Megamouth Shark, Megachasma pelagios Taylor, Compagno & Struhsaker 1983
A Megamouth Shark, Megachasma pelagios. Source: NOAA Photo Library. License: Public Domain
Video of a Megamouth Shark filmed off Komodo Island, Indonesia, July 2017.
Underwater footage of the 6th Megamouth Shark ever discovered. Captured near Los Angeles and tethered overnight, this shark was released after being tagged with two acoustic transmitters. The Megamouth migrated to feed in deeper waters during the day, before returning to near surface waters at night - perhaps following the daily migration of mesopelagic zooplankton, especially euphausid crustaceans.
Megamouth Shark, Megachasma pelagios Taylor, Compagno & Struhsaker 1983
More Info
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Distribution |
Worldwide, in tropical and temperate pelagic habitats from approximately the surface down to 1,500 m. The species is known from only 102 specimens (as of August 2015). This oceanic pelagic species undertakes daily vertical migrations, spending daylight hours in deeper epi-pelagic waters, and returning to near-surface waters at night. The Megamouth may be following the daily vertical migration of the mesopelagic prey on which it feeds - krill, other crustaceans, jellyfishes and possibly small fishes. Itabashi et al. (1997) suggested that the composition of the liver oil of the Megamouth Shark, along with its body coloration and catch records, indicates that the species most likely inhabits epipelagic depths (0-200 metres) rather that deeper waters. |
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Features |
Vertebrae: 125. Almost tadpole-like in shape, with a huge head, and tapering body and tail; Eyes semicircular with no nictitating membrane; snout very short, broadly-rounded; mouth huge, broad, terminal with thick rubbery lips; jaws protrusible with small, hooked teeth in many rows. Gill openings moderately long, not extending onto top of head, internal gill slits with many rows of papillose finger-like gill rakers. Two relatively low angular dorsal fins, pectoral fins long, narrow; anal fin small, pelvic fins of moderate size. Caudal fin long, asymmetrical, lower lobe well-developed; upper pre-caudal pit present; keels and ridges absent from tail base. The pectoral fin of the Megamouth Shark appears to be remarkably flexible and mobile, unlike that of many fast swimming sharks which have stiff and relatively immobile pectoral fins. The flexibility and mobility of the pectoral fin is thought to provide stability at slow swimming speeds (Tomita et al. 2014). |
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Size |
Maximum length: Female 7 m; male 5.5 m. |
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Colour |
Dark greyish to bluish-black or blackish-brown above, paler below, with white fin tips and a silvery lining to the inside of the mouth. Snout just above upper jaw with a bright white band, seen only when the upper jaw is protruded. |
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Feeding |
Along with the Whale Shark (Rhincodon typus) and the Basking Shark (Cetorhinus maximus), the poorly known Megamouth Shark is one of three living filter-feeding sharks. The Megamouth is a planktivore, feeding on a variety of zooplankton, including euphausid shrimps, copepods and pelagic jellyfish. Kempster & Collin (2011) examined the Megamouth Shark at the Western Australian Museum when it was moved to a new display case. They found that most of the electrosensory organs (Ampullae of Lorenzini) were located on top of the head, presumably because of the short snout and terminal mouth of the Megamouth Shark is terminal, rather than the mouth being positioned on the underside of the snout like most other sharks. The Megamouth Shark lives in the oceanic midwaters, and Kempster & Collin suggest that the electrosensory organs on the shark’s head can even detect the weak electrical fields produced by its tiny planktonic prey. The authors also suggest that the spacing and orientation of the electrosensory pores on the head enables M. pelagios to use passive electroreception to maximise feeding efficiency. |
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Biology |
Although little is known of the biology of this species, like other mackeral sharks, the Megamouth is assumed to be ovoviviparous (aplacental viviparous). The largest embryos probably engage in embryonic oophagy, feeding on additional eggs produced by mother. Males showing recent evidence of copulation have been collected, and at least one female had what appeared to be mating scars. More information on the life history and anatomy is available in Yano et al. (1997), Last & Stevens (1994, 2009), Compagno (2001) and Kempster & Collin (2011). |
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Fisheries |
Taken as a very rare incidental bycatch of various high-seas and coastal fisheries, including commercial littoral drift gillnets, set fish traps, and pelagic longlines and purse-seines, vulnerable to pelagic gillnets and pelagic trawls (Compagno 2005). The Megamouth is preyed upon by Sperm Whales and Cookie Cutter Sharks (Isistius brasiliensis). |
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Conservation |
IUCN Red List: Data Deficient. |
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Remarks |
With its flabby body, and weakly calcified skeleton and soft thought to be a very slow swimmer. |
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Similar Species |
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Etymology |
Megachasma is from the Greek megas, megalos (great), and chasma (cave or chasm), in reference to the huge mouth. The species name pelagios is Greek (of the sea). The scientific name therefore means 'great chasm of the open sea'. |
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Species Citation |
Megachasma pelagios Taylor, Compagno & Struhsaker 1983, Proc. Calif. Acad. Sci. 4 43(8): 96, figs 2-5. Type locality: about 42 km northeast of Kahuku Point, Oahu Island, Hawaii Islands, 21°51'N, 157°46'W, depth about 165 m. |
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Author |
Bray, D.J. 2020 |
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Resources |
Megamouth Shark, Megachasma pelagios Taylor, Compagno & Struhsaker 1983
References
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Berra, T.M. 1997. Some 20th century fish discoveries. Environmental Biology of Fishes 50: 1–12.
Berra, T.M. & Hutchins, J.B. 1990. A specimen of Megamouth Shark, Megachasma pelagios (Megachasmidae) from Western Australia. Records of the Western Australian Museum 14(4): 651-656.
Berra, T.M. & Hutchins, J.B. 1991. Natural history notes on the Megamouth Shark, Megachasma pelagios, from Western Australia. Western Australian Naturalist 18(8): 224-233.
Clark, E. & Castro, J. 1995. ‘Megamamma’ is a virgin: dissection of the first female specimen of Megachasma pelagios. Environmental Biology of Fishes 43: 329-332.
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Compagno, L.J.V. 1990. Relationships of the Megamouth Shark, Megachasma pelagios (Lamniformes: Megachasmidae), with comments on its feeding habits. NOAA Tech. Rep. NMFS 90: 357-379.
Compagno, L.J.V. 2001. Sharks of the World. An annotated and illustrated catalogue of shark species known to date. Bullhead, mackerel and carpet sharks (Heterodontiformes, Lamniformes and Orectolobiformes). Rome : FAO, FAO Species Catalogue for Fisheries Purposes No. 1 Vol. 2 269 pp.
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