manta

Manta ray Temporal range: 23–0 Ma[1] PreЄ Є O S D C P T J K Pg N Early Miocene to Present
Manta ray at Hin Daeng, Thailand
Conservation status
Vulnerable (IUCN 3.1)[2]
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Chondrichthyes
Subclass:	Elasmobranchii
Order:	Rajiformes
Suborder:	Myliobatidae
Family:	Mobulidae
Genus:	Manta Bancroft, 1829

The genus Manta contains two species of manta rays: the Reef Manta Ray (Manta alfredi) and the Giant Oceanic Manta Ray (Manta birostris),^[3] which are the largest species of the rays in the family Mobulidae, and the largest rays in the world. The largest recorded oceanic manta specimen was more than 7.6 metres (25 ft) across, with a weight of about 2,400 kilograms (5,300 lb), while reef mantas are typically 3 metres (9.8 ft) to 4 metres (13 ft) in disc width, with a maximum possible size of about 4.5 metres (15 ft). Manta rays are circumglobal and are typically found in tropical and subtropical waters, although oceanic manta rays can be found in temperate waters.^[3] Oceanic mantas reside in deep water, pelagic zones, making periodic visits to cleaning stations at seamounts and coastal reefs. Minimal concrete information exists on oceanic manta movements, but they are generally believed to be more transient and migratory than the smaller reef mantas, which tend to be resident to shallower coastal habitats. Manta rays have the largest brain-to-body ratio of the sharks, rays and skates (Elasmobranchii), with ratios approaching what is expected in mammals rather than in fish.^[4]

Taxonomy

At one time it was thought that there were many species of manta. More recently, scientific consensus had it that there was just one species,^[5] a view supported by mitochondrial DNA studies.^[6]

However recent studies suggested that manta rays actually comprise at least two different species, the giant manta (Manta birostris), which migrates, and another smaller one called the reef manta (Manta alfredi), which does not.^[7][8][9] The use of the "alfredi" name is questionable. The species alfredi was first used in Krefft's description of Prince Alfred's manta ray in 1868.^{[10] [11]} Modern genetic studies have shown that Ceratoptera alfredi (Krefft, 1868), revised as Manta alfredi (Krefft, 1868), is a synonym of Manta birostris (Donndorff, 1798). The genus is generally considered to be in need of revision. Even the accepted name Manta birostris is often incorrectly ascribed to Walbaum (1792).

Video of a manta ray

Etymology

The term manta derives from the Spanish word manta, meaning cloak or blanket. This term originated from a type of trap traditionally used to catch rays that has a form resembling a blanket.^[12]

Manta Rays have many common names including, Atlantic manta, Pacific manta, devilfish, and just manta.

Description

Manta rays have a distinctive body shape with triangular ‘wings’ and paddle-like lobes extending in front of their mouths. The average disc width is 6.7 metres (22 ft) and the average weight is 1,300 kilograms (2,900 lb)^[4] They are generally dark on the upper surface, ranging from black to greyish-blue and brown, with pale undersides; individuals have a unique pattern of blotches and scars that can be used to identify them. The large, cavernous mouth is situated at the front of the body and contains 18 rows of teeth on the lower jaw.^[13]

Anatomy

Some ancestral characteristics degenerated due to the feeding change. For example, all that remains of the teeth is a small band of vestigial teeth on the lower jaw, almost hidden by the skin. The number and size of their dermal denticles are also reduced. Manta rays have a much thicker mucus body coating than other rays. Their spiracles are small and non-functional, as all water is consumed orally. Mantas have a tail similar to stingrays, but they have lost their stinger and are harmless to divers.^[14]

Life history

Reproduction

The breeding behaviour observed for manta rays is similar to other closely related rays. Copulation occurs near the surface, no deeper than one metre below. It begins with the male chasing the female, for up to half an hour, both often closely followed by a train of hopeful suitors. Such mating trains seem to be triggered by a full moon. The male bites the pectoral fin and then moves its claspers into the cloaca, holding it there for one minute to one and a half while copulation takes place.^[15] The developing eggs remain inside the female’s body for possibly as long as 12 months and hatch internally so that she bears live young. The average litter size is two pups, and there is often a two year gap between births.^[16]

Behaviour

Underside of manta ray with remoras at Ningaloo Reef

Manta rays frequently visit cleaning stations where small fish such as wrasse, remora, and angelfish swim in the manta's gills and over its skin to feed, in the process cleaning it of parasites and dead tissue. Like other species in the shark family they must swim to keep from sinking, so their stay at a cleaning station is characterised by slow circuits.

Mantas sometimes breach the surface, launching themselves into the air. The Maldives are a hotspot for plankton and consequently for reef mantas. A population of 6–7,000 is resident throughout the year.^{[citation needed]}

They are often described as "flying" through the water on their large "wings", and individuals have been observed to jump clear out of the water, possibly in a form of communication or play.^[13]

Ecology

Feeding

Manta rays are bottom feeders and filter feeders. Mantas feed on plankton, fish larvae and the like that they strain from the water passing through their mouths and out of their gills as they swim. They catch their prey on gill rakers, flat plates of russet-colored spongy tissue spanning spaces between the manta's gill bars. An average-sized manta is estimated to consume 20–30 kilograms (44–66 lb) of plankton per day.

