The megamouth shark, Megachasma pelagios, is one of the most enigmatic creatures in the ocean. Discovered in 1976, its unique nature necessitated the creation of an entirely new family, genus, and species to classify it. Due to its preference for deep, offshore waters, the megamouth is rarely observed in its natural habitat, contributing to its mysterious reputation.
Identifying the Megamouth Shark
The megamouth shark is distinguished by its massive, bulbous head and soft, flabby body. Its common name comes from its immense, broad, terminal mouth, which extends well behind the eyes. This mouth is lined with rubbery lips and contains hundreds of rows of tiny, hooked teeth, which are not used for biting or tearing prey.
The shark is a large animal, typically reaching 13 to 18 feet (4 to 5.5 meters), with some females documented at over 23 feet. Its coloration is dark gray-brown on the dorsal side, contrasting sharply with its paler, almost white ventral surface. The body is stout and tapers toward its asymmetrical tail fin.
The megamouth possesses a less muscular structure than active predators, indicating it is a slow swimmer. Its two dorsal fins are comparatively small, and it lacks the caudal keels that aid stability in fast-swimming sharks. This morphology suggests a passive existence in the deep ocean, prioritizing energy conservation. A distinctive feature is a bright, white band of tissue on the upper jaw, which may serve as a lure to attract small prey in the dark depths.
Diet and Feeding Strategy
The megamouth shark is a filter feeder, similar to the whale shark and basking shark. Its primary diet consists of zooplankton, including krill, copepods, and small shrimp.
The feeding mechanism relies on ram filtration. The megamouth swims slowly through plankton aggregations, keeping its enormous mouth open to scoop in water and prey. Specialized, finger-like projections called gill rakers line the gill arches, functioning as a sieve.
As water passes over the gill rakers, food particles are trapped and filtered out. The shark then closes its mouth to swallow the collected food mass. The bioluminescent tissue around its mouth may illuminate the area, attracting light-sensitive plankton toward the open jaws. Stomach contents consistently confirm this planktivorous diet, often featuring euphausiid shrimp.
Assessing Human Interaction and Risk
The megamouth shark poses virtually no threat to humans. Its biology, diet, and habitat minimize any possibility of harmful encounters. As a passive filter feeder, it lacks the inclination or physical adaptations to attack or consume a large mammal.
The species spends most of the day in the mesopelagic zone, or “twilight zone,” typically at depths of 500 feet (about 150 meters) or more. It performs a daily migration, rising into shallower waters, sometimes as close as 40 feet (12 meters) from the surface, to feed on plankton at night. This movement pattern means it rarely occupies waters where human activity is concentrated.
Confirmed sightings are extremely rare, with fewer than 300 individuals observed or caught since its discovery in 1976. Most interactions occur accidentally when the shark is caught as bycatch in commercial fishing nets. There are zero recorded instances of the megamouth shark exhibiting aggression toward humans in the wild.
The low risk is a direct consequence of the shark’s deep-water lifestyle and reliance on microscopic prey. Its slow nature and specialized feeding apparatus confirm its gentle disposition.