Megamouth shark

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Megamouth shark
Megamouth shark japan.jpg
Conservation status
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Subclass: Elasmobranchii
Superorder: Selachimorpha
Order: Lamniformes
Family: Megachasmidae
Taylor, Compagno & Struhsaker, 1983
Genus: Megachasma
Taylor, Compagno & Struhsaker, 1983
Species: M. pelagios
Binomial name
Megachasma pelagios
Taylor, Compagno & Struhsaker, 1983
Megachasma pelagios distmap.png
Range of megamouth shark (in blue)

The megamouth shark (Megachasma pelagios) is an extremely rare species of deepwater shark, and the smallest of the three planktivorous sharks, besides the whale shark and basking shark. Since its discovery in 1976, few megamouth sharks have been seen, with 59 specimens known to have been caught or sighted as of June 2014, including three recordings on film. Like the other two filter-feeders, it swims with its enormous mouth wide open, filtering water for plankton and jellyfish. It is distinctive for its large head with rubbery lips. It is so unlike any other type of shark that it is usually considered to be the sole extant species in the distinct family Megachasmidae, though suggestion has been made that it may belong in the family Cetorhinidae, of which the basking shark is currently the sole extant member.[2] In addition to the living M. pelagios, however, two extinct megamouth species – the Cretaceous M. comanchensis and the OligoceneMiocene M. applegatei – have also recently been proposed on the basis of fossilised tooth remains.[3][4]

Description[edit]

Mouth of preserved specimen

The appearance of the megamouth is distinctive, but little else is known about it. It has a brownish-black colour on top, is white underneath, and has an asymmetrical tail with a long upper lobe, similar to that of the thresher shark. The interior of its gill slits are lined with finger-like gill rakers that capture its food. A relatively poor swimmer, the megamouth has a soft, flabby body and lacks caudal keels.

Megamouths are large sharks, able to grow to 5.5 metres (18 ft) in length. Males mature by 4 m (13 ft) and females by 5 m (16 ft). Weights of up to 1,215 kg (2,679 lb) have been reported.

As their name implies, megamouths have a large mouth with small teeth, and a broad, rounded snout, causing observers to occasionally mistake megamouth for a young orca. The mouth is surrounded by luminous photophores, which may act as a lure for plankton or small fish. Their mouths can reach up to 1.3 m (4 ft 3 in) wide.[citation needed]

Behaviour[edit]

In 1990, a 4.9-m (16-foot) male megamouth shark was caught near the surface off Dana Point, California. This individual was eventually released with a small radio tag attached to its soft body. The tag relayed depth and time information over a two-day period. During the day, the shark swam at a depth of around 120–160 m (400–525 ft), but as the sun set, it would ascend and spend the night at depths of between 12 and 25 m (39–80 ft). Both day and night, its progress was very slow at around 1.5–2.1 km/h (1–1.3 mph). This pattern of vertical migration is seen in many marine animals as they track the movement of plankton in the water column.[5] The shark captured in March 2009 was reportedly netted at a depth of 200 m (660 ft).

Reproduction[edit]

Reproduction is ovoviviparous, meaning that the young sharks develop in eggs that remain within the mother's body until they hatch.

Discovery[edit]

The first megamouth was captured on November 15, 1976 about 25 miles off the coast of Kāneʻohe, Hawaiʻi, when it became entangled in the sea anchor of United States Navy ship AFB-14.[6] Examination of the 4.5-m (14.7-ft), 750-kg (1,650-lb) specimen by Leighton Taylor showed it to be an entirely unknown type of shark, making it – along with the coelacanth – one of the more sensational discoveries in 20th-century ichthyology.[7]

Known specimens[edit]

Worldwide sightings of the megamouth shark

As of July 2014, only 59 megamouth specimens have been caught or sighted, the most recent being one caught by Japanese fishermen. They have been found in the Pacific, Atlantic and Indian oceans. Japan, the Philippines, and Taiwan have each yielded at least 10 specimens, the most of any single area, amounting to more than half the worldwide total. Specimens have also been sighted in or come out of the waters near Hawaii, California, Mexico, Indonesia, Australia, Brazil, Senegal, South Africa and Ecuador.

