The biggest shark in the world can be over 60 feet long, has a mouth that can be over four feet wide and has about 27,000 teeth in that big mouth, which sounds pretty scary. But is this shark going around the ocean chomping on kayaks like they are hard shell tacos? Despite some crummily photoshopped photos you may find on the Internet that show otherwise, the answer is no. Instead these sharks spend their time going around chomping on animals that may be smaller than the letters you are reading on this screen.
This shark I am talking about, the dual record-holder of biggest shark and biggest fish living today, is the whale shark.
Whale sharks are definitely big. The longest whale shark measured was almost 62 feet long (I got that number here), which is about as long as ten of me stacked on each others' heads. Some people think they have seen whale sharks even bigger than that. Even so, that does not mean every whale shark in the world is over 60 feet long. In fact, hardly any of them are. Saying whale sharks can be over 60 feet long is kind of like saying humans can be over 8 ½ feet tall, just because the tallest person ever measured was 8 feet 11 inches tall.
If you told some Martians that humans can be over 8 ½ feet tall and then they stop on Earth because they need to pick up supplies and they are expecting to see a bunch of humans all over 8 ½ feet tall walking through the aisles of Walmart, they are going to be really disappointed by seeing all these shoppers who are almost all under 6 feet tall (the average heights of people around the world varies, but all those averages are under six feet).
Similarly, if you spend a lot of money to go on a snorkeling trip that promises the opportunity to bother a bunch of whale sharks in their natural habitat and you expect all the whale sharks you see to be over 60 feet long, you are probably going to be really disappointed by all the 10 to 40 foot long whale sharks you end up seeing.
Despite the occasional giant over sixty feet long, the average length of whale sharks is probably around 30 feet long, almost half the size of the record-holder. (In general, whenever you are looking at the size ranges for any animal, remember that the biggest ones at the top of the size range are the ones in the Guinness Book of World Records and not the norm.)
But even a 30 foot long shark sounds pretty scary. Particularly one with about 27,000 teeth. But, do you know what it uses those teeth for?
Whale sharks eat mainly plankton, which are animals like these:
Like copepods and many fish larvae, most plankton are smaller than Tic-Tacs. With their giant mouths, whale sharks do not need to chew things smaller than Tic-Tacs. They just swallow them whole. Because of that, they don’t actually need teeth. Whale sharks catch food by either swimming straight ahead and trying to get as many small animals as possible into their mouth, like their mouth is a butterfly net, or whale sharks will stop swimming, like this guy…
…and then start sucking in all the small animals around them, like their mouth is a giant underwater vacuum cleaner.
Whale sharks can then separate the animals they want to eat from the stuff in their mouth they don’t want to eat, using these things in their mouths called filter pads, which are kind of like spongy rakes.
Whale sharks cannot just eat a mouthful of plankton and they’re full, though. They have to eat lots of plankton in order to get all the energy and nutrients they need. One scientific study observed that a 20-foot whale shark was eating about 45 pounds of plankton a day to survive. And, the bigger the whale shark is, the more they have to eat.
So why do whale sharks have thousands of teeth in their mouth if they don’t use them? For the same reason that you have a tailbone. You have a tailbone because your great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-grandparents had tails (actually, I’m pretty sure there need to be a few thousand more or so “greats” in there). The descendants of your excessively-great grandparents eventually started doing fine without tails, to the point that the children born with smaller tails were more likely to have children of their own than those born with longer tails. Over millions of years those tails were slowly disappearing until now when all that is left of our ancestors’ tails is a small bone in our butts that does not do much of anything except break when we fall on it too hard.
Similarly, the whale sharks’ great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-great-grandparents had large teeth they used for biting things (actually, I’m pretty sure there need to be a few thousand more or so “greats” in there too). Eventually, through, the descendants of those excessively-great whale shark grandparents started having better luck getting enough food by eating plankton than by eating large animals. The need for those big teeth went away, and over millions of years the teeth got smaller and smaller until now when they’re basically just little nubs. (Scientists call features like these “vestigial structures”).
So if you are in the water and you ever see a 60-foot whale shark swimming towards you, don’t worry that it is going to eat you, unless of course you are a copepod. (Though whale sharks are also known to eat animals bigger than Tic-Tacs, as you can see in this video from the BBC's Planet Earth documentary series, but even the prey in this video are pretty small compared to you.)
To learn more about sharks, read my book Sharks and Dolphins: A Compare and Contrast Book.
Online References and Resources
Natural History. "The Biggest Fish: Unraveling the mysteries of the whale shark."
PeerJ. "Sizing ocean giants: patterns of intraspecific size variation in marine megafauna."
Zoology. "Feeding anatomy, filter-feeding rate, and diet of whale sharks Rhincodon typus during surface ram filter feeding off the Yucatan Peninsula, Mexico."
Photos and Images:
Click the photos and images used above to find their sources.