SHARK ANATOMY

Sharks have a range of adaptations that make them perfectly suited to their environment. It's no wonder they've gained a reputation for being some of the most impressive and formidable predators on the planet!

Click here to view our Shark Anatomy Poster (pdf).


Kitefin skeleton © Wikimedia Commons, Ryan Somma.  

SKELETON 

A sharks skeleton is made of cartilage. This is strong and durable, yet much more flexible and lighter than bone. Being lighter helps sharks to stay afloat and reduces the amount of energy they need to move about. The flexibility of cartilage also allows them to make tight turns quickly. Making them one of the most agile animals in the ocean.

FUN FACT - scientists can tell the age of a shark by counting the rings on their backbone!


Shark skin illustration © Marc Dando.
 
 

SKIN

Shark skin is covered with millions of tiny teeth called dermal denticles. These point backwards, reducing surface drag and helping the shark swim faster. As sharks grow they shed their denticles, replacing them with larger ones.

Denticles vary in shape according to the species and where they are on the body. Some are so big that the shark uses them as defensive spines or shields!

FUN FACT - the hydrodynamic efficiency of shark skin has been replicated by swimming costume manufacturers. It's said that their costumes help improve swimming times. This is so effective that they were labelled ‘technology doping’ and banned from Olympic competition.

Tiger teeth © Wikimedia Commons, Stefan Kühn.  

TEETH 

Made of enamel, shark teeth are strong and appear in huge numbers in the fossil record.

Sharks fend for themselves immediately after birth, so they're born fully equipped. They have many rows of teeth which are constantly being replaced. Ensuring they always have a full set of razor-sharp pearly gnashers.

FUN FACT – sharks replace their teeth approximately every 2 weeks. Some species can lose 30,000 teeth in their lifetime!

We can tell what a shark eats by the shape of its teeth. Flat crushing teeth are perfect for eating shellfish. Pointed teeth for gripping fish. And sharp serrated teeth for larger prey, such as seals.

A shark’s teeth may change with age as the diet of a pup may differ to that of an adult.

Shark fin © James Lea.  

FINS

These provide balance and stability in the water. Sharks have a large dorsal fin which provides balance. Usually they'll also have a smaller dorsal fin further back towards their tail. Their pectoral fins are used to steer and lift themselves in the water. And their tails are used to propel themselves forward.

The size and shape of a shark’s fins and tail can vary greatly.

Faster sharks (such as the Shortfin Mako) tend to have shorter crescent shaped tails. Whereas slower moving sharks (such as the Bluntnose Sixgill Shark) have longer thinner tails.

Sadly, high demand for shark fins has contributed to the decline of many shark species.


Shark gills illustration © Marc Dando.  

GILLS

To breathe many shark species have to remain in constant forward motion. As they swim water is driven through their mouth and out over their gills. A process known as ‘ram-ventilation’. As water passes over the gills, oxygen is absorbed into tiny blood vessels and transported around the body. 

Yet, some less active sharks (such as Nurse Sharks and Zebra Sharks) have got around this. They're able to spend lots of time lazing around by sucking water into their mouth and squeezing it over their gills.

Sandtiger Shark © Dray van Beeck.  

SINK OR SWIM

To help keep them buoyant sharks rely on:

  • a light skeleton
  • the lift effect produced by their fins as they move through the water
  • large livers that store low density oils
In some sharks the liver makes up 25% of their total body weight! In mammals this is only 5%. Unfortunately there's huge demand for shark liver oil, which is used in cosmetics. So this adaptation that's so integral to their survival, also makes them vulnerable to human exploitation.

Some sharks, such as the Whitetip Reef Shark, are able to rest on the seabed. To resume swimming they’ll propel themselves forward with their tail..

FUN FACT - the Sandtiger Shark can hover motionlessly by gulping water at the surface, trapping air in their stomach. Often they can be seen letting bubbles out of either their mouth…or the other end..


Oceanic Whitetip Shark © Andrew Bellamy.  

MUSCLES

Sharks have 2 types of muscle - red and white. Red muscle works by breaking down the fat in the shark’s body. It has a good blood supply and helps the shark swim for long periods of time. White muscle works by using energy from the breakdown of glycogen (sugars). Enabling sharks to make short fast sprints when catching prey or escaping danger.

Long bundles of muscle fibres run from the top of a shark’s head to the tip of its tail. When these contract a series of undulations are produced along the body. This enables the shark to propel itself through the water with its tail. More pronounced muscle contractions produce faster speeds. But, to conserve energy, sharks will build up speed with a series of muscle contractions, then stiffen their body to cruise through the water.

White Shark © Sean Sequeira.  

TEMPERATURE CONTROL

Most fish are cold blooded, so their body temperature fluctuates with their environment. But did you know that mackerel sharks can warm their blood. Mackerel sharks include the White Shark, Porbeagle, Salmon Shark, Shortfin Mako and Longfin Mako. So, In either sense of the meaning, White Sharks are not the 'cold-blooded killers' they're made out to be.

Retaining warmth makes them much more efficient predators. A lot of heat is lost through a shark’s gills, where blood vessels are exposed to cooler water. To minimise heat loss mackerel sharks have a network of tiny capillaries which act as a heat exchange system (known as a rete mirabile). Blood vessels carrying warm deoxygenated blood to the gills pass alongside cold oxygenated blood going to the body. As they pass in opposite directions heat is exchanged and returned to the muscles.

FUN FACT – the body temperature of mackerel sharks can be 10°C higher than the surrounding water.

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