Death of Manta Ray Sheds New Light on Species

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.