The Megamouth shark (Megachasma pelagios) is a species of shark belonging to the family Megachasmidae. It is the sole extant species belonging to its family, in the order of Lamniformes. 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 (described in 1983), few Megamouth sharks have been seen, with fewer than 100 specimens being observed or caught. Like the other two planktivorous sharks, it swims with its enormous mouth wide open, filtering water for plankton shrimp and jellyfish. It is distinctive for its large head.
Researchers have predicted the feeding patterns of Megamouth sharks in relation to the other two planktivorous sharks; the three plankivourous sharks have ram feeding in common, as it evolved from ram feeding swimming-type ancestors that developed their filtering mechanism to capture small prey like plankton. The Megamouth shark more than likely used a three-step feeding method combining ram and suction, described further below.
Family: Megachasmidae – Megamouth Sharks
Genus: Megachasma
Species: pelagios
Phylum– Chordata
Class– Chondrichthyles
Order– Lamniformes
Common Name– Mackerel Sharks
Family– Megachasmidae
Common Name– Megamouth Sharks
Genus– Megachasma
Species– pelagios
Status: IUCN Red List LEAST CONCERN
Average Size and Length: Their length at birth is unknown. Mature males have been measured at around 400 cm/13.1 feet. Mature females have been measured at around 500 cm/16.4 feet. The maximum recorded has been greater than 550 cm/18 feet.
Average Weight: Weights of up to 2,679 pounds have been reported.
Current Rare Mythical Sightings: There are two extinct species, M. alisonae (Priabonian) and M. applegatei (Oligocene–Miocene) that have been recently proposed to belong to Megachasmidae based on fossilized tooth remains. However, species M. comanchensis (Cretaceous), was classified and considered based on similar teeth morphology as well, but on fact is not related, and has been recently re-classified as an odontaspid shark in the genus Pseudomegachasma. Therefore, the recent proposals may not have any weight. Fossils, data and time will tell.
(Shimada, K. 2007. “Mesozoic origin for megamouth shark (Lamniformes: Megachasmidae)”. Journal of Vertebrate Paleontology 27:512–516)
(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)
(Shimada, Kenshu; Popov, Evgeny V.; Siversson, Mikael; Welton, Bruce J.; Long, Douglas J. (2015-09-03). “A new clade of putative plankton-feeding sharks from the Upper Cretaceous of Russia and the United States“. Journal of Vertebrate Paleontology. 35 (5))
The first Megamouth shark 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. The species was identified as being of a new genus within the planktivorous shark species. Examination of the 14.7-foot, 1,650-pound specimen by Leighton Taylor showed it to be an entirely unknown type of shark. It was one of the greatest discoveries of the 20th century. The pectoral fin of the Megamouth shark was studied, along with the skeletal and muscular system of the Megamouth shark to show its phylogenetic relationship to the other two sharks (Tomita, Taketeru; Tanaka, Sho; Sato, Keiichi; Nakaya, Kazuhiro (21 January 2014). “Pectoral Fin of the Megamouth Shark: Skeletal and Muscular Systems, Skin Histology, and Functional Morphology“).
In 1990 a 15-16-foot male Megamouth shark was caught near the surface 7 miles off the coast of Dana Point, California. Fisherman brought it to port, and it survived, awaiting scientists to arrive. It also survived the shallow water for a day in an effort to video tape the shark (https://www.latimes.com/archives/la-xpm-1990-10-22-mn-2320-story.html).
March 30, 2009: Off Burias Island in the Philippines, an 880- to 1,100-pound, 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.
June 12, 2011: A 10-foot 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 for Scripps Institution of Oceanography and Mexican researchers to study the structure of its muscles and gills (Falcon, E. 2012).
May 7, 2014: A 13-foot, 1,500-pound female Megamouth shark was captured at a depth of 2,600 feet 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 (McMurray, K 2014).
June 30, 2014: A 1,100-pound female Megamouth 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 (McMurray, K 2014).
January 28, 2015: A 15-foot 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 (https://sharkdevocean.wordpress.com/2015/01/28/megamouth-shark-washes-up-in-philippines-and-is-only-the-60th-weve-ever-seen/).
April 14, 2016: A 16-foot deceased Megamouth shark was caught in a fisherman’s net in Japan’s Mie Prefecture, around three miles off Owase Port. The shark weighed an estimated 2,000 pounds (McMurray, K. 2016).
May 1, 2017: A 9.8-foot deceased Megamouth shark washed up at Barangay Baluarte in the Misamis Oriental, a region in the Northern Mindanao of the Philippines. The estimated 1,300-pound shark was buried to prevent locals from consuming the fish, as authorities were unsure of the cause of death (McMurray, K. 2017).
May 22, 2017: A live Megamouth shark was found in a fishing net off Sunosaki lighthouse in Tateyama, Chiba Prefecture, Japan. The estimated 16-20-foot female was filmed by Asahi Shimbun photographer and examined by a TV celebrity marine biologist who calls himself Sakana-kun.
July 25, 2017: A Megamouth shark was recorded on video at Gili Lawa Laut near Komodo island, Indonesia, as it swam slowly past divers Penny Bielich and Heikki Innanen. The shark appeared to have at least one remora attached.
February 11, 2018: A juvenile male measuring 14.2 feet in length was accidentally entangled in a fishing net off the coast of Negros Oriental in the Philippines. The body of the deceased shark was towed back and buried at Barangay Villareal later that afternoon. It was exhumed the following day so scientists could conduct a necropsy and get tissue samples for research (http://northboundasia.com/2018/02/12/rare-megamouth-shark-dies-fishnet-entanglement-negor/).
