Sharks Reading Comprehension Lesson

Ancient Ocean Predators

Sharks are among the oldest animals on Earth. Fossil evidence shows that sharks have existed for more than 450 million years — meaning they survived all five of the Earth’s mass extinction events, including the one that wiped out the dinosaurs 66 million years ago. Today, there are more than 500 species of sharks, ranging in size from the dwarf lanternshark, which fits in a human hand, to the whale shark, the largest fish in the ocean, which can grow to 40 feet and weigh as much as 40,000 pounds.

Unlike most fish, sharks do not have bones — their skeletons are made entirely of cartilage, the same flexible material that makes up human ears and noses. Cartilage is lighter and more flexible than bone, which helps sharks move efficiently through the water. Sharks also lack a swim bladder, the gas-filled organ that most fish use to control their buoyancy. Instead, sharks must keep swimming to avoid sinking. Their large livers, filled with oil lighter than water, also help them stay afloat.

Sharks are apex predators — they sit at the top of the marine food chain. Most sharks are carnivores that eat fish, squid, rays, seals, and other marine animals. Some larger sharks, like the great white, also eat marine mammals such as sea lions and dolphins. The whale shark and the basking shark, despite being giants, are filter feeders that eat only tiny plankton and small fish, straining enormous quantities of water through their gill rakers as they swim slowly forward with their mouths open.

Remarkable Senses and Ocean Importance

Sharks have an extraordinary array of senses that make them highly effective hunters. They can detect smell from hundreds of yards away and can sense tiny amounts of blood in the water. Their lateral line — a row of sensory cells running along both sides of their body — detects vibrations and pressure changes in the water, alerting them to nearby movement. Sharks also have a sixth sense: special organs called the ampullae of Lorenzini that can detect the weak electrical fields produced by the muscles of other animals. This sense allows sharks to locate prey hiding under sand or swimming in complete darkness.

Many people fear sharks because of their portrayal in movies and media, but shark attacks on humans are extremely rare. On average, sharks kill fewer than 10 people worldwide per year. Bees, wasps, and dogs each kill far more people annually than sharks do. Humans, by contrast, kill approximately 100 million sharks every year — for their fins (used in shark fin soup), their meat, their liver oil, and as accidental bycatch in fishing nets.

Sharks play a vital role in maintaining healthy ocean ecosystems. As apex predators, they regulate the populations of the animals they prey on, preventing any one species from becoming too dominant. When shark populations decline, the effects ripple through the entire food chain. Conservation groups and governments around the world are working to protect sharks through fishing regulations, bans on shark finning, and the creation of shark sanctuaries in their feeding and breeding grounds.

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