June Elasmobranch of the Month: Megamouth Shark
Written by Linda Weiss
As its name indicates, the Megamouth shark has a very large mouth, stretching all the way across its large, round, blunted head. Its head is larger in diameter than any other part of its body, giving it a tapered shape from head to tail. Megamouths can weigh over 1179 kg (2600 pounds), though the average weight is closer to 800 kg (1,760 pounds). The average length of the Megamouth is 5 meters (16 feet). The topside of the Megamouth is grey to brown or blackish, while underneath it is cream to white in color. It also has a thin, white band underneath its snout. The dorsal fins are relatively small for the sharks’ size, with the first dorsal fin twice as large as the second one. The pectoral fins originate low on the shark’s side just behind the gills. The caudal (tail) fin is forked with the upper lobe significantly larger than the lower lobe. The upper and lower jaws are filled with small, slender, tack-like teeth that curve inward.
Image Credit: NOAA
Habitat and Distribution
The Megamouth is a rarely seen species, with the first know specimen observed in 1976, and much is still unknown about its existence. It is known to inhabit ocean depths ranging from near the surface to 1,000 m (3, 280 feet). It is suspected the change in depths occurs as it moves to feed on various prey in the water columns. The known distribution of this shark includes the Atlantic, Pacific, and Indian Oceans with recorded sitings off the coasts of Australia, Japan California and the Hawaiian Islands.
The Megamouth is a plankton, filter feeder, cruising through the water with its mouth open filtering out small prey such as shrimp, krill, jellyfish, and copepods (tiny crustaceans).
Little is known about the reproduction of the Megamouth shark, including gestation period and litter size. Eggs are fertilized inside the female, receiving nourishment from yolk sacs for development until being live-birthed, fully developed. (ovoviviparous). The developing embryos may eat their lesser developed siblings inside the uterus.
The IUCN Red List of Threatened Species currently lists the Megamouth shark as Least Concern, with an unknown population trend.
Image Credit: Tom Haight/Seapics.com
This shark species is not targeted by either the commercial or sport fishing industries, However, it is subject to by-catch from commercial fishing practices. The only known predators to the Megamouth are sperm whales and cookie cutter sharks. Cookie Cutter sharks are small, deep water sharks, that leave round wounds on the bodies of larger ocean animals, where it bites out chunks of flesh.
Florida Museum of Natural History
The IUCN Red List of Threatened Species
Kyne, P.M., Liu, K.M. & Simpfendorfer, C. 2019. Megachasma pelagios. The IUCN Red List of Threatened Species 2019: e.T39338A124402302. https://dx.doi.org/10.2305/IUCN.UK.2019-1.RLTS.T39338A124402302.en. Downloaded on 09 June 2020.