The Great White Shark

The great white shark is one of the most fearsome predators in our seas.  Averaging about 12 to 16 feet in length as adults1 they are the third largest carnivorous animal in the ocean only being out done by orca’s and the sperm whale. They inhabit waters all over the world, from New Zealand to the Mediterranean and prey mostly on seals and sea lions that inhabit these temperate waters. To catch such elusive and agile animals such as sea lions, great white sharks have evolved several physiological features and behavioural adaptations.

known distribution of great white sharks

The most recently noted behavioural adaptations of great white sharks is called anchoring2 and has been noted by Neal Hammerschlag of the University of Miami along with partners from the University of British Columbia and and texas state after their experiments in False Bay in South Africa3. Anchoring is the use of a specific position on the sea floor that a great white can stalk unnoticed by its prey before turning upwards and striking it from below in the hope of injuring or killing its victim. The researchers found after monitoring 3404 attacks by great whites that the sharks use certain anchor points under water to position themselves to catch their prey. The underwater anchor points were discovered to be specific to a certain shark, and that great whites do not just attack at random5. Neal Hammerschlag found that an anchor point that an individual great white uses is related to several factors, for example dominance. They found that the most successful anchor points were used by the biggest and most experienced sharks. These dominant sharks found the best anchor points in relation to competition for prey, environmental factors and the distribution of Cape fur seals6. However it was found that the position of the anchor points did not relate to the distribution of the seal population. The older sharks therefore seem to be the better hunters, either because after more experience they learned where the best anchor points were to catch prey, or these larger sharks were trying to exclude the smaller, younger sharks from the best hunting areas, so that they have more food for themselves7.

There are several physiological features that great whites have evolved similarly to other sharks that allow them to obtain food. One such feature is the Ampullae of Lorenzini which is a form of electro receptor that detects electrical currents created by other organisms. This helps to detect any potential prey. This sensory feature is extremely sensitive as a great white can detect minute currents.

The great white’s colouration acts as camouflage from both looking down on to the shark and looking up. The dorsal side of the sharks is a very dark blue which when looking down upon simulates the darkness of the sea water. And from below looking up on the ventral side the colouration is white to replicate the sun’s rays down through the water.

great white shark colouration
known distribution of great white sharks

The great white shark is also extremely streamlined, and has tremendous power due to its high metabolic rate. When attacking prey from below their power through the water often causes the sharks to completely breach. In cases like this, the shark will cover its eyes with protective slits just before it strikes its prey to prevent any damage. To generate such thrust through the water, the great white shark has two main muscles that run the length of its body8. This muscle is divided into two types, red and white. The white muscle is what helps in the short sharp bursts that the great white uses to strike its prey. Momentum is created as the length of muscle on one side contracts whilst the other relaxes, then the other side contracts whilst the other relaxes. This action causes the tail to move from side to side. The head stays straight to reduce the effects of drag as the tail moves.red/white muscle These are simply a few features that aid the great white shark in finding and catching prey to make it one of the most successful predators in the our oceans.

References

1)      http://www.geocities.com/RainForest/Andes/2771/info.html

2)      http://www.newscientist.com/article/dn17345-great-white-sharks-are-serial-killers-of-the-sea.html

3)      http://www.sciencedaily.com/releases/2009/06/090621195618.htm

4)      http://www.geocities.com/RainForest/Andes/2771/info.html

5)      http://www.newscientist.com/article/dn17345-great-white-sharks-are-serial-killers-of-the-sea.html

6)      http://www.sciencedaily.com/releases/2009/06/090621195618.htm

7)      Journal of Zoology, DOI: 10.1111/j.1469-7998.2009.00586.x

8)      http://www.diveplanet.co.nz/dplfoxgwresearch/anatomy/muscle.asp

Photo References

1)      http://scienceray.com/biology/marine-biology/the-truth-about-the-great-white-shark

2)    http://www.networkroundtable.org/wp-content/uploads/2009/01/great-white-shark-002.jpg

3)     http://www.diveplanet.co.nz/dplfoxgwresearch/anatomy/muscle.asp

8 years ago

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