This filter-feeding shark moves through its habitat eating krill, plankton, jelly fish, shrimp, and copepods. Yet most plankton is found near the surface, so it is something of a mystery how Megamouth manages to find enough to eat.

What does the Megamouth shark eat?

First captured off Oahu, Hawaii, in November 1976 and now known from 
 only 14 specimens from scattered locations around the globe, the Megamouth 
 Shark (Megachasma pelagios) is one of the most spectacular 
 ichthyological discoveries of the 20th Century.<h4>Just the Facts:</h4><img src="http://www.elasmo-research.org/education/color_illos/megachasma-pelagios_sm.gif" width="200" height="72">Size:Birth: unknown; 
 smallest free-swimming specimen was 6 ft (1.8 m) long 
 Maturity: males 14 ft (4 m); females no data 
 Maximum: 17 ft (5.2 m)Reproduction:Maturity: no data for 
 either sex 
 Mode: ovoviviparity 
 Gestation: no data 
 Pups: no dataDiet:Habitat: Open Ocean, Deep SeaDepth: 40-545 ft (12-166 m), possibly to 3,300 
 ft (1,000 m)Distribution: Central Pacific, 
 Tropical Eastern Pacific, Amazonian, West African, South East Asian, Western 
 Australian, JapaneseNamed for its huge, bathtub-sized jaws and rubbery lips, Megamouth is 
 highly unusual among deep-sea sharks in that it is apparently a 
 filter-feeder. Along the inner lining of its gills are rows of 
 cartilage-cored, finger-like gill rakers, which the animal almost 
 certainly uses to strain food from the surrounding seawater. Known prey of 
 the Megamouth Shark consists entirely of planktonic animals, including 
 euphausiid shrimps, copepods, and the Pancake Jellyfish (Atolla 
 vanhoeffeni). Yet most plankton is found near the surface, so it is 
 something of a mystery how Megamouth manages to find enough to eat.<img src="http://www.elasmo-research.org/education/ecology/images/megachasma-gill-rakers.jpg" alt="Megamouth gill rakers" width="200" height="364">Megamouth gill rakersBecause the Megamouth Shark’s upper jaw features great sheets of 
 silvery, reflective tissue, it has been speculated that its lower jaw 
 might be bioluminescent and the creature may use living light to draw 
 planktonic prey to itself. Had this been true, Megamouth would have been 
 by far the largest known bioluminescent organism. Unfortunately, 
 histological examination of its lower jaw tissues revealed no 
 light-producing organs — another beautiful theory slain by an ugly fact.Examination of Megamouth’s anatomy has revealed that its jaws are 
 highly protrusible and its basihyal (‘tongue’) is large and unusually 
 mobile. In theory, coordinated jaw protrusion and basihyal flexure could 
 significantly expand the volume inside Megamouth’s throat, creating a 
 partial vacuum to help suck in planktonic prey. While this makes good 
 intuitive sense, confirmation or refutation of this scenario will have to 
 await documentation via film footage of a Megamouth feeding in the wild. 
 As well established as is the field of comparative anatomy, there is only 
 so much one can learn from a lifeless specimen.In October 1990, scientists had a rare opportunity to track the daily 
 movements of a Megamouth (specimen #6) off Dana Point, southern 
 California. A 16-foot (5-metre) male specimen, it spent the daylight hours 
 at depths of 400 to 550 feet (120 to 166 metres). At night, it rose to 
 depths of 40 to 80 feet (12 to 25 metres) and returned to the depths 
 before dawn. This individual Megamouth was tracked continuously for only 
 50.5 hours — two complete day-night cycles — but that was long enough to 
 determine that its vertical movements were strongly correlated with 
 ambient light levels. From the sum total of data collected at the time, 
 the researchers concluded Megamouth is a vertical migrator that probably 
 moves up and down as part of a complex community of mesopelagic animals 
 known collectively as the Deep Scattering Layer (for its ability to 
 scatter depth sounding echoes).<img src="http://www.elasmo-research.org/education/ecology/images/megachasma_feed-left.gif" alt="Megachasma feeding 
© R.Aidan Martin, ReefQuest 
Centre for Shark Research" width="383" height="366">The 
 tracking data also revealed that Megamouth swims very slowly. The 
 telemetered individual moved southward at an average rate of 0.7 miles 
 (1.2 kilometres) per hour, but this speed was probably against a steady 
 current of 4 to 10 inches (10 to 25 centimetres) per second. Adjusting for 
 the opposing current, the shark’s actual speed relative to the water was 
 about 0.9 to 1.3 miles (1.5 to 2.1 kilometres) per hour. This is less than 
 half the average cruising speed recorded for large predatory sharks, such 
 as the White Shark (Carcharodon carcharias) and Tiger Shark (Galeocerdo 
 cuvier), but only slightly slower than swimming speeds recorded for 
 other large planktivorous sharks, such as the Basking Shark (Cetorhinus 
 maximus) and Whale Shark (Rhincodon typus). But, at present, we 
 cannot be sure whether Megamouth’s slow cruising pace is due to its 
 filter-feeding mode of life, a strategy for saving energy in the 
 nutrient-poor mesopelagic, or simply an artifact of the physiological 
 sluggishness of muscles in the cold water characteristic of the deep-sea.Little is known about the reproductive biology of Megamouth. Two male 
 specimens captured off southern California in the late fall displayed 
 evidence of recent or impending mating. The claspers of Megamouth #2 were 
 oozing sperm and the clasper tips of Megamouth #6 were extensively abraded 
 and bleeding, possibly indicating it had mated recently. The lower jaw of 
 Megamouth #6 also showed abrasion, possibly due to a female grasping it 
 during mating. Taken together, such circumstantial evidence suggests that 
 Megamouth mating in the tropical eastern Pacific may occur during October 
 and November.The Megamouth Shark is occasionally observed at the surface during 
 daylight hours. In October 1990 a pair of sea kayakers off Dana Point, 
 California saw what was very probably a large Megamouth rise slowly and 
 swim briefly along the surface. In August 1998, a Megamouth (#13) — 
 estimated to be 16 feet (5 metres) long — was observed and photographed at 
 the surface off Manado, Indonesia, apparently being attacked by a pod of 
 three Sperm Whales (Physeter macrocephalus). Whether the whales were 
 attempting to feed on the hapless shark or simply playing with it, as a 
 cat does with a mouse, is not clear from the reports and photos. 
 Vulnerability to predators may partially explain why Megamouth is so 
 rarely seen at the surface during daylight hours. And it may also explain 
 why such a large and otherwise conspicuous species was not ‘discovered’ 
 until so very recently.<img src="http://www.elasmo-research.org/education/ecology/images/megamap.jpg" alt="Map of Megamouth records (Jan 2007)" width="478" height="205">Most of our accumulated knowledge about Megamouth as a living creature 
 has been deduced from dead or moribund specimens. At least three Megamouth 
 specimens have been found stranded on shallow, sandy beaches, one in 
 Western Australia (#3) and two in Japan (#4 and #5). It is hard to imagine 
 a healthy deep-sea shark entering such shallow waters and stranding. Even 
 the 16-foot (5-metre) male tracked off southern California (#6) was caught 
 in a gillnet and kept overnight tethered on a short leash in a shallow, 
 silty bay before it was outfitted with a telemetric device and released. 
 Thus, a great deal of what we think we know about the Megamouth may be 
 based on aberrant, ill, or moribund individuals.But, as our exploration of the deep-sea continues into the 21st 
 Century, opportunities to observe, film, and study the Megamouth Shark 
 will undoubtedly increase, revealing new secrets and raising new questions 
 about its mysterious life.

