Diving with Manta Rays

Devil Rays - Graceful Gliders

We have done some of the world's best manta ray dives and know that the joy of diving with mantas is difficult to overstate. Manta rays capture divers' imaginations since they move so gracefully and majestically through the water - whether frolicking in the surf, or enjoying the skin care treatment of a mantaray cleaning station. Find out more about these beautiful and mysterious fish ...

There are few sights more awe inspiring for scuba divers than watching manta rays performing their graceful somersaults. These magnificent creatures are frequently seen feeding alone or in small groups near the surface at Thailand scuba diving sites such as Koh Bon, Komodo in Indonesia, the Maldives, Black Rock in Myanmar, Kadavu in Fiji, and other near shore waters near coral and rocky reefs.

Mantarays are strong pelagic swimmers, possibly able to cross the open ocean and so often host one or more clinging remora, or sucker fish. Remoras have their first dorsal fin modified into a sucking disc. While the remoras do not harm their host directly (apart from sore skin where attached), the manta ray does use more energy in swimming.

Manta Ray Fact Sheet

Family name: Myliobatidae, subfamily Mobulinae
Order name: Batoides
Common name: Mantaray
Scientific name: Manta Birostris

Distinguishing Features

Manta rays grow to 6.7m wide, weigh up to 1,400kg, and are the largest of all rays. The Spanish word for blanket is 'manta' and aptly describes the unique spherical body shape of this animal.

Also known as "devil ray" with graceful pectoral 'wings', manta rays are easily recognised by their paddle-like cephalic lobes projecting forward from the front of the head (actually extensions of the pectoral fins, supported by radial cartilages), and a very broad, rectangular terminal mouth.

Mantas vary in colour from black, grey-blue, to red-brown on the upper surface of their cartilage body, sometimes with white shoulder patches and blotches, and almost pure white on the lower surface of their pectoral fins and body disc. Their body patterns show individual variation and helps identify individuals.

There are also regional differences in manta ray colour patterns. For example, specimens from the eastern Pacific often feature dusky to mostly black undersurfaces, while those from the western Pacific are typically snow white underneath.

Although it's difficult not to recognise an adult manta ray, juveniles are similar to mobula rays (of which there are 9 species) that grow to 3 metres and share paddle-shaped cephalic lobes and gracefully curved pectoral wings. Mantas are now thought to be a single species, and mobulas are most readily distinguished by the position of the mouth - mantas have terminal mouths (located at the front of the head), whilst mobulas have sub-terminal mouths (located underneath the head, similar to many sharks).

Behaviour

A manta ray is capable of rapid speed and juveniles sometimes leap well clear of the water, landing with a loud slap, sometimes performing 2 or 3 of these jumps in succession. The act seems to be playing or social behaviour - the great, crashing splash of their re-entries can often be heard from miles away. Getting rid of parasites may also play a role, much like breeching whales.

Mantarays frequently visit reef-side "cleaning stations" to let cleaner wrasse remove small parasites from skin and gill cavities, sometimes several lining up to wait their turn.

Seemingly inquisitive, manta rays may sometimes approach and even solicit attention from divers, apparently enjoying the tactile stimulation provided by human contact as well as the bubbles from scuba units. In areas frequented by divers, however, they often become very wary and cease to approach.

When approached rapidly or grasped, they roll onto their backs, dive, or swim away rapidly, righting themselves only when some distance away. Entering the water carefully so as to not scare manta rays away will greatly increase the enjoyment of your encounter and protect the manta rays from injury. Hovering and staying still will eventually allow the manta ray to approach you. It's best to position yourself a long the bottom or near a cleaning station to observe them close up.

Touching a manta ray, even if they present their bellies for a rub, will remove some of the mucus that protects the against marine infections. Stay within their vision and let them decide if they want to approach you. Although some manta rays seem to enjoy the bubbles from the SCUBA unit on their bellies, avoid exhaling bubbles into their face, as it may scare them off.

