friend and trusty assistant Laura, and Frida Lara from Pelagios Kakunja – a Mexican-based research and conservation organization – we were leading a citizen science dive expedition onboard the Quino El Guardian live-aboard. The islands were one of Frida’s main study locations for her PhD research, so she knew the dive sites like the back of her hand. Frida is a fellow shark lover and the stories of her dive experiences in the area made me even more excited to get under the water. 

Such expeditions are a win-win as they enable researchers to get out to remote field sites and collect data, as well as provide an opportunity for scuba divers to learn more about the places and species they are diving with, experience things from a scientist’s perspective and assist with research. 

I was particularly excited about the Revillagigedo trip, as it had been on my bucket list for years. Since I started working with manta rays in 2013, I’d heard stories about the mantas of Socorro. Apparently they were the friendliest that people had ever encountered. Inquisitive and curious of divers, they often came close enough to take a spa bath in your bubbles. It sounded too good to be true, and I was dying to experience it for myself.

Our mission was to collect manta ray tissue biopsies for a genetics study (part of my Phd work), as well as take photos of the manta rays we encountered to add to a long-term identification catalogue managed by colleagues at the Pacific Manta Research Group. Manta rays have unique spot-patterns on their underside that enable us to identify each individual, like a fingerprint. By collecting and cataloguing ID photographs, scientists can track individuals over time and build up an idea of the population that inhabits an area. It’s a simple, non-invasive and effective way of learning about wide-ranging marine species. We also had to trial a method of floating drop cameras that Frida intended to use for shark studies on an upcoming research trip, deploy an acoustic receiver station to pick up the signals from tagged animals in the area and to conduct microplastics tows for a colleague looking at the impact of plastics on manta rays. It was a busy agenda, but luckily we had a team of keen citizen scientists to help us out.

There was a buzz of anticipation before our first dive as everyone excitedly put on wetsuits and made sure their dive gear was set up and ready to go. Photographers triple-checked that cameras were charged and underwater housings sealed. Frida, Laura and I made sure we had all of our equipment, jumped in one of the small boats with the dive group and zoomed towards our first dive site – El Cañon. As we approached the drop point and put our masks on, Frida looked at me and said with a smile: “look out into the blue for tigers,” and with that, we rolled back into the bluest water I have ever dived in. 

I have to be honest, my first thought was “damn, this is cold”. Spoiled from years of diving in the tropics, the cooler waters of Revilla certainly took a bit of getting used to. The reefscape was different too, in place of the carpets of coral and small, colorful reef fish were stark rocky pinnacles and steep walls dropping off into the deep. This was the perfect environment for the big pelagic animals that we had come here to see.

The first day did not disappoint, we saw mantas and I managed to collect a few biopsies while Frida and the team deployed the acoustic receiver. Giant manta rays can grow to a whopping seven-meter wingspan. They are gentle giants though, feeding on tiny planktonic animals in the water column and don’t have a stinging barb. Mantas are absolutely amazing creatures to encounter in the wild. Sadly though, they are threatened and global numbers are in decline. This is mainly due to fisheries that target them for their gills which are used in traditional Asian medicines and being caught as by-catch in other fisheries. 

The mantas we saw were extremely chilled. They hovered above us and were truly mesmerizing to watch as they use their wing-like pectoral fins to propel themselves through the water, I had a feeling things were just getting started. 

As the trip progressed, the dives got better and our smiles grew wider. Day 3 took us to the tiny islet of Roca Partida, the northernmost island in the chain. From the surface, Roca Partida looks just like a tiny floating iceberg, painted white with guano. But from below, it was a majestic cathedral spire rising up from the deep and piercing the surface. As the currents rushed around the rock, shoals of trevally congregated in groups so big they blocked out the light. Hammerheads lurked in the deeper waters, Galapagos sharks and yellow-fin tuna hunted in the blue, and white-tip reef sharks formed cuddle-puddles in the rocky indents dotted into the rock face. I didn’t know which way to look, I was awe-struck. We only saw a single manta in the distance, but that didn’t bother me at all. Frida, Laura and I fought the currents and circumnavigated the rock at least twice on every dive trying to keep up with all the action. 

The pièce de résistance was El Boiler, a submerged volcanic seamount off San Benedicto famous for encounters with manta rays and curious dolphins. Within minutes of us dropping into the blue, the mantas arrived and it turns out that the stories were true. This was unlike any interaction I’d ever had. The mantas were inquisitive, they circled around the group, cruising slowly past at eye level and some hovered right above you – letting the bubbles tickle their underside. When we swam to the other side of the seamount, they seemed to follow us – it was incredible. Even when we began to ascend they came up with us. Towards the end of the dive, a group of playful bottlenose dolphins had arrived and kept circling us. One of the larger females was heavily pregnant and especially interactive with the divers. 

Frida taking photo - Steph Venables.jpg

The atmosphere on the boat was electric. When it was time for the third dive of the day, everyone was in their wetsuits and ready to go, keen to get back in and see if the mantas had stuck around. What we didn’t realize is that we were about to drop in for one of the most memorable dives of our lives. The mantas were still there, and at one point we swam a little deeper to get a biopsy of a melanistic male. After I had taken the sample we were approached by a pregnant dolphin, she swam up and stopped in the water column in front of us, hanging vertically and staring with inquisitive eyes. I looked over to see the rest of the group surrounded by mantas and dolphins, I couldn’t believe this place! We realized it was time to start our ascent and as I reached the surface, Frida stuck her head out of the water and yelled: “she’s giving birth!” 

Amazingly, the female dolphin had followed the rest of the divers to the surface and was swimming around with them, mid-birth, with the tiny tail sticking out! This was unheard of. To top it off the manta rays had sensed the excitement and were circling underneath, turning upside down to check out the action. After 10 minutes at the surface, the female decided it was time to go and with a flick of her tail she swam away, leaving us speechless and laughing with joy, what had just happened? We were incredibly lucky, dolphin births are rarely witnessed in the wild and as we hadn’t seen the calf come out fully, the group was hoping that everything was okay. The good news is that a group diving at El Boiler a few days later saw the same female with a newborn calf by her side, phew!

It was a trip of a lifetime. We saw 32 individual manta rays, over seven shark species and had a unique dolphin experience. Revillagigedo had certainly lived up to everyone’s expectations and we had plenty of time to recount the memorable moments on the long trip back to the mainland. 

Did you know? 

  • Manta rays are elasmobranchs, they are related to stingrays and sharks and their skeleton is made entirely of cartilage. They belong to the mobulid family, which are commonly known as devil rays because of their horn-like cephalic fins at the front of their heads.

  • There are two recognized species – the giant manta ray (Mobula birostris) and the reef manta ray (Mobula alfredi). Both species are found throughout the tropics and sub-tropics, mostly in the Indian and Pacific oceans and the Caribbean. 

  • Mantas are the largest of the living rays, with the bigger of the two species reaching a wingspan of over seven metres. They are gentle giants, feeding on zooplankton – tiny animals that they filter out of the water column with their gills.

  •  They are most often encountered at ‘cleaning stations’. These are specific areas of reef inhabited by cleaner fish. These small fish ‘clean’ the manta rays by picking parasites and dead skin off their bodies and cleaning inside their mouths and gills.

Images by: Doug Keim & Steph Venables

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