Shark Report: The Megamouth Shark

October 1, 2009

Release from: The Beach Resident

This month will mark the 8-year anniversary of my documentation of a very rare shark off the coast of California. It was only the 15th time it had been documented by scientists. Since my encounter with this species, 27 additional individuals have been reported from around the world.

On November 15, 1976, a U.S. Navy ship off the coast of Oahu, Hawaii made what may be considered as one of the greatest discoveries in shark science. A shark unlike any previously recorded had become entangled in a deep-water net. This first specimen would eventually lead scientists to create not only a new genus and species, but an entirely new family (Megachasmidae) in order to accurately place this creature. Since its initial discovery, a total of only 42 individuals have been recorded worldwide, the majority of which were incidentally caught in fishing nets. Sightings of this particular species of shark have been reported around the world — Polar seas excluded — with numerous sightings occurring in Japan, Taiwan, and California. Several experts have described this species as “one of the rarest species in the oceans,” and its occurrence is “less often than that of Bigfoot.” Due to the lack of information regarding this species, especially that of live individuals, the majority of the knowledge has been derived from the necropsies of dead specimens, firsthand accounts from field researchers, and two observations of live individuals in their natural habitat.

The megamouth shark is one of the three giant filter-feeding shark species, a grouping that also includes the whale shark (Cetorhinus maximus), and the basking shark (Rhincodon typus). It is considered large, attaining a maximum size of at least 17 feet. The body of this shark has loose, soft skin, weak muscle tissues, and a poorly calcified cartilaginous skeleton relative to that of other sharks. Distinctive characteristics of this species are the extremely large mouth, a bulbous head, and a dirty white coloration of the lower jaw, which often includes dusky spots.

As with the other filter feeders, this species has numerous rows of extremely small teeth, and poses relatively no danger to man. Until the live capture, tagging, and monitoring of a megamouth in late 1990, knowledge of the behavior of this animal was virtually nonexistent. For three days off the coast of southern California, the radio transmitters attached to a captured animal revealed a daily vertical migration pattern. It appeared to remain in relatively deep water during the daylight hours, and returned to the midwater depths at night, presumably feeding on plankton as it ascended. Another live megamouth observation of the coast of Indonesia in 1998 revealed an additional aspect of megamouth ecology: predators. A group of three sperm whales was observed attacking a mature megamouth shark. Although this individual lived through this encounter, markings from this attack were present in the gill regions and dorsal area. It remains unknown whether this attack was due to actual predation or mere curiosity.