Giant Oceanic Manta Ray, Manta birostris
The largest ray in the world is the giant oceanic manta ray. It is found in the open water of all the major oceans of the world. In the eastern Atlantic it can be seen from New Jersey to Uruguay; in the western Atlantic from the Azores Islands to South Africa; in the eastern Pacific from southern California to Peru and in the western Pacific from Japan to New Zealand. It also can be seen in the entire Indian Ocean. This manta ray will swim in deep water but enter the shallows around reefs for periodically cleaning, this is when another fish, called a cleaner fish, will attach itself to the ray and remove dead skin, parasites, and other unwanted particles from the giant manta’s body.
The giant oceanic manta ray has a large disc shaped body with triangular wings extending outward. The body is black on the top with a white patch creating a “T” on the head and the belly is cream or white with dark splotches. It has a small fin on the back with a spine directly behind it on the slender, flattened tail.
The eyes are located on the side of the head with a large mouth located in front that contains rows of tiny teeth on the bottom jaw. There are two lobes extending forward from the wings called ‘cephalic lobes‘. While swimming, these lobes are rolled into a spiral. There are five gills on each side, located on the belly just behind the head.
Being the largest ray in the world, a wingspan of 25 feet has been reported, but typically it is around 15 feet, which is usually twice the length of the body. The manta has an average weight of 2 tons, but some have been reported weighing close to 3.
The diet of the giant oceanic manta ray consists mainly of plankton, but it will sometimes consume small to moderate sized fish. When feeding, it will unroll the cephalic lobes to direct water into the mouth, while rolling in slow somersaults. The water passes through gill rakers, a sponge-like tissue located between the gills that separate the food from the water.
During the mating process several males will chase the female sometimes for days, and the dominant male will catch the female and clasp on the tip of her wing with his mouth. Mating is done belly to belly by internal fertilization with the male using ‘claspers’, the reproductive organ, to fertilize the egg.
The egg will develop for 12 months and will hatch inside the female. She will give live birth to one–occasionally two–young (called a pup) every 2 – 5 years. The pup will have a wingspan of 4 – 5 feet and can double in size within the first year.
Giant oceanic manta ray can live up to an estimated 40 yrs. The only known predators are the orca, killer whales, and large sharks.
The giant oceanic manta ray has been harvested for the skin, liver, and food, but more recently the Chinese use the gill rakers in the medicine trade. With it frequently being caught in fishing nets, slow birth rate, and ease of capture, there has been a sharp decline in the population of this species, and is on the endangered species list as vulnerable.
A fishing ban has been implemented in Hawaii, Mexico, the Philippines, Ecuador and New Zealand, while an export ban in the Maldives for all ray species is in place. This has been done to protect the giant oceanic manta ray from a further decline in population.
Image Caption: Giant Oceanic Manta Ray at Hin Muang, Thailand. Credit: Jon Hanson/Wikipedia (CC BY-SA 2.0)