I have a distinct memory from when I was a young lass of a visit to an aquarium on one of our family’s many trips to the eastern U.S. I have no idea what aquarium it was – probably the New England Aquarium in Boston, but that’s just speculation. The point is, I remember one thing from the trip, and it was this: I was looking down into a large, cylindrical pool. It went pretty far down, and we were standing at the top, so the bottom was pretty unclear.
The tank was filled with hundreds of stingrays (this is probably an exaggeration but to my child’s mind it was an enormous amount). Most stingrays in the tank were fairly small, maybe three or four feet across, but deep at the bottom of the tank what I thought was simply part of the floor was another ray. It was massive. To me it looked like this giant took up the entire floor of the tank. Thinking back I’m fairly certain that wasn’t true, but it certainly dwarfed the rest of the stingrays in the tank.
I remember very clearly the feeling I felt when I first saw that animal. It was a mixture of awe and fear, something I still feel when I contemplate the big creatures of the sea. Somehow the name manta ray got associated with that memory, even though I’m positive it wasn’t actually a manta. But still that one memory has made me appreciate the greatness of the manta ray, so now I’d like to share that.
Manta rays are cartilaginous fishes, which have a form of hardened cartilage as their skeleton instead of bones, which is characteristic of other rays and sharks. There are actually two species of manta ray, the resident reef manta and the giant oceanic manta. Reef mantas are the smaller of two, usually growing to about 11 feet. Giant mantas certainly live up to their name. The biggest specimens can reach a wingspan of up to 23 feet and a weight of 4,400 pounds. The two species differ in behaviour as well. As their name suggests, reef mantas tend to stay around reefs and coastal waters while oceanic mantas spend more time in the open ocean, and are much more migratory.
Manta rays basically fly through the water; they beat their pectoral fins like wings which force water backwards and propels them forward. The animals must constantly swim in order to keep oxygenated water flowing over their gills. Mantas that get caught in fishing nets often suffocate because they are held motionless in the nets.
Despite their great size, manta rays are very docile creatures, and feed on some of the smallest animals in the ocean. Manta rays are filter feeders. They swim into swarms of plankton with their mouths wide open, letting gallons and gallons of water flow into their mouths and out through gill slits. Any plankton in the swallowed water is trapped by feathered plates that line the gill slits, where they can easily be swallowed by the manta. They look pretty funny when they feed; not only are the manta’s mouths wide open but they use cephalic fins on either side of their face to help filter in plankton. This may be effective, but it is a bit ridiculous looking:
One of the most fascinating aspects of manta rays is their interactions with other ocean species. They are commonly used as a kind of ‘sea bus’ by a number of fishes. Some simply swim with the mantas, using their body to reduce drag and save energy while swimming. Other fish, called remoras or suckerfish, use specialized fins to attach themselves directly to the manta ray. They often shelter inside the manta’s gigantic mouth, to rest and gain protection. The white suckerfish spends its entire adult life inside manta ray’s mouths. Can you imagine living your whole life in another creature’s mouth? I can just picture the housing ad: ‘Prime real estate in great location. Large windows with great view. Contact seller for details.’ And then the small print: ‘Buyer accepts all risks of swallowing and crushing.’
Although manta rays don’t get a large benefit form these hitchhikers (suckerfish can actually leave wounds on the mantas from their constant sucking), there are other fish that manta rays take advantage of. Manta rays are a magnet for parasites, which attach themselves to every available surface the manta has to offer, including their mouths and gills. To counter these pests, mantas go to cleaning stations on reefs, where certain species of fish feed on the parasites. The mantas open their mouths wide and let these fish swarm over their bodies and in their mouths and have a great feast, while the manta rays get cleaned. Often manta rays have preferred cleaning stations, and will visit the same one over and over.
Manta rays are incredible creatures, though much is still unknown about them, especially the giant ocean rays, as they are hard to find and thus difficult to study. Although the meat of mantas is edible, it is tougher than most fish, so these graceful animals are not usually hunted for food. However, recent developments in Chinese medicine have created a demand for manta ray gill plates, which have supposed health benefits that are not supported by any literature or science. But because of this demand, many mantas are being killed solely for these gill plates; the meat is nearly worthless and carcasses are often sold for animal food.
Stingrays captivated me when I was a little girl; they still fascinate me. So little is actually known about these species that new surprises will continue to emerge about these animals. For example, manta rays have the largest brains of any fish, and the brains are also relatively large even when compared to the manta’s body size. But almost nothing is known about the intelligence of manta rays, though the fish show a high level of social interaction and a marked curiosity towards humans. I can only hope more research and awareness will help us learn about these creatures and preserve them for many, many years to come.