The megamouth shark (Megachasma pelagios) is one of the most mysterious species of sharks out there! With less than 300 sightings ever recorded by scientists, there is so much we do not know about these fascinating, elusive animals. For example, we are still baffled by how megamouth sharks feed. They are slow-swimming filter-feeders, So how do they find food? And how do they get enough to support their huge bodies?
Megamouths are Quite Mysterious
From the few we have managed to study, we know that megamouths are very large - reaching a maximum size of 7.1 metres. Yet, unlike other large sharks species, they are not muscular predators. On the contrary, they have a bizarrely flabby body and swim incredibly slowly. They don't need to bother going any quicker! Like whale sharks (Rhincodon typus) and basking sharks (Cetorhinus maximus), megamouths are "filter-feeders". They swim very slowly through the water with their huge mouths open, filtering microscopic organisms called "plankton" out of the water to eat. You don't need much muscle to chase down this kind of prey! To learn more, you can check out Electric Feel (Nakaya, 2001; Nakaya et al, 2008; Kempster & Collin, 2011).
In fact, some scientists have even wondered whether megamouths move at all to feed... Some have suggested megamouths might lure their food directly into their mouths, while they remain motionless! (Nakaya, 2001; Nakaya et al, 2008).
Megamouths live in the deep ocean, as far down as 1,000 metres (which is why they are so difficult for scientists to study). In this twilight zone, very little light can penetrate from the surface. Therefore, light colours stand out more starkly against the dark background. Megamouths have light-coloured stripes around their lips and scientist think this might function to attract prey (Nakaya, 2001).
Glowing in the Deep
Some have even wondered if the lips go a step further and actually glow in the dark! A few sharks are equipped with specialised cells in their skin that allow them to fluoresce and some can actually create their own light! To learn more you can check out Never Break the Chain, Twinkle Twinkle, Little Shark and Glowing in the Deep. So some scientists have wondered if the megamouths are capable of something similar, which would help to lure in their prey (Nakaya, 2001; Nakaya et al, 2008; Kempster & Collin, 2011).
To answer this question, a team of scientists took a close look at the mouth and throat of a megamouth shark. They looked at the structure of the skin under microscope, and measured the production and/or reflection of light from this tissue (Duchatelet et al, 2020).
They did not find any "photophores" (cells which are capable of producing light) in megamouths, but they did find that the white band in their mouth was especially reflective of light. This means they cannot actually produce light themselves, but they are able to reflect light very effectively. This would mean any light filtering in from the surface or any light produced by other animals (known as "bioluminescence") would make the mouth of the megamouth look very bright and stark. Therefore, they concluded that their white lips allow megamouths to efficiently lure in unsuspecting prey (Duchatelet et al, 2020).
An Ongoing Mystery
Whether megamouths move whilst feeding is still unknown, just like so much else about them! They still remain a huge mystery to us! In some ways this is great news, because it means that incredible, exciting, new discoveries are still to be made! Hopefully, as our methods and technology develops, we will be able to learn more about this bizarre and secretive shark!
Acknowledgements
Great thanks to Alex 'Sharkman' Buttigieg for his assistance in writing this article. To see more of Alex's work, you can check out his blog at Sharkman's World.
References
Duchatelet L, Moris VC, Tomita T, Mahillon J, Sato K, Behets C & Mallefet J (2020). The megamouth shark, Megachasma pelagios, is not a luminous species. PLoS One, 15(11): e0242196. Access online.
Jaume D & Duarte C (2012). General Aspects Concerning Marine and Terrestrial Biodiversity. Access online.
Kempster RM & Collin SP (2011). Electrosensory pore distribution and feeding in the megamouth shark Megachasma pelagios (Lamniformes: Megachasmidae). Aquatic Biology, 11, 225–228. Access online.
Nakaya K (2001). White band on upper jaw of megamouth shark, Megachasma pelagios, and its presumed function (Lamniformes: Megachasmidae). Bulletin of Fisheries Sciences Hokkaido University, 52:3, 125-12. Access online.
Nakaya K, Matsumoto R & Suda K (2008). Feeding strategy of the megamouth shark Megachasma pelagios (Lamniformes: Megachasmidae). Journal of Fish Biology, 73:1. Access online.
By Sophie A. Maycock for SharkSpeak
