what are mobulid rays?

Manta and devil rays, known collectively as mobulids, are some of the most beautiful, fascinating and enigmatic creatures in our oceans.

Close relatives of all sharks and rays, these cartilaginous, filter-feeding fish range throughout the tropical and sub-tropical oceans of the world. Born into a life of perpetual motion, they can never stop moving, as they must keep water flowing over their gills to respire. Their daily and seasonal movements are tuned to the ebb and flow of the ocean currents that breathe life into their world, bearing the planktonic food upon which they depend.

Reef Manta Ray, Manta alfredi, Hanifaru Beyru, Baa Atoll, Maldives © Guy Stevens, Manta Trust 2016.jpg

what are manta rays?

The Gentle Giants of the Sea

Manta rays are giants of their kind, with the largest individuals reaching seven metres in width and weighing up to two tonnes. Despite their colossal presence, mantas are gentle creatures. They have the largest brain of all fish, and their intelligence and curiosity make encounters with manta rays a truly magical experience. It is little wonder that for many years they have been well known and loved by the SCUBA diving community. More recently, they have also found mainstream popularity with a wider, global audience, featuring in ground-breaking wildlife documentaries such as the BBC’s Blue Planet II. Their obvious intellect and complex social interactions set manta rays apart from other fish, but as they have only been scientifically studied in detail for around a decade, much of their life history remains a mystery. 


Identifying the Manta Species

In 2009, scientists established that there are at least two distinct species of manta ray; the giant oceanic manta (Mobula birostris), and the reef manta (Mobula alfredi). There are several morphological and behavioural differences that distinguish the species apart. The most obvious differences relate to their body size, their colouration, and their habitat use, and are described below. However it‘s worth noting these are only rules of thumb - some mantas look very similar to the other species! There are also black-morph individuals found in both manta species.

Genetic work is continuing to further define the true nature of this separation, both for mantas and devil rays. For example, as recently as 2017 genetic studies revealed that manta rays are more closely related to devil rays than previously thought, and that they all belong to the same genus 'Mobula' (whereas before they separated as Manta and Mobula). Further still, researchers are currently debating the existence of a third species found exclusively around the Yucatan Peninsula in the Mexican Caribbean.

Reef Manta Ray Dorsal Markings 3, Unknown Location © Guy Stevens, Manta Trust (E).jpg

Reef Manta Ray (Mobula alfredi)

  • Can grow to have a wingspan up to four metres.

  • Spend their lives resident to certain reefs and atolls in shallow or coastal areas.

  • Feature a distinct Y-shaped shoulder pattern.

  • Spots usually found between their gill slits.

Oceanic Manta Ray, Manta birostris, Southern Spur, Fuvahmulah Atoll, Maldives © Guy Stevens Manta Trust 2015 (15).jpg

Oceanic Manta Ray (Mobula birostris)

  • Can grow to have a wingspan up to seven metres.

  • Live in deeper waters out in the open ocean.

  • Feature a distinct T-shaped shoulder pattern.

  • Spots rarely found between their gill slits.

  • Typically have dark mouths and dark bands along the edges of their pectoral fins on their ventral surface.

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what are devil rays?

We know even less about devil rays than we do mantas; they are shy and elusive, making them harder to observe and study in the wild.

Devil rays are the manta’s smaller and more elusive relatives. They are generally very shy towards divers, making it hard to observe and study their behaviour in the wild. But what they lack in size, they make up for in acrobatic enthusiasm. During courting events, several of the pygmy devil ray species (particularly Mobula munkiana) are known to aggregate in vast shoals that number in the thousands - delivering one of the ocean’s greatest spectacles. As a shoal gets bigger, individual rays start to propel themselves out of the water, reaching heights of over two metres, before belly-flopping back into the ocean with a crash. More and more join in over time, until the air is filled with leaping rays. The reason for this behaviour is unclear, but scientists believe the most likely purpose is communication. It could be that the louder splashes created by the biggest individuals are those most likely to attract a mate, but that does not seem to stop smaller rays joining in the excitement. Even less is known about devil rays than mantas; they are generally very shy towards divers, making it hard to observe and study their behaviour in the wild.

Manta and devil rays first appear in the fossil record around 28 million years ago; evolving from bottom dwelling rays, they adapted to life in the water column. They are defined by their specially modified gill plates, which they use to strain zooplankton from the water column. Mobulid rays have a conservative life history strategy; they take a long time to reach sexual maturity, are slow to reproduce, and tend to give birth to a single pup every two to five years following a nine to twelve month pregnancy. This strategy may have served them well for millions of years, but unfortunately these traits, paired with their highly migratory nature, now leave mobulids extremely vulnerable to overexploitation by man.

Photo by Rory Moore.

Photo by Rory Moore.

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