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Shark Info   (02-15-1999)



Shark Accidents or Shark Attacks ? 2/2

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Which shark species are really dangerous?

Dr. E. K. Ritter

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Marie Levine

  Fact Sheet:

Biology of the Megamouth Shark

Dr. J. F. Morrissey

Fact Sheet: Biology of the Megamouth Shark

By Dr. John F. Morrissey

The history of discovering the megamouth shark (Megachasma pelagios) is almost as interesting as its biology. Actually, one should have discovered this species, whose representatives usually reach a length of 500 cm, many years ago. The first specimen was, however, not seen until November 15, 1976. That particular shark, which was a 446 cm long male, was caught unawares by a U.S. Navy ship off the coast of Kahuku Point in Oahu, Hawaii, as they pulled up their drag anker in which the shark had become entangled. Oddly enough, no scientific description of this fascinating shark was available until 1983 (Taylor et al., 1983), although a year before its unique parasites had been identified (Dailey and Vogelbein, 1982). Astonishingly enough it took almost an additional ten years before another megamouth was sighted. Up until then biologists had assumed that their rarity was due to the fact that they normally lived in deep, pelagic ocean regions.

The second individual was caught by anglers on November 29, 1984 - almost eight years following the first find - with a deep sea net off the coast of Catalina Island in California (Lavenberg and Seigel, 1985). This 449 cm long male was preserved and today can be viewed by the public in the Los Angeles County Museum in California.

Meanwhile, scientists had to wait several years more before another megamouth shark was caught, this time on August 18, 1988. This third specimen was a 515 cm long male which was washed ashore in the vicinity of the Mandurah Estuary about 50 km south of Perth, West Australia (Berra and Hutchins, 1990; Berra and Hutchins, 1991) and was put on exhibit in the West Australian Museum. Its find was significant because it showed that its territory had extended to the eastern part of the Indian Ocean. Its large territory, stretching from California to West Australia, is typical for deepsea species because conditions in the deep ocean are relatively stable.

The first megamouth shark was thus not discovered until 1976 and only after 12 years were three additional specimens caught. Subsequently, megamouth sharks unexplainably began to appear worldwide. In the 10 years following the third catch, nine additional specimens were sighted, six of them as of November 1994. Up until today, no one has proposed a hypothesis to explain the sudden boom of this shark family.

The fourth megamouth shark, a large male, was found on the sandy shores of the Shizuoka prefecture, Japan, on January 23, 1989, before the animal was rewashed into the ocean (Nakaya, 1989). On June 12, 1989, a 500 cm long individual got himself caught in a fixed net. He was freed from his predicament because he was mistaken for a basking shark (Cetorhinus maximus) (Miya et al., 1992). The next animal, a 495 cm long male, was caught in a drift net on October 21, 1990, off the coast of Dana Point, California. It became famous because it was followed for more than 50 hours nonstop using a bearing transmitter (Lavenberg and Seigel, 1985). Another stranded megamouth shark was spotted by a birdwatcher on November 29, 1994, in Hakata Bay, Fukuoka, Japan. This 471 cm long individual was the first female to be observed and served as a basis for multinational scientific investigation (Yano et al., 1997). This eighth catch was important because it was the first proof of this species' presence in the Atlantic Ocean, and also because the animal was substantially smaller than the others. The not yet sexually mature male (approx. 180 cm long) was caught on May 4, 1995 in the funnel net of a French commercial tunafishing vessel off the coast of Dakar, Senegal (Sˇret, 1995). Surprisingly, the next megamouth shark was also a young male from the Atlantic. This specimen was caught accidentally on Septemer 18, 1995, on the hook of Brasilian trawl line fishers off the coast of southern Brazil (A. Amorim, personal note). The last three specimens, all of them 500 cm long females, were caught only recently in the tropical waters of the West Pacific. The tenth was caught on May 1, 1997, off the coast of Toba, Japan (Yano et al., from newspaper reports), the next one off the coast of the Philippines (Morrissey and Elizaga, from newspaper reports) and the last one on April 23, 1998, off the coast of Atawa, Japan (Yano et al., 1998), exactly 25 km from the location were the tenth one was caught.

Megachasma pelagios

In 1990 this megamouth shark (Megachasma pelagios) was marked with a radio beacon and followed for more than 50 hours.

