Distinguishing Features
They can grow to 6.7m wide, weigh up to 1,400 kg, and are the largest of all rays. The Spanish word for blanket is 'manta' and aptly describes the unique body shape of this animal. 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, as well as species.
There are also regional differences in 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 can be similar in appearance to mobula rays (of which there are 9 species) that grow to 3 metres and share cephalic lobes and gracefully curved pectoral wings. However, mobulas don't have paddle shaped lobes, they have shorter pointed ones which look a little like horns, earning them the common name 'devil rays'. Mobula rays can also be distinguished by the position of the mouth - mobulas have sub-terminal mouths (located underneath the head, similar to many sharks), whilst mantas have terminal mouths (located at the front of the head).
Until recently they were considered to be of a single species but now the genus has been re-evaluated into 2 distinct species - the giant manta ray (Birostris) and the reef manta (Alfredi), officially identified in 2009 by Andrea Marshall. They both have worldwide distribution and sometimes exist in the same region. Their genetic divergence has been confirmed by DNA testing.
Manta birostris is the larger and more widely distributed of the 2 species. It is more commonly found off shore and is believed to be more migratory. Manta alfredi is smaller and is found closer to shore. A possible 3rd species, is being investigated around the Atlantic coast of the Americas.
There are many differences between the 2 identified species. From photographs of the manta's underside, sufficient of these differences can be seen to assist with identification. These include ventral markings which occur higher than the lowest gill openings only on Manta alfredi. Also there is a dark band that runs all along the rear of only Manta birostris from wing tip to wing tip.Behaviour
They are 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.
Manta rays 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 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 them away will greatly increase the enjoyment of your encounter and protect them 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 them 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 them, 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 on one, even 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. They may simply swim along allowing plankton to pass into their mouths, or if it is concentrated they may practise "barrel swimming" 'head-over-heels' to make the most of the localised bounty. They have also been seen to feed by swimming along the seabed if the plankton is concentrated near the floor.Reproduction
The manta ray 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, males chase the female, eventually 1 grasping the tip of 1 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 125 cm 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 they 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 (Oman), 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.
Manta birostris appears to be more widely distributed, reaching as far north as California and Rhode Island in the USA, North Africa and Japan. They also reach as far south as South Africa, New Zealand and Uruguay. Manta alfredi is widespread throughout the Asia Pacific region as well as the Indian Ocean.
While there is considerable overlap, it is worth noting that the coastlines of the Americas seem to be the preserve of birostris, while sightings in the central Pacific region are overwhelmingly of alfredi.Ecological Considerations
Found in every tropical ocean, they stand apart as the largest of all rays; but just as mantas obtain 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 have been taken over a period of 6 months. In the Philippines, increasing pressure on local fisheries has forced fishermen to look to these giant rays as an alternative meat source.
Another factor leading to increased manta 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 harvest will spread to the Western Pacific.
In the Philippines fishermen are licensed to catch mantas using 1 km-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 species population, together with low birth rates and small litters, leaves them highly vulnerable.
When it was discovered that entire populations of whale shark and manta ray had been decimated in the Philippines, a ban prohibiting their harvesting 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 manta rays. 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.
