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| Great white shark. |
Great white sharks, as featured in the 70s blockbuster
movie Jaws, are not monstrous man eating sharks but instead great predators of
the sea that hunt marine life. Known for their great size and as the largest predatory
fish on Earth, males reach an average of up to 5.2 m (17 ft) in length while females
generally grow larger in size. Great white sharks have
been recorded to reach a remarkable length of 6.4 m (21 ft).
Being cartilaginous fish, sharks are made
up of cartilage and have a streamlined body designed to cruise easily through
water with little effort. Their snouts are large and conical in shape with a strong
jaw lined with rows of teeth making a total of up to 300 triangular, serrated and razor sharp teeth. Great whites have an outstanding sense
of smell and organs that can sense electromagnetic fields generated by animals
and humans alike. These sharks, along with mako and whale sharks, will die from lack
of oxygen obtained through their gills if they stopped swimming.
Their colouration helps with camouflage in the
sea, with slate-grey upper bodies and white underbellies (hence the name great
white sharks). Due to the white underside and grey dorsal area that break up
the outline of the shark, it can be difficult to spot the shark from the side,
below and above.
These ferocious predators of the sea have
no natural predators other than the killer whale and are legally protected in
South Africa. Great whites live on average up to 70 years or more, making them the
longest living of all cartilaginous fish.
Shark spotters
The Shark Spotting
Programme was founded in 2004 due to the increase in number of great white shark sightings along the shores of
Cape Town and thus the fear of beach goers, predominantly in False Bay. Shark
spotters are employed and plotted along the coast, seven days a week during daylight
hours, in high platforms to scan seashore waters for sharks, and once sighted
the alarm is raised.
Shark spotters flag meanings
·
No flag = no spotter on duty
·
White Flag (with a solid black shark) = shark has been spotted, sires have
been sounded, or after serious shark incident at the beach.
·
Red Flag (with solid white shark) = high shark alarm, 1 hour after shark
seen, high risk of shark activity.
·
Black Flag (with shark outline) = poor spotting conditions, no shark
seen.
·
Green Flag (with shark outline) = spotting conditions good, no shark
seen.
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| Shark spotting flags. |
Habitat
Great whites establish their cruising
waters in all major oceans that fall in the temperature range from 12 through to 24 °C (54 to
75 °F). They swim along coastal countries such as the United States,
Japan, Chile, Australia and South Africa and are found in the Mediterranean seas.
One of the highest numbers of great white
shark populations are found swimming between Dyer Island and Geyser Rock off the coast of the Gansbaai coastline, dubbed Shark Alley. Seal Island is situated in the middle of
False Bay, some 30km out to sea from Cape Town, and is home to about 64 000
seals, three species of cormorants among other sea birds and even some penguins.
Between February and May great white sharks make a return to Seal Island to
hunt seals, often drawn to the northern tip where sick or wounded seals are
found.
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| Great white breaching. |
Behaviour
In South Africa, great whites follow a
dominance hierarchy that is determined by the size, sex and rights of the resident:
females are dominate over males, while larger sharks dominate smaller sharks
and residents of the area dominate newcomers.
During hunting, these sharks tend to
resolve conflicts with other sharks using rituals and displays instead of taking
on one another in combat. Great white sharks are one of the few sharks known to
engage in spy-hopping, which entails the lifting of their heads above the
surface of water to gaze as other objects such as potential prey. These
magnificent sharks propel themselves out of the water into the air by
travelling up to speeds of 40km/h under water, which is known as breaching.
According to
scientists, great white sharks behave differently in False Bay at Seal Island than
anywhere else along the South African coastline.
Diet
Great white sharks are carnivorous predators of the sea who prey on and eat fish, seals, sea lions, sea
turtles, sea otters and sea birds. Ambush hunters by nature, they take on their
prey by means of surprise attacking from below. When the shark bites, it shakes its head side-to-side,
helping the sharp teeth cut off large chunks of flesh.
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| The jaws of a great white shark. |
Reproduction
Not much knowledge is known about the
reproduction and mating of the colossal great whites. Male great white sharks are
believed to reach sexual maturity between 9 and 12 years of age while females
are ready for mating between 13 to 16 years old.
Great whites are ovoviviparous, meaning
eggs develop and hatch in the uterus and then continue to grow for between 14
to 18 months until birth. The youngsters are then delivered during spring and
summer.
Did you know
Great white sharks are responsible for the
highest number of reported and identified unprovoked yet fatal shark attacks on
human.
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