Wednesday, May 9, 2012

Giant Ray...Surf Underwater

There are stingrays, electric rays, and other rays, and we even eat some of them. Baked, marinated and roasted, cooked, fried, etc. etc. But under the sea, there is one ray that may reach a huge size of about 7.6 metres (25 feet) wide-almost as wide as a hang-glider. This is the Giant Oceanic Manta RayOceanic mantas reside in deepwater, 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, with ratios approaching what is expected in mammals rather than in fishes. 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) 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. (Wikipedia)

Manta rays frequently visit cleaning stations where small fish such as wrasseremora, 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.
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.

Their preys???
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.
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.

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. 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.


Anonymous said...

ever wanted to go back again?

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