The megamouth shark, Megachasma pelagios, is an extremely rare deep-sea species first encountered by scientists in 1976. Named for its massive, cavernous mouth, it is one of only three known shark species that filter-feed, alongside the whale shark and the basking shark. Its large head and soft, flabby body are adaptations for its plankton-based diet and sluggish lifestyle in the deep ocean.
The Primary Prey
The diet of the megamouth shark is composed almost entirely of small, pelagic invertebrates, or zooplankton. Despite the shark’s large size, it feeds on organisms that are only a few millimeters in length. The bulk of its caloric intake comes from euphausiids, which are commonly known as krill. These small shrimp-like crustaceans form dense swarms in the water column, providing an efficient food source for a filter feeder. The megamouth shark also consumes small copepods, which are another form of abundant zooplankton. Occasionally, the diet may be supplemented with other small marine creatures, such as jellyfish and shrimp larvae. For instance, the pancake jellyfish, Atolla vanhoeffeni, has been identified in the stomach contents of some megamouth sharks.
Specialized Feeding Mechanics
The megamouth shark employs a specialized filter-feeding method that involves straining prey from the water column. This process is facilitated by unique anatomical features, most notably its extremely wide, terminal mouth, which can extend behind its eyes. The jaws are lined with numerous rows of tiny, hooked teeth, but these are too small for biting and instead function as part of the filtering apparatus.
The filtering itself is performed by finger-like projections called dermal papillae or gill rakers that line the interior of its gill slits. As the shark takes in water, these structures act like a sieve, trapping the small prey while allowing the water to pass out through the gills.
While it was initially thought to be a simple ram feeder that swims with its mouth continuously open, like the basking shark, anatomical studies suggest a more complex feeding action. The megamouth likely uses an intermittent feeding style that involves a degree of suction, which is sometimes referred to as ‘engulfment feeding’. This is accomplished by the sudden expansion of the oral cavity and protrusion of the jaws, creating a negative pressure to draw water and prey inside. This mechanism allows the shark to take in a large volume of water—up to 150 gallons in a single gulp—before expelling it and swallowing the trapped organisms.
Habitat and Hunting Strategy
The megamouth shark is a deep-water inhabitant of the bathypelagic and mesopelagic zones of the open ocean. Its hunting strategy is directly linked to the movement of its prey, which undergoes a daily pattern known as diel vertical migration.
During the day, the shark typically remains in deeper waters, often between 650 and 3,300 feet (200 to 1,000 meters) below the surface. As the sun sets, the megamouth ascends to shallower waters, sometimes as close as 40 to 80 feet (12 to 25 meters) from the surface, to follow the upward migration of krill and copepods. This movement allows the shark to feed in the epipelagic zone where plankton concentrations are highest at night.
The shark’s slow-swimming nature and soft body are suited to this passive hunting strategy of intercepting dense prey schools. It has been hypothesized that a bright, white band on the shark’s upper jaw may play a role in attracting prey in the dark depths. Although the shark itself does not produce bioluminescence, studies suggest this band reflects light from bioluminescent plankton. This reflective feature may serve to either lure prey closer or create a contrast that helps the shark target the densest aggregations of its food source.