11 Intriguing Details About the Megamouth Shark

Recently, a fisherman near Shizouka, Japan, captured a female Megamouth shark (Megachasma pelagios), which was later dissected in a public event. While much about this elusive shark remains a mystery, here are some key facts we’ve gathered.

1. The Megamouth shark was first identified in 1976 after a U.S. Navy research ship retrieved an adult male specimen near Oahu, Hawaii.

The 1983 scientific paper detailing the new species covered its discovery, preservation, and anatomical examination:

The vessel had deployed two large parachutes as sea anchors at a depth of roughly 165 meters in waters with a seabed depth of around 4600 meters. When the parachutes were retrieved to the surface … one of them had ensnared a massive adult male shark measuring 4.46 meters (14.6 feet) in length and weighing 750 kilograms (1653 pounds). The AFB-14 crew recognized the shark as unusual and, after considerable effort, managed to bring it aboard. The shark was transported to the Kaneohe Bay facility of the Naval Undersea Center and secured alongside the dock overnight. … Initial observations suggested it represented a highly distinct, previously undocumented species, prompting the decision to preserve it intact. The shark was hoisted by its tail using a Navy crane, but the caudal fin broke off, causing the shark to fall back into the water, necessitating retrieval by divers. The shark was flash-frozen at Hawaiian Tuna Packers in Honolulu while a large preservation tank was constructed. On November 29, 1976, the shark was transported frozen to the Kewalo dock site of the National Marine Fisheries Service for thawing and formalin injection. Further examination … confirmed it as a lamniform shark unassignable to any known genus or family, leading to its classification as Megachasma pelagios, a new genus and species, and the establishment of the new family Megachasmidae.

2. Since its discovery, there have been only 55 confirmed sightings (along with a few unverified reports), including the specimen captured last week (shown below).

3. According to the paper announcing the species, newspapers coined the name: “It was referred to as the ‘Megamouth shark’ due to its unusually large oral cavity. This common name has since been widely adopted by researchers, and we propose it as the accepted common name for the species."

4. It is one of only three known filter-feeding sharks, alongside the basking shark and the whale shark. Researchers suggest that the Megamouth glides through krill swarms with its mouth wide open, extending its jaw (which exhibits "extreme protrusibility," as noted in the 1983 paper) and expanding its buccal cavity to draw in prey, then expelling water through its gills.

Diagram illustrating the Megamouth's extendable jaw; via Archive.org.

5. The Megamouth shark has a vast range, inhabiting the Indian, Atlantic, and Pacific Oceans.

6. While most sharks average around 6.5 feet in length, the Megamouth grows significantly larger. It can reach at least 17 feet, with some specimens exceeding this: one found off Taiwan's coast measured over 23 feet, and another, caught and released near California, may have been up to 25 feet long. Even Great Whites don’t reach such sizes. As noted in the 1983 Megamouth study,

This new shark joins the ranks of the few giant sharks that commonly exceed 4 meters in length, including the broadnose sixgill shark (Hexanchus griseus), Pacific sleeper shark (Somniosus pacificus), Greenland shark (S. microcephalus), whale shark (Rhiniodon typus), great white shark (Carchawdon carcharias), tiger shark (Galeocerdo cuvier), and great hammerhead (Sphyrna mokarran). The common thresher (Alopias vulpinus) and bigeye thresher (A. superciliosus) also surpass 4 meters, but their elongated caudal fins make their bodies relatively smaller compared to other giant species. While new small shark species are discovered regularly, giant sharks are rare, with most described in the 18th and 19th centuries.

7. It’s not an efficient swimmer. According to the Florida Museum of Natural History, “the Megamouth is less active and a weaker swimmer compared to the basking or whale sharks. Its poor mobility is likely due to its flabby body, soft fins, asymmetrical tail, lack of keels, and weak calcification.”

8. The Megamouth shark possesses 50 rows of small teeth on each jaw, with only the first three rows being functional.

9. While we know it as Megamouth, in Dutch, it’s called grootbekhaai; in French, it’s requin grande gueule; and in Spanish, it’s referred to as tiburón bocudo.

10. Researchers attached a radio tag to a male Megamouth caught in a net in 1990 and monitored its movements for two days. This revealed that the species undergoes vertical migration. Tom Haight, who swam alongside the shark and photographed it during tagging and release, noted that "From dawn to dusk, it swam slowly at depths of 450 to 500 feet against the current, likely feeding on krill present at that depth during the day. From dusk to dawn, it rose to 39 to 46 feet below the surface to feed on krill as they ascended. This deep daytime behavior may explain why the Megamouth is so rarely seen."

11. Scientists witnessed a Megamouth shark being attacked by sperm whales near Italy. "The dorsal fin base and gills bore signs of the whales' assault, and the shark was swimming slowly and appeared disoriented at the surface," the researchers reported. Other Megamouth specimens have shown marks believed to be from cookiecutter sharks, which, as described by the Florida Museum of Natural History, "attach to their prey using suction-like lips and sharp upper teeth. Once secured, the small shark rotates its body, carving out a circular plug of flesh with its serrated lower teeth, leaving a perfectly round hole in its prey."

To learn more about the Megamouth shark, visit the Florida Museum of Natural History.