Sharks Apex Predator of the Sea

shark swimming in ocean

Some of the larger sharks are hyper-carnivorous apex predators. They have little fear of other animals, including humans. They are large, fast, and deadly killing machines. Because of their incredibly well-constructed bodies and highly efficient hunting and survival skills, sharks have remained relatively unchanged for over 400 million years. There are over 520 types of sharks, including the Great White Shark, Hammerhead Shark, Tiger Shark, Whale Shark, Bull Shark, etc. Sharks range in size from the massive 18m whale shark to the 20cm dwarf lantern shark. The scientific name for sharks is Chondrichthyes elasmobranchs.

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Shark Description What is a Shark?

Great white shark jaws, mouth and teeth

Sharks belong to a family of fish with a cartilaginous skeleton, two rigid dorsal fins, five to seven gill slits and don't have a swim bladder. Highly active sharks tend to be sleek and streamlined fish. Less active ones tend to be fairly flat. The larger and more active sharks cruise and hunt in the upper and middle depths of the oceans. Smaller ones tend to stay near the seafloor.

Shark Skeleton

Sharks don't have an internal skeleton. Instead, they have thick skin composed of tough but flexible interwoven fibres made of cartilage. (The same kind of stuff that our nose and ears are made of). These fibres form a solid tube-like framework onto which all its muscles and organs are attached. You can think of a shark's skeleton as being similar to the composite skin of an airplane. One advantage of a cartilaginous skeleton is that it is much lighter than an equivalent bony skeleton.

Sharks Don't Have a Swim Bladder

Unlike most other fish, sharks do not have a gas-filled swim-bladder to control buoyancy. Instead, sharks maintain buoyancy with large oil-rich livers and by their light skeletons. These characteristics alone cannot keep the shark buoyant, and they would sink to the bottom if they don't keep swimming. Sharks counter this sinking tendency by constantly swimming forward—a bit like how an airplane stays aloft by getting a dynamic lift by moving through the air.

Shark Skin

Photo: Shark skin

Sharks have no overlapping scales covering their bodies like other fish. Instead, they have very rough skin made up of thousands of tiny, tooth-like scales called ' dermal denticles'. These denticles feel very rough when rubbed in a forward direction but flatten and smoothen in a backward direction reducing hydrodynamic drag, making swimming more efficient and quieter than bony fish. Dried shark skin was once used as sandpaper and non-slip hand-grips for swords.

Shark Teeth

Photo: Great white shark teeth

Some sharks have multiple rows of teeth, which they lose and are replaced continuously. These multiple rows of teeth grow inside the jaw and are steadily moved forward to replace those in front which may be worn or lost. Some sharks can grow as many as 35,000 teeth in their lifetime.

The shape of the teeth is related to the shark's diet. Sharks that feed on molluscs and crustaceans have dense and flattened crushing teeth. Those that feed on fish have needle-like gripping teeth. Those that feed on large mammals have pointed lower teeth for grabbing and triangular serrated upper teeth for cutting. Plankton-feeders have small non-functional teeth.

Shark Jaws

Sharks have an unusual dislocatable jaw structure. In most animals, the upper jaw is firmly attached to the skull and doesn't move. The lower jaw is hinged onto the skull and moves in an up and down direction.

In sharks, the upper and lower jaws form a special biting unit which sits beneath the skull. When a shark attacks its prey, it thrusts its mouth - consisting of this biting unit of both the upper and lower jaws forwards to grab its prey. All sharks are capable of this feat, but it is most prominent in those such as the great white shark. It is this terrifying extended mouth with razor-sharp teeth that most people envision when they think of a shark.

Shark's Eyes

Shark eyes are similar to most other animals. They have eyelids but do not blink as the surrounding water cleans their eyes. Some have a nictitating membrane, sometimes referred to as a third eyelid (like an eagle), to protect the eyes while hunting. Some sharks, such as the great white shark, roll their eyes backwards to protect them when attacking prey. They have excellent eyesight and identify an object by the contrast it makes to its background. Unlike bony fish, their pupils can dilate and contract.


Shark's Sense of Smell

Sharks have an excellent sense of smell. Some specifies can detect blood in seawater in quantities as low as one part per million.

Shark's Hearing

Sharks have a small opening on the sides of their heads that lead to their inner ear. It is not certain exactly how well they can hear.