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Science & Nature

First captured off Oahu, Hawaii, in November 1976 and now known from only 14 specimens from scattered locations around the globe, the Megamouth Shark (Megachasma pelagios ) is one of the most spectacular ichthyological discoveries of the 20th Century.

Birth: unknown; smallest free-swimming specimen was 6 ft (1.8 m) long Maturity: males 14 ft (4 m); females no data Maximum: 17 ft (5.2 m)

Maturity: no data for either sex Mode: ovoviviparity Gestation: no data Pups: no data

Habitat: Open Ocean, Deep Sea

Depth: 40-545 ft (12-166 m), possibly to 3,300 ft (1,000 m)

Distribution: Central Pacific, Tropical Eastern Pacific, Amazonian, West African, South East Asian, Western Australian, Japanese

Named for its huge, bathtub-sized jaws and rubbery lips, Megamouth is highly unusual among deep-sea sharks in that it is apparently a filter-feeder. Along the inner lining of its gills are rows of cartilage-cored, finger-like gill rakers, which the animal almost certainly uses to strain food from the surrounding seawater. Known prey of the Megamouth Shark consists entirely of planktonic animals, including euphausiid shrimps, copepods, and the Pancake Jellyfish (Atolla vanhoeffeni ). Yet most plankton is found near the surface, so it is something of a mystery how Megamouth manages to find enough to eat.

