Today on Jonathan Bird’s Blue World, the incredible world of sharks and their diversity! Hi, I’m Jonathan Bird, and welcome to my world! ( music ♪ ) Before any animals existed on land, sharks ruled the oceans. They have been around for over 250 million years. Many people think that because they are ancient animals, they are in some way primitive. But as it turns out, sharks are highly evolved sophisticated animals with amazing adaptations for survival!The fact that sharks have survived so long demonstrates the incredible effectiveness of their anatomy. And lets face it–250 million years worth of evolution has got to count for something! Over 400 species of sharks live in the oceans across many habitats. Some, like the Caribbean Reef shark, live on shallow tropical coral reefs. Others, like the blue shark, are pelagic, living far from land in the open ocean. The Greenland shark lives in the freezing waters of the arctic, while the Tiger shark prefers the tropics. Sharks are fish, but there are several key things that differentiate them from other kinds of fish. Sharks are everywhere, but what are they? Sharks and their close relatives the rays differ from the bony fishes in several ways. First, sharks and rays have a soft flexible skeleton made of cartilage. The cartilaginous skeleton makes the shark more flexible than similarly-sized bony fishes. Also, sharks and rays have no swim bladder. A bony fish uses an organ called a swim bladder to maintain neutral buoyancy, so it can hover like a hot air balloon. The fish adds or removes gas from its swim bladder through its bloodstream to increase or decrease its buoyancy. The shark’s lack of a swim bladder means that, unlike bony fishes, the shark tends to sink. To stay off the bottom, sharks have to keep moving. While the shark uses its tail fin in a back and forth motion to provide forward thrust, its pectoral fins work like airplane wings to provide lift. Like an airplane wing, as long as the fins move forward through the water, they provide lift to keep the shark up. Not too long ago, scientists thought all sharks had to swim at all times, not just to stay off the bottom, but to keep water moving over their gills. For some species like the hammerhead, this is true. Hammerheads must keep swimming at all times to force water through their gills. Ironically, if they stop swimming they’ll drown. But many species of sharks sometimes stop swimming and rest on the bottom, gulping water to ventilate their gills. This is a Lemon shark, common in the Caribbean, taking a break resting on the sand. It gulps water to breathe. Nurse sharks also spend a lot of time resting on the bottom. Bottom-dwelling species of sharks like the Wobbegong actually live their entire lives on the bottom. They are camouflaged to look like a rock covered in algae, and they hunt by being very patient and waiting for an unsuspecting fish to come close. With such a long evolutionary history, sharks have had plenty of time to refine their senses. For example, most sharks have an incredible sense of smell. Extrapolations on experiments on shark smell have suggested that some sharks can detect one drop of blood dissolved in as much as one million gallons of water! Sharks also have senses we can’t even begin to experience. Sharks have an electrosensory system that allows them to detect the extremely minute electrical currents generated by the muscles of a swimming fish. The snout of a shark is covered in tiny pores called Ampullae of Lorenzini, which convert electrical impulses in the water to an electrical signal in the shark’s nerves. Therefore the shark can “feel” extremely tiny electrical currents in the water– a skill it uses to hunt, even in complete darkness. Speaking of darkness, many people believe that sharks have poor eyesight. Not true! They don’t see in color, but they have sharp eyesight, and super powerful night vision. That’s because they have a shiny “mirror” called the tapedum lucidem located behind the retina that reflects light back through the retina a second time, increasing its sensitivity. Many sharks like to hunt at dawn, dusk and night, because they can see their prey much better than the prey can see them. Sharks are also the only fish to have eyelids. They’re called nictitating membranes and sharks use them to protect their eyes when something gets too close. Sharks never need to go to a dentist, since they don’t really care about cavities. They have many rows of teeth. As old teeth break or become too dull, they fall out and new ones rotate into place. For the entire life of a shark, it never runs out of new teeth, and it never worries about the teeth it has. And you may find this hard to believe, but sharks are really important in the ecosystems of the ocean.You’ll never see a fish that needs glasses. That’s because a nearsighted fish would quickly be devoured by a shark. So sharks help keep fish populations healthy by weeding out the sick and the weak. Healthy fish can get away from sharks, so they reproduce and make more fish. As top predators, sharks have an important role to play. And because they do not reproduce quickly, sharks are vulnerable to overfishing. And while many people are afraid of sharks, most do not represent a threat to people at all. The world’s largest shark, the Whale shark, grows larger than a bus, but eats only plankton and small fish. Even mean looking sharks with pointy teeth like the Sand Tiger shark prefer to eat fish and never attack people. The more we learn about sharks, the more we discover how little we know about them. Even the idea of a feeding frenzy isn’t really true. I get up close to sharks all the time while they are feeding and I have never been bitten. This group of over 30 Caribbean reef sharks is competitively feeding on a frozen chum ball. They are all around me, but they are not interested in biting me. They know that there is food available, and I’m not it, so I just sit back and enjoy watching the action. ( music ♪ ) And when all the bait is gone, the action is over, and I’m perfectly fine. Far from being the horrific monsters of legends, sharks are actually highly evolved and sophisticated animals with a range of senses and abilities unmatched in the animal world. The study of sharks may teach us many things about our world and maybe even about ourselves.

