The physical structure of sharks is a key factor, influencing their hunting and living habits. Generally, sharks are cylindrical in shape with tapered edges. This streamlined structure allows these carnivorous hunters to cut through the water in pursuit of their prey. Most sharks average a length of about 5.8 to 7 metres, much the same as human beings. The smallest species, known as the Lantern Shark, measure less than 20 centimetres, while the enormous Whale Shark (believed to have been the ‘whale’ described in the Biblical account of Jonah) measures an astounding 12 metres, on average.
The colouring of a shark’s body has been designed with camouflage in mind. The top of the shark, the dorsal side, is darker than the ventral side, or underneath, of the body. This ensures that, when seen from above, the darker side of the body blends in with the blackness of the ocean’s depths.
When viewed from beneath, its lighter ventral side is much the same shade as the surface of the ocean, which is brightened by sunlight. Some sharks have stripes or spots, particularly in their early years. Others become lighter over time, while still others remain one colour for their entire life span.
The skeleton of the shark is different from other fish species in that it includes no bone. It is all cartilaginous. In some areas of the body, the cartilage has calcified to make it somewhat harder and firmer, but it still does not qualify as bone. The jaw is not attached to the rest of the cranium, and its teeth are not embedded in the jaw but, rather, in the gums. There are rows of teeth (serrated for some species and flattened for others) that are replaced on a regular basis to ensure that the animal is always equipped with sharp, effective weapons and tools.
The shark’s skin is made up of dermal denticles. These collagenous fibres act as a corset and an exoskeleton. Shark skin is used as sandpaper and, when treated, as leather. The muscles are attached directly to these collagenous fibres, which is effective in saving energy. There are tiny ‘teeth’ on the skin that are in place to reduce turbulence, allowing the shark to cruise unhindered through the water. A shark cannot swim backwards due to the structure of their fins. Their tails are used for forward thrust and propulsion while the caudal fin assists. The pectoral fins keep the animal lifted, working against the downward pushing of the caudal fin, and assisting in steering. Depending on its specific needs, different sharks have different tails.
Sharks breathe by means of gills, not lungs. They usually have between 5 and 7 sets of lateral gill slits.
Sharks offer an intriguing combination of beauty, fascinating design and impressive hunting adaptations. While they continue to instil fear into the hearts of bathers, surfers and fishermen, they certainly continue to impress researchers. Their sheer size, strength and agility have proven effective in creating a species known for their killing skills and ferocious tactics.