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Predators' Playground

By Chris & Monique Fallows

 

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Great White Shark Breaching
Great White Shark, Carcharodon carcharias, breaches out of water to seize imitation seal towed as a lure, False Bay, South Africa Image #: 002881

Slowly the great fish turns, responding to the sound, which was imperceivable at first but now clearly audible. With long gracious sweeps of the crescent-shaped tail the huge spindle-like body moves effortlessly towards the source that has attracted it. From 20 metres below the surface the great white shark (Carcharodon carcharias) begins to angle itself upward toward the surface with ever-increasing thrusts of its huge tail. Now rapidly the source of the sound and vibration is becoming clearly visible, the shape and sound that 60 million years of evolution have taught it represents food and survival. The small, young of the year, Cape Fur Seal (Arctocephalus pusillus pusillus) porpoises along, unaware of the rapidly approaching danger only metres below. The huge shark, only a body length away, exerts every muscle to its full extent. Its eyes begin to roll back. The lower jaw starts to open, but where there should have been forceful contact there is only a glancing strike as the young seal bounces off the side of the cavernous jaw.

The little seal has caught a glimpse of the approaching shape that instinct has taught it to fear more than any other. Reacting in a split second it has made a desperate veer to the left. Both seal and super predator cartwheel two metres up into the air in a blur of motion and a cascade of water. Each strikes the water, with very different thoughts as to what the next 30 seconds holds for them. The great shark twists its massive form to once again try to line up on the hapless little seal that appeared to have been a sure meal only seconds before. The little seal, even at the tender age of six months, remains composed, keeping a watchful eye on the head of the shark. It is the mouth, filled with five rows of serrated teeth, that the seal must avoid if it is to survive. By tucking in behind the mouth and not allowing the shark enough room to line up head-on, the little seal now has a very good chance of surviving.

After several minutes of aerial & aquatic combat the great white shark turns away and banks deep, knowing that the energy required to catch the now-alert little seal will not be replaced by the meal itself. The little seal now rapidly porpoises for Seal Island where its companions lounge around unaware of the drama that has just transpired. As the seal climbs up the steep western side of the island to safety, a crimson trail marks its path. A crescent shaped slice on its flank is a grim reminder of its recent encounter.

This is the sort of event that makes Seal Island, False Bay, South Africa one of the most unique predatory battlegrounds on earth. Since beginning our observations of great white shark hunting behaviour at Seal Island in the mid nineties we have discovered much of what was previously believed about these masters of their realm is in fact far from reality. They are not, as was previously thought, solitary animals. With dozens of tagged sharks, we often see the same individuals together, suggesting some sort of social relations. Seal Island is 400m long and around 100m wide. At its highest point the island protrudes 11m above sea level. As far as the animals that live there are concerned, there is no place on earth other than Seal Island. And all are aware of the great white shark. Old broken shards of a wooden shack still litter the island. This shack was the home of the sealers and guano collectors that lived on the island up until the early 1980’s. Now up to 64000 cape fur seals dominate the island. Bulls weigh up to 400kg and establish harems during the November to December mating season. They defend their territories violently against rival bulls. Females and juveniles occupy the island for most of the year. Seals are very sociable animals and cavort around the island with one another, barking, coughing and sleeping. Females are protective mothers and vehemently defend their young from any possible threat. They do, however, have to feed. Three quarters of their diet consists of fish. To obtain it, they have to leave the safety of the island and pass through the Ring of Peril.

The Ring of Peril is a notorious area at the south end of the island where all the conditions for successful predation favour the great white shark. The seals must cross this area to get to the feeding grounds each day. It is an area where the island’s shelf drops off sharply, allowing great whites to go undetected until the final approach. The seals are aware of this and gather at an area we call the Launching Pad. They build up in numbers until a group numbering from 5 to 50 decides to leave. The first group to leave is almost always followed by a second and sometimes a third group. There is relative safety in numbers and the continual jostling for the safest position within the group creates confusion for any shark attempting to single out a particular individual. This is where the harsh reality of nature comes into play. The youngest seals are almost always unable to keep up with the group and are left behind, making them an attractive proposition to a hunting great white. Although it is the exception to the rule, we have on occasion observed the hunter blast through the middle of the departing group, causing seals to scatter in all directions. The great white has far more success when attacking a single seal.

African penguins (Spheniscus demersus) number around 100 on the island and are occasionally used for apparent target practice. We have seen great whites attack them on several occasions, sometimes even breaching on them, but only once have we observed a shark consume a penguin.

The ever-alert black-backed kelp gulls (Larus dominicanus vetula) have established a vantagepoint on a flat bed of rock that overlooks the Ring of Peril. We have named this area the Gallery. In the early morning the gulls wait at the Gallery for the explosion of water that heralds the great white shark hunting a seal. They immediately rush over, hovering expectantly for their share in the kill. More than 100 gulls at a time will compete violently for the scraps after the coup de grace. Often our first indications of a predation are these gulls. Their survival in winter depends on their reaction time in getting to a predation, as it is the first gull to the kill that reaps the greatest rewards. It is the subtleties of Seal Island, such as the birds in the gallery or the behaviour of the seals in their rafts on the launch pad that indicate the abundance of patrolling great whites.