Individuals swim in slow vertical loops while feeding, possibly in an effort to concentrate prey items. The fleshy projections on either side of the mouth also funnel prey; when not feeding, these lobes are either furled or closed in front of the mouth. Manta rays are often host to remoras (Remorina spp.), which attach to the underside of larger specimens and consume food that falls from the mouth.^[13]

In the Maldives they frequently feed by skimming the surface, but when plankton concentrations are particularly high, hundreds of rays will assemble and form a feeding vortex, sometimes in the company of whale sharks. ^[17]

Predation

Large sharks and in some circumstances orcas, are the manta's main predators.^[18]

Relation to humans

Aquaria

Manta rays are very rarely kept in captivity, primarily due to their size. Only four aquariums in the world display manta rays.^[19] One notable example is "Nandi", a manta ray that was accidentally caught in shark nets off Durban, South Africa in 2007. Rehabilitated, and outgrowing her aquarium, uShaka Marine World, Nandi moved to the larger Georgia Aquarium in August 2008, where she resides in its 6.2-million-gallon "Ocean Voyager" exhibit. A second manta ray joined that aquarium's collection in September 2009, dubbed "Tallulah." A third manta ray has recently been added to the Ocean Voyager exhibit.^[20]

The Okinawa Churaumi Aquarium also houses manta rays in the "Kuroshio Sea" tank, the second-largest aquarium tank in the world. On 16 June 2007, the first manta ray born in captivity was born at the aquarium. Although the pup born in 2007 did not survive, the aquarium has also since seen the birth of two more manta rays in 2008 and 2009.^[21]

The Lisbon Oceanarium also hosted a manta ray, Manta birostris, from 2002 until releasing it in 2007. A devil ray, Mobula mobular, was introduced in 2003 and lives there still.

Culture

Moche manta ray 200 AD Larco Museum Collection Lima, Peru

The ancient Peruvian Moche people worshipped the sea and its animals. Their art often depicts manta rays.^[22] Not knowing about their gentle nature, two 1930s movies played on the manta's "fearsome" appearance: 1930's The Sea Bat, starring a pre-Frankenstein Boris Karloff, and 1936's The Sea Fiend, later re-issued as the 1946 Devil Monster.

In 2009, SeaWorld Orlando debuted Manta, a flying roller coaster themed to resemble the manta ray, along with an exhibit featuring other ray species. A similar attraction will debut at SeaWorld San Diego in 2012.

The original Opel Manta A sports coupe build in the 70s in Germany derives its name from its distinctive front section that is designed to imitate the shape of the Manta rays "face".

The American alternative rock band Pixies has also recorded songs called "Manta Ray" and "Dancing the Manta Ray." In 2010, the alternative band Ludo released a song titled "Manta Rays."^[23]

The Manta Ray is one of the animals available in the Marine Mania expansion pack of Zoo Tycoon and its sequel Zoo Tycoon 2.

Status

Threats

Manta rays are subject to a number of anthropogenic threats. Unlike their bottom-dwelling relatives, mantas must swim constantly in order to flush oxygen-rich water over their gills, making them vulnerable to entanglement and subsequent suffocation. Mantas cannot swim backwards, and because of their protruding cephalic fins, they are prone to being caught in trailing fishing line, nets, and even loose mooring lines. Mantas will often attempt to free themselves by somersaulting, tangling themselves further. In the case of loose, trailing line, it is possible for the line to cut its way into the fleshy appendages of a manta as it swims, eventually resulting in irreversible injuries such as loss of cephalic fins and damage to pectoral fins, or even death if the wounds are severe enough. Similarly, mantas are often entangled in gill nets used in coastal and pelagic fisheries, resulting in suffocation and death in most cases.^[24]

While bycatch and accidental deaths are likely to heavily impact slow-growing manta populations, targeted fisheries for manta rays are even more harmful. In the last decade, demand for manta gill rakers—the tough, cartilaginous structures protecting the gills and straining plankton from the water—has been growing in Traditional Chinese Medicine practices, although the remedy calling for dried gill rakers has not been shown to be traditional. As a result of growing demand in Asia, targeted fisheries have developed around the world, including in Sri Lanka, Indonesia, West Africa, and Central and South America.^[25] Each year, thousands of manta rays—primarily oceanic mantas—are being caught and killed purely for their gill rakers. A recent fisheries study in Sri Lanka estimated over 1,000 oceanic mantas being caught for their rakers in the country's fish markets each year.^[26] In comparison, oceanic manta populations at key aggregation sites around the world are all estimated to be significantly less than 1,000 individuals.^[27] Targeted fisheries for oceanic manta rays in the Sea of Cortez in the '80s and '90s wiped out the local manta population, which to date has still not recovered. Intense, targeted fisheries for manta rays have long-term detrimental effects, due to the low reproductive rates and long lifespans of mantas.

Conservation

In 2011 Mantas became strictly protected in international waters thanks to its recent inclusion in the Convention on Migratory Species of Wild Animals (CMS). The CMS is an international treaty organization concerned with conserving migratory species and habitats on a global scale. Although individual nations already protected manta rays, it often migrates through unregulated waters, putting it at increased risk from overfishing.

The International Union for Conservation of Nature (IUCN) declared giant manta rays as ’vulnerable with an elevated risk of extinction’ in November 2011.^[28]

The Manta Trust is a UK based charity dedicated to research and conservation efforts for manta rays. The organization's web site^[29] is also an information resource for manta conservation and biology.

Gallery

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  Manta ray off Ishigaki Island.

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  Manta ray feeding over coral.

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  Close-up of manta at Manta Point in Bali

See also

• List of prehistoric cartilaginous fish

References

This article incorporates text from the ARKive fact-file "Manta ray" under the Creative Commons Attribution-ShareAlike 3.0 Unported License and the GFDL.

External links

Wikimedia Commons has media related to: Manta birostris

• Microdocs: Manta ray
• Manta Ray videos and news stories from the BBC including footage of the possible new species
• Manta birostris, IUCN Red List of Threatened Species
• Manta ray media at ARKive