On March 30, 2009 off Burias island in the Philippines, an 880- to 1,100-pound (400- to 500-kilogram) 4-metre (13-foot) megamouth shark died while struggling in a fisherman's net and was subsequently taken to nearby Donsol in Sorsogon province, where it was examined by scientists, before being butchered and sold.[8][9][10]

On 12 June 2011, a 3-m (10-ft) dead juvenile male was found by fishermen near the western Baja California peninsula coast, in Sebastián Vizcaíno Bay. It was picked up by the same fishing vessel that in 2006 captured another megamouth specimen in Sebastián Vizcaíno Bay, which has led Mexican scientists to believe that the megamouth could be a seasonal visitor to the Baja California peninsula. The new specimen was taken to Ensenada, where it was photographed and sliced in order for Scripps Institution of Oceanography and Mexican researchers to study the structure of its muscles and gills.[11]

On May 7, 2014 a 3.96-m (13-ft) 1,500-lb (680-kg) female shark was captured at a depth of 2,600 feet (790 m) off the coast of Shizuoka, Japan. The body was dissected in front of the public, by staff at the Marine Science Museum in Shizuoka City, Japan.[12]

On June 30, 2014 a 1,102-lb (500-kg) female shark was captured in the shallow waters of Cagayan de Oro in the Philippines. Samples were sent to the Bureau of Fisheries and Aquatic Resources in northern Mindanao (BFAR-10) and the outer skin is to be stuffed for a local museum.[13]

See also[edit]

For a topical guide to this subject, see Outline of sharks.

References[edit]

  1. ^ L. J. V. Compagno (2005). "Megachasma pelagios (Megamouth Shark)". IUCN Red List of Threatened Species. Version 2014.3. International Union for Conservation of Nature. Retrieved 16 December 2014. 
  2. ^ C. Knickle, L. Billingsley & K. DiVittorio. "Biological profiles: basking shark". Florida Museum of Natural History. Archived from the original on 21 August 2006. Retrieved 16 December 2014. 
  3. ^ Shimada, K. 2007. Mesozoic origin for megamouth shark (Lamniformes: Megachasmidae). Journal of Vertebrate Paleontology 27:512–516. (Link at BioOne)
  4. ^ Shimada, K., Welton, B.J., and Long, D.J. 2014. A new fossil megamouth shark (Lamniformes, Megachasmidae) from the Oligocene-Miocene of the western United States. Journal of Vertebrate Paleontology 34:281-290.
  5. ^ Piper, Ross (2007), Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals, Greenwood Press.
  6. ^ Leighton R. Taylor, L. J. V. Compagno & Paul J. Struhsaker (1983). "Megamouth – a new species, genus, and family of lamnoid shark (Megachasma pelagios, family Megachasmidae) from the Hawaiian Islands". Proceedings of the California Academy of Sciences 43 (8): 87–110. 
  7. ^ Tim M. Berra (1997). "Some 20th century fish discoveries". Environmental Biology of Fishes 50 (1): 1–12. doi:10.1023/A:1007354702142. 
  8. ^ Aca, E.Q. 2009. Megamouth Shark # 41: Megamouth shark in Whale Shark waters. Florida Museum of Natural History Ichthyology Department.
  9. ^ "CTV: Rare megamouth shark caught, eaten in Philippines". Ctv.ca. 2009-04-07. Retrieved 2010-06-17. 
  10. ^ "MEGAMOUTH SHARK FOUND: National Geographic". News.nationalgeographic.com. Retrieved 2010-06-17. 
  11. ^ "Elusive megamouth shark snared in Mexico". 
  12. ^ "Rare Megamouth shark caught in Japan". 
  13. ^ "Another rare Megamouth Shark caught". 

External links[edit]