(2 of 3) MANTA RAY - Demystifying this enigmatic creature of the deep
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Mark's work also includes a photo-identification program, which involves photographing the ventral surface, or underside, of individual rays. "The markings on the belly of a manta are akin to a human fingerprint," Mark said. "So by recording and creating a database of images of different mantas, we're again learning more about the resident population as well as about migratory animals that may stop off here to feed or breed."
Why is such information important?
"We've no idea what the standing Australian or global population of mantas is," Mark said. "Nor what impact humans have on these amazing animals. But given they're an unprotected species, and mankind's track record in driving wildlife to the brink, it's time we knew more."
While research can be carried out on dead manta rays, it's far more difficult to study them while they're living. They usually die in captivity, refusing to eat and apparently experiencing huge stress when confined. Three mature mantas living in an aquarium in Okinawa, Japan, are the only ones known to have survived for any length of time in a tank, but the size of the tank is massive 200 tonnes of seawater kept at 24.7°C - and they've been there sinc~ just after birth
A HEARTY APPETITE
MOUTH AGAPE and flapping slowly in swirling loops towards the sun dappled surface, a manta feeds. Nearby, I watch as the gigantic filter-feeder unfurls its cephalic lobes and uses them like slender, artistic hands, sweeping water into a cavernous mouth.
On scuba at 10 m near Lady Elliot's Lighthouse Bommie, I'm a guest at the manta's dining table, and as I settle down to watch, I'm mesmerised.
Nearing the surface, and having finished the first course, the manta points its lobes to the sea floor and plunges down, stopping a metre from me. Then, it begins its spiralling ascent - believed to concentrate or herd the plankton - once again.
The manta ray, like the whale shark, feeds on plankton - a mix of tiny plant organisms, crustaceans and small, schooling bony fishes - by filtering plankton-rich water through its gills) which are composed of pinkish-brown spongy tissue arranged in flattened, horizontal plates.
But the manta hasn't always been a filterfeeder. Nine to 12 rows of grinding teeth in its bottom jaw attest to this. Now covered by a thin layer of soft skin, the teeth are remnants of an evolutionary era when mantas hunted larger prey.
Today, the only biting a manta does is during mating.
IT'S ALL IN THE BREEDING
BELIEVED TO BE sexually active from about five years of age, manta rays mate in the summertime in depths of 1-10 m when water temperatures are 26-29°C.
Playing a game of cat and mouse just before copulation, several males court a female, swimming closely behind her at faster-than-usual speeds (9-12 kmfh). This courtship lasts for 20-30 minutes before the female decreases her speed, allowing a male to nip the tip of one of her pectoral fins (wings), severely hampering her swimming ability. The male then positions himself on the underside of the female, abdomen to abdomen, and inserts one of his claspers (paired sex organs developed along the inner margins of the pelvic fin) into her cloaca (vent). This usually lasts 90-120 seconds. Once the sperm is released, the male continues biting the female's fin for a minute or so before swimming off. Another male, which circles the couple during mating, then moves in and repeats the process. After the second encounter, the female swims away, leaving other courting males behind reinforcing the belief that the most dominant males mate, ensuring the continuity of the strongest gene pool.
Gestation takes about 13 months, during which time the one or two developing pups are wrapped in a thin-shelled "egg" that hatches inside the mother. Soon afterwards, the female gives birth in relatively shallow water, where the pups remain for several years before expanding their range further offshore. When born, they measure 1-1.5 m in width and weigh up to 11 kg, while their fins are wrapped in an s-shape one above and one below the body. They double their size in the first year of life.
RECENT RESEARCH into the anatomy of the manta ray has concluded that this intriguing animal has one of the largest brains of all cartilaginous fishes, and that the portion of it that deals with reasoning is highly developed.
I pondered this when I met Superman - a 4 m wide manta named for the white, diamond-shaped blaze on his otherwise blueblack belly - while snorkelling off Lady Elliot. He'd circled me a few times, an inquisitive eye following my movements, before coming in close enough to touch. And then we were swimming together wing-beat and fin-kick - on the surface of the ocean; just Superman and me.
Had he sized me up and reasoned that, given his size and stature, I posed no threat? Or was he coming in closer to inspect an oceanic curiosity?
I'll never know the answer - but like any good comic-book heroine, I fell for my superhero that day: hook, line and sinker
A)Marine biologist Mark Simmons (above) attaches a data logger to the mooring line at Lighthouse Bommie. The data logger records the time, identification number and position of tagged mantas passing within a 500 m radius of it. Back in the dive boat (right), Mark searches for mantas swimming near the surface.
Early morning on the reef and we're hanging, motionless, as two giant mantas - elusive as shadows glide overhead, momentarily blocking the sun.
