1. Sep, 2017

The Great White: some myths and facts

The name Great White shark (Carcharodon Carcharias)  comes from their snow-white ventral bellies.  The dorsal sides of their bodies are usually gray, which makes  them to blend in perfectly with deeper  darker layers of the water. Great whites (GWs) live in almost all coastal and offshore waters which have water temperature between 12 and 24 °C. Greater concentrations are found in the USA  (Northeast and California; e.g. Farallon Islands), Japan, Oceania, Chile, the Eastern Mediterranean and South Africa (with the most dense populations around Dyer Island)

Picture of Great White taken at Isla Guadalupe

Anatomy and behavior The GW is a viviparous epipelagic  fish, observed mostly in the presence of colonies of fur seals (Arctocephalus), sea lions, cetaceans, other sharks, and large bony fish species. The injuries seen at the often scarred  bodies of females  are mating scars, but could also result from  bites from  their prey, like the powerful  elephant seal  (Mirounga angustirostris). Male great whites on  the average measure 3.4 to 4.0 m long, females 4.6 to 4.9 m According to J. E. Randall, the largest white shark reliably measured was a 5.94 m individual reported from Ledge Point, Western Australia in 1987.

GWs  have the typical torpedo-shape of the of mackerel sharks (Lemnidae) which, combined with their muscular tails, can propel them through the water at speeds of 24 kmph, or even brake the water surface when they attempt a vertical attack on  prey swimming at the surface. A breach is the result of a high speed approach to the surface with the resulting momentum taking the shark partially or completely clear of the water. It is a hunting technique employed by GWs whilst hunting seals. Because the behavior is unpredictable, it has been very hard to put on film or video. It was first photographed by Chris Fallows and Rob Lawrence who developed the technique of towing a slow-moving seal decoy to trick the sharks to breach. Between April and September, scientists may observe around 600 breaches. Most successful attemps occur in the early morning.

GWs are known to migrate over large distances in the ocean: According to a recent study, California great whites have migrated to an area between Baja California Peninsula and Hawaii known as the White Shark Café to spend at least 100 days before migrating back to Baja. A similar  study tracked a different great white shark (nicknamed Nicole)  from South Africa swimming to Australia's northwestern coast and back, a journey of 20,000 km in nine months (see also my earlier Blog).  The GW is one of only a few sharks known to regularly lift its head above the sea surface to gaze at other objects such as prey, also known  as spy-hopping

Reputation Many superlatives haven   been used to characterize the dangerous side of GWs: ‘magnificent monster’, ‘terrifying creature’, ‘razor sharp teeth, beady black eyes’, ‘the ocean’s deadliest predator lurking beneath the waves’, ‘ ready to  strike without