Megamouth gill rakers

Because the Megamouth Shark’s upper jaw features great sheets of silvery, reflective tissue, it has been speculated that its lower jaw might be bioluminescent and the creature may use living light to draw planktonic prey to itself. Had this been true, Megamouth would have been by far the largest known bioluminescent organism. Unfortunately, histological examination of its lower jaw tissues revealed no light-producing organs — another beautiful theory slain by an ugly fact.

Examination of Megamouth’s anatomy has revealed that its jaws are highly protrusible and its basihyal (‘tongue’) is large and unusually mobile. In theory, coordinated jaw protrusion and basihyal flexure could significantly expand the volume inside Megamouth’s throat, creating a partial vacuum to help suck in planktonic prey. While this makes good intuitive sense, confirmation or refutation of this scenario will have to await documentation via film footage of a Megamouth feeding in the wild. As well established as is the field of comparative anatomy, there is only so much one can learn from a lifeless specimen.

In October 1990, scientists had a rare opportunity to track the daily movements of a Megamouth (specimen #6) off Dana Point, southern California. A 16-foot (5-metre) male specimen, it spent the daylight hours at depths of 400 to 550 feet (120 to 166 metres). At night, it rose to depths of 40 to 80 feet (12 to 25 metres) and returned to the depths before dawn. This individual Megamouth was tracked continuously for only 50.5 hours — two complete day-night cycles — but that was long enough to determine that its vertical movements were strongly correlated with ambient light levels. From the sum total of data collected at the time, the researchers concluded Megamouth is a vertical migrator that probably moves up and down as part of a complex community of mesopelagic animals known collectively as the Deep Scattering Layer (for its ability to scatter depth sounding echoes).

The tracking data also revealed that Megamouth swims very slowly. The telemetered individual moved southward at an average rate of 0.7 miles (1.2 kilometres) per hour, but this speed was probably against a steady current of 4 to 10 inches (10 to 25 centimetres) per second. Adjusting for the opposing current, the shark’s actual speed relative to the water was about 0.9 to 1.3 miles (1.5 to 2.1 kilometres) per hour. This is less than half the average cruising speed recorded for large predatory sharks, such as the White Shark (Carcharodon carcharias ) and Tiger Shark (Galeocerdo cuvier ), but only slightly slower than swimming speeds recorded for other large planktivorous sharks, such as the Basking Shark (Cetorhinus maximus ) and Whale Shark (Rhincodon typus ). But, at present, we cannot be sure whether Megamouth’s slow cruising pace is due to its filter-feeding mode of life, a strategy for saving energy in the nutrient-poor mesopelagic, or simply an artifact of the physiological sluggishness of muscles in the cold water characteristic of the deep-sea.

Little is known about the reproductive biology of Megamouth. Two male specimens captured off southern California in the late fall displayed evidence of recent or impending mating. The claspers of Megamouth #2 were oozing sperm and the clasper tips of Megamouth #6 were extensively abraded and bleeding, possibly indicating it had mated recently. The lower jaw of Megamouth #6 also showed abrasion, possibly due to a female grasping it during mating. Taken together, such circumstantial evidence suggests that Megamouth mating in the tropical eastern Pacific may occur during October and November.

The Megamouth Shark is occasionally observed at the surface during daylight hours. In October 1990 a pair of sea kayakers off Dana Point, California saw what was very probably a large Megamouth rise slowly and swim briefly along the surface. In August 1998, a Megamouth (#13) — estimated to be 16 feet (5 metres) long — was observed and photographed at the surface off Manado, Indonesia, apparently being attacked by a pod of three Sperm Whales (Physeter macrocephalus ). Whether the whales were attempting to feed on the hapless shark or simply playing with it, as a cat does with a mouse, is not clear from the reports and photos. Vulnerability to predators may partially explain why Megamouth is so rarely seen at the surface during daylight hours. And it may also explain why such a large and otherwise conspicuous species was not ‘discovered’ until so very recently.

Most of our accumulated knowledge about Megamouth as a living creature has been deduced from dead or moribund specimens. At least three Megamouth specimens have been found stranded on shallow, sandy beaches, one in Western Australia (#3) and two in Japan (#4 and #5). It is hard to imagine a healthy deep-sea shark entering such shallow waters and stranding. Even the 16-foot (5-metre) male tracked off southern California (#6) was caught in a gillnet and kept overnight tethered on a short leash in a shallow, silty bay before it was outfitted with a telemetric device and released. Thus, a great deal of what we think we know about the Megamouth may be based on aberrant, ill, or moribund individuals.

But, as our exploration of the deep-sea continues into the 21st Century, opportunities to observe, film, and study the Megamouth Shark will undoubtedly increase, revealing new secrets and raising new questions about its mysterious life.

Deep Sea: Megamouth Shark

What does the Megamouth shark eat?

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