The Megamouth Shark, Megachasma pelagios, is one of the most intriguing large creatures in the ocean, having eluded scientific discovery until the late 20th century. This species represents one of the most recent identifications of a major marine vertebrate. As one of the world’s three known filter-feeding shark species, its enormous mouth and massive, soft body give it a truly distinctive appearance. The Megamouth Shark remains a globally rare animal.
The Context of Discovery
The scientific world officially met the Megamouth Shark on November 15, 1976, entirely by accident near the Hawaiian Islands. The discovery took place about 25 miles northeast of Kahuku, off the coast of Oahu, when a U.S. Navy research vessel, the AFB-14, was retrieving equipment. A large, unfamiliar shark had become hopelessly entangled in the vessel’s parachute sea anchor at a depth of roughly 165 meters (541 feet).
Upon pulling the massive specimen to the surface, the crew and attending scientists were met with a sight unlike any previously cataloged fish. The 4.5-meter (14.7-foot) male shark, weighing about 750 kilograms (1,650 pounds), was clearly a new species, so distinct it could not be placed in any existing shark family. This single individual provided the foundational specimen for the scientific description of Megachasma pelagios, establishing the species and its own unique family, Megachasmidae, a decade later.
A Biological Profile
The Megamouth Shark is easily recognized by its massive, bulbous head and extremely wide, terminal mouth. Its mouth can measure well over a meter across, and it features a jaw lined with numerous rows of small, hooked teeth, which are not used for biting or tearing. The shark’s body tapers toward a long, asymmetrical tail fin, giving it a somewhat flabby and less streamlined appearance compared to active predatory sharks.
The average adult size for this species is around 5.5 meters (18 feet), though the largest female specimen recorded reached 7.1 meters (23.3 feet). Its coloration is generally dark brown or black across the back and sides, contrasting with a much lighter, whitish underside. A distinctive feature is a bright, reflective white band along the upper lip, which is thought to play a role in its feeding strategy.
Habitat and Feeding Strategy
The Megamouth Shark is a global deepwater species, with records confirming its presence across the Pacific, Atlantic, and Indian Oceans. It primarily inhabits the open ocean, or pelagic zone, and is known to engage in diel vertical migration. This involves the shark spending its daytime hours in deeper, darker water, typically between 120 and 160 meters (390–520 feet) below the surface.
As the sun sets, the shark ascends to shallower depths, sometimes as high as 12 to 25 meters (39–82 feet), where it spends the night feeding. This migration follows the movement of its primary food source: zooplankton, which includes small crustaceans like krill and copepods.
The shark feeds by slowly swimming with its enormous mouth open, ram-filtering large volumes of water to strain out its tiny prey. The reflective white band on its upper lip is thought to attract prey in the dark water.
Scientific Study and Rarity
Since its initial discovery in 1976, the Megamouth Shark has been confirmed in only a small number of sightings and specimens worldwide, underscoring its rarity. Because the species lives in the vast, deep pelagic zone, studying its behavior, reproduction, and population dynamics is challenging. Most knowledge of the species comes from individuals accidentally caught in fishing nets or those that strand themselves on beaches.
Limited encounters have allowed for the deployment of satellite tags, which provided the first data on its slow swimming speed and vertical migration patterns. These opportunities, combined with morphological and genetic analysis, have solidified its classification as the sole living member of the family Megachasmidae. Scientists continue to piece together the life history of this elusive filter feeder from the few dozen documented occurrences across the globe.