The two manta ray species are the world’s biggest rays: The giant oceanic manta ray, at its heftiest, may reach seven meters (23 feet) from wingtip to wingtip and weigh about two tons (4,440 pounds), and the reef manta ray isn’t much smaller. The immense size of these docile plankton eaters - found globally in tropical, subtropical and, in the case of the giant oceanic manta ray, temperate waters - wards off most predators, but large sharks and orcas can and do hunt them.

Probably the most significant manta ray predators are large sharks, which are found everywhere the rays are and which possess the size, strength and weaponry to tackle such formidable fare. Among the shark species mentioned in the literature as probable manta hunters are the bull shark and tiger shark, both apex predators in the manta’s tropical and subtropical range. In fact, scientists have positively identified manta ray remains in the stomach contents of bull sharks and have recorded tiger sharks hunting and eating these rays.

Other predatory sharks big enough to conceivably prey on mantas include the great white, which exceeds six meters (20 feet) in length; the swift mako sharks; the oceanic whitetip, among the tropical open ocean’s most widespread predators; and the great hammerhead, which has a taste for rays. Finally, researchers have also recorded gray reef sharks hunting and feeding on manta rays, though their primary prey is fish and squid.

Evidence for shark attacks on mantas isn’t hard to come by: Numerous studies have shown shark-bite scars and amputations on living rays. More than three-quarters of reef mantas observed in fieldwork off the southern Mozambique coast showed such injuries, with tiger and bull sharks thought the most likely attackers.

Research off the island of Maui revealed a significant proportion of reef mantas bore shark-attack wounds. Of the scarred mantas, some 93 percent appeared to have been attacked from the side or from behind.

Many more adults than juveniles carried shark bites, which researchers hypothesize could mean that young mantas seek out environments less frequented by sharks or that mature rays are more likely to survive shark attacks and therefore possess healed wounds.

Orcas, or killer whales, have been documented preying on manta rays in the Galapagos Islands as well as New Guinea. In the Galapagos, mantas appear to be a common food item for these formidable cetaceans.

In 2004, tourists filmed a small pod of orcas killing and consuming a giant oceanic manta, an incident discussed in the Latin American Journal of Aquatic Mammals. A female or subadult orca rammed the manta from above and drove it toward the seafloor, which, the authors note, the whale may have used to pen in the ray.

They suggest the slowness and defenselessness of mantas may make them energy-efficient food for orcas and possibly useful training prey for young whales. The false killer whale, a smaller orca relative, has also been proposed as a potential threat to mantas.

Both subsistence and commercial fishing for manta rays make human beings a predator of the animal in their own right. Manta flesh - especially from the wings and rear of the body - is eaten outright, while apothecaries render the gill rakers into medicinal products.

Humans also harvest mantas for their hides, as shark bait and simply as sportfishing trophies; living rays are taken for the aquarium trade as well. Both direct harvest and ​bycatch​, or accidental catch, threaten manta populations in some areas, such as the Gulf of California and Indonesian waters; the International Union for the Conservation of Nature lists both manta ray species as vulnerable.