© Shark Info / Tom Haight

Today, megamouth sharks are known in all tropical waters, with the exception of the western Indian Ocean. In all likelihood, this species inhabits all tropical waters and is probably more frequent than it appears by virtue of its vertical migration. The telemetric chase of the sixth specimen (Nelson et al., 1997) confirmed earlier assumptions that this species usually inhabits the deep sea, which may explain the sporadic appearance of only 12 specimens. The shark was chased for two whole days and spent its days in medium depths of 149 m (at a local water depth of 700 - 850 m) and nights in medium depths of 17 m. Accordingly this animal remained in the epipelagic zone, following the vertical migration of zoo plankton which it lived on (Forward, 1987; Hu, 1978). Transmitter data disproved earlier fears that megamouth sharks had problems in finding sufficient plankton in the deep sea (Diamond, 1985). In addition, the discovery of this behavior refuted earlier hypotheses - which had not been verified by histological tests (Nakaya et al., 1997) - which claimed they needed a luminescent organ in their mouth (Taylor et al., 1983).

The Megachasma pelagios is a fascinating species of shark which is surrounded by many unsolved mysteries. The answers to the many open questions on the natural biology of these animals will probably be found in accidental findings of further specimens.

Literature cited

    Berra, T. M., and Hutchins, B. (1991). Natural history notes on the megamouth shark, Megachasma pelagios, from Western Australia. Western Australia Naturalist 18, 224-233.

    Berra, T. M., and Hutchins, J. B. (1990). A specimen of megamouth shark, Megachasma pelagios (Megachasmidae), from Western Australia. Records of the Western Australian Museum 14, 651-656.

    Dailey, M. D., and Vogelbein, W. (1982). Mixodigmatidae, a new family of cestode (Trypanorhyncha) from a deep sea, planktivorous shark. Journal of Parasitology 68, 145-149.

    Diamond, J. M. (1985). Filter-feeding on a grand scale. Nature 316, 679-680.

    Forward, R. B., Jr.1987. Crustacean larval vertical migration: a perspective, pp. 29-44 in: Signposts in the sea (W. F. Hernkind and A. B. Thistle, eds.). Florida State University, Tallahassee.

    Hu, V. J. H. 1978. Relationships between vertical migration and diet in four species of euphausiids. Limnol. Oceanog. 23(2): 296-306.

    Lavenberg, R. J., and Seigel, J. A. (1985). The Pacific's megamystery - megamouth. Terra 23, 29-31.

    Miya, M., Hirosawa, M., and Mochizuki, K. (1992). Occurrence of a megachasmid shark in Suruga Bay: photographic evidence. Journal of the Natural History Museum Institute, Chiba 2, 41-44.

    Morrissey, J. F. and E. T. Elizaga. In Press. Capture of megamouth #11 in the Philippines. Philippine Journal of Science.

    Nakaya, K. (1989). Discovery of a megamouth shark from Japan. Report of the Japanese Society for Elasmobranch Studies 26, 36-39.

    Nakaya, K., Yano, K., Takada, K., and Hiruda, H. (1997). Morphology of the first female megamouth shark, Megachasma pelagios (Elasmobranchii: Megachasmidae), landed at Fukuoka, Japan, pp. 51-62 in: Biology of the Megamouth Shark (K. Yano, J. F. Morrissey, Y. Yabumoto and K. Nakaya, eds.). Tokai University Press, Tokyo.

    Nelson, D. R., McKibben, J. N., Strong, W. R., Jr., Lowe, C. G., Sisneros, J. A., Schroeder, D. M., and Lavenberg, R. J. (1997). An acoustic tracking of a megamouth shark, Megachasma pelagios: a crepuscular vertical migrator. Environmental Biology of Fishes 49, 389-399.

    Séret, B. (1995). First record of a megamouth shark (Chondrichthyes, Megachasmidae) in the Atlantic Ocean, off Senegal. Cybium 19, 425-427.

    Taylor, L. R., Compagno, L. J. V., and Struhsaker, P. J. (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, 87-110.

    Yano, K., O. Tsukada, and M. Furuta. 1998. Capture of megamouth no. 12 from Atawa, Mie, Japan. Ichthyol. Res. 45(4): 424-426.

    Yano, K., Morrissey, J. F., Yabumoto, Y., and Nakaya, K. (1997). Biology of the megamouth shark (Tokyo: Tokai University Press).

    Yano, K., Yabumoto, Y., Tanaka, S., Tsukada, O., and Furuta, M. In Press. Capture of a mature female megamouth shark, Megachasma pelagios, from Mie, Japan. Cybium.

(7707 characters inkluding literature)

* Dr. John F. Morrissey is Assistant Professor at Hofstra University, New York, and author of several publications on the Megachasma pelagios.

May be published only by indicating the source: Shark Info / Dr. John F. Morrissey



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