March 14, 2011

Megamouth sharks (Megachasma pelagios) are one of the three living species of filter-feeding sharks, along with the whale shark and basking shark. They are also among the rarest and least understood of sharks - only 50 animals have been seen since the species was first identified in 1976.

A recent study by Kempster & Collins analyzed the electrosensory organs on the head of a megamouth shark that stranded in Western Australia in 1988. They found that the sensory organs, called Ampullae of Lorenzini, were located mostly on the dorsal (top) side of the shark’s head, with few on the lateral or ventral (under) sides, a different pattern than in most other shark species. They suggest that this difference could be due to the unique anatomy of megamoutMegamouth_Sharkh sharks, which have their mouth at the front of the head rather than on the ventral side as in most other sharks.

The authors suggest a model for how these rarely observed sharks may feed. They propose that megamouth sharks use a bioluminescent (light-producing) organ at the top of their mouths to attract prey in their dark, deep-water environment. The electrosensory organs on the shark’s head can detect the weak electrical fields produced by even tiny planktonic prey, and a certain level of electrical signal would indicate that it is time for the shark to begin to feed.

The full manuscript is Kempster, RM and Collin, SP. (2011) Electrosensory pore distribution and feeding in the megamouth shark Megachasma pelagios (Lamniformes: Megachasmidae). Aquatic Biology 11:225-228. (doi:10.3354/ab00328)

(Megamouth photo courtesy of https://www.sharks.org.za/)

A rare video of these prehistoric-looking beasts can be found on the terrific ARKive Site: http://www.arkive.org/megamouth-shark/megachasma-pelagios/video-00.html

Megamouth Shark Electrosensory System