Author: Bee Smith
Megamouth shark
Megachasma pelagios
The megamouth is mega cool!
Megamouth shark: Credit Zola Chen
Key Features & Appearance
The megamouth shark is named after its proportionally large mouth. It is a giant shark, reaching up to 5.5m or possibly 6m, with females maturing at 5.17m and males at 4.26m. Its large mouth also has distinctive large, rounded pectoral fins. Its body is dark grey on the dorsal side and light grey on the underside, with dark grey spots on the chin and large doll-like brown eyes. Its dorsal surface is rough and sturdy, like a typical shark, but its underside is soft and velvety.
Habitat & Distribution
It is known as a deep sea species but inhabits deepwater during the day and moves to shallower water at night. Though it is thought to go as deep as 1000m, it is believed to tend to stay in relatively shallow depths of the deep sea, at around 150m.
It is said to be distributed globally, but there are hotspots in Taiwan, Japan, the Philippines, and the west coast of the Americas from Southern California to Peru. Genetic samples from specimens caught in Taiwan and Mexico indicate a single, highly migratory, interbreeding population. It is a rare species, with the globally reported sightings totaling below 300, most of which are dead specimens either washed up on shore or caught by fisheries.
Megamouth being released after tagging Credit Zola Chen
Diet
It is one of only three filter-feeding sharks, along with whales and basking sharks. Its diet mainly consists of zooplanktonic prey such as krill, jellyfish, shrimp larvae, squat lobsters, and crab larvae.
Reproduction
Reproduction was thought to be ovoviviparous due to its positioning within the shark family tree (it is a species of mackerel shark). In December 2023, this was confirmed when the first pregnant megamouth washed up in the Philippines.
Threats
One threat that used to face megamouths was that fisheries in Taiwan targeted them. However, in 2020, it became illegal to catch megamouths in Taiwan, so if they are caught, they must be released. However, this policy has some issues, both for the megamouths and the fisheries. To help investigate whether the megamouths survive after being released, the author and her team recently filmed three megamouths being caught and released in this fishery in Taiwan and tagged two of these megamouths.
Status
Due to the species rarity, it is classified as data deficient according to the International Union for Conservation of Nature (IUCN) Red List of Threatened Species.
Fun Fact
The megamouth was discovered in 1976 when one was caught in the anchor of a United States Navy ship in Hawaii.
Works Cited
Additional information is from the authors in-person interviews regarding the megamouths, and experience in-water with megamouths, in Taiwan.
YU, CHIJU & JOUNG, SHOOUJENG & HSU, HUAHSUN & LIU, KWANGMING & YAMAGUCHI, ATSUKO. (2024). Feeding ecology of two filter feeding sharks in the northwestern Pacific Ocean. 10.21203/rs.3.rs-4166667/v1.
Liu, Shang-Yin Vanson & Joung, S. & Yu, Debbie Chi-Ju & Hsu, Hua-Hsun & Tsai, Wen-Pei & Liu, Kwang-Ming. (2018). Genetic diversity and connectivity of the megamouth shark ( Megachasma pelagios ). PeerJ. 6. e4432. 10.7717/peerj.4432.
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. Proc. Calif. Acad. Sci. 43(8):87-110.
Watanabe YY, Papastamatiou YP. Distribution, body size and biology of the megamouth shark Megachasma pelagios. J Fish Biol. 2019; 95: 992–998. https://doi.org/10.1111/jfb.14007