Reef manta ray
|Reef manta ray|
|M. alfredi in the Maldives|
The reef manta ray (Manta alfredi) is a species of ray in the family Mobulidae, one of the largest rays in the world. Among generally recognized species, it is the second-largest species of ray, only surpassed by the giant oceanic manta ray (a currently unrecognized species from the Caribbean region also appears to be larger than the reef manta ray).
The species was described in 1868 by Gerard Krefft, the director of the Australian Museum. He named it M. alfredi in honor of Alfred, Duke of Edinburgh, the first member of the British royal family to visit Australia.
Reef manta rays are typically 3 to 3.5 m (9.8 to 11.5 ft) in disc width, with a maximum size of about 5.5 m (18 ft). Long included in M. birostris, the status of the reef manta ray as a separate species was only confirmed in 2009. The reef manta ray is found widely in the tropical and subtropical Indo-Pacific, but with a few records from the tropical East Atlantic and none from the West Atlantic or East Pacific. Compared to the giant oceanic manta ray, the reef manta ray tends to be found in shallower, more coastal habitats, but local migrations are sometimes reported. Manta birostris is similar in appearance to Manta alfredi and the two species may be confused as their distribution overlaps. However, there are distinguishing features.
The reef manta ray can grow to a disc size of up to 5 m (16 ft) but average size commonly observed is 3 to 3.5 m (11 ft). It is dorsoventrally flattened and has large, triangular pectoral fins on either side of the disc. At the front, it has a pair of cephalic fins which are forward extensions of the pectoral fins. These can be rolled up in a spiral for swimming or can be flared out to channel water into the large, forward-pointing, rectangular mouth when the animal is feeding. The eyes and the spiracles are on the side of the head behind the cephalic fins, and the 5 gill slits are on the ventral (under) surface. It has a small dorsal fin and the tail is long and whip-like. The manta ray does not have a spiny tail as do the closely related devil rays (Mobula spp.). The color of the dorsal side is dark black to midnight blue with scattered whitish and greyish areas on top head. The ventral surface is white, sometimes with dark spots and blotches. The markings can often be used to recognise individual fish. Manta alfredi is similar in appearance to Manta birostris and the two species may be confused as their distribution overlaps. However, there are distinguishing features.
Physical distinctions between oceanic manta ray and reef manta ray
The first difference could be the size because the giant oceanic manta ray is bigger than the reef manta ray, 4 to 5 m (13–16 ft) on average versus 3 to 3.5 m (9.8–11.5 ft) on average. However, if the observed rays are young, their size can easily bring confusion. Only the color pattern remains a fast and effective way to distinguish them. The reef manta ray has a dark dorsal side with usually two lighter areas on top of the head, looking like a nuanced gradient of its dark dominating back coloration and whitish to greyish, the longitudinal separation between these two lighter areas forms a kind of “Y”. While for the oceanic manta ray, the dorsal surface is deep dark and the two white areas are well marked without gradient effect. The line of separation between these two white areas form meanwhile a "T".
Difference can also been made by their ventral coloration, the reef manta ray has a white belly with often spots between the branchial gill slits and other spots spread across trailing edge of pectoral fins and abdominal region. The oceanic manta ray has also a white ventral coloration with spots clustered around lower region of its abdomen. Its cephalic fins, inside of its mouth and its gill slits are often black.
Distribution and habitat
The reef manta ray has a widespread distribution in tropical and subtropical parts of the Indo-Pacific, with few records from the warm East Atlantic and none in the West Atlantic or East Pacific. It can be observed in several often-visited regions such as Hawaii, Fiji, French Polynesia, Micronesia, Bali, Komodo, Maldives, Mozambique, Australia and the Philippines. It is primarily found in coastal regions.
Reef manta rays live in a more or less identical wide area with the possibility of short migration to follow the zooplankton. They therefore have a relatively sedentary behavior with precise areas for cleaning and feeding still within close proximity of coasts, reefs or islands.
The reef manta ray, as the oceanic manta ray, is ovoviviparous. After mating, the fertilized eggs develop within the female's oviduct. At first, they are enclosed in an egg case and the developing embryos feeds on the yolk. After the egg hatches, the pup remains in the oviduct and receives nourishment from a milky secretion. As it does not have a placental connection with its mother, the pup relies on buccal pumping to obtain oxygen. The brood size is usually one but occasionally two embryos develop simultaneously. The gestation period is thought to be 12–13 months. When fully developed, the pup is 1.4 m (4 ft 7 in) in disc width, weighs 9 kg (20 lb) and resembles an adult. It is expelled from the oviduct, usually near the coast, and it remains in a shallow-water environment for a few years while it grows.
Status and threats
Because of its large size and velocity in case of danger (24 km/h or 15 mph escape speed), the reef manta ray therefore has very few natural predators which can be fatal to it. Only big sharks, as for example the tiger shark (Galeocerdo cuvier), the great hammerhead shark (Sphyrna mokarran) or the bull shark (Carcharhinus leucas), and also the false killer whale (Pseudorca crassidens) and the killer whale (Orcinus orca) are known to kill and eat mantas. The reef manta ray may escape an attack, leaving it with a part of the wing missing.
The reef manta ray is considered to be vulnerable by the IUCN in its Red List of Threatened Species because their population decreases drastically over the last twenty years due to overfishing. Whatever is the type of fishing (artisanal, targeted or bycatch),the impact of the latter on a population which has a low fecondity rate, a long gestation period with mainly a pup at the time, a late sexual maturity can only be seriously detrimental to the species that can not compensate for the losses over several decades. In recent years, fishing for manta rays is significantly boosted by prices of their gill rakers on the market of the traditional Chinese medicine. Pseudo-medicinal virtues assigned to them without proven scientific basis and a clever marketing strategy generate significant demand.
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