What Are 10 Facts About Sharks?

These marine predators are classified as cartilaginous fish, belonging to the Selachimorpha superorder. Unlike most fish species, sharks have skeletons made entirely of cartilage, which is the same flexible tissue found in human ears and noses.

This unique skeletal structure allows sharks to move with incredible agility through water, as cartilage is lighter and more flexible than bone. While their skeleton lacks bones, some parts contain calcium deposits that provide extra strength, particularly in their jaws and vertebrae.

Sharks are covered in unique placoid scales, also known as dermal denticles, which set them apart from other fish. These microscopic scales are remarkably similar to human teeth, featuring an outer enamel layer, dentine, and a pulp cavity. This structure makes shark skin both hard and rough.

These specialized scales serve two crucial functions: they reduce water resistance, allowing sharks to swim faster while using less energy, and provide natural protection against parasites.

The scales grow from the dermis (inner skin layer) and emerge through the epidermis, creating a highly effective natural armor.

Most sharks lack the gill covers (opercula) that other fish use to push water through their gills. Instead, they rely on continuous swimming to force oxygen-rich water over their gills, a process called ram ventilation. This explains why many shark species never seem to stop moving.

Great white sharks (Carcharodon carcharias) and mako sharks (Isurus oxyrinchus) are obligate ram ventilators, meaning they must keep swimming to survive. However, species like nurse sharks (Ginglymostoma cirratum) and reef sharks (Carcharhinus species) have evolved specialized muscles called buccal pumps that allow them to push water over their gills while resting.

Sharks have evolved unique ways to protect their eyes without traditional eyelids. Most species can rotate their eyeballs back into their sockets when needed, particularly during hunting or defensive situations.

Some species, like the great white shark (Carcharodon carcharias), have developed a specialized nictitating membrane, which is a transparent, protective third eyelid that slides across the eye during close encounters with prey. Tiger sharks (Galeocerdo cuvier) and hammerhead sharks (Sphyrna species) also possess this membrane.

Additionally, shark eyes are coated with a reflective layer called tapetum lucidum, similar to cats' eyes, which enhances their vision in low-light conditions.

From murky depths to crystal waters, read this other article to learn how sharks' eyes adapt to different environments.

A shark's body is a masterpiece of aquatic design. The streamlined, torpedo shape helps them cut through water with minimal resistance.

Unlike most fish that use a swim bladder, sharks rely on their oil-rich liver for buoyancy. The liver stores a substance called squalene, which is lighter than water. In the basking shark (Cetorhinus maximus), this organ makes up 25% of its total weight, acting like a natural flotation device.

The shark's asymmetrical tail provides enhanced thrust and maneuverability.The upper lobe of the tail is larger than the lower one, creating an upward force that counteracts the shark's natural tendency to sink.

The paired pectoral fins act as wings, generating lift as the shark moves. The dorsal fins prevent rolling, while the anal fin maintains stability during sharp turns. This arrangement lets sharks execute precise movements with minimal energy expenditure, which is essential for both hunting and long-distance swimming.

The lateral line on a shark's sides acts like underwater sonar, letting them sense nearby movement and vibrations. This natural radar works through tiny pores that pick up disturbances in the water.

Working alongside the lateral line, the ampullae of Lorenzini form a network of jelly-filled sensors. These detect electrical fields, which are signals that all living creatures produce. That's why a great white shark (Carcharodon carcharias) can detect a fish's heartbeat, even in dark waters.

Together, these systems make sharks master hunters. The blacktip reef shark (Carcharhinus melanopterus) combines both senses to track prey in murky water, while the nurse shark (Ginglymostoma cirratum) uses electrical detection to find fish hiding in sand. Beyond hunting, these senses help sharks navigate using Earth's magnetic field and track changes in water temperature.

Curious about where sharks hunt? Explore the open ocean world of pelagic fish.

When mating, male sharks use modified fins called claspers to deliver sperm to females. After this, each shark species follows one of three paths:

• Port Jackson sharks (Heterodontus portusjacksoni) wrap their eggs in protective cases, known as mermaid's purses, and leave them to develop on the seafloor.
• The great white shark (Carcharodon carcharias) keeps its eggs inside. Pups grow using yolk until they're ready to emerge, fully formed.
• Like mammals, tiger sharks (Galeocerdo cuvier) nourish their pups through a placenta-like system before giving live birth. They can carry up to 80 pups in a single pregnancy.

The length of shark pregnancy varies widely. For example, nurse sharks (Ginglymostoma cirratum) carry their young for six months, while spiny dogfish (Squalus acanthias) pregnancies last two years.

Sharks grow rows of teeth throughout their lives. When one tooth falls out, another slides forward to replace it.

The great white shark (Carcharodon carcharias) loses about 2,400 teeth per year. A tiger shark (Galeocerdo cuvier) can burn through 24,000 teeth in its lifetime.

Each tooth type serves a purpose. Bull sharks (Carcharhinus leucas) have thick, triangular teeth for crushing, while mako sharks (Isurus oxyrinchus) sport needle-like teeth for gripping slippery fish.

Most sharks carry 5-15 rows of developing teeth behind their front row. When a tooth breaks or wears down, it takes just one week for a new tooth to move up and replace it.

Ever wonder who wins the chomp championship? See how shark bites measure up against nature's strongest jaws.

Sharks act as ocean health managers in two key ways. First, they clean the seas by removing sick, weak, and dead animals. This prevents diseases from spreading through marine populations and keeps prey species genetically strong.

Second, sharks control prey numbers. Without enough sharks, fish populations can grow too large, damaging coral reefs and disrupting food chains. When shark numbers drop in an area, the whole marine ecosystem suffers.

Without these predators, coastal ecosystems can collapse, as seen in areas where shark populations have declined.Their role as top predators has shaped marine life for over 400 million years.

July 14 marks International Shark Day, but shark conservation needs attention year-round. Despite their role in ocean health, shark populations face serious threats from overfishing.

Some shark species have declined by 70% in recent decades. Fishing for shark fins kills about 100 million sharks yearly. Without strict fishing limits and protected areas, many shark species could vanish from our oceans.

Sharks need time to recover, they grow slowly and have few babies. A female shark might take 15 years to mature and have just two pups per year. This makes them very vulnerable to overfishing.

Sharks face a bigger threat than you think. Learn more about what's putting these ocean predators at risk in this other article.

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