Creature Feature: Flying Mobula Rays

As summer approaches, I get excited looking ahead to my adventure to La Paz, Mexico, at the end of it. Why you ask? Because I am hoping I might catch a glimpse of those beautiful creatures known as the flying mobula ray.

Mobula rays are larger rays, often mistaken for mantas, that are mainly known for their aerobatic breaching.  These rays, also known as “devil fish”, have been reported to breach as high as 6 feet above the water in the Sea of Cortez (Gulf of California). While doing some research for this “Creature Feature” I came to find out that very little is known about these rays. It has been said that there are more questions than answers about them. For instance, nothing is known about what happens to the mobula ray or where it goes between being a pup and a mature adult – it just seems to disappear during this time.

Members of the Family Mobulidae, which does include the larger manta rays, there are four species of mobulas found in the Sea of Cortez (tarapacana, thurstoni, munkiana, and japanica), but it is very difficult to distinguish the different species unless you can get up close and personal with them. Amongst the locals of Baja, the different mobulas, along with the mantas, are all lumped under the name “cubana”. However, mobula mukiana found in the Punta Arena de la Ventana area have a greater propensity to perform airborne flips which led to fisherman in that area to call them “tortillas”. Tortillas have a tendency to jump more frequently than other mobula, never grow larger than 3-4 feet and are more inclined to school.

The reason for breaching, which is exclusive to the smaller mobulid varities, still remains a mystery to researchers, however, a few opinions have been formed. Some think breaching is a means by which to dislodge the parasite-cleaning remoras that attach themselves. Then there are those that feel it may be a way to keep fit for gathering food. While others feel it may be a cooperative form of hunting, much like whales forming bubble circles. It is thought that the vibrations from breaching may cause prey to be driven downward to other rays waiting to feed below. Then there are those that feel it may simply be a form of play.

Mobulas are known to feed on “krill” (euphausiids) or “mysids” (mysidium) which are planktonic crustaceans. These rays feed by filtering the tiny shrimp-like creatures through plates in their gills. It is believed that much of the mobulas migration is based on following their food source.

Except for the mobula japanica , mobulids do not have spines or stingers in their tails as a defense mechanism.  They must rely their size and speed to escape. Another interesting fact about mobula rays is they have disproportionately large, complex brains compared to other fish. “In fact, the weight of their brains relative to their body weight is comparable to many mammals.”[1] It has been documented that mobulids, particularly manta rays, have exhibited “un-fishlike”, almost curious or playful, behavior amongst other rays, and scuba divers as well.

The fight to protect mobulids is on the rise as we discover these creatures have a “long lag time in population response to harvesting”.[2] They have a very slow rate of reproduction, what appears to be producing only a single pup every 2-3 years, making them extremely vulnerable to stock depletion.[3] For species like these, it may take decades to recover from excessive mortality from fishing and accidental by-catch. I hope that efforts to protect these beautiful creatures are successful so that generations after us will be able to view their spectacular aerobatics and gentle splendor.

Notes [4] & [5]

[1] Albert, Paul and Michael, 26 June 2005, "The Flying Mobulas of the Sea of Cortez".

[2] Musick, John, "Ecology and Conservation of Long-Lived Marine Animals".

[3] Dr. Nortarbartolo di Sciara

[4]McEachran, J.D. and G. Notarbartolo di Sciara, 1995. Mobulidae. Mantas, diablos. p. 759-764. In W. Fischer, F. Krupp, W. Schneider, C. Sommer, K.E. Carpenter and V. Niem (eds.) Guia FAO para Identification de Especies para los Fines de la Pesca. Pacifico Centro-Oriental. 3 Vols. FAO, Rome.
[5] Last, P.R. and J.D. Stevens, 1994. Sharks and rays of Australia. CSIRO, Australia. 531 p.