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    Sea life: Great white sharks

    • 08 July 2011
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    Tony and I went to Gansbaai to meet some great white sharks late last month. There’s more about our day out here, but here are some of my underwater pictures from the day. They are not particularly amazing, partly because I’m more inclined to be prolific than brilliant when you put a camera in my hand, and partly because the conditions in the water were mixed.

    A 3 metre great white rising towards the bait

    A 3 metre great white rising towards the bait

    Though the water was very clean and blue, it was incredibly rough in the cage, and to be honest half the time I just wanted to look at the massive 4 metre creature cruising in front of me rather than fidget with my camera. But the sun came out, the water was crystal clear, and we had the most wonderful day (until we came home and found the house had flooded in our absence… Another story!).

    Most of the sharks appeared from below

    Most of the sharks appeared from below

    Great white sharks (Carcharodon carcharias) grow to up to about 6 metres in length, and can weight up to 2.5 tons. They are believed to live at least 30 years, and are incredibly mobile in the world’s oceans – a shark tagged in Gansbaai swam to Australia and back within about nine months. The shark was named Nicole.

    3.5 metre female

    3.5 metre female

    The Dyer Island great white shark population comprises mainly transient visitors who arrive and leave all year round, but is one of the world’s densest. They visit the area partly to feast on the 60,000 strong Cape fur seal population on Geyser Rock, and it is thought that they socialise or breed during the summer in the shallow waters of a nearby area close inshore.

    This distinctively scarred shark stayed with us for a while

    This distinctively scarred shark stayed with us for a while

    The sharks make full use of the water column, diving to up to 1,200 metres. Their typical hunting behaviour – rushing up from below to surprise prey – is well-known, and we noticed that most of the time we could see sharks below the cage in the deeper water, and that a lot of the animals approached the bait from below. The sharks in Gansbaai do not breach (jump clear out of the water), however, whereas this behaviour is common at Seal Island in False Bay.

    Rising from the depths

    Rising from the depths

    Males and females can be differentiated by the claspers that are present on the males’ underbellies. None of my National Geographic-quality pictures illustrate this and I’m too shy to elaborate, however, so you’ll have to hit Google hard if you want more information. Richard Ellis’s book, Great White Shark, is a good source of a lot of the information we currently have about great white sharks, even though it is slightly dated.

    Checking out the bait on the surface

    Checking out the bait on the surface

    Females mature at 4.5 to 5 metres in length and males are generally slightly smaller. We don’t usually get the absolutely huge females here – they seem to be more prevalent at the Farallon Islands off California. They have a complex social hierarchy, and we observed that when more than one shark was near the boat, they were reluctant to chase after the bait. Lacking protective membranes over their eyes, they roll their eyes back at the moment of attack, making them vulnerable.

    Swimming away from the bait

    Swimming away from the bait

    These creatures are astonishingly gifted in the sensory department, with excellent hearing, vision, sense of smell, and the ability – thanks in part to their ampullae of Lorenzini – to sense electrical currents and vibrations in the water column.

    What big teeth - a 4 metre visitor

    What big teeth - a 4 metre visitor

    They are thus superlative predators, thanks also in part to their capacity for keeping their body temperature above that of the surrounding water. This makes them smarter, faster and more awesome than most other fish. They have, like tuna, a rete mirabile – essentially a counter-current heat exchanger that uses blood flowing towards the gills (where it will cool down) to warm blood flowing back from the gills (that is already cool). In this way nothing is wasted.

    Seeing them in the flesh was completely head-spinningly wonderful to me. The ethics of baited shark diving do give me sleepless nights on occasion, and it’s something I’d like to explore in more detail, but – as Georgina Jones pointed out – anything that gets people to look at sharks as wonderful, powerful and magnificent creatures rather than flavouring for soup is surely a good thing.

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