How many stars are in the universe? How many fish are in the sea? Can these things even be counted? Or does the answer approach infinity?

How about one specific type of fish, like the shark? Surely we could get an accurate count of just the sharks, right? Actually, probably not!

There happen to be so many different types of sharks that it would be impossible to count them all. There could be a billion or more sharks in all the oceans around the world.

Up until the 16th century, mariners called sharks “sea dogs.” Today, scientists believe there are more than 400 different species of sharks in the world.

The smallest of these — the dwarf lanternshark — is less than seven inches long. The largest — the whale shark — can grow as long as 60 feet, making it the largest fish in the world. (Remember: Whales are mammals, not fish!)

Scientists believe that sharks are older than dinosaurs. The earliest known sharks existed more than 450 million years ago.

Unfortunately, it is rare to find complete fossil remains of sharks. This is because sharks don’t really have bones.

Instead, they have skeletons made of cartilage, which is a kind of connective tissue strong enough to give support but softer than bone. Humans have cartilage in their ears and noses.

Sharks can be found in all seas around the world. Most sharks live in saltwater, but a couple of species — bull sharks and river sharks — can live in freshwater or saltwater.

Unfortunately, many shark species are under attack and are decreasing in numbers every year. Experts estimate that 100 million sharks are killed by people each year.

Sharks are eaten as seafood in many areas, including Japan and Australia. Commercial and recreational fishers are believed to be responsible for the reduced populations of some shark species.


72 Join the Discussion

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    • Hi, Kadoodle! There are many reasons why people kill sharks, but one of the main reasons is to eat them. In many parts of the world, people eat sharks. Some cultures even use parts of a shark’s body as a type of medicine. We’re glad you visited Wonderopolis today and asked such a great question! :-)

    • Thanks so much for sharing your shark story, Nmb! It must have been really cool to see a such a WONDERful creature like that up close! :-)

    • i know rigth they are the best craetures in the world and about your story what kind of shark was it tiger or mabey the great white just kidding and if you love sharks so much mabey you should become a marine biologist!

  1. We liked your Wonder of the Day. We knew some things about sharks already, but we learned a lot more from your information. The dwarf lanternshark is really small compared to the whale shark. Did you know that there is a show called Dolphins of Shark Bay? We are still wondering what shark has the biggest population. Thank you! :), Mrs. Mac’s Class

    • Thank you for visiting Wonderopolis and for leaving us this GREAT comment, Mrs. Mac’s Class! We’re super glad you learned some new things about sharks today! You taught US something, too! We learned that there is a show called Dolphins of Shark Bay! It’s about a group of dolphins who live in a bay where a LOT of sharks live (and eat!). Here is a link to the the program for our other Wonder Friends who might like to know more about it: :-)

    • Thanks for visiting this Wonder of the Day® about sharks, Madison! There are many, many different types of sharks, including Great Whites, in the oceans of the world. Because there are so many different sharks in so many different bodies of water, it would be impossible to count them all. Can you believe there could be a billion or more sharks in all the oceans around the world? That’s a LOT of sharks! :-)

  2. I love learning about sharks! I never knew that our ears and noses were made out of cartilage. At that, I didn’t know that shark skeletons were cartilage. I always wonder, will there ever be an exact count of how many sharks there are in the ocean?

    • It’s really hard to tell, Josh, but that’s an AWESOME question! Maybe some time in the future, someone will invent a special machine that locates, identifies and counts all the creatures in all the oceans! Until then, we’ll just have to WONDER how many sharks there actually are. :-)

  3. I have always loved learning about sharks. I thought it was really interesting when you said that whale sharks can grow up to 60 feet long and that lanternsharks can grow to be less then seven inches long, or that human’s ears and noses where made up of cartilage. Do you think that someone knows the exact number of sharks in the sea?

