The megamouth shark is a mysterious deep-sea giant discovered only in 1976.

Nature · Published 29 September 2026 Swipe more like this →

In short: Rarely seen and poorly understood, the megamouth shark is a filter-feeding enigma. Measuring up to 5.5 meters, this deepwater creature was unknown to science until a chance encounter with a Navy vessel. It remains one of the most elusive and fascinating discoveries in the history of modern ichthyology.

First identified in 1976 after becoming entangled in a sea anchor off the coast of Hawaii, the megamouth shark (Megachasma pelagios) represents a unique lineage. It is the smallest of the three known filter-feeding sharks, distinct from the whale and basking sharks. While fossil records suggest the species may have existed 36 million years ago, molecular studies indicate its evolutionary history could stretch back as far as 100 million years. The shark is characterized by a soft, flabby body, a large bulbous head, and a brilliant silvery-white band on its upper lip, which researchers once theorized might be bioluminescent before determining it is simply highly reflective.

The megamouth is a vertical migrator, a behavior shared with many marine animals tracking plankton. Tracking data shows that these sharks spend their days at depths of 120 to 700 meters, ascending to shallower waters as the sun sets. Despite their massive size, they are relatively slow swimmers, moving at speeds of roughly 1.5 to 2.1 kilometers per hour. Their diet consists primarily of zooplankton, including krill, jellyfish, and shrimp larvae, which they capture using finger-like gill rakers as they swim with their mouths open.

As of March 2025, only 296 specimens have been recorded worldwide, with the majority found near Japan, the Philippines, and Taiwan. Genetic analysis of samples from Taiwan and Mexico suggests that these sharks form a single, highly migratory, interbreeding population. While much of their behavior remains hidden, recent observations have provided glimpses into their social lives, including potential courtship rituals. Whether they are solitary wanderers or social foragers, the megamouth continues to challenge our understanding of deep-sea biodiversity and the evolution of filter-feeding mechanisms in sharks.

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