100 Replies to “Shark Biology | JONATHAN BIRD’S BLUE WORLD”

  1. This is probably my favourite video of yours. I greatly enjoyed the footage and am happy you took some time to highlight the ecologic importance of sharks.

  2. This is wonderful. I love that you constantly remind people that sharks aren't man-eating animals. I would LOVE diving with sharks when I get my scuba diving certificate this summer.
    Are you planning on diving in sweden sometime soon??

  3. hey frnds checkout my blogs

  4. i love this so much I'm starting scuba diving and i was scared because of the sharks even though i love them and this is helping me so much thank you

  5. BlueWorldTV sharks are almost godlike. Through their daily activities like eating prey, weeding out the sick and the weak, and scavenging on large carcasses that few other creatures could access on their own, sharks control basically everything, like prey population size, gene pools of said prey, water quality, atmospheric oxygen levels and even the climate is influenced by sharks. They have been doing this for over 400 million years, so everything in the ocean has evolved a dependency on sharks in some way or another. This also means that land ecosystems depend on sharks for their survival. This is why we need to protect sharks, or everything will be doomed. I'm a huge fan of sharks.

  6. Sharks are really old fish there was on Earth for over 450 millions years and The Sharks is my favorite animals number 5🦈

  7. Jonathan, when you die, if you could come back as any animal in the ocean from coral all the way to blue whales, which animal would you choose? I think I’d choose to be a Tiger Shark!

  8. I have fear for sharks, whenever I swim in the sea, I would always swim near the shore. Thank you for sharing this informative video.

  9. I am very much impressed …listening ur speaking sound & style as well… be honest it gonna be my learning process …

  10. I love sharks and just want to know everything just everything about them……..
    Actually I want to be just like you….see creatures and study about them.
    Explore ocean's and etc..

  11. I want to be a marine biologist …and hope to learn and pursue my passion through your channel …it's great just..😊 ..
    Please make videos about what it takes to be a marine biologist… As you know all ….bcos you are what I want to be😊😊

  12. From what I hear Lorenzini was a human & therefore doesn't have ampullae, so why does the name of the ampullae imply they belong to him??? They don't – they belong to sharkies!!! How about we rename them Lorenzini ampullae, then they're still named after the human, without the implication they belong to him. They're ampullae of SHARKY. Otherwise, pretty comprehensive wee vid there!!! Oh & one more thing: their teeth are made of the same stuff as our fingernails, which is also on sharkies what they use to protect their skin…

  13. hey good content man there are a lot of people who think sharks are dangerous but you are totally opposite thanks for this content. bye

  14. Hey thanks for liking my comment . It will be awesome if you could give a shout-out in your next video . I am a huge fan

  15. never seen one up close.but fellow dive buddies made an encounter off cape may new jersey years ago..I saw the was awesome..

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