Megamouth Shark, Megachasma pelagios Taylor, Compagno & Struhsaker, 1983

Introduction

The Megamouth Shark is an extremely rare and unusual species of deepwater shark. It is easily recognised by its huge, soft head and large mouth which is positioned at the anterior margin of the head. While feeding it swims with its enormous mouth wide open, filtering water for plankton and jellyfish.

Identification

The Megamouth Shark is easily recognised by its huge, soft head and large mouth which is positioned at the anterior margin of the head. The inside of the mouth is silvery, and the jaws are covered with many small, hook-like teeth. The Megamouth Shark has two unequal sized dorsal fins, a strongly heterocercal tail, and lacks any distinctive body markings. Its colour varies from grey to blueish-black above and is pale grey below. The tips of most of the fins are usually white.

Habitat

There are only infrequent sightings of this species. It lives in the ocean possibly between depths of 150 m to 1000 m.

Distribution

The first Megamouth specimen known was collected off Kaneohe, Hawaii on 15 November 1976. The research vessel AFB-14 of the Naval Undersea Centre had deployed two large parachutes as sea anchors at a depth of about 165 m in water of bottom depth 4600 m. When these parachutes were hauled aboard, the crew found a 4.46 m long male Megamouth Shark entangled in one of them. The fish was brought ashore because the crew recognised that it was unusual.

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.

The sixth specimen caused a sensation because it was captured and studied alive. It was caught off Dana Point, near Los Angeles. This 5 m long individual was tagged with an ultrasonic transmitter. The fish was tracked for the next 50 hours. Results from the 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 map below shows the Australian distribution of the species based on public sightings and specimens in Australian Museums. Source: Atlas of Living Australia.

Feeding and diet

It is a filter-feeder which eats plankton including, shrimps, copepods and pelagic jellyfish.

References

1. Berra, T.M. & J.B. Hutchins. 1990. A specimen of Megamouth Shark, Megachasma pelagios (Megachasmidae) from Western Australia. Rec. W.A. Mus. 14(4):651-656.
2. Hutchins, B. 1992. Megamouth: Gentle Giant of the Deep. Australian Natural History. 23(12): 910-917.
3. Last, P.R. & J.D. Stevens. 1994. Sharks and Rays of Australia. CSIRO. Pp. 513.
4. Lavenberg, R.J. & J.A. Seigel. 1985. The Pacific's Megamystery - Megamouth. Terra. 23(4): 29-31.
5. Miya, M., Hirosawa, M. & K. Mochizuki. 1992. Occurrence of a Megachasmid Shark in Suruga Bay: Photographic Evidence. J. Nat. Hist. Mus. Inst. Chiba 2(1):41-44.
6. Springer, V.G. & J.P. Gold. 1989. Sharks in Question: The Smithsonian Answer Book. Smithsonian Institution. Pp. 187.
7. Stevens J.D. 1987 Sharks. Golden Press. Pp. 240.
8. Taylor, L.R., Compagno, L.J.V. & P.J. Struhsaker. 1983. Megamouth - A new species, genus, and family of lamnoid shark (Megachasma pelagios, family Megachasmidae) from the Hawaiian Islands. Proc. Cal. Acad. Sci. 43(8): 87-110.
9. Yano, K., Yabumoto, Y., Tanaka, S., Tsukada, O. & M. Furuta. 1997. Capture of a mature Female Megamouth Shark, Megachasma pelagios, from Mie, Japan. Proc. 5th Indo-Pacific Fish Conference, Noumea. Soc. Fr. Ichtyol.: 335-349.