The megamouth shark is a shark with a huge mouth, bulbous head and protruding jaws. On an average they are 4.5 m (15 ft.) in length and weigh around 750 kg (1650 lb). A captured female weighed a whopping 1040 kg (2288 lb), had 55 tooth rows on the upper jaw and 75 on the lower jaw. The teeth of megamouth sharks are small and used to filter food. The body is flabby and cylindrical and the eyes are rather small. Megamouths are slow swimmers.
Why should I be aware of this?
- Megamouth shark is so rare and is seen so infrequently that science can't confirm its existence.
- It's pretty amazing that an animal as large as this was discovered so late. Though some specimens found indicate that they have been in contact with humans for some time, evidently there was a lack of recognition by the humans that what they had was something new at the time or unusual.
All about Megamouth Shark
An extremely rare megamouth shark was caught by Filipino fishermenin April 2009. This was only the 41st time the species has been seen in the 33 years since its discovery.
Megamouth shark, which was first discovered in 1976 in Hawaii, is a member of the same order of sharks that includes white sharks, basking sharks and mako sharks. It's one of a kind, and is the only member of its group, the only member of its family, and the only member of its genus.
A second specimen was caught in November 1984 at a depth of no more than 38 m, in a gill net 14 km off Santa Catalina Island, California. This 4.5 m long male is now at the Los Angeles County Museum.
The third known specimen was beach-stranded at Mandurah, Western Australia in August 1988. The day before it stranded surfers who mistook the shark for a whale, tried to coax it into deeper water to prevent it being stranded. This 5.15 m long male is now registered in the Western Australian Museum fish collection as WAM P.29940-001.
The fourth and fifth specimens were recorded from Japan. The fourth was washed ashore at Hamamatsu in January 1989. The fifth specimen was netted alive off Suruga Bay, then released.
A vertical migrator
The sixth specimen captured was the most important as it was studied alive by being tagged with an ultrasonic transmitter. A 50-hour study showed that the shark is a vertical migrator. The fish spent the daylight hours at a depth of about 170 m, but at dusk swam up to a depth of about 12 m and stayed there throughout the night. This vertical migration coincides with the vertical migration of the euphausid shrimps that are part of the Megamouth Shark's diet.
The megamouth shark has been spotted off the coasts of Hawaii, California, Japan, the Philippines, Senegal, Indonesia, and western Australia in the Pacific and Atlantic Oceans. It is a deep-ocean creature and comes up to the surface to feed. They have been spotted in both temperate and tropical waters of the Pacific.
Megamouth sharks spend most of their time in at mid-depth but does come to the surface, mostly to chase the large masses of krill as they go up and down in the water column during their natural, daily migrations.
- The megamouth has really very poorly calcified skeleton, which is a characteristic of all deepwater animals, be they sharks or bony fishes. 
- The megamouth’s skin tissue tends to get very flabby because pressure under water there doesn't reward the increased turgidity of tissue. 
- The only sharks that get bigger than the megamouth are the whale shark, basking shark and a very large white shark, all of which can grow to be just under 20 feet [six meters] in length. 
- Reproduction is ovoviviparous, meaning that the young sharks develop in eggs that remain within the mother's body until they hatch. 
Relatively little was known of their habits until researchers fitted a megamouth – the sixth one discovered – with a pair of ultrasonic transmitters and tracked it for two days in 1990. The research indicated that the sharks spend the daytime in waters up to one kilometre deep and surface only at night to feed on plankton, small fish and jellyfish - usually at a depth of around 15 meters. 
- Megamouth Shark
- What is a megamouth shark? Is it still a scientific mystery?
- Rare megamouth shark caught in Philippines