Death of Manta Ray Sheds New Light on Species
Monday, July 2, 2007
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.