Manta Rays are the largest species of ray, and one of the largest living fish. The biggest specimens have a wingspan of 7 metres and can weigh over 1,300 kilos.
They have huge triangular pectoral fins which are flapped like wings to move through the water, although incredibly agile, and able to perform acrobatic breaches, flips and somersaults above the ocean surface, mantas are unable to swim backwards. To breathe they must also move constantly to keep water circulating in their 5 pairs of gill slits, these characteristics make them vulnerable to entanglement and suffocation.
Like whale sharks, manta rays are filter feeders that consume large quantities of minute creatures such as zooplankton, krill, shrimp and planktonic crabs. To feed they open their large triangular mouth and use their horn-like cephalic fins to channel food into it. They have 300 rows of very small teeth on their lower jaws and do not have a barb on their tail.
The manta ray eggs develop in the female's oviduct and the embryos feed first on the egg yolk, when they hatch within the mother they feed on milky secretions. After 12-13 months the pups (usually one or two) are expelled from the oviduct. They are small versions of mature manta rays and do not receive any parental care. Because of their long lives and low reproduction rate manta populations are vulnerable.
Mantas are pelagic, they are found alone or in groups swimming in temperate, subtropical and tropical waters, they are believed to migrate great distances and have been recorded diving to depths of 500 metres. Much of their life remains a mystery.
In the past mantas were described as devil fish due to ignorance and superstition that they resembled bats, another species which still suffers from human ignorance and superstition. In fact mantas have the highest brain to body ratio of all the sharks and rays. Researchers are finding that they are gentle, curious, intelligent creatures that seem to recognise individual divers, can be taught to roll over by hand signals and have reportedly lifted divers in trouble to the surface. Diving and snorkeling with mantas is growing in popularity around the world, close supervision is required in these increasingly crowded sites since touching a manta removes their slime coating which makes them vulnerable to infections and lesions.
Like all marine species mantas face the danger of pollution, over fishing and microplastic but they now have another threat to contend with. There is a growing market for manta gill rakers in Chinese medicine, its spruikers claim that it can cure ailments from chickenpox to cancer, and its increasingly affluent yet obviously ill informed customers believe this nonsense and their demand is killing huge numbers of mantas all over the world.
Fortunately the Australian Government has increased protection for manta rays in our waters but unfortunately globally their numbers are declining dramatically.