    • Thanks so much for leaving us this SUPER comment, Haley, and for sharing all the awesome facts you learned about sharks today! We like learning about sharks, too! We’re pretty sure that no one knows the exact number of sharks in the sea. There are so many different sharks swimming in so many different bodies of water! Maybe some day we will know for sure, though! :-)

    • Hi, Izabella! We don’t know everything…we just WONDER a LOT! We like how all of our Wonder Friends out there (like you!) WONDER, too! Thank you for letting us know you learned some new things about sharks from exploring this Wonder of the Day®! :-)

  4. There was so much information, I learned so much in this wonder. My favorite fact was up until the 16th century, mariners called sharks “sea dogs.” I thought that was funny because I just got a dog. Thanks for the cool wonder!!!!!!!

    • Hello, Yasmin! That’s great news! We’re glad you were able to learn some new things and get help with your weekly inquiry by exploring this Wonder of the Day® about sharks! :-)

    • Hello, Pizzacuttercat! Thank you for leaving us another comment on another Wonder today! We LOVE that you are learning so many cool things! The most frequent reason people kill sharks is for food. Some cultures eat sharks for nourishment and some use parts of a shark’s body for medicinal reasons. Thanks for WONDERing a little bit more about this Wonder of the Day®! :-)

  5. I really do wonder how many sharks are in the ocean with the people killing the sharks? So, how many sharks are there in the ocean?

    • We like how you’re WONDERing more about sharks, Jordan! No one knows the exact number of sharks in the ocean, although we know LOTS of Wonder Friends who would LOVE to find out the exact number (including everyone here in Wonderopolis)! With so many oceans and seas in the world, and so many different types of sharks out there swimming in them, it is difficult to gather an exact number! :-)

  6. I thought today’s wonder was AWESOME!!!!!!! I LOVE sharks! They are so cool and interesting. Every single week of shark week I would watch it until midnight. I know so much about sharks everyone calls me the fish, because I love learning about different fish and about the ocean. I think you guys should do a wonder on Marine Biology. I would be so happy!

  7. I have always wondered what the populations of sharks in the ocean is. The species are never all to be found. I never knew that no one could know the population of sharks, and since they are reproducing and dieing at the same time. I never knew that up into the 16th century that sharks were called sea dogs. That was very interesting. I’m just curious, but what is the age a shark reaches before it dies. Thank you wonderopolis for listening!!!!!!!!!!!!!!!!!!!!

    • We think it’s AWESOME that you stopped by this Wonder about sharks, Team McNeil 18! You sure learned a LOT about them! We’re not sure how old sharks can get…we’ll both have to do a bit more WONDERing about that! :-)

  8. That’s sad to hear that these poor creatures are killed. Oh, well. At least there’s more! I think tomorrow’s wonder is about playing in a band!

    • We agree that it’s sad some sharks are killed, Jordan. We appreciate you visiting this Wonder and learning about these important creatures of the sea with us. You are a GREAT Wonder Friend! :-)

  9. I am William H. I am from AIS school – Year 2. I am very interested about the sharks. I have some questions for Wonderopolis about the shark:
    1. How many teeth do sharks have?
    2. How many sharks are killed by human beings each year?
    3. The average life expectancy of a shark?

    • Hey there, William H! We are so excited that you’ve developed some Wonders of your own!

      Sharks have an average of 230 teeth… they have five rows of 46 teeth! That’s a lot of teeth! They also fall out and break easily, so sharks have a lot of teeth over a lifetime.

      We Wonder if you can do some more WONDERing of your own to answer questions two and three! You’re doing a SUPER job! :)

  10. Many thanks Wonderopolis’s reply but I wonder about my question is: “The average life expectancy of a shark?”

    Look forward to your soonest reply…

  11. Hey Wonderopolis, I am Levin from AIS school-Year2. I am very interested about sharks. My question about sharks is:
    Do sharks have a tongue?

