Megamouth shark (Megachasma pelagios)

Physical characteristics

The megamouth can reach lengths of around 5.5 metres and has a broad, soft body with a rounded snout and very large lips. Its mouth contains many small teeth that are not adapted for cutting large prey; instead the species passes water over gill rakers to trap plankton and tiny organisms. Several distinctive features—such as a huge oral cavity, a relatively blunt head, and a dark dorsal surface—help distinguish it from other large filter-feeding sharks.

Distribution and habitat

Records show the megamouth occurs in tropical and temperate waters of the world oceans. It has been reported from the Indian Ocean, the Atlantic Ocean, and the Pacific Ocean. Most encounters come from deep or offshore waters; individuals are sometimes seen nearer the surface at night, suggesting they follow vertically migrating plankton.

Behavior, diet and ecology

The species is a filter feeder that consumes planktonic crustaceans, gelatinous organisms and small fishes. Observations and stomach contents indicate it feeds by swimming slowly with an open mouth to engulf plankton-rich water. Some researchers have suggested light-producing tissues inside the mouth or throat may help attract prey, but details of its feeding ecology remain under study.

Discovery, records and conservation

Because megamouths are seldom observed, knowledge about their life history, population size and reproductive habits is limited. Most information comes from stranded or bycaught individuals and occasional field observations. The rarity of records complicates formal conservation assessments; the species is vulnerable to incidental capture by fisheries and to threats that affect pelagic ecosystems.

Notable facts

• Unusual among sharks for its filter-feeding strategy and very large mouth.
• Only the sole living species in the family Megachasmidae.
• Continues to be the subject of curiosity in marine biology and fisheries science.