Sep 23, 2011

Guy Harvey on “The Manta Ray”

by Guy Harvey

Dr. Guy Harvey

I was four hundred miles west of Grand Cayman, on the continental shelf just to the east of Isla Mujeres, Mexico looking for bait balls of sardines with sailfish feeding on them, while shooting an episode of my TV show “Portraits from the Deep”. Frigates birds circling over the bait will normally announce the presence of sailfish, but just a hundred yards ahead of the boat, I spotted a frothy commotion. Big splashes and the tips of large fins broke the surface sending up volumes of white water. It looked like a sea monster was about to erupt from the surface as we quickly motored on over to see what was happening.

It seemed that two large manta rays were chasing an even bigger manta ray. I jumped in the water, camera in hand and finned hard toward the group of animals that were doing circles in front of me, tearing up the surface in their frantic efforts to keep up the chase.  The large female turned directly at me, and with great beats of her twenty foot wings she came head on and swept just a foot beneath me, as I sucked in my stomach to make room for her passing. The two males in ardent pursuit also went by below me. I swiveled to continue the sequence and then she angled her left wing down and dived like a fighter jet, and went out of sight, with the two suitors in hot pursuit. It was two fourteen foot males trying to entice a twenty foot female to mate, but she was having nothing to do with them!

In the Atlantic Ocean manta rays are found in areas with a high concentration of plankton, such as in the western Caribbean off the coast of Mexico and Belize, and in the southern Caribbean off Venezuela, in the same areas frequented by whale sharks

Manta rays are different from all other pelagic rays in that they have two large fleshy lobes, called cephalic limbs on their head, that look like horns, hence the other name given to them , “Devil Ray”. These are actually paddle like in shape and while the ray is feeding with its large terminal mouth wide open they help guide food into the open mouth while swimming forward, often at great speed. In Mexico and Coats Rica, I have seen them attack schools of balled up sardines with rapid lunges and great determination.

When swimming along these horns are rolled up neatly for streamlining. Their coloration is generally dark brown or black on the upper surface, white on the lower surface, with a number of irregular black blotches. Sometimes there is more black than white on the underside. There may be areas of white streaks on the upper side, and sometimes the tips of their magnificent wings have white. Each animal is distinct and different. The smaller related species, the Devil Ray has a brown or even tan upper surface. Their tails are thin but generally quite long

Guy's first hand observation of Manta Ray's has inspired the artwork depicted on this t-shirt from his sportswear collection

A set of gill rakers on their gill bars catches all the microscopic organisms in the same way for other large plankton feeders such as whale sharks, and basking sharks.

Little is known about growth rates and their life history. Opportunities for study have come about recently because of their ability to survive in captivity in large aquaria such as at the Georgia Aquarium, and at Atlantis in Nassau, Bahamas. Mantas are reported up to twenty five feet across, weighing three tons. They probably reach maturity at a large size, and are long lived animals as are all the other large cartilaginous fishes, the sharks and rays. They give birth to fully formed miniatures of themselves that weigh up to thirty pounds.

Adult mantas have few natural predators, such as large sharks and orcas, but most are killed by humans, some are caught in gill nets or harpooned for food as seen on the Pacific coast of Mexico and the Orient, and many are taken as by-catch on long lines set for tunas and swordfish. Oh yes, a manta will eat a bait on a line. I caught and released a couple in Costa Rica while live baiting for black marlin. I have cut off and set free many mantas hooked on long lines in the eastern Pacific. Many mantas are caught in purse seines set on flotsam in the yellowfin tuna and big-eye tuna fishery in the tropical eastern Pacific.

As with most large oceanic animals manta rays are overexploited wherever they occur. However their popularity in certain islands frequented by divers is their saving grace in such accessible locations. Given the choice of seeing a huge manta glide by on twenty foot wings or see it cut up in pieces on an Asian dock, I think most people would choose the former. It is our collective responsibility to conserve the marine environment and protect the biodiversity of our planet.

Good fishing, safe diving.

Guy Harvey

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