Megamouth Shark

A shark found in a parachute

In November 1976, a research ship hauled in two parachute sea anchors off Hawaii and found a 4.46 m shark tangled in one. It was a new species. Scientists named it in 1983 and called it Megachasma, Greek for “yawning hole” or “open mouth”.

A mouth built to scoop

The mouth is very broad, and its corners reach back past the eyes. The jaws are huge and can slide forward. Scientists believe the shark swims slowly through a swarm of krill (small shrimp-like crustaceans) with its mouth open, pushes its jaws forward and expands its mouth cavity to suck the prey in. Then it shuts its mouth and squeezes the water out through its gills.

Its teeth are small. Each jaw has about fifty rows of small teeth, but only three rows are in use. Its prey includes krill, copepods (tiny crustaceans) and jellyfish.

Light trick A white band runs across the front of its snout. A 2020 study found no light organs in any of the skin it examined, strong evidence that the shark is not luminous. The band’s denticles, tiny tooth-like scales, may instead reflect glow from bioluminescent plankton.

Soft, slow and huge

A study of 27 megamouths caught off eastern Taiwan found they weighed 210 to 1,147 kg. FishBase gives a maximum length of 709 cm for a female, about 23 feet. This is a soft giant: its skin is very loose and its skeleton is soft and poorly calcified. The Florida Museum calls it a poor swimmer.

One tracked shark stayed at 12 to 25 m during the night, then dived to 120 to 160 m at dawn and returned to shallow water at dusk.

Spread across three oceans

The megamouth lives in the Indian, Pacific and Atlantic oceans, between about 40 degrees north and 40 degrees south. A 2021 study counted 261 landing and stranding records worldwide, with the majority from the western North Pacific. Animal Diversity Web names cookiecutter sharks as a predator, and in 1998 three sperm whales were seen attacking a 5 m megamouth in Indonesian waters.

The IUCN Red List rates it Least Concern, assessed in 2018, but a 2021 study notes that what is known of its biology and fisheries is still very limited.