A Whale of a Shark

Whale sharks are simply fascinating. Weighing in at several tons (some estimated as much as 40!), and stretching up to 45 feet or more in length, they are the largest fish in the world. Despite their enormous size, this threatened species has proved remarkably difficult to study in the wild. Only in recent decades have scientists begun to uncover more about Rhincodon typus. So what do we know about whale sharks?

They may be big, but these are gentle giants.
Though whale sharks have more than 300 rows of tiny teeth, they are actually filter feeders. The sharks gather fish eggs, plankton, krill, and small fish like sardines and anchovies as they swim along with their gigantic (almost 5 feet wide!) mouths hanging open. As water filled with these tiny morsels runs through the shark’s gills, the food is trapped in 20 spongy filter pads inside their throats.

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They’re unusual feeders.
There are many filter feeders in Earth’s oceans, but the whale shark is a bit different. It is the only filter feeding shark that can feed while stationary. By opening and closing their mouths, whale sharks create suction, drawing snack-filled water into their mouths. The sharks have even been spotted hovering vertically, as though standing on their tails, while they feed using this method.

They travel alone, but like to dine together.
Whale sharks are unusual because, unlike most filter feeders, they live in warm tropic and sub-tropic waters, which actually produce less of the plankton and other food whale sharks like to eat. Because of this, the sharks have to travel great distances – sometimes thousands of miles – to find enough food. But each year some warmer, coastal areas bloom with more food than usual, like when coral reefs spawn. Whale sharks are attracted to these big buffets, and gather in huge numbers to chow down. These gatherings are a fairly recent discovery. It wasn’t until the 1990s that it became widely known that whale sharks gather in large groups to feed off the coasts of places like the Yucatan, Madagascar, Australia, and the Philippines. Local fishermen had known about the gatherings for generations, but for the scientific community, this was big news about a fairly elusive species.

They birth live pups.
It was also in the 1990s that scientists learned for sure that whale sharks give birth to live young. Fertilized eggs stay inside the female’s body, drawing on the nutrients of a yolk until the young pups emerge, small but fully formed. One whale shark was documented as carrying as many as 300 young in various stages of development! But even though scientists have learned how whale sharks give birth, and research continues, there are still many mysteries around where whale sharks give birth.

Their spots tell a story.
Scientists can identify individual whale sharks by looking at the spots on each animal’s back. Just like human fingerprints, each whale shark’s spots are unique. With the help of special software (originally developed by NASA to analyze images from the Hubble Space Telescope), scientists use photos submitted by their colleagues and whale shark enthusiasts to track the movements of specific sharks using spots and scars as identifying markers. This helps the community gather data on how and where whale sharks travel.

They dive deep.
Whale sharks can dive to pretty extreme depths. In fact, they can dive up to a mile deep, and one tagged shark in the Gulf of Mexico was recorded diving up to 6,325 feet. Though scientists aren’t sure why they do this, some believe that it’s a way to regulate their body temperature, keeping cool while still staying on the move. They just have to be sure to surface again to warm up afterwards!

They need our help.
Whale shark skin is up to five inches thick, but even that doesn’t protect them from human activities. Because they tend to feed near the ocean’s surface, whale sharks are especially vulnerable to certain threats from humans. They can be accidentally struck by moving ships, or hunted more easily by those looking to harvest their fins or meat, which is so thick and firm that it’s been dubbed by some as ‘tofu shark’. Whale sharks are also accidentally caught by fishermen – especially by those looking for tuna. For reasons that scientists don’t yet understand, tuna often gather around whale sharks. Together, these threats have caused whale shark populations to decline, and the IUCN lists the species as vulnerable, stating that much more data is needed to protect these incredible animals. In addition to more research, because whale sharks travel so widely, it’s clear that they need protection not just in individual countries, but around the world. These sharks migrate across invisible borders – international efforts like those at CITES and international fisheries will be key to helping whale sharks survive.