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Guy Harvey

I was 400 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. 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 and we quickly motored over to see what was happening.

It seemed that two large manta rays were chasing an even bigger manta ray. What an opportunity to get some unique footage. 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. You could almost hear the tires squealing underwater. They moved away rapidly just as I got closer for the shot, but then the large female turned directly at me, and with great beats of her 20 foot wings she came head-on at knots 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 swivelled to continue the sequence and then she angled her left wing down and dove like a fighter jet and disappeared, with the two suitors in hot pursuit. It was two 14 foot males trying to entice a 20 foot female to mate, but she was having none of it.

In the past I have had many encounters with large manta rays, in remote locations such as Cocos Island, in the Galapagos and many times off Guatemala, Costa Rica and Panama while out fishing. But nothing compared to the excitement of this encounter.

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. Because the Cayman Islands are in an oceanic desert or an area of low productivity, we do not often encounter manta rays here. However they pass by in their migrations and have been spotted by divers, sometimes for several consecutive days before moving on.

Manta rays are different from all other pelagic rays in that they have two large fleshy lobes, called cephalic limbs, on their head. These 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 Costa Rica, I have seen them attack schools of balled up sardines with rapid lunges and great determination.

As with the whale shark, the mouth is terminal; not under-slung beneath the snout as seen in all other species. They breathe as water is forced over their gills in their forward motion and do not pump water over their gills or use their spiracles in respiration as do the benthic species of rays.
When swimming along these horns are rolled up neatly for streamlining. Their colouration is generally dark brown or black on the upper surface and white on the lower surface, with a number of irregular black blotches, although there may be more black than white on the underside. There can be areas of white streaks on the upper side and sometimes the tips of their wings are white, but each animal is distinct and different. Their tails are thin but generally quite long.

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

Manta rays are known to jump a great deal, and often the first encounter is seeing a manta going high into the air, often spinning a number of times, before crashing back on the surface. This can be repeated several times, often in association with other mantas. Underwater they can appear to show off or play in front of a diver by doing acrobatic loops, often backwards, many times. Atlantic Mantas and Pacific Mantas are probably the same species
Little is known about growth rates and their life history. Some attempts to tag them with satellite tags have taken place in the western Pacific where individuals regularly inhabit certain reefs such as seen in Yap and Palau. 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 have been reported up to 25 feet across, weighing three tons. They probably reach maturity at a large size and are long lived animals as are sharks and rays. They give birth to fully formed miniatures of themselves that weigh up to 30 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. A manta will eat 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. Given the choice of seeing a huge manta glide by on 20 foot wings or see it cut up in pieces on an oriental 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.   WH
Good fishing, safe diving.

Guy Harvey PhD.
guyharvey.com