MANTA RAYS

Manta Rays

The Manta Ray

Manta ray is the common term for two species of rays: Manta birostris, the giant manta, and the smaller Manta alfredi, known as the reef manta. Manta rays are fish and are closely related to sharks, skates, and other rays which are collectively known as elasmobranchs because they have skeletons made of cartilage instead of bone.

Manta rays are easily recognized by their magnificent size. Giant mantas can grow to 22 feet from wingtip to wingtip and can weigh up to 3,000 pounds, making them the largest of the more than 500 species of rays and skates. Reef mantas are a little smaller, growing to 18 feet across. Although related to sting rays, there are no stingers on the mantas long-whip like tail.

Richard Akhtar/Matava/Marine Photobank

Manta colors vary from black to white, and there are even some spotted varieties. Because each pattern is distinct, researchers use them to identify individual mantas. Like sharks, manta rays skin is covered by dermal denticals which gives it a rough feel like sandpaper.

Biology

Where are manta rays found?

Manta rays are found worldwide in tropical, subtropical, and temperate waters. The giant manta is commonly found offshore, while the reef manta, as its name suggests, is found inshore near coral and rocky reefs. Manta rays live in the open ocean, swimming continuously through the water column instead of resting on the sea floor like other rays. Although much of their time is spent near the surface, they have been known to dive to depths of 100 feet.

Sometimes, mantas even take to the air, jumping out of the water and sailing several yards to avoid predators or remove parasites. This behavior may even be a communication technique between rays, used for mating or just to play.

What do manta rays eat?

Like whale sharks, manta rays are filter feeders that primarily eat microscopic plankton and krill, with the occasional small fish. As a manta ray swims, it takes in water with the help of its cephalic fins on either side of its mouth. The water then passes through the mantas comb-like gill rakers (tiny projections on the gills), which filter out the food while the water exits through the gills.

Leaping manta rays Paolo Macorig/Marine Photobank

A full-grown adult can consume up to 60 pounds of food every day. And because mantas have the largest brain to body weight ratio of all shark or ray species, they can remember where to find the best feeding spots.

How long do manta rays live?

Manta rays are believed to live to 40 years. Manta rays only reproduce once they reach a certain size, which can take as long as 8 to 10 years. Mantas give birth to live pups that hatch and develop from an egg inside the mother. The gestation period is about a year, and usually one pup is born every two to three years.

One female may give birth to only 10 pups over her lifetime, and this low reproductive rate is one reason that manta ray populations are vulnerable.

Threats to Manta Rays

Fishing is the main threat to manta rays around the world. Manta ray fisheries exist in several countries with Indonesia, Sri Lanka, and India having the largest documented landings. Because many of these fisheries have historically been unregulated or underreported, true catch levels are unknown. However, the number of documented landings for giant mantas alone is about 3,400 each year.

Manta rays are highly demanded in international trade markets. Their cartilage is used as filler in shark fin soup, and their skin is used to produce shoes, wallets, and sandpaper. In many Chinese communities, manta ray gill rakers are believed to treat a variety of ailments, including cancer. Because of the high demand, one pound of manta gill rakers can sell for over $200.

A manta ray caught on fishing line

Gavin Parsons/www.gavinparsons.co.uk/Marine Photobank

Even in fisheries that do not target mantas, they often end up caught on the line or in the nets anyway. Manta rays are incidentally caught in large-scale fisheries that use longlines, gillnets, drift nets or purse seines. Other threats to manta rays include boat strikes, habitat loss, climate change, and pollution. Manta ray populations are currently unknown, but it is estimated that global populations have decreased by more than 30% (and as high as 80% in some regions) over the last 75 years.

Conservation

Both manta species are listed as Vulnerable by the International Union for Conservation of Nature (IUCN), and the Convention on the Conservation of Migratory Species of Wild Animals (CMS) lists the giant manta on its Appendices I and II as a species of international concern. In the United States, Hawaii became the first state to protect manta rays when it passed a law in 2009 that prohibited capture of the species. Other nations around the world have taken steps to protect manta rays including the Republic of the Maldives, the Philippines, Mexico, Ecuador, and New Zealand, although these laws are not always enforced. Neither species of manta ray is protected by the Convention on International Trade in Endangered Species (CITES) or the U.S. Endangered Species Act.

A single dead manta ray is estimated to be worth $40 to $50. However, the estimated value of a single manta over its lifetime is $1 million, because it provides repeated ecotourism opportunities. The estimated yearly value for the gill raker trade is $11 million compared to the yearly estimated value of manta dive tourism, which is $27 million. Despite the manta rays ecological and economic importance, it is increasingly threatened by human activity. Although there is still much to learn about these mysterious rays, the future of mantas remains uncertain.

Sources

Florida Museum of Natural History

Shark Savers

IUCN Red List of Threatened Species

Wild Aid