Hawaiian Marine Life Profiles: Fish
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Found in Exhibit:
most commonly found along Kona Coast
The largest winged creature on earth doesn't soar through the skies overhead. It glides through the sea, descending to depths of more than 100 feet. Its Hawaiian name is hahalua. Its English name, derived from the Spanish word for cloak, is manta ray.
Inhabiting tropical waters between 35 degrees north and south latitudes, manta rays evoke a sense of excitement and curiosity. Mantas with 22-foot wingspans and even one at 30 feet have been recorded. The most common are in the 12-16 foot range. Weight estimates for the largest are about 3,000 pounds. Studies of smaller, related species suggest a lifespan of about 25 years.
Manta rays are filter feeders, equipped with two flap-like cephalic lobes that guide plankton-rich waters into their mouths. Internal plates of pinkish-brown sponge-like tissue sieve microscopic plankton, small fish, and tiny crustaceans from the water. Opportunistic remoras - hoping for a free meal - often attach themselves to a manta ray's undersides and consume any leftover scraps. Mantas are attracted to any area rich in zooplankton. While feeding, they swim in slow vertical loops, a behavior most often observed at night when plankton tends to rise toward the surface. Lights attract plankton, thereby attracting manta rays.
Mantas are equipped with 300 rows of tiny peg-like teeth not used for feeding. Like the scales or denticles also found inside a manta ray's mouth, their purpose is related to courtship and mating. Prior to copulation - a 90 second process wherein the male swims belly-to-belly with the female and inserts one of two claspers into her cloaca - the male first chases the female and bites at her pectoral fins.
The female gestation period is roughly 12 months. Only one or two uterine-milk-fed pups are born per litter, with females recovering a year or so before rebreeding. Births are rarely witnessed or recorded. Newborns measure 3-4 feet across.
On June 16, 2007, a manta ray gave birth at the Okinawa Churaumi Aquarium in Japan, one of few aquariums worldwide displaying manta rays. Mama manta rubbed her belly on the floor of the aquarium then soared toward the surface - ejecting her baby as a rolled-up tube that rapidly unfurled and began to swim on its own. The event was broadcast throughout Japan on NHK television, but the baby died five days later, due, in part, to injuries inflicted by the male parent.
Newborns - on their own at birth - are most often spotted in shallow, protected waters with abundant food sources. Later, they venture into deeper waters. Adult migrations remain a mystery, but mantas appear on schedule at certain times and places. Tagging efforts now underway may begin to explain how far they travel and where they go in between times.
Mantas are related to sharks and stingrays - but without stingers or fearsome teeth. For reasons unknown, they evolved into filter-feeding creatures sharing similar characteristics. Eyesight and sense of smell are superior and they can detect electromagnetic fields, a sixth sense that may help them navigate and find food. From birth to death, they spend their lives swimming, never sleeping as humans do. Scientists speculate that some part of their brains may shut down for rest periods while other parts remain awake to coordinate movement.
Each manta ray displays its own unique, identifiable pattern of patches, spots and blotches on shoulders and underside. Base colors range from dark brown to grayish blue or black. Mantas from the eastern Pacific tend to have black undersides while those from the western Pacific mostly have white undersides. All are genetically related.
Like whales, mantas occasionally breach, leaping clear of the water and landing either head first, tail first or performing a complete somersault. They often frequent wrasse-operated cleaning stations and seem to relish the attention.
Once sought for their meat, oily livers, and sandpapery hides, manta ray populations in the Philippines and off the Pacific coast of Mexico were decimated during the 1990's and have not recovered. Today, mantas are little hunted except by large sharks such as the tiger shark and by Indonesian fishermen seeking prized components of traditional Asian medicines. Many mantas still fall victim to drift or set nets in both the Western Pacific and Indian oceans, raising concerns for their sustainability.
In Hawaii, they are a tourist attraction, drawing admirers to the coast of Kona where they gather to feed at night in front of the Mauna Kea Beach Hotel. Divers should never touch, ride or even brush up against them because human contact robs them of a protective mucous layer, leaving them vulnerable to lesions and marine infections.
So little is known about these magnificent creatures that scientists are still attempting to document their ecological and scientific importance. What we do know is that our world would be a poorer place without the beauty, grace and mystery of the manta ray.