The ocean’s largest shark relies on vision more than previously believed.
Residents and visitors to Cape Cod received a harsh warning ahead of the July 4th weekend: beware of great white sharks. Given the heightened threat of these sharks in recent years, this isn’t a complete outlier. Sharks are having difficulties finding food supplies further out at sea, thus they have started creeping on the Cape’s limits in pursuit of seals year after year.
That somber story, however, is not near the top of shark news this week. Another sign that the planet is sick of us humans has been discovered: the world’s largest shark has fangs all on its eyeballs.
A team of researchers from Japan’s Okinawa Churashima Research Center determined that these monster predators acquired a unique protective mechanism for their vision: dermal denticles, in the research publication “Armored eyes of the whale shark.”
These denticles are not unusual. Shark skin is covered in v-shaped scales. They are structurally similar to small teeth. This characteristic assists sharks in reducing turbulence and drag when gliding through the ocean, making them an even more terrifying fish—a tough request for a shark that may grow to be 62 feet long.
Whale shark mouths are fearsome, with over 300 rows of small teeth. Whale sharks are one of three shark species that filter-feed, hence their teeth play no part in feeding. Plankton, krill, jellyfish, sardines, and anchovies make up the majority of their food. Small tuna and squids that cross their path will be eaten. Otherwise, these enormous swimmers are content to take in whatever comes their way.
Given their eating patterns, whale shark vision was assumed to be unimportant. This species is remarkable in that it lacks any kind of eyelid or protective mechanism—until now. Not only can whale sharks’ dermal denticles preserve their vision, but the research led by Taketeru Tomita uncovered another trick:
“We also show that the whale shark has a powerful ability to withdraw its eyeball into its eye socket.”
The researchers observed these gigantic sharks in an aquarium, providing them with a rare opportunity to observe one of the ocean’s largest creatures (They also studied deceased sharks). The eye denticle differs from the rest of their scales in that it is developed for abrasion resistance rather than ocean stealth.
“In the whale shark, the coating of the eye surface with denticles is presumably advantageous in decreasing the risk of mechanical damage to the eye surface.”
Despite their enormous size, whale sharks have extremely small eyes that account for less than 1% of their entire length. Their visual center in the brain is also small. With this discovery, the researchers concluded that vision is more crucial than previously thought.
“Contrary to popular belief, the highly protected features of the whale shark eye appear to highlight the importance of vision in this species.” Martin demonstrated that whale shark eyes actively monitor divers swimming 3–5 m away from the animal, implying that whale shark vision plays a major role in short-range perception.”
When you’re unlikely to come across a whale shark while swimming just off the coast, this is just another example of how organisms adapt to their surroundings.
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