    • Hey there, Levin B! We’re so excited that you’ve been WONDERing about sharks on your own– nice work! The shark tongue is very different from the human tongue, but it serves the same purpose– to taste! It’s called basihyal. Unlike the human tongue, sharks can’t move their tongue around– it’s stuck to the bottom of the mouth! :)

    • Not to worry, Isabella! The most important thing to remember is that you’re leaning and WONDERing with us– it’s okay if you don’t always guess the next Wonder of the Day®! :)

    • Hey there, Wonder Friend Briauna! Thanks for sharing your comment with us– we hope you’ll do some more WONDERing of your own about how many sharks are swimming in the ocean! Keep up the great WONDERing! :)

    • What a great question, Karina! While we cannot count the number of sharks remaining (there are quite a lot– that would be a lot of counting), we can estimate. We hope you’ll do some more research about sharks and let us know what you find! We’re interested to hear more! :)

    • Great minds think alike, Zareiha! We’re glad you visited Wonderopolis today and have been WONDERing about sharks of all kinds! We would love to know how many there are in the world, but that would take some time… we would have to figure out how to count all of them! :)

  12. 100 million sharks per year… worldwide, that’s roughly one shark per person per lifetime. I have to admit I once tried shark-fin soup at a wedding in the Far East. I feel a bit guilty about it, but at least my consumption is still below world average.

    I’m wondering, can any level of shark fishing be considered sustainable and humane?

    • Hey there, Richard! Thanks for sharing your comment with us! It sounds like you’re an adventurous eater, Wonder Friend! Right now, sharks are endangered, so it’s tough to find a way to hunt them without hurting the population right now. However, if we can reduce commercial fishing for sharks, we might be able to help them leave the endangered list. Great questions, Richard! :)

  13. We learned that 100 million sharks are killed by people each year. That made us feel sad and disappointed. We were surprised to learn that sharks don’t have bones. We felt our ears to feel what cartilage felt like.

    • Hi Mrs. LaLonde’s Class, thanks for visiting us on this terrific Tuesday! We are so glad you shared how you felt after learning about sharks and human deaths each year. We are sad to learn about that too, and we hope all our Wonder Friends are extra careful on their next trip to the ocean. We want everyone to be safe and have fun! :)

      What a super connection you made – we’re glad you’re able to Wonder about cartilage without being close to a shark! Great work! :)

    • Hi Frankie! Large sharks like the Great White Shark will eat anything from smaller fish like mackerel to dolphins! They’ve even been known to eat sea turtles! Do you like sharks? Thanks for WONDERing with us! :)

  14. I loved learning about sharks. My favorite fact was that sharks have existed more than 450 million years! I can’t believe that they are older than the dinosaurs! Do you know which ocean has the most sharks?

    • Hi Elizabeth! Thanks for WONDERing with us! It is pretty WONDERful how old sharks are! Many sharks migrate through the oceans so that would be hard question to answer! Can’t wait to WONDER with you more! :)

    • Thanks for WONDERing with us, Tom! We encourage you to explore your question by doing research online and in books about sharks. Your librarian can probably help you find the answer! :)

    • Hi, Adam! Megalodon did exist over 1.5 million years ago! Scientists haven’t found evidence that this species of shark still roam the oceans today, however.

    • Hi, Noah Burnside! We do not have a WONDER specifically about megalodons. We encourage you to keep WONDERing and do more research at your library!:)

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Have you ever wondered…

  • How many sharks are in the ocean?
  • How many different species of sharks are there?
  • What is the largest shark?

Wonder Gallery

shark_shutterstock_55409443imagemegalodon_monster_sharks_still_alive_Vimeo Video

Try It Out

Ready to get up close and personal with some sharks? No, put away your snorkel and fins. There’s no need to get wet on this virtual adventure!

Check out the Monterey Bay Aquarium’s Open Sea webcam for a sneak peek at some sharks. You can also head over to Discovery Channel’s website to take a virtual dive to learn more about several different types of sharks.

If you just can’t get enough of sharks, check out these videos of different types of sharks in action:


Still Wondering

Check out National Geographic Education’s Crittercam: Tiger Sharks video to explore the warm, summer waters of Shark Bay, home to thousands of tiger sharks.


Wonder Categories/Tags



cartilage  ocean  shark  species 

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