The megamouth shark, Megachasma pelagios, stands as one of the ocean’s most enigmatic and recently identified large sharks. Its discovery in the late 20th century captivated the scientific community, revealing a creature unlike any previously known. This rare and unusual shark holds an almost mythical status due to its infrequent sightings and distinctive appearance. It highlights the deep sea’s hidden biodiversity, sparking curiosity about what other large species might remain undiscovered.
Unveiling the Megamouth Shark
The megamouth shark is distinguished by a large, wide, bulbous head and a remarkably broad mouth that extends behind its eyes. Its body is stout and tapers posteriorly, with a brownish-black coloration on its dorsal side and a white underside, sometimes featuring a white band along the upper jaw.
Mature males average about 4 meters (13 feet) in length, while females can reach up to 5 meters (16 feet). The first megamouth shark was unexpectedly discovered on November 15, 1976, when it became entangled in the sea anchor of a United States Navy ship off the coast of Hawaii. This accidental encounter led to the classification of an entirely new family, Megachasmidae.
The megamouth shark is one of three known filter-feeding shark species, alongside the whale shark and basking shark. It feeds by swimming with its mouth open, filtering zooplankton such as krill, jellyfish, and small crustaceans from the water. Its mouth contains numerous rows of small, peg-like teeth, but these are not used for biting prey; instead, specialized gill rakers within its large gill slits efficiently capture its microscopic food.
Dispelling the Extinction Myth
Despite its rarity, the megamouth shark is not extinct. The misconception often arises because of how infrequently it is observed in its natural habitat. Since its initial discovery in 1976, there have been hundreds of confirmed sightings and captures worldwide, with over 270 individuals recorded as of early 2025. These encounters span the Pacific, Atlantic, and Indian Oceans.
The infrequency of sightings is primarily attributed to the megamouth shark’s preference for deep-water environments, making direct human observation challenging. Its elusive behavior and the vastness of its oceanic habitat mean that most documented encounters have been incidental, often as bycatch in fishing nets. For instance, a notable number of specimens have been caught off the coast of Taiwan.
Recent sightings, such as two megamouth sharks observed swimming together off San Diego in September 2022, provide valuable insights into their behavior and distribution. The species’ naturally low encounter rate should not be mistaken for absence from the planet.
A Glimpse into Its World
The megamouth shark primarily inhabits the deep, open ocean, ranging from near the surface down to depths of 1,500 meters (about 4,900 feet). This deep-water preference presents challenges for scientists attempting to study its life cycle and behavior. Much of what is known comes from accidental captures or strandings, limiting research.
The shark exhibits diel vertical migration, ascending to shallower waters (around 12-50 meters) at night to feed on plankton and descending to deeper waters (120-700 meters) during the day. This slow movement allows it to follow its prey through the water column. While typically solitary, at least one instance of two megamouth sharks observed together suggests potential social interactions.
Reproduction is thought to be ovoviviparous, with eggs hatching inside the mother and young feeding on unfertilized eggs before birth. The species is currently listed as “Least Concern” by the International Union for Conservation of Nature (IUCN), but this status is largely due to a lack of sufficient data on its population size and trends. Incidental bycatch in commercial fisheries represents a potential threat, underscoring the need for continued monitoring and research for its long-term conservation.