By Courtney Mattison
For those who have spent time underwater with giant manta rays, the experience they recall sounds dreamlike and meditative. The Mission Blue expedition team felt this phenomenon firsthand at the Revillagigedo Archipelago, an open ocean oasis for giants of the sea. “The mantas are like sirens tempting you to go deeper and deeper following their seductive ocean acrobatics,” remarked Shari Sant Plummer after a day of diving with them at Roca Partida, the smallest of these four volcanic islands. She continued:
The mantas here seem to love divers! They want your attention and if you stop paying attention to them, they will remind you… They’re like my dog that comes and nudges my arm when I’m on the computer so that I’ll come play with him. I’ve never seen a manta like that before. There was one tonight that would not leave me alone. For example, when I was trying to take a good close-up photo of a Galápagos shark, the manta seemed almost jealous of me taking pictures of something else… showing off it’s belly, like, ‘Look at me! Look at me!’ literally getting in my face, looking me right in the eye, engaging me.”
Spanning up to seven meters from wingtip to wingtip, the giant oceanic manta (Manta birostris) is the world’s largest species of ray, yet it filter feeds on microscopic plankton from the water column. “It breaks your heart to leave them,” said Shane Taylor of Fins Attached after spending an entire safety stop being circled by the gentle giants. He continued:
It’s almost like they have a deeper understanding of what we’re trying to do to help them. It’s amazing how intelligent, how social and how accepting they are of us humans. I don’t know of too many other species on the planet that are so welcoming to a strange presence, and it’s not like they’re used to people; we’re pretty remote out here. The mantas get nothing from us—no food or anything—besides social interaction that in some way they must enjoy. That’s why it’s so hard when it is time to leave, because you just don’t want to. They want to share the attention too, making sure that everyone gets some.
Manta ray bellies, spotted with black and white markings, serve as a way for researchers to identify individual animals. Lead expedition scientist, Dr. James Ketchum of Pelagios Kakunjá, compiles images of these markings into the Pacific Manta Research Group Database—a visual database of individual manta rays, many of which have been fitted with tracking tags. “Mantas are visually identified by taking photos of the spots and markings on their bellies,” Dr. Ketchum says. He continues, “Each individual manta can be identified in this way because the spot patterns are very specific, like fingerprints.”
Researchers are trying to find out more about where mantas migrate, feed and reproduce in order to better protect them. The mantas are tracked using acoustic and satellite transmitters. With acoustic tagging, scientists can determine the mantas’ residency and daily movements in and out of a particular site or islands. With the satellite tagging they can study their actual routes and migratory patterns, including depth and temperature preferences.
The giant mantas of Revillagigedo appear to stay in local waters, but move between the different islands of the archipelago, with some recorded movements to the Gulf of California and Puerto Vallarta about 250 nautical miles away. They are protected within the Revillagigedo Archipelago Biosphere Reserve, an area established in June 1994 by the Mexican Government to tightly control access and safeguard biodiversity. Nevertheless, these mantas are threatened by commercial fishing.
As mantas feed on plankton in the water column, researchers are finding that they also accidentally ingest microplastics. Tania Pelamatti, a PhD Student with Pelagios Kakunjá, is currently measuring the quantity of floating microplastics in the waters of Revillagigedo Archipelago. She is also taking samples of manta tissues in order to measure the accumulation of chemical pollutants leached by ingested plastics. Working with Tania, Andrea Asunsolo-Rivera, a student scientist with Pelagios, collected plankton tows to detect levels of microplastics for this study in the Revillagigedo Biosphere Reserve during Mission Blue’s latest expedition.
Mantas are already directly threatened by Asian market demand for their gills and wings, although giant mantas are a species protected under CITES (the Convention on International Trade in Endangered Species). The added threat of poisoning by microplastics is arguably more difficult to control than fishing, putting these iconic animals in harm’s way despite efforts to protect them. Mission Blue seeks to raise awareness about the beauty and vulnerability of these incredible animals in order to support further protections for them. Learn more about Pacific mantas in the TED Talk below by Dr. Robert Rubin.