Flash photography and video doesn't seem to bother the manta ray, but do not disturb them if they are engage in feeding, cleaning or mating. Direct eye contact is considered a friendly connection, which they also seem to enjoy. Remember to never ride a manta ray, event though it may appear as if they present themselves for a ride.

Feeding Habits

Even though mantas have up to 300 rows of small peg shaped teeth (the size of pin heads) only on the lower jaw, they really are gigantic filter-feeders, preying on planktonic crustaceans and small schooling bony fishes.

The 2 fleshy lobes of cephalic fins are unrolled and held at a downward angle to create a funnel guiding prey into their enormous mouth. Feeding often occurs near or at the surface where plankton accumulates.

Reproduction

The mantaray is ovoviviparous with a usual litter size of 2 - each pup wrapped in a thin-shell that hatches inside the mother, later to be born alive. Birth occurs in relatively shallow water, where the young remain for several years before expanding their range further offshore. Like sharks and other rays, mantas are fertilized internally.

Male manta rays have a pair of penis-like organs called claspers, along the inner part of their pelvic fins. During courtship, male chase the female, eventually one grasping the tip of one of her pectoral wings between his teeth, and pressing his belly against hers.

Then, the male flexes one of his claspers and inserts it into her vent. Copulation lasts about 90 seconds. The fertilized eggs develop inside a mother manta's body for an unknown length of time that may exceed 12 months.

Life Cycle

A newborn manta ray is about 125cm wide and growth is rapid, doubling in size during the first year of life.

Males mature when they reach a size of about 4 metres, females at about 5 metres; it is unknown what age this is. Likewise, it is not known how long manta rays live, but best guesses are about 25 years.

Predation

Only large warm water sharks, such as the tiger shark are known to prey naturally upon manta rays.

Distribution

Manta ray distribution is circum-tropical, around the globe, generally between 35 degrees north and south latitude.

This area includes South Africa, Madagascar, Mozambique to Somalia; in the Gulf of Aden, Red Sea, Arabian Sea, the Bay of Bengal, Burma (Myanmar), Thailand, Malaysia, Indonesia, Philippines, Cambodia to southern Japan, northern Australia, Micronesia, New Caledonia, Fiji, New Guinea, Solomon Islands, Hawaii, southern California to northern Peru, North Carolina to southern Brazil, the Azores, and Senegal to Liberia.

Ecological Considerations

Found in every tropical ocean, the great manta ray stands apart as the largest of all rays; but just as mantas are obtaining star status with scuba divers, promising increased eco-tourism revenues, their populations around the globe are in peril.

The harvest of manta rays in eastern Indonesia has increased exponentially in just a few years. It has been estimated that over 1,500 mantas have been taken over a period of 6 months. In the Philippines, increasing pressure on local fisheries has forced fishermen to look to the manta as an alternative meat source.

Another factor leading to increased manta ray harvests is the new demand for brachial gill plates which are used in traditional Chinese medicine. Its skin has also been exploited for such as wallets and handbags. Overall this represents a 10-fold increase in farming over historic levels and it is feared that this increased manta ray harvest will spread to the Western Pacific.

In the Philippines fishermen are licensed to catch mantas using 1 kilometre-long drift nets about 30m in height. These nets also catch dolphins and endangered turtles, which are being marketed as shark meat. This overexploitation of manta populations, together with low birth rates and small litters leaves manta rays highly vulnerable.

When it was discovered that entire populations of whale shark and manta ray had been decimated in the Philippines, a ban prohibiting the harvesting of mantas was imposed in 1998. But this was short-lived. 4 years later, due to the lack of resources to implement a sustainable management system, and political pressures from fisherman, the ban was lifted.

A delicate balance exists between the economic well being of small fishing villages, demand for Chinese medicine and the protection of mantarays. Helping local groups protect ecosystems that are frequented by these rays for tourism may be the only viable solution. Conservation efforts need to work internationally and with local communities to protect these majestic creatures.

Dive Sites

More detailed information on manta ray diving destinations:

Australia

Burma - Myanmar

Fiji

Indonesia

The Maldives

Thailand

Dive The World Recommendations: Irian Jaya, the Maldives, Black Rock and Koh Bon.

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