(© Trevor Sewell/Electron Microscope Unit, University of Cape Town)
BIG SHARK SKIN
Speedy SwimmersĮxtreme close-up of great white shark skin denticles. These sharks include the great white shark ( Carcharodon carcharias), mako shark ( Isurus sp.) and whale shark ( Rhincodon typus). But some sharks are unable to pump water this way and, if they stop pushing water into their mouths by swimming, will suffocate. This is called buccal pumping and is used by many sharks that spend their time sitting still on the seafloor like nurse sharks ( Ginglymostoma cirratum), angel sharks ( Squatina sp.) and wobbegongs ( Orectolobidae). When they’re resting, many shark species pump water over their gills to make sure the oxygen never stops flowing. The gills extract oxygen from the seawater, after which the water is expelled through the gill slits behind its head.
After water flows into a shark’s mouth as it swims, it closes its mouth, forcing the water over its internal gills. Unlike bony fishes, which have one gill slit on each side of their bodies, most sharks have five slits on both sides that open individually (and some shark species have six or seven). Filter-feeding sharks that sift tiny plankton from the water still have teeth, but they are very small and aren’t used for feeding.Īnother defining feature of sharks is their array of gill slits. Sharks that eat shellfish have flatter teeth for breaking shells. Others have razor-sharp teeth for biting off chunks of prey, allowing them to attack and eat larger animals than bony fishes of the same size. Some have pointed teeth for grabbing fish out of the water. A shark can lose and replace thousands of teeth in its lifetime! Not all shark teeth are the same, however. Unlike people, which have a limited number of teeth in their lifetime, sharks are constantly shedding their teeth and replacing them with new ones. Cartilage is much lighter than bone, which allows sharks to stay afloat and swim long distances while using less energy.Įvery shark also has several rows of teeth lining its jaws. This is a defining feature of elasmobranchs, as most fish have skeletons made of bone. Like other elasmobranchs (a subclass of animals that also includes rays and skates), sharks have skeletons made of cartilage-the hard but flexible material that makes up human noses and ears. No matter their size, all sharks have similar anatomy. The smallest shark, a dwarf lantern shark, is rarely seen and little-known. Anatomy, Diversity & Evolution Anatomy What makes a shark a shark? To protect them, communities and companies around the world are enacting science-based fisheries management policies, setting up shark sanctuaries, and banning the practice of shark finning and the trade of shark fins. (This is despite the fact that you are more likely to be killed by a lightning strike than bitten by a shark, and more likely to be killed by a dog attack than a shark attack.) Combined, these actions have decreased many shark populations by 90 percent since large-scale fishing began.Īll of this puts these incredible animals-and the ecosystems in which they play a role-in jeopardy. And because of needless fear spurred on by films such as Jaws, the instinct for some is to hurt or kill sharks that come near-such as the controversial shark culling in Australia.
Sharks are accidentally caught in nets or on long line fishing gear. Rising demand for shark fins to make shark fin soup, an Asian delicacy, has resulted in increased shark fishing worldwide an estimated 100 million sharks are killed by fisheries every year. Sharks and their relatives were the first vertebrate predators, and their prowess, honed over millions of years of evolution, allows them to hunt as top predators and keep ecosystems in balance.īut sharks are in trouble around the world. Wherever they live, sharks play an important role in ocean ecosystems-especially the larger species that are more “scary” to people. They are found in just about every kind of ocean habitat, including the deep sea, open ocean, coral reefs, and under the Arctic ice. They come in a variety of colors (including bubble gum pink), and some feed on tiny plankton while others prefer larger fish and squids. They range in size from the length of a human hand to more than 39 feet (12 meters) long half of all shark species are less than one meter (or about 3 feet) long. That generalization does sharks a huge disservice, as they have far more variety than that. Yet when most people think of these cartilaginous fish, a single image comes to mind: a large, sharp-toothed and scary beast. There are more than 500 species of sharks swimming in the world’s ocean.
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