Wildlife – Great White Sharks

“In 1995 we were out in False Bay, fishing around Seal Island, home to about 15 000 Cape Fur Seals at any one time, and we witnessed a huge Great White shark breaching next to our ski-boat.

As it happened within 2 metres from our boat, we first thought that the shark was in fact trying to jump into the boat, but later discovered a young seal pup alongside the Boat and realised that it was after the seal, and thankfully, not us …”

"By increasing your knowledge and understanding of sharks you will be more informed to make choices that promote ocean conservation." ~ Sharklife

Man’s fear of this incredible predator has not been helped by movies like “Jaws”. Due to the declining numbers, Great Whites are protected along the coasts of South Africa, South Australia, California (USA).

They are also found along the coasts of Japan and the Mediterranean. It is probable that Great Whites migrate along trans-oceanic routes in search of food and/or mates.

The Great White shark is very streamlined with a torpedo-shaped body, pointed snout, crescent-shaped tail, 5 gill slits, no fin spines, anal fin, dorsal fin (on its back) and two pectoral fins (on its sides). It has a white underbelly and its top colour is blue-grey.

Statistics

• Length : 3.7 – 4.9 m (12 – 16 ft)
• Largest Great White on record : 7 m (23 ft), weight 3200 kg (7000 lbs.)
• Mature sharks : females are larger than males, estimated to bear young from 12 – 14 years old
• Young (called pups) : up to 14 pups, born live, 1.5 m (5 ft)
• Colouring : white underbelly, top is blue-grey
• Teeth : +-3000 teeth, triangular, serrated, razor-sharp, usually about 7.5cm (3 in) long, located in rows
• Longevity : unknown – estimated to be 100 years
• Killing technique : short powerful bursts, rips off chunks of meat
• Social grouping : Solitary, sometimes travel in pairs

Hunting

Great Whites usually hunt around kelp forests and reefs. While they do not consider humans as prey, they also hunt in the surf zone which make its interaction with humans very dangerous. Common attacks are on surfers (perhaps due to the similarity of the visual outline) or speargun-fishermen (the tremor of their kill usually attracts the shark). Most Great White attacks are however not fatal. It is believed that after the shark has ‘tasted’ its prey, it moves on (we apparently don’t taste so good).

Great Whites (like other elasmobranchs) use special sensory pits (ampullae of Lorenzini) to detect electromagnetic pulses. These sensory pits are concentrated on their snouts and along a lateral line that runs down the length of their body, which enables the shark to detect the size of an animal and whether it is injured or disorientated. When hunting fast prey, Great Whites also use their vision and smell. Their sense of taste is well-developed, while their touch and hearing senses are good, not great.

With the blue-grey top markings, Great Whites are well camouflaged when striking from below. They mainly feed on seals, tuna and other types of sharks / rays. Should a Great White come across a whale carcass, to get as much of the rich blubber, it would feed as long as possible. Their most spectacular hunting method is the newly-discovered “breaching”, where a shark “jumps clean out of the water”.

Breaching

The interesting thing about this form of “breach” hunting or predation by Great White sharks, is that it only recorded to occur around Seal Island in False Bay. It is thought that the main reason it occurs is that the sharks have adapted to this form of hunting as it produces the best returns. Remember, a seal can quite easily outmaneuver a shark, by twisting and turning and the only way the shark can guarantee itself a meal, with the least amount of effort, is through this ambush “breaching” action.

What happens is that Seal Island is surrounded by a deep channel, ranging from 20 metres wide to about 200 metres wide and when the seal packs return from their feeding excursions, the sharks lie in wait for them. When prey is identified, the shark hurtles out from the depths of this channel, hits its prey with its snout or jaw, stunning or disabling the seal, before consuming it. The force of this beast propelling itself upwards, sends it 2 to 3 metres into the air, out the water.

Seal Island is roughly the size of a football field, not suitable for human habitation, but home to about 15 000 seals, a large colony of cormorants, seagulls and also a few penguins. Up until the early seventies, the young seal pups were harvested for their skins, in so doing, keeping the seal population in check, but since then, the seal population has increased enormously. This in turn has attracted the Great White shark population back to False Bay.

As much as we welcome the return of the Great White shark population, it is a double edged sword, bringing much heartache to our community. About 10 months ago, a young 14 year old, living down the road from us, lost his leg to a Great White shark, while surfing at Muizenberg Beach and in November last year an elderly lady was attacked and her remains never found, while swimming less than 100 metres off Fish Hoek beach. We as a family are very keen watersport enthusiasts and have seen these sharks on a very regular basis, with a few very close shaves ourselves.” – Andy Rice, Cape Town, 25 March 2005

Breeding

Great White females give birth to 4-14 fully formed pups (aplacental viviparity) that are about 1.5 m (5 ft) long. Eggs are fertilized
and hatched within the female. Pups are nourished by eating unfertilized eggs and smaller siblings as there is no placenta. There is no maternal care-giving and the pups swim away immediately after birth.

It is believed that Great White females only bear their first young from the age of 12 to 14 years (or when they reach about 4 m, which could take 20 years). Young Great White sharks eat fish (including other rays and sharks), and then as they mature, they move onto mammals such as seals and sea lions.

Conservation

Great Whites are not protected all over the world yet, and are freely hunted / killed in some countries’ waters. The sharks are also utilised for wasteful shark fin soup. We strongly encourage tourists all over the world not to purchase any shark teeth, jaws or shark leather products.

Please check out the Sharklife website? They also offer shark training courses for scuba divers!

Let’s save our ocean’s top predator!