Scientific Study: Armored eyes of the whale shark by Taketeru Tomita, Kiyomi Murakumo, Shinya Komoto, Alistair Dove, Masakatsu Kino, Kei Miyamoto, and Minoru Toda
The eye is the part of your body that takes in information from the world around you. It must be on or near your body’s surface, making it vulnerable to potential harm from getting hit, exposure to harmful chemicals, or infection. To protect against these dangers, many animals have eyelids that cover their eyes. For example, certain sharks have an extra eyelid called a nictitating membrane that completely covers their eyes when eating. Alternatively, other sharks don’t have this extra eyelid, so they have different ways to keep their eyes safe. They might retract their eyeballs into their head or rotate their eyeballs back into their sockets.
For example, certain sharks have an extra eyelid called a nictitating membrane that completely covers their eyes when eating.
Scientists in Japan studied how the whale shark protects its eyes. Unlike other sharks, the whale shark has its eyes positioned at the front corners of its head, sticking out quite a bit. This makes them more susceptible to getting hurt when swimming through objects that are floating in the water. The scientists examined a preserved eyeball of a whale shark that was kept at the Okinawa Churashima Research Center in Japan. Additionally, one of the researchers swam alongside two whale sharks kept at the Okinawa Churaumi Aquarium and recorded their eye movements using a GoPro camera. To document eye retraction, the researchers used a portable ultrasound device.
The study showed that whale sharks have eye denticles. Unlike other animals, whale sharks don’t have eyelids to protect their eyes. This means that the surface of their eyes is more vulnerable to damage than other parts of their body that are covered by tough, mineralized scales called dermal denticles. To compensate for this, whale sharks developed eye denticles, which can help reduce the risk of eye damage. Eye denticles haven’t been found in other sharks, even those closely related to whale sharks, so it seems that eye denticles are a unique feature that sets whale sharks apart from other sharks. The study also found that whale sharks can actively retract their eyes, pulling them back into their sockets and, at the same time, rotating them slightly downwards.
This study brings new insights into the visual abilities of whale sharks. People used to think that because their eyes are relatively small, whale sharks rely less on vision compared to other senses. However, the results from the study reveal that despite their small eyes, whale sharks have highly protected eye features. This suggests that vision may play an important role in this species, contrary to what was previously believed.
References
- Tomita, T., Murakumo, K., Komoto, S., Dove, A., Kino, M., Miyamoto, K., & Toda, M. (2020). Armored eyes of the whale shark. PLoS ONE, 15(6), e0235342. https://doi.org/10.1371/journal.pone.0235342
- Whale shark. Georgia Aquarium. (2022, October 10). https://www.georgiaaquarium.org/animal/whale-shark/