| |
(1 of 3) MANTA RAY - Demystifying this enigmatic creature of the deep
STAINED COBALT BLUE, the back of a manta ray is difficult to distinguish from the ocean in which it lives. Its underbelly, however, is a stark white canvas splashed with grey - a dash here, a dot there - and I'm staring up at one, just an arm's length away.
Together we hang, as though suspended on puppeteer's strings, before glassy bubbles from my regulator float upwards, tickling the animal's belly, making it squirm and then slowly move away on silent, beating wings
Manta rays are often encountered around the coral bomrnies, or outcrops, of Lady Elliot Island, a compact coral cay at the southern extent of the Great Barrier Reef Marine Park. They congregate here to be preened by cleaner wrasse - small fish that feed on skin parasites and pieces of loose flesh.
And my aquatic mate hadn't finished with the service. In two wing-beats it moves to the opposite side of the bommie, and suspended once again, is now eyeball to eyeball with me. The experience is pure, unadulterated magic
IDENTIFYING A MANTA
ONE OF THE LARGEST, yet least-known of fishes, the manta ray is found mainly in tropical waters throughout the world. In Australia, they are encountered along the reef edges of Queensland and Western Australia, where tidal action pumps rivers of eggs, larvae and tiny crustaceans the manta's preferred diet - into the open sea; but they've also been spotted as far south as Montague Island in southern New South Wales. Like other members of the shark and ray family, the manta's internal structure is'based on tough but flexible cartilage, not bone. And it's cartilage that helps this graceful animal "fly" through the water (see Under the skin).While sharks are a manta's distant
cousins, eagle and cownose rays, which are closely related, look so similar that people often mistake them for juvenile mantas.
But once you've identified a manta's distinctive features, there's little confusion. A manta has cephalic lobes -large, fleshy protrusions that sprout forward like horns trom its snout; a very broad, rectangular mouth at the front of the head; and, a short, barbless tail. Mantas also grow larger than other rays - wingspans stretch to 9 metres - and top the scales at 1500 kilograms. Finally, they move swiftly in open water, at up to 24 km/h, but are more often seen by humans being preened by wrasse at "cleaning stations" or while feeding.
Primarily solitary animals, manta rays congregate in shallow water to breed, resembling squadrons of stealth bombers when they do.
SO MUCH TO LEARN
DESPITE THE GROWING fascination with manta rays, little is known of their biology, behaviour or movements. Australian Geographic Society-sponsored marine biologist Mark Simmons is committed to learning more.
"Next to nothing is known about these enigmatic creatures," Mark told me as we floated over The Coral Gardens, a confetti of tropical corals and shimmying fishes on the north-western side of Lady Elliot.
Mark has radio-tagged three manta rays believed to be part of a 40-strong population permanently living in the waters surrounding the island.
"I've also placed a data logger in the water near one of the coral bommies where [scuba] divers commonly encounter mantas," Mark said. "When a tagged manta swims within a 500 m radius of the data logger, it records the time, position and identification number of the animal. After six months, the information on the data logger has confirmed that these animals appear to be permanent residents. Continued monitoring, and the placement of a few more data loggers around the island, will hopefully reveal more."
Caption 1:Like a languid bird in a cloudless summer sky, a graceful manta ray wings through the waters of the Great Barrier Reef pursued by fastidious cleaner wrasse. Cloaked in mystery, the manta is the largest of the rays and is found throughout the world's tropical waters.
Caption 2:
A)Eye spy. Unlike most ray species, whose eyes are set on top of the head, manta eyes (right) are located at the side of its head directly behind the cephalic lobes, or horns. To observe these majestic animals, slip into the reefstippled water surrounding Lady Elliot Island (below) in Queensland, where a research program sponsored by the Australian Geographic Society using radio tagging and photo identification, is under way.
B)Trailing plumes of CO2 and festooned with cameras, these divers marvel at a manta. Growing up to 9 m wide and weighing in at more than 1.5 tonnes, these rays are members of the elite "megafauna" club, which includes whales and the plankton-eating wha/f shark.
Caption 3:
A)Uncannily resembling a squadron of stealth bombers (below), manta rays swim off WA'S central coast near Ningaloo Reef. Mostly solitary animals (right) that roam the seas propelled by their undulating "wings", they congregate to breed during summer.
B)UNDER THE SKIN The skeletal structure of a manta ray, including its skull and spine, is based on cartilage not bone. This adaptation, which is almost exclusive to sharks and other members of the ray family, reduces body weight and helps with buoyancy. Movement is achieved by muscle contractions that cause wave-like ripples along its pectoral fins, or wings.
C)PIPES AND ORGANS Covered in thick, sandpaperlike skin, a manta's internal organs are well protected by its cartilaginous skeleton. Its liver, which is at least six times larger than its heart, is rich in oil. This aids the animal's buoyancy, allowing it to hang almost motionless in the water.
Caption 4:
A)Lolly-coloured fish rush an approaching manta that's come to be cleaned at Anchor Bommie off Lady Elliot Island. Once above the coral outcrop, the manta will open its mouth and gills to allow the small fish to feed on parasites and pieces of loose flesh inside.
B)Australian-first research at Lady Elliot Island. Using a hand-held spear gun, Clint Hempsall (bottom) implants' a lipstick-sized radio tag (below left) into the coarse skin of the ray's shoulder. But finding a suitable candidate for tagging isn't always easy. While snorkelling (below right), Clint searches, pulled along by a boat to cover maximum territory.
Continued with 2 of 3 MANTA RAY
|
click to download flash player