The Flying Mobulas of the Sea of Cortez

Written and Researched by Paul Albert

Photographs and Story by Michael Albert

6.26.05

Not far from Cabo Pulmo, an unpaved road cuts its way along the eastern shore of the Sea of Cortez. Cows with prominent ribs and slow strides make way for the occasional truck. Along the road, the distance is marked by the appearance of an Ironwood tree and three or four cows lying in its slight shadow. Cardon cacti, tremendous thirty foot towers of resilience, occupy the rest of the dirt and sand.

It is early April and my pickup has been spitting up earth for the last 25 miles. I turn the ignition off and wait for the dust to dissipate. It would have been easy to miss those tiny flashes of light in the corner of my eye. And it would have been impossible to hear the faraway sound of sporadic clapping over the engine din. A couple miles out, one could not be quite sure what they are. Dolphins? Fish? One look through the binoculars and it is clear these were living things which I have never seen before. They are mobula rays.

There couldn't be more than 60 minutes of light left. My brother begins to set up camp while I scramble to unlash the kayak resting on the roof of my pickup. As my kayak arrows towards the activity, I grow anxious, willing the sun to stay up a just a bit longer. About half an hour later, I am paddling among them, in the middle of a pancake commercial, flapjack-like creatures tumbling over themselves, flying everywhere, some of them off in the distance, some only feet away. From the shore, which is now far away, the impromptu camp too small to be seen, you'd think there were a dozen, maybe twenty, but here, sitting on my kayak surrounded by them, it becomes immediately clear, there were hundreds.

And it isn't too long before I glance down and I am forced once again to revise upward my earlier figure. I look down into the plankton-rich green water and note that as far as I can see, the ocean is carpeted with the creatures, thick with black flesh. There they are, hundreds of them gliding in unison with each other, a parade of black kites.

 

Both mantas and mobulas are members of the Family Mobulidae, a group about which, very little is known. It is not uncommon to mistake mobulas for mantas. One researcher I spoke with was careful to make the distinction; another used the names interchangeably. Among many locals, this kind of distinction is all but ignored. Any of the four species of mobulas in the Sea of Cortez (tarapacana, thurstoni, munkiana, and japanica) along with the giant manta ray all go by a single name: cubana. It is not exactly the most delicate of nicknames; cubana means, literally, “Cuban.” Apparently, the dark skin of mobulas and manta rays is reminiscent of members of the island-nation to the east.

Mantas, the most well known of, which is the Pacific Manta Ray, can grow quite large; disc lengths have been measured at twenty-three feet. On the other hand, no mobula on record has ever exceeded ten feet. For this article, I showed the group of photos published here to three different research scientists. All agreed the pictures depicted a member of the genus mobula, but each thought it was a different species.

There are conclusive methods for distinguishing between different species of mobula; inspecting a photo, however, can perform few of them. Among some of the particularly nondescript varieties of mobula, size, shape, and coloration all tend to be different but never distinctly so. To be sure, there are distinguishing differences between species, but they are the kind that require an intimacy between observer and mobula not possible in the wild: examining whether the crown of teeth are smooth, having a look at the cranial nerves.

Knowing that this species of mobula have disc widths of little more than a meter does not help. Variations in disc width among different species can be slight: 300 centimeters. And who is to say that all these jumping mobula are not juveniles of some much larger species?

If I'm confused, I'm not alone. The science of naming mobulids has undergone substantial upheaval in the last few decades. In 1987, Italian scientist Dr. Giuseppe Notarbartolo di Sciara published research describing a species of mobula new to the scientific community: Mobula munkiana he called it. He tells me that fishermen local to Punta Arena de la Ventana (a region not far from where I first slipped my kayak into the Sea of Cortez) had long been familiar with these mobulas. When he was visiting Baja California, he noted that the fisherman called this species with the propensity for airborne flips, “tortillas.”

Tortillas, he says, jump more frequently than other mobula, never grow larger than a meter and are more inclined to school. Notarbartolo di Sciara tells me he believes these photos to be of Mobula munkiana . It is “my best bet, ” he says.

Dr. Notarbartolo di Sciara's research has led him to believe that munkiana dines almost exclusively on a diet of Mysidium. Mysids are planktonic crustaceans. Dr. Carlos Villavicencio Garayzar, the director of the Elasmobranch Laboratory at the Universidad Autonoma de Baja California Sur sits in his office, the desert mountains outside his window. He does not speak with assurance about which kind of mobula eats which kind of food. He does suggest to me that mobulas, in general, tend to eat euphausiids or “krill.” Winter conditions, he explains, particularly the kind found in the open water between Isla Cerralvo and San Jose del Cabo produce a boom of euphausiids. Instead of using teeth, mobulas have sophisticated filtering plates in their gills, which act as a sieve, trapping the tiny shrimp and shrimp-like creatures.

For some time now, the comings and goings of the mobula have remained something of a mystery. Why will a large school spend a couple days in one area, only to seemingly disappear for a few weeks, thereafter? Dr. Notarbartolo di Sciara has suggested these “pulses,” as he calls them, are due to the munkiana's pursuit of Mysidium. Munkiana may be unique among mobulids because it seems to spend its summers in the northern part of the Sea of Cortez and its winters in the southern portion near Cabo Pulmo and its neighbor to the North, La Paz, where I am now. Notarbartolo di Sciara has proposed two competing explanations: it may be a function of competition for resources between munkiana and its larger cousins, or it could be a simple matter of chasing after the Mysids, going where they go.

Whoosh! Without warning, a mobula emerges from below the surface, its long flat body glistening in the evening light and whip for a tail trailing behind. Flap, flap, flap, maybe a somersault or two, and then smack! It happened again and again. Single flips. Straight-up belly flops. Double flips. I see a single mobula leap a few times in succession; others leap only once and then disappear. I witness mobulas partially emerging from the water, one third of the wingtip still immersed, and rotate around that tip. Sometimes, I don't even see that. All that is visible is the swirl of water left behind. Notarbartolo di Sciara writes that when he was in the Sea of Cortez some twenty years ago, he even observed triple flips. According to him, some mobulas leap at heights of up to two times their disc width or up to six feet high.

Breaching is a common behavior among mobulids; it is said to be exclusive to the smaller varieties. For those of us who have witnessed a mobulid's sanguine underwater undulations, it may be hard to believe, but it would not have been uncommon long ago to hear tall tales of devil rays leaping out of the water and crashing through a ship's hull.

At least in the popular press and on the Internet, there is no shortage of explanations for why mobulids jump. Such sources invariably begin, “Scientists think….” Turns out, none of the mobula experts with whom I speak offer any definitive explanation; few would even endorse one over another. Karey Kumli is a research associate at the Pacific Manta Research Group located at Santa Rosa Junior College. She cautions me not to call any of the batch of current explanations theories; unsupported by evidence, they are, at best, opinions.

Is it to dislodge the parasite-cleaning remoras that attach to their backside? Is it some way of keeping fit, of practicing the underwater gathering of food? Could it be a form of play? What if jumping was a form of cooperative hunting, a way of tricking vibration-wary mysids into migrating downwards and into the open mouths of other mobulas below?

I decide to speak with Keller Laros, a dive master based out of Hawaii. Laros created a “Manta Ray Specialty Course” for scuba divers. He has logged long hours underwater observing Pacific Manta Rays, the largest of munkiana's mobulid cousins. According to him, the smaller manta ray's out-of-water acrobatics is not unlike its feeding behavior below the surface. Underwater, mantas have been observed doing loop after loop in the same place, concentrating their prey into a tight area. As they circle, they direct the green soup into their mouths with the cephalic lobes found on each side of their head.

 

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