Leaping Mobula Rays

A loud clap makes us jump and spin 180 degrees to see what's going on behind us. It almost sounded like a distant gunshot, but there is nothing there, just the deep blue waters of the Sea of Cortez. We left La Paz yesterday to explore the beautiful turquoise bays of the nearby islands Espirito Santo, Partida and Los Islotes which are a nature reserve. Last night on anchor was rather rough since the infamous southwest Corumel winds picked up in the middle of the night and transformed our peaceful anchorage on Isla Partida into a rollicking trap with three foot waves. As soon as the sun came up, we were out of there. The good thing is you don't have to go far to escape the Corumel. We just rounded the island to the sheltered east side. It's quiet and calm here. And there it is again, another loud clap not too far away from our boat. And this time we can see who, or more accurately what, is causing all the noise. It's a ray, about 4 ft across, jumping high out of the water and belly flopping back down with a loud smack. There are more. Entire groups of rays are leaping out of the water, flapping their “wings” a couple times, and belly flopping back into the ocean. A few rays even go a step further and do a couple somersaults, head over tail, before smacking back into the water. Friends had told us about the rays, but it's incredible to see them with our own eyes.  From a distance, they look like kernals of popcorn, popping out of the water one after another.  It is an amazing show to watch. Of course, the first question Chris and I were asking each other during the show was why on earth are these rays jumping out of the water? Is it parasite removal? Mating behavior? A feeding method? What is the story?

A flying mobula ray

A ray flapping its "wings" as it leaps out of the water.

A somersaulting ray.

Here's a short video we took from our boat of the rays popping out of the water like popcorn. This was taken on a small point and shoot camera though, and there are much better, professional videos of the same rays on youtube, if you want to see more.

Once we returned to La Paz, I started reading up about the rays and found it is actually quite an interesting story.  We could tell the rays were likely from the manta family because of the “horns” protruding from their head and the shape of their body.  What we didn’t know is there are actually five different species of rays from the manta family (Mobulidae) present in the Sea of Cortez.  Besides the well-known giant manta (Manta birostris), there are four other species, smaller in size, from the genus Mobula.  Three of these species are present in the southern Sea of Cortez during the spring and summer, while only one species inhabits this area in the winter. This made our leaping rays easy to identify! The species is called Mobula munkiana and has several common names such as the smoothtail mobula, the pygmy devil ray, and Munk’s devil ray.  Although my favorite is the local name for them, “tortilla.” Surprisingly, this species wasn’t described until 1987, even though local fishermen have known about them for a long time.  As a result of their recent “discovery,” little is known about M. munkiana’s life history, such as how long do they live and where do they reproduce? Little is also known about where they go when they leave the La Paz area.  Large schools have been observed during the summer months in the northern Sea of Cortez, but it seems they have also been spotted all the way south to Peru.  And they don’t appear very consistent with their choice of location either; often they are only present in an area for a few days and then they disappear for weeks to months. One hypothesis is they may be following their favorite prey, mysid shrimp, although other factors could also play a role such as sea surface temperature or competition with other species.  It makes us feel very lucky to have been in the right place at the right time to see them! Another identifying characteristic of these rays is they are one of the only Mobulid species (out of the five present in the Sea of Cortez) that are consistently seen traveling in large schools. And although all mobulid rays are known to jump out of the water, it is thought the tortilla leaps out of the water more frequently than the other species. The other species tend to be more solitary and a bit less flighty.

Which brings me back to our original question, why are these rays jumping out of the water?  Well, like many questions in biology, no one really knows, though everyone has a theory.  I was able to rule out one of our early speculations that it may be mating behavior.  According to the main paper published on these guys, no reproductive activity was observed during the fall and winter, and they are believed to mate during the spring and summer.  Current theories floating around include it is an attempt to dislodge remoras (small suckerfish), it may be a form of cooperative hunting, it is accidental as a result of wild swimming during feeding, or they are just playing.  Personally, I like the last theory best. Watching the tortillas leap and somersault out of the water during the setting sun couldn’t help but bring a smile to our faces; it just looked like so much fun to see how long you could remain airborne before crashing back into the deep blue water.    

Tortillas appearing to have a good time in the water.

References

Albert, P. and Albert, M. 2005. The Flying Mobulas of the Sea of Cortez.  Available at: http://www.malbertphoto.com/mobulas1.html

Bizzarro, J.J., Smith, W.D. and Clark, T.B. 2006. Mobula munkiana. In: IUCN 2013. IUCN Red List of Threatened Species. Version 2013.2.

Notarbartolo-Di-Sciara, G. 1988. Natural history of the rays of the genus Mobula in the Gulf of California. Fishery Bulletin 86 (1): 45-66.

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