It was these subtleties that we did not understand in mid-1996 when we first entered the spellbinding world that is Seal Island. What we found was to change our lives forever. Having seen the interest great whites showed towards surface-borne objects, we decided to tow a life jacket behind my little 3,5m inflatable (all I could afford as a student). The result was spectacular. A 2,5m great white took to the air with my life jacket firmly wedged between its jaws. So began our love affair with the flying great whites of Seal Island.

Today, five seasons down the track, our inflatable has been replaced by a sturdy high-powered research & photographic catamaran ideal for natural observation. To date we have seen 310 successful predations, and 336 attempted predations where the seals have managed to outwit their much larger adversary. This does however show the incredible success rate of the great white with 48 percent of all attempts ending in a successful hunt (compared with about 35% for lions, for example).

The sharks use the depth of water to camouflage themselves as they track along the bottom, then at the opportune time angle upward, constantly gaining speed until the point of contact. This often results in their massive bodies being launched several meters clear of the water in one of nature’s most spectacular displays of power. Some of the sharks we recognise by our colour-coded tags have shown themselves to be far more successful in this hunting strategy than others. A 3,0m shark named Black-White-Black, due to his tag colours, has been seen to make three kills in 10 days. On the other hand we have seen another shark make five attempts in a week, all culminating in failure.

Without fail the most exciting behaviour occurs when a great white actually misses with the initial strike and the David & Goliath battle begins. It is usually on the flat calm days or days when a light NW wind (the prevailing winter wind) gently ripples the surface that the seals are somehow able to detect the approaching sharks and defy death at the last moment. On such days the waters are usually clear, and any approaching sound or vibration is clearly heard and felt. Once the shark has missed, the seal does not, as expected, flee for the safety of the island, but rather it tries to get as close to the area behind the jaws as is possible. The shark’s objective is to once again line the seal up in front of its mouth. The chase can go on for several minutes with both shark and seal being airborne on up to six occasions. The longer the battle wages, the more it swings in the seal’s favour.

The fact that the seal may survive one attack does not mean it is safe. The commotion caused by a chase often attracts other great whites to the scene of the skirmish, and the seal is often faced with a fresh adversary after its initial pursuer has given up. We have had heart-wrenching moments where we have seen a small seal outwit two separate attackers and get really close to the island only to be snatched at the last moment by yet another ever-vigilant shark.

Over 80 percent of all predations occur on seals less than a year old. The reason is that these small seals often return to the island on their own, and behave in a carefree way within the Ring of Peril. These young seals also present the lowest risk for the great sharks, as they do not have the strength of the adult seals, which can easily inflict deep gashes or even potentially deadly eye gouges with their powerful claws and teeth. Prime seal-hunting season for great whites is between May - October when there are no migratory fish species in False Bay. This is due to offshore winds that chill the bay's waters, sending the fish up the east coast. They must hunt fur seals to survive. It is also during May & June that the fattened-up pups (with a high-energy yield) start making their first solo sorties to go feed, and thus make easy targets for the sharks.

It is this gladiatorial contest between predator and prey that keeps us transfixed. For over 120 days per year we sit and wait in the Ring of Peril, cameras poised, knowing that somewhere beneath us, the white sharks are also waiting for that single moment when a seal forgets the unwritten rules of survival. Outside of the May -Oct season at Seal Island, they cruise the ocean undetected, adding to the mystique that surrounds them, and leaving large pieces of the puzzle of their lives conspicuously absent.

The breaching behaviour at Seal Island is unique in terms of its intensity and regularity. At the other Great white hunting grounds around South Africa, the behaviour is vastly different. Mossel Bay, 400km to the East of Cape Town, also boasts a seal colony close to shore numbering in the region of 6000 seals. Great whites also breach in this area, but not nearly with the same regularity that they do at Seal Island. The sharks in this area swim very close to the very popular bathing beaches, yet there are very few incidents of harassment or attack. The sharks that we tag at Seal Island have been resighted at Mossel Bay, showing the distinctive East-West summer migration and the semi-nomadic behaviour of great whites.

Dyer Island is probably the best-known great white hunting ground in S.Africa, due to the huge exposure the multitude of commercial cage-diving operators have given the area. We worked at Dyer Island for 4 years before it became commercialised. Even in those times predation was never as intense as at Seal Island. Most of the area around Dyer Island is shallow. Thus the sharks are forced to hunt the seals on a horizontal plane and seldom breach. Dyer Island’s seal colony numbers in the region of 50000 animals, providing an abundance of food. Another site where great whites regularly occur in S.Africa is Struisbaai, which is 250km East of Cape Town. Although there is no seal colony, the area has large shoals of migratory summer fish moving around the bay. This is what the sharks come to feed on in the area in the summer months.