Shark's Electroreception & Lateral Line

Sharks have numerous electroreceptors called ampullae of Lorenzini around its head. These receptors are the most sensitive of any animal. They can detect the electromagnetic fields produced by animals in the sea. They also use these sensors to detect the earth's magnetic field and use this for orientation and navigation.

Sharks can also detect vibrations in water with their Lateral line, which runs the length of their bodies.


Shark Habitat Where Do Sharks Live?

Photo: Shark swimming

Sharks live in most ocean habitats and are widespread in tropical to temperate zones. They are found in shallow coastal waters to the deepest, darkest and coldest parts of the open seas up to a depth of about 2,000 meters. Larger sharks can travel as much as 80 kilometres a day in search of food.

Most sharks are bottom dwellers and live just above the seabed. Some are also found closer to shore and also live in river estuaries. A few, such as the Northern River shark and spear-tooth shark (endangered), live in freshwater rivers.


Shark Diet What Do Sharks Eat?

All sharks are carnivores. Each species has its own food preferences depending on its lifestyle and habitat. Sharks usually feed in the evenings and at night.

Photo: Shark airborne to catch its prey

Apex predator sharks, such as the great white and tiger shark, are fearless and will attack animals much larger than themselves.

A great white shark's diet includes sea lions, dolphins, turtles, small whales, other sharks and even sea birds. The great white usually attacks its prey from below and strikes so fast that most of its victims have little time to react. They have been known to leap great heights out of the water in pursuit of prey. Smaller prey they bite and swallow whole. Larger prey their grasp with their sharp dagger-like lower teeth and triangular serrated upper teeth and rip them apart into smaller pieces so they can be swallowed.

Photo: A shark herding fish

Sharks that feed on other fish, including other sharks, have long needle-like gripping teeth. These are well suited for catching small fish. The shake kills its prey by biting it and swallows the fish whole.

Photo: Whale Shark - filter feeder

The largest sharks, such as the whale shark, are filter-feeders. These sharks strain small fishes, krill, larvae and other types of plankton out of the water. They eat huge quantities of tiny animals. Filter feeders have tiny non-functional teeth.

Photo: Bottom feeding shark

Bottom-feeders, are usually rather small and scurry along the ocean floor. These sharks usually feed on molluscs, crustaceans, bottom fishes and invertebrates such as lobsters, crabs, snails, octopuses, squids and various echinoderms.

Bottom feeding sharks don't have as many teeth as the larger sharks. Their teeth are large, strong and slab-like. The flat teeth make cracking open shells easier. The Port Jackson shark, for example, has two types of teeth to process its food. The front teeth are pointed for grasping its prey and the back teeth are flat and molar-like for crushing hard shells.


How Sharks Swim Why are Sharks Like Airplanes?

Photo: How a shark swims

Bony fish have a special organ called a swim bladder, which keeps them floating at the desired depth. Sharks do not have swim bladders. They compensate for this by swimming continuously to prevent themselves from sinking.

Sharks swim through water in a manner very similar to how airplanes fly through the air. Both an airplane and a shark would fall to the ground (ocean floor in the case of a shark) if they did not keep moving through their medium. This is because both require dynamic lift to keep them afloat.

The shark's front pectoral fins act in a similar fashion to an airplanes wings, providing lift. Dynamic lift is only provided when an appropriately shaped object is moving through its medium. In the case of an airplane this is provided by its engines which thrust the plane forward, and the wings provide the necessary lift. In the case of the shark, its powerful tail provides it with forward motion, and its front fins provide the necessary lift. When the shark tilts its fins upwards, it can rise. When it tilts them downwards, it can dive. An airplane accomplishes the same outcome using the flaps on its wings. A shark has to keep moving constantly to stay floating at a desired depth.

The vertical dorsal fins on its back act as rudders and together with adjustments its makes to its pectoral fins steer the shark through the water.


Shark Reproduction Three Main Forms of Reproduction

All sharks practise internal fertilisation, where the male inserts a clasper into the female’s cloaca and releases sperm. Once fertilised, the development of the young follows one of three modes of reproduction. The gestation periods of various sharks aren't fully known. It is thought that it ranges from several months to as long as two years.

Some sharks lay eggs encased in a tough leathery eggcase. These eggs have unique attachment mechanisms such as sticky mucus filaments, tendrils and horns to assist them in fixing themselves to the seabed, reefs or seaweed. The Port Jackson shark even lays spiral-shaped eggs that wedge themselves in crevices, etc. These eggs can take between 6-9 months to hatch, at which time a miniature version of an adult emerges from the egg.