Teeth and Jaw: Visually, there is dark spotting on the lower jaw. The huge terminal mouth extends behind the eyes, and has many small and hooked teeth. Its lips have been described as rubbery. Inside of the upper lip is a silvery-white, which is very visible when the mouth is open. It was proposed in the mid-1980’s that the lower lip might glow with the upper, white band used as a reflector, but that hasn’t been proven. This white band is present in both sexes. It has been proposed that their mouths can reach up to 4.3 feet wide, but this is not confirmed. It is also proposed that Megamouth sharks have up to 50 rows of teeth in their upper-jaw and up to 75 rows of teeth in their lower-jaw. Females seem to present fewer teeth rows than males. Upper and lower jaws have a symphyses toothless space, but it is larger in upper jaw. A difference between the upper and lower teeth was recognized on a female specimen. The first five upper teeth are smaller than the first five lower teeth; the more distal upper teeth are smaller than the lower teeth; the cusps of the lower teeth are more acute and longer than those of the upper teeth.
Head: The Megamouth shark has an unmistakable long and large, bulbous head with a short and rounded snout.
Denticles: Megamouth sharks have very small mucous on the tongue, and dermal denticles that differ in shape and size at each region of the body. There are many pigment cells on the dorsal side, but none on the ventral side.
Tail: It has an asymmetrical tail with a long upper lobe, but no caudal keels.
Demographic, Distribution, Habitat, Environment and Range: The Megamouth shark is more than likely found worldwide in the tropics. There aren’t many records. They are oceanic, coastal and offshore. They are found between 16-131 feet on the continental shelf, and between 26-545 feet offshore over very deep water. They more than likely perform a diel vertical migration, searching for plankton. They migrate to the surface at night, and stay deeper by day.
As of 5 March 2018, only 99 Megamouth specimens had been caught or sighted. 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, Puerto Rico, Ecuador, and possibly Vietnam.
Some scientists believe that Southern California might be a mating area for megamouth sharks in the fall.
Diet: Planktivore; they feed on plankton, particularly krill, or shrimp and even jellyfish.
It is preyed on by the semi-parasitic Cookiecutter shark, and possibly whales.
The 13th specimen was apparently witnessed being attacked by whales with apparent marks on the dorsal and other fins.
Ram-Suction Index: The Megamouth shark more than likely is high on the suction side of the RSI, sucking in plankton to feed. However, the three planktivorous sharks have ram feeding in common, so it may use a combination of both. More than likely, it feeds in a three-step method:
Passive-swimming slowly with mouth open, straining plankton from the water.
Vertical-floating vertically, with little to no forward movement, using a suction method to draw prey into their mouths.
Active-suction filter-feeding while swimming steadily, enabling the whale sharks to draw water into their mouths at higher velocities. This type of feeding is also called “ram-filter feeding”.
They open their mouths, let water come in and their bodies filter out food, and release the water and any debris back into the ocean.
Aesthetic Identification: The body of the Megamouth shark is dark grey dorsally, and white ventrally. There are light margins to blackish pectoral and pelvic fins. The interior of its gill slits is lined with gill rakers that capture its food. The body has been described as stout, soft and flabby.
Biology and Reproduction: The Megamouth shark may have bioluminescent tissue inside its very large mouth to attract prey.
Tissue samples were obtained from twenty-seven Megamouth sharks caught in a two year period off the Hualien coast (eastern Taiwan), and two caught in Baja California, Mexico, and samples taken from GenBank in order to perform a population genetic analyses of the Megamouth shark; the results indicated no genetic diversity between populations found in different geographical locations, which indicates the species forms a single, highly migratory, interbreeding population )Liu, Shang-Yin ‘Vanson’; Joung, Shoou Jeng; Yu, Chi-Ju; Hsu, Hua-Hsun; Tsai, Wen-Pei; Liu, Kwang Ming (5 March 2018). “Genetic diversity and connectivity of the megamouth shark“).
Megamouth sharks show a decrease in specific gravity in the form of a soft, and poorly calcified cartilaginous skeleton; very soft, loose skin; and loose connective tissue and muscles.
As of July 2017, the preserved and partially dissected head of a Megamouth shark was on display at Osaka Aquarium in Osaka, Japan.
Not much is known about the reproduction of the Megamouth shark, but they are presumed viviparous/ovoviviparous with oophagy. The claspers of the first captured megamouth were fully described. Its claspers were relatively slender, with tip elongated, forming a very narrow, slender process. Apparently, two male specimens showed evidence of recently mating. There is also possible evidence that males may try to old down females during copulation, for one was found to have similar lower jaw wounds like that in other mating sharks.
The ovary of the megamouth is similar to other mackerel sharks and this suggests that megamouth embryos are oophagous (the first well-developed embryo eats the other eggs in the uterus). The 12th megamouth captured is the only known mature female. The total length of this specimen was 5.44m and the expanded uteri measured 260mm. The right ovary possessed a large number of whitish yellow eggs (Florida Museum, 2019).
A few species of parasites are found internally in megamouth sharks, including specimens of a cestode worm species (Corrugatocephalum ouei) and specimens of a poorly known trypanorhynch (Mixodigma leptaleum) recovered from the intestine contents of the 7th megamouth. A microscopic parasite (Chloromyxum) was also found in this megamouth from its gall bladder.
Behavioral Traits, Sensing and Intelligence: The Megamouth shark is suggested to be considerably less active than the other filter-feeding sharks, the Whale shark and Basking shark.
Speed: They are more than likely slow, poor swimmers.
Megamouth Shark Future and Conservation: They are considered of least concern, however there is very little data to support much and they are quite rare.
Megamouth Shark Recorded Attacks on Humans: Not a threat to humans.