The two species of manta rays are the world’s biggest rays: The giant oceanic manta, at its heftiest, may reach 7 meters (23 feet) from wingtip to wingtip and weigh about 2 tonnes (4,440 pounds), and the reef manta 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, temperate waters -- wards off most predators, but large sharks and orcas can and do hunt them.
Probably the most significant predators of manta rays 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. Other predatory sharks big enough to conceivably prey on mantas include the great white, which exceeds 6 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.
Shark Attacks on Mantas
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 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 the researchers hypothesized 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.
Whales as Manta Predators
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.
Humans as Manta Predators and Harvesters
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 species as vulnerable.