Another group of sharks have the embryos develop inside eggs that remain in the mother's body until they are ready to hatch. Once the baby sharks hatch inside their mother, she will then give birth to the live young.

In viviparity reproduction, a baby shark receives nutrients and oxygen through an umbilical cord and develops inside its mother, similar to placental mammals.

Some sharks have up to 100 pups at a time, while others may have as few as two or three. As soon as shark pups are hatched or born, they swim away and live independent lives.


Shark Life Cycle What Kills Sharks?

shark swimming

Photo: Shark swimming

Each shark species has its own unique life cycle. Broadly speaking, most sharks live for 20-30 years. Some can live for as long as a hundred years. Because of their slow reproductive rates, the length of time for them to reach sexual maturity and their longevity, sharks are very susceptible to population depletion.


Shark Threats and Predators What Kills Sharks?

Large adult sharks are apex predators and have few natural enemies. However killer whales (Orcas) have been known to prey on these sharks. Shark eggs and juvenile sharks fall prey to many predators larger than themselves.

Humans are the greatest threat to shark populations. Up to 100 million sharks are killed each year due to commercial and recreational fishing. Flake, frequently used to make fish and chips, is actually the flesh of several different species of small shark.

A cruel human practice is called finning. Here fishermen capture live sharks, cut off their fins, and dump the finless animal back into the water. The resulting immobile shark dies a cruel death from suffocation or is eaten by predators.


Shark Conservation Status Are Sharks Endangered?

Commercial and recreational shark fishing is allowed. But due to the significant decline in their numbers, the following shark species are protected in Australia:

CRITICAL: Grey Nurse Shark and Speartooth Shark
ENDANGERED: Northern River Shark
VULNERABLE: Grey Nurse Shark, Whale Shark, White Shark, Dwarf Sawfish, Queensland Sawfish, Freshwater Sawfish, Green Sawfish, Dindagubba, Narrowsnout Sawfish


Shark Attacks Are sharks Dangerous?

Shark Attack Video

Video: Excellent video about shark attacks

Four species of sharks responsible for most shark attacks on humans. They are the White, Tiger, Bull and Whaler sharks.

Sharks don’t find humans tasty. Unfortunately, humans venture into their territory and are often mistaken for prey. Most people are bitten only once and released. This suggests that the shark releases the person as soon as it realises that it doesn't taste like its usual prey and abandons the bite, but this could still cost you an arm or leg or death from bleeding.

• Shark Attacks! — Learn All About Sharks Attacks


25 Shark Facts

  1. Sharks range in size from the massive 18m whale shark to the 20cm dwarf lanterns-hark.
  2. There are over 520 species of shark living in the the world's oceans.
  3. Most sharks are harmless and don't hunt humans.
  4. Only four sharks have been known to attack humans.
  5. These are the great white, oceanic white-tip, tiger, and bull sharks.
  6. Bull sharks are the most aggressive.
  7. You are four times more likely to die from bumping into another person than by bumping into a shark.
  8. Shark attacks on humans are usually a case of mistaken identity. The shark has mistaken a human for a seal or turtle.
  9. They don't like the taste of human flesh.
  10. Sharks have sandpaper-like skin.
  11. They have no bones. Instead they have thick cartilaginous skin that acts as a skeleton.
  12. Cartilage is the same stuff our nose & ears are made of.
  13. Unlike other fish, sharks lack swim-bladder to keep them afloat.
  14. They have to swim continuously to stay from sinking.
  15. Sharks lose and replace their teeth continuously.
  16. A shark can replace up to 35,000 teeth in its lifetime.
  17. The shortfin mako is the fastest shark. It can swim at up to 50 kph.
  18. Some sharks 'sleep swim' to keep water flowing over their gills so they can breathe.
  19. Females of some shark species can reproduce without a male to fertilise their eggs.
  20. Dried shark skin was once used as sandpaper and for non-slip hand-grips for swords
  21. Some sharks, if inverted or stroked on the nose, go into a trance and are paralysed.
  22. Not all sharks live in the sea. Some live in large freshwater rivers.
  23. Fish and chips shops sell "flake", which is shark meat.
  24. Sharks were on the earth 300 million years before the dinosaurs.
  25. Many species of sharks are threatened with extinction.



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