Megamouth shark

Megamouth shark

The **megamouth shark** (*Megachasma pelagios*) is a species of deepwater shark. It is rarely seen by humans and is the smallest of the three extant filter-feeding sharks alongside the whale shark and basking shark. Since its discovery in 1976, few megamouth sharks have been seen, with 63 specimens known to have been caught or sighted as of May 2017, including four recordings on film. Like the other two planktivorous sharks, 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 the suggestion has been made that it may belong in the family Cetorhinidae, of which the basking shark is currently the sole extant member. In addition to the living *M. pelagios*, however, two extinct megamouth species – the Priabonian *M. alisonae* and the Oligocene–Miocene *M. applegatei* – have also recently been proposed on the basis of fossilized tooth remains. However, the Cretaceous-aged *M. comanchensis* has been recently reclassified as an odontaspid shark in the genus *Pseudomegachasma*, and is in fact unrelated to the megamouth shark despite similar teeth morphology, instead being a case of convergent evolution with the megamouth.

## Description

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. The megamouth is therefore considerably less active than the other two large filter-feeding sharks, the basking shark and the whale shark. The megamouth has a stout body and a long, wide bulbous head, which make it look very different from more typical lamniform sharks such as makos and great whites.

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. This white band is present in both sexes and is thought to be used as a means of identification to other megamouth sharks. Their mouths can reach up to 1.3 m (4 ft 3 in) wide.

## Behavior

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 (390–520 ft), but as the sun set, it would ascend and spend the night at depths of between 12 and 25 m (39 and 82 ft). Both day and night, its progress was very slow at around 1.5–2.1 km/h (0.93–1.30 mph). This pattern of vertical migration is seen in many marine animals as they track the movement of plankton in the water column. The shark captured in March 2009 was reportedly netted at a depth of 200 m (660 ft).

Several megamouths have washed up alive on beaches. The exact reason for this remains a mystery.

## Reproduction

Reproduction is ovoviviparous, meaning that the young sharks develop in eggs that remain within the mother's body until they hatch. Mating has never been observed in this species due to the remoteness and inaccessibility of their preferred environment.

## Known Megamouth specimens

As of 24 May 2017, only 63 megamouth specimens have been caught or sighted. They have been found in the Pacific, Atlantic and Indian oceans. Japan, the Philippines, Vietnam, 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.

The original type specimen, caught in 1976, became entangled in the sea anchor of a United States Navy ship off of Kāne'ohe, Oahu, Hawaii. It was later examined by Leighton Taylor, who named the species as "megamouth".

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.

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.

On May 7, 2014 a 4 m (13 ft) 680 kg (1,500 lb) female shark was captured at a depth of 800 m (2,600 ft) 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.

On June 30, 2014 a 500 kg (1,100 lb) 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, mounted along with the jaw, is on display at the D' Bone Collector Museum in Davao.

On January 28, 2015 a 4.5 m (15 ft) deceased megamouth shark was found by residents of Barangay Marigondon, in Pioduran town, Albay, Philippines. It is now on display at the Albay Parks and Wildlife, opened to the public since March 3, 2015 which coincided with Albay's celebration of the World Wildlife Day. The megamouth shark was preserved through taxidermy, and is now considered one of the more precious collections of Albay, a leading province in environment protection.

On April 14, 2016 a 5 m (16 ft) deceased megamouth shark was caught in a fisherman's net in Mie Prefecture, of the Japanese island of Honshu around three miles off the Owase Port. The shark weighed an estimated 907 kg (2,000 lb)

On May 1, 2017 a nearly 3 m (9.8 ft) deceased megamouth shark washed up at Barangay Baluarte in the Misamis Oriental, a region in the Northern Mindanao of the Philippines. The estimated 600 kg (1,300 lb) shark was buried to prevent locals from consuming the fish as authorities were unsure of the cause of death.

On May 22, 2017 a live megamouth shark was found in a fishing net off Sunosaki lighthouse in Tateyama, Chiba Prefecture, Japan. The estimated 5 m (16 ft) to 6 m (20 ft) female was filmed swimming around the net and being examined by Sakana-kun, a professor emeritus of the Tokyo University of Marine Science and Technology. The shark died the following day.

In July 2017, a megamouth was filmed alive and seemingly healthy off the island chain of Gili Lawa Laut near Komodo Island by a british diver named Penny Bielich. The encounter was one of the few times a megamouth was filmed in an area with relatively shallow water.