Great white ID
Quite simply, great whites are grey on top with a white underbelly – for perfect camouflage from above and below. The white belly blends in with the sky and the dark back blends in with the rocks below.
Great white addresses
Great whites swim the oceans of the world. Concentrations, or ‘hot spots’, are found in the temperate waters of south-western Australia, South Africa, California and Mexico.The densest known population is right here, around Dyer Island, South Africa!
They are pelagic fish. That means they prefer the upper layers of the sea, but also venture down to 1 280m. They are mostly seen in coastal waters where the pickings are rich. Seals, whales, dolphins, other sharks and large bony fish make a good shark diet.
We’ve recently realised that great whites spend a lot of time in the open ocean too. When ‘Nicole’, a female great white, was tracked to Australia and back, we learned so much more about their migration and behaviour. In fact, great whites have the longest recorded migratory range of any marine creature. Nicole covered a staggering 22 000km from Dyer Island (South Africa) to western Australian and back in just under nine months! Her average swimming speed was 4.7km/hr. She spent 60% of her time in the top 5m of water,
20% in the area below that and 20% down at her maximum depth of 980m.
The white shark is an apex predator – right at the top of the feeding pyramid – and is vital to a healthy marine ecology. The only animals who attack them are other great whites, sperm whales and orcas.
These apex predators take their pick of the buffet, choosing fish, smaller sharks, turtles, dolphins, seals and sea lions – or even the blubber of dead whales.
Great whites are partly warm-blooded. Most of their body is kept at 14°C above the temperature of the surrounding water. They are economical with their calories and can go for weeks between meals. With one bite, great whites gobble about 14kg of flesh, and can gorge on several hundred kilograms of food. Do they like the taste of humans? Well, humans are not exactly healthy for a great white because its digestion is too slow to cope with the human body’s high ratio of bone to muscle and fat…
Great whites of up to 7m (21ft) long have been reliably reported, but their average length is around 6m (18ft). They’re over a metre long at birth (3 to 5ft).
No one really knows how long great whites live. It’s hard to find out because they lead lonely lives and are so migratory. Research in recent years should bring us closer to knowing.
Great whites have powerful sensing mechanisms – a mega sense of ‘smell’ and an ability to sense the electrical fields radiating from living creatures.
They ‘breathe’ via gills, so nostrils are solely for sniffing out prey. Each nostril is divided in two, separating the water into two flows, one incoming and one outgoing. The water flows over sensory organs covered with millions of olfactory cells connected to the ‘smelling’ centre of the brain. The great white is one big swimming nose!
They hunt down prey with an unusual electrical field detection system. Minute capsules filled with a gel-like substance are sensitive to electrical discharges as small as .005 microvolts! Sensory cells pick up these signals and transmit the information to the brain. All marine creatures generate small electrical fields – where their skin meets the water, from the mucous membranes in the mouth and gills of fish, or from the blood of wounded animals. The great white ‘reads’ the signals and decides who’s swimming normally, who’s panicking, or who is incapacitated.
A sharky grin
When a great white attacks, it thrusts its jaw forward. This makes for the widest possible grab and lets teeth grasp the prey.
Sharks’ teeth change over time depending on what they eat. Smaller sharks, less than 3m, generally eat fish. These young sharks have pointed teeth so that their jaws can pin prey. As they get bigger, they start to add larger prey such as seals and dolphins. To dismember such big animals, their top teeth become stronger, serrated and triangulated. The lower teeth stay pointed so that the shark can still pin the prey.
What’s with the eyes?
Much like human eyes, shark eyes have a light-sensitive layer at the back called the retina. A shark’s retina has millions of microscopic rod cells helping the shark see in dim light.
In low light, shark eyes shine like a cat’s. That’s because the tapetum, a layer of shiny cells behind the retina, reflects light back through the eye helping them see even better in low light. In bright light the tapetum can be covered with dark cells to cut reflection and protect the retina.
Sharks have two eyelids to protect their eyes. Often the eyelids don’t meet. Some sharks have a third eyelid (nictitating membrane) – useful protection when attacking prey. If there’s no nictitating membrane they roll the eyeballs back under the true eyelids – and there’s the white-eyed look.
Mystery and reproduction
Male great whites are ready to breed when they reach approx 3.8m long. Females are ready at approx 4.8m. Though they both have a hole near the pelvic fins called the cloaca, you can see the difference between male and female sharks.
Male sharks have modified pelvic fins called claspers. They also have two muscular sacs in their abdominal wall which they fill with seawater. Internally males have testes that produce sperm and secrete male hormones.
Female sharks are mostly bigger than male sharks. Other than that, they look the same, except they don’t have claspers. Inside, they have a pair of ovaries where female hormones and eggs are made – interestingly, usually only the right ovary makes eggs.
We know almost nothing about how and where great whites mate. Some believe that making a large kill has a soporific effect on them that may lead to mating.
We have never seen a great white give birth, though we know they are ovoviviparous. That means the eggs grow inside the female, hatch there and carry on growing until they are born between spring and summer. They give birth to between 4 and 14 pups and may have only 4 to 6 litters in a lifetime. At birth, the pups are about 1.5m long and are already able hunters. They grow quickly, reaching 2m after their first year of life.
White shark titbits
White sharks store extra fat in two large livers and draw on these stores when times are hard. The livers help to keep the shark buoyant.
The dorsal fin is flexible (bendy) and works with the tail to make the shark agile.
The dorsal fin is as individual as a fingerprint – the trailing edge and the arrangement of notches in the fin is unique.
The great white is the only apex predator that hasn’t been kept successfully in captivity. Where it’s been tried, the sharks were released due to stress.
Conservation: It’s tough at the top
Being at the top of the food pyramid means white sharks are vital to a balanced marine ecology. They control the populations of prey species and weed out the sick and wounded. A healthy ocean depends on a robust population of apex predators. Sadly, the survival of the great white is threatened by the ignorance and greed of humankind who continue needlessly to slaughter them. Responsible tourism promotes conservation, awareness and respect for the great white shark. We work towards sustainable populations of great whites in the waters of the world.