B)Just as our fingerprints help distinguish us, a manta's belly markings (left and far left with remoras or sucker fish attached) identify it. Using photos taken at Lady Elliot Island, Mark Simmons (below, at left) and fellow marine biologist Richard Fitzpatrick compile a database of mantas that will help determine the number of migratory rays visiting the island.
A)Looking more sci-fi creation than open-water animal,the larvae of a mantis shrimp (right - Squilla sp.) is one of hundreds of microscopic crustaceans and plants (middle) that comprise the ocean's plankton community. Another is the copepod (far right- Pontelina sp.)Photo - Peter Parks/imageqest3d.com. All become food for the manta ray as they are filtered through its large, striated gills. Illustration- David Kirshner
B)Mouth agape and gills flared, a hungry manta feeds (above) Illustration- David Kirshner. Using its cephalic lobes, the manta sweeps plankton-rich seawater into its cavernous mouth before straining it through spongy filters (left) Illustration- David Kirshner. With plankton captured and then moved into the digestive system, the water is passed out through the gills. Mantas eat about 15 per cent of their body weight each week.
C)Pirouetting upwards in a broth of plankton, the feeding ritual begins. Kilo upon kilo of tiny crustaceans are swept into a mouth designed to trap them and filter out their watery carriage.
A)Rough and tumble. The mating process for mantas involves an exhaustive game of cat-andmouse and pectoral fin-biting. In the initial phase, two or more males pursue a female, chasing her at speeds of up to 12 km/h for around 30 minutes before the dominant male moves in.Photo by Michael S Nolan/Seapics
B)Not your average sexual encounter. The five basic steps of manta mating are chase, bite, copulate, bite and release; the last four taking just two minutes.
C)Biting the female's pectoral fin, a male manta will then position himself stomach to stomach with the female and insert his clasper, or reproductive organ, into her vent for 90 seconds or so. During this time, the pair, which began mating near and parallel to the surface, sink slowly, like falling leaves, towards the ocean floor.Photo by Michael S Nolan/Seapics
D)A female manta. (below) flees amorous males after a se'cond mating - immediately after the first - took place. The second male circled the male and female during the initial copulation. Photo by David Kearns/Seapics
- Scientific name: Manta birostris
- Distribution: Throughout the world in tropical seas between 35°N and 35°S,mainly over continental shelves
- Size: <9 m across
- Weiqht <1500 Kg
- Speed:<24 km/h
- Colour: Blue-black to greenish grey-brown above, frequently with irregular paler shoulder patches; predominantly white underneath with pale-grey markings but sometimes same as above with white markings
- Food: Plankton sieved through gills
- Reproduction: Give birth to 1-2 live young
A)Finning face down over The Coral Gardens, you enter a riotously colourful world of barracuda, triggerfish, reef sharks and rays.
B)Huddled in a cosy coral cave, a metre-long flowery cod (above - Epinephelus fuscoguttatus) appears oblivious to the passing parade of technicolour fish. A 10 cm long pink anemonefish (right - Amphiprion Perideraion) ventures from the protective tentacles of its host anemone; its mate remains partially hidden. Marine biologist Richard Fitzpatrick takes a close look at an olive sea snake (far right - Aipysurus laevis). A curious animal, this species often approaches divers, wrapping itself around their arms or legs before moving on.
C)diagramma labiosum - A sackful of slate sweetlips swamp the camera lens of photographer Mark Spencer as they hover under a coral ledge off Lady Elliot Island.
A)After enlisting the services of cleaner fish at Anchor Bommie, Lady Elliot Island, a manta turns tail at dusk and heads for deeper water off the continental shelf. Mantas apparently do this to avoid predators such as tiger sharks, which hunt in shallow waters at night. But like many of the manta's as yet unknown behavioural traits, its nighttime movements remain a mystery.
B)PLAN YOUR EXPLORATION of one of the world's most exceptional natural wonders, the Great Barrier Reef, using the completely
revised and updated Australian Geographic Great Barrier Reef map. Jam-packed with fascinating information, from greenturtle nesting on Lady Elliot Island to handy hints on negotiating the Inner Passage - the reef's main north-south shipping channel that stretches 2000 km from the Tropic of Capricorn to Cape York - this map is your guide to smooth sailing,turquoise seas, exquisite coral reefs and jewel-bright tropical fish. Split in two for ease of use, the map also features the Queensland coastline from Maryborough to Cape York as well as the Torres Strait Islands. So when you pack the sunscreen and a snorkel, be sure to include your copy of our Great Barrier Reef map
C)AUSTRALIAN GEOGRAPHIC thanks Tony Walsh, Queensland Tourism; Chris Cahill, Steve Heath, Alan Simpson, Robbo, Aeron, Jamie and all the Lady Elliot Island staff; Apollo Australia; Richard Frtzpatrick and the Undersea Explorer; Melissa McMahon; Debra Simmons; Clint and Joanne Hempsall; Rick Martin, ReefOuest; Kazunari Yano; Peter Last and all those featured in the article for their assistance.
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