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July 5, 2007

First birth of a manta ray in captivity

It took place on June 16, 2007 in the Okinawa Churaumi Aquarium in Japan.

Long story short: The female ray was born with its wings folded: they gradually unfurled to a span of 1.9 meters (about 6 feet).

Here's Rick Weiss's July 2, 2007 Washington Post story about the event, which was broadcast live nationwide in Japan on NHK television.

The video above is 59 seconds long; that below lasts 32 seconds.

    Death of Manta Ray Sheds New Light on Species

    So you're a pregnant manta ray, and you're about to give birth to a baby with, oh, a six-foot wingspan. How on Earth will you manage that?

    Now, for the first time, scientists can answer that question: You gently flap your glorious, 13-foot-wide wings to swim to the bottom. You rub your swollen belly on the ground for a while. Then you gain a little altitude and, with a forceful push, you eject your precious bundle as a rolled-up, burrito-like tube, which promptly unfurls to begin its new life as one of the strangest and least-understood marine animals on the planet.

    Those are a few details that have come to light from the first birth of a manta ray in captivity, on June 16 at the Okinawa Churaumi Aquarium in Japan.

    While America was tracking Paris Hilton's jail routine, Japan was enthralled with video coverage of the birth, which was broadcast nationwide on NHK television.

    Unfortunately, the baby ray died five days later — in part from injuries inflicted by its father for unknown reasons before it was moved to a separate tank. But short as its life was, the newborn added some data points to the largely blank page of what is known about this largest species of ray.

    Until now, for example, no one knew how long the gestation period is for mantas. In the Okinawa aquarium's huge tank, where the mother was observed mating on June 8 last year, it was 374 days, or one year and nine days.

    That long developmental period strengthens scientists' fears that a combination of slow maturation to adulthood, infrequent pregnancies and long gestation means manta ray populations can only slowly replenish themselves. Although the creatures are found worldwide in tropical and temperate waters, can live for decades and are not considered endangered overall, populations have failed to recover in some areas that have been overfished or degraded environmentally.

    That's a warning sign, scientists said, that these close relatives of sharks could benefit from some of the attention and respect that their cousins routinely attract.

    "Everybody always loves the big, toothy things, but there are more species of rays than sharks, and they are often overlooked," said David A. Ebert, who studies rays and related species at the Pacific Shark Research Center at Moss Landing Marine Laboratories in California. "You look on television, it's always 'Shark Week.' It's never 'Ray Week.' "

    Of the many species of rays — including the infamous stingray that last fall killed television naturalist Steve Irwin — mantas, which differ from other rays because their mouth is at the front of their body rather than on their underside, are especially unstudied. With enormous wingspans that can exceed 20 feet, they require more space than most aquariums offer.

    Yet in recent years, researchers have begun to unveil some of the manta's secrets.

    Rachel Graham, of the Wildlife Conservation Society, has attached small sound-emitting "pingers" to several manta rays in the Flower Garden Banks National Marine Sanctuary off the Gulf Coast of Texas. Three underwater receivers, each 12 to 40 miles apart, have allowed her and others to get a sense of how widely mantas travel.

    Some, it turns out, are homebodies, spending virtually all of their time in a few local spots. But at least one manta left the area for two years, then came back to hang around again, said sanctuary superintendent G.P. Schmahl, who hopes to find funding to attach more receivers on some of the many oil rigs in the Gulf.

    The fact that at least some individuals apparently migrate widely — perhaps to favorite mating or feeding grounds — may help explain another recent finding about rays: Despite their huge geographic range and their great diversity of skin color (some have white underbellies, others black, and many have mottled patterns that make them individually identifiable), genetic tests indicate that all manta rays belong to the same species.

    In between feeding forays, which amount to cruising with their mouths open to catch tiny plankton, mantas like to hang out at "cleaning stations" — reefs where small parasite-eating fish congregate and offer their services.

    "They'll pull up and kind of hover there, and the little fish will come up and poke around on their skin... giving them a once-over," Schmahl said. Once their cloaks have been cleaned ("manta" shares linguistic roots with the Spanish word for "cloak"), they are off again, their frontal fins pointed characteristically ahead of them, helping to direct plankton-rich water into their gaping maws.

    For the most part, mantas are friendly giants, known to brush up against divers like snuggling cats. In fact, a manta's brain is about the size of a cat's, and most of it appears to be devoted to sensory perception, said Alan Henningsen, a research specialist at the Baltimore Aquarium.

    They have an excellent sense of smell, Henningsen said, mediated by two nostrils, or "nares," which detect amino acids, hormones and other chemicals in water. They have great night vision, too, and can even detect electromagnetic fields — a sixth sense that may aid in food detection or navigation.

    Friendly though they usually are, these 1,000-plus pounds of pure muscle can wreak havoc. Not long ago, a manta got tangled in the surface-based hose that was supplying air to a Gulf of Mexico diver.

    "It swam to the surface, pulling the diver up too quickly," Schmahl said. "It gave him a severe case of decompression sickness," known as the "bends."

    Back in Okinawa, there are hopes for another pregnancy and birth so more can be learned about the reproductive biology of mantas. In some rays, the mother's uterus secretes a milk-like substance for the developing baby, while in others, the fetuses have structures resembling placentas and umbilical cords. Those systems are more reminiscent of mammals than fish, although details — especially for mantas — remain obscure.

    Once the newborn is waterborne, mom doesn't look back. From there, it must depend on its own wits — and on the good will and good sense of humans. In some areas, such as around Indonesia, fishermen have wiped out populations to feed the growing trade in dried manta ray "horns," or brachial elements, which are a prized component in traditional Asian medicine.

    Those horns have earned mantas the nickname "devil rays." Time will tell who the real devils are.

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July 5, 2007 at 10:01 AM | Permalink


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