Evolutionary History

The manta ray (Manta birostris) belongs to a group of fish called the elasmobranchs, comprised of the sharks, skates and rays. This group contains approximately 1100 different species. First appearing in the fossil record about 370 million years ago, elasmobranchs can be seen today throughout the world's oceans and, in a few cases, some river and lake systems. Elasmobranchs differ from the vast majority of all other fish by having a skeleton which is comprised of tough, flexible cartilage (as opposed to bone), specialized teeth that are replaced throughout their lifetime, and skin covered with small, dense, tooth-like scales.

Skates and rays evolved from their shark ancestors about 150 million years ago, their broad bodies and wing-like pectoral fins distinguishing the 600 species from other cartilaginous fish. Their flattened shape is generally an adaptation to life on the sea bed; however a few species, like the manta ray, have taken to open water.

General Characteristics

Manta rays themselves first appeared in the fossil record about twenty million years ago and are one of ten living species in the family Mobulidae; all are filter feeders and can be found throughout the tropical oceans of the world. The other nine living species within the family are called the mobula rays; smaller in size than the manta ray, they are very wary of divers and so are much harder to observe closely underwater.

The manta ray is the largest ray species, and one of the biggest animals in the ocean, with a maximum wing-span of over 6.8 metres (22ft) and weighing up to 2000kg (4,400lbs). Like their close relative the whale shark, they feed on tiny planktonic animals (zooplankton), funnelling them into their mouths with two modified fins (cephalic fins) on the front of their head. When the manta ray is not feeding the cephalic fins are curled up into horn-like projections in front of its head, giving rise to the common name of devil ray. However, sinister demons they are not, these massive rays are in fact highly curious and intelligent animals which pose no threat to responsible divers and snorkellers. They have the largest brain of all the shark and ray species, which is in fact proportionally much more comparable in size to the brain of a similar sized mammal, indicating a complex and highly developed mental function.

Large wing-like pectoral fins propel manta rays through the water with great power and graceful ease, while their massive bodies provide shelter for hitch-hiking fishes like the remoras. They attach themselves to the mantas using a suction fin on the top of their heads, but do not harm the mantas, which appear not to be bothered by their presence. Manta rays are born with very long tails, but these are often bitten shorter by predators, such as sharks, as the manta ages. Unlike other closely related species manta rays lack any defensive spines at the base of their tail, and rely on their speed and size to elude predation. Its not uncommon however to see a manta with large shark bites out of its pectoral fins, or even one of its cephalic fins.

Manta rays occur in two colour morphs; the first is the black morph, where the manta is largely black on both its dorsal and ventral surface, with some small

areas of white spots and patches. The second morph is the chevron; this is by far the more common of the two morphs, where the manta has a black and white chevron patterned dorsal surface with a white ventral surface. This ventral surface is often covered in black spots and patches, creating a unique pattern on each manta ray which can therefore be used for identification.

Cleaning Stations

Manta rays often visit specific locations on a reef to have their bodies cleaned of parasites and dead tissue by small cleaner fish. These fish are commonly wrasses, although many other fish groups; such as angelfish, butterflyfish and gobies are also known to partake in cleaning. This relationship is mutually beneficial to both the manta ray, which would otherwise be unable to rid themselves of harmful parasites, and the cleaner fish, which get an easy meal. It's also good for divers, as these cleaning stations provide the ideal location for getting excellent, close up views of these amazing animals as they glide within inches of the reef and the divers. Manta rays are naturally very inquisitive animals and will frequently approach divers; this level of curiosity and voluntary human interaction is very rare in most wild animals (especially marine animals) and adds weight to the theory that these are relatively intelligent and highly social animals.

Manta Reproduction

Very little is known about the reproductive lifecycle of manta rays, as yet nobody has documented the birth of one, and only a few people have been lucky enough to witness matings. During the mating season the larger female manta rays test the suitability of potential mates by leading them on a chase, the males line up behind the female all vying for position until the closest male will eventually grasp one of the female's fin-tips in his mouth. Both manta's rise up towards the surface and mate belly to belly while falling downwards towards the reef. All sharks and rays have internal fertilization; males have two modified pelvic fins (known as claspers) and they insert one inside the female during mating to fertilize her. After mating it's not known how long the female mantas are pregnant for, but it's thought to be about a year. During this time usually just a single pup is nourished by milky secretions from the lining of the mother's uterus, until it is born at a size of about 1metre (3ft) and ready to fend for itself.

Conservation and Protection

Manta rays are currently listed as "Near Threatened" by the World Conservation Union (IUCN). It's known that several populations around the world are severely depleted, but not enough scientific work has been carried out to properly assess this species as a whole. Almost nothing is known about their population ecology, use of critical habitat, movements or reproduction, all of which are important if we are to accurately asses the state of the species. What is clear though are some of the threats that mantas face; drift nets and long lines entangle and kill mantas, mainly as a by-catch of the intended target fisheries. While in the Philippines, Mexico and Indonesia manta fisheries have decimated local populations. Some countries however have taken steps to enforce their own national protection for manta rays; the Maldives has a large population of manta rays which have complete protection and a thriving dive tourism industry which they help to support.

Threats to Mantas Manta rays are listed as 'near threatened' by the World Conservation Union and the full impact from the threats they face is not yet known more...

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