Ka Mo‘olelo Moana: Elusive megamouth shark discovered by accident in 1976

There are estimated to be more than 400 known species of sharks worldwide, and one first discovered off the coast of Kaneohe remains one of the strangest and most significant species discovered in the 20th century.

This curious-looking shark, dubbed megamouth for its very large expandable jaws, was accidentally captured in 1976 when it became entangled with a parachute anchor line from a naval research vessel and subsequently died from the entanglement. When examined by researcher Layton Taylor, it was concluded that it was a new species previously unknown from deep water.

This first specimen of megamouth currently resides preserved at the Bishop Museum on Oahu. As of 2012, only 55 cases of captures or encounters with the elusive megamouth shark have been reported with the majority of these found either dead or dying after accidental capture. Only seven confirmed megamouths have been reported as examined and released alive thus far.

The largest megamouth captured was around 17 feet long, though most of the other specimens have been between 14 to 15 feet long. It has a grayish body with white tips on its pectoral fins and a silvery lining in its large mouth. The teeth of the megamouth shark are very small and curved backwards toward the jaws. It was these teeth that snagged into the parachute anchor on the research vessel that led to the discovery of the first megamouth in 1976.

Fossilized teeth from the Miocene epoch, around 26 million years ago, from a then- unknown species discovered in 1961 in sandstone deposits in California have since been matched to the megamouth, making it one of the oldest known sharks still in existence today. It has been dubbed a “living-fossil” and likened to the Coelacanth, a species of prehistoric fish once thought to have been long extinct, in importance of its discovery.

While little is known about the lifestyle of the megamouth shark, examination of the known specimens has revealed that it is a filter-feeding shark, similar to whale sharks, which also are occasionally seen in Hawaiian waters. It is known to feed on plankton, copepods, shrimp and jellyfish, and it is believed to use its greatly expandable mouth to suck food in a vacuum “slurp-gun” fashion. The silvery reflective lining in the mouth is believed to attract prey to the jaws of the megamouth.

What little is known of its behavior is from data collected from a living megamouth captured off Dana Point, Calif., in 1990. This megamouth (the sixth known specimen) was released with acoustic tags, and tracked for 48 hours by researchers. It was discovered that this individual would dive to depths of 394 to 634 feet during the day but ascend to shallower depths of 40 to 82 feet at night. This has led to the theory that megamouth sharks are following a large gathering of tiny planktonic animals that form a moving layer in deep water known as the Deep Scattering Layer, as the stomach contents of dead megamouth shark specimens contain many of the animals that make up this layer of plankton.

The megamouth shark is an example of an animal from a prehistoric past that managed to go undetected for a long time due to the vastness of the world’s oceans. It serves today as a reminder that there is still much of the ocean that we do not know.

* Mike Ogata is an ocean naturalist at the Maui Ocean Center. He has worked at the aquarium for 15 years, beginning as a volunteer in the Education Department. “Ka Mo’olelo Moana,” or “The Ocean Story,” is a monthly column submitted by the Maui Ocean Center. It is open from 9 a.m. to 5 p.m. daily in Maalaea. For more information, call 270-7000.