Biology of the megamouth shark

This video is about megamouth sharks.

By Kazuhiro Nakaya in Japan:

Biology of the Megamouth Shark, Megachasma pelagios (Lamniformes: Megachasmidae)

Graduate School of Fisheries Sciences, Hokkaido University 3-1-1, Minato-cho, Hakodate, Hokkaido 041-8611, Japan

Abstract

All records to date (end of June, 2008) of the megamouth shark, Megachasma pelagios were analyzed and the biology of the megamouth shark was inferred from them. The megamouth shark is a wide-ranging species, distributed from the tropical to temperate seas, with the most numerous occurrences in the western North Pacific Ocean. Young individuals tend to be distributed in warmer waters, while mature individuals broaden their habitat to higher latitudes. Males become mature at about 4 m in total length and females at about 5 m. The megamouth shark may copulate all year round, giving birth to young
in warmer waters, and may be spatially segregated by sex.

The discovery of the megamouth shark was one of the ichthyological highlights of the last century.

The first specimen of the megamouth shark was accidentally collected in Hawaii in 1976, and the species was eventually named Megachasma pelagios by Taylor, Compagno and Struhsaker (1983). The second specimen was captured in 1984 in California, U.S.A., eight years after the capture of the first Hawaiian specimen (Lavenberg and Seigel, 1985). The third specimen was found stranded in 1988 off western Australia in the Indian Ocean (Berra and Hutchins, 1990). Then, the fourth and fifth specimens were reported from Japan in 1989 (Nakaya, 1989; Miya et al., 1992). The sixth specimen was captured and released in California with a sonic transmitter (Lavenberg, 1991), and its horizontal and vertical movements were recorded for a few days (Nelson et al., 1997). These specimens were all giant males of about five meters in total length, except for the fifth one of unknown sex, and finally the first female megamouth was caught in Japan in 1994 (Takada et al., 1997).

At present, the worldwide total of megamouth shark captured, found stranded or sighted is forty specimens. Some of the specimens were studied for their morphology and phylogenetic relationships, but most of them were discarded, consumed or not studied. Among the few studies available, Nelson et al. (1997) reported part of their way of life, showing that the megamouth shark makes clear daily vertical movements within depths shallower than 200 meters. However, most of the biology of the megamouth shark still remains to be disclosed.

The purposes of the present study are to synthesize the scattered information of the 40 specimens recorded as of June, 2008, to study the morphological and biological evidence of each specimen, to analyze their capture data, and to discuss the biology of the megamouth shark.

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