Sharks 101 | National Geographic


(ominous music) – [Narrator] They glide through the water with unmistakable grace, remnants of an ancient past, they dive and they rise from the ocean’s murky depths to it’s sun-kissed shallows, rousing fear and awe like no other creature in the sea. The world’s biggest
living fish is a shark. Of the estimated 34,000 species of fish, the largest are whale sharks. These gentle giants usually
grow to about 40 feet long and weigh an estimated 15 tons. Their mouths alone can
span four feet wide. The gigantic whale shark however, pales in comparison to the largest fish that ever existed, the megalodon. Dating to over 20 million years ago, it’s thought that the prehistoric shark could of reached 80 feet long, weighing up to around 70 tons. Unlike whale sharks, the
megalodon was carnivorous, and consumed any creature that fit into it’s nearly 10 foot wide mouth. Throughout their lives
some species of shark can shed over 30,000 teeth. Unlike humans who are born with a set number of teeth in their jaws, sharks have a seemingly limitless supply. They can grow, lose, and
replace their teeth as needed. Furthermore, most sharks have multiple rows of teeth in their jaws. The jaws of a great white shark, the largest predatory fish in the sea, can contain up to seven rows that hold up to 300
teeth at any one point. Most sharks, as they hunt their prey, end up losing their teeth individually. However, the cookiecutter shark loses and replaces the teeth in
it’s lower jaw all at once. Sharks are built for speed. The fastest known shark, the mako shark, can reach speeds of up
to 46 miles per hour. This speed is largely due to their body’s hydrodynamic design. Many sharks have torpedo shaped heads that allow them to cut through the water with little resistance. Plus, shark skin is covered
with flat, v-shaped scales, called dermal denticles. The denticles help water
flow smoothly over the skin, which reduces friction and helps sharks swim quickly and quietly. Sharks also have skeletons made of cartilage instead of bone. Cartilage is a much
lighter material than bone so sharks have less weight to carry. Sharks may lay eggs, or bear live young. Egg laying sharks only
lay a few large eggs. They may come in various forms, such as sacks called mermaid
purses or corkscrews. These eggs act as external wombs in which shark embryos
complete their development. However, most sharks
give birth to live young. Called pups, the young of
most live bearing species gestate for around one year. Some even begin practicing
their predation skills while in the womb. Before they are born, the
sand tiger shark pups compete with their siblings. In fact, the strongest pup
in each of the two wombs devours its weaker brothers and sister. Some sharks are at risk of extinction. Every year an estimated 100 million sharks are killed worldwide, in large part for the shark fin trade. The sharks are caught
and their dorsal fins are removed and sold at a hefty price, primarily in Asia. In traditional Chinese culture, serving and eating shark fin is a sign of status and wealth. Because of the high demand
and value of shark fins, some shark populations have plummeted by up to 70% causing a ripple effect in ecosystems and endangering
at least 74 shark species. However, measures are being
taken to protect sharks with a number of countries and
jurisdictions cracking down on unsustainable shark fishing. In China, shark fin soup
is no longer allowed to be served at government banquets. A move hailed by shark conservationists. Through continued international
conservation efforts, the loss of sharks may be curbed, allowing the creatures in
all their power and grace to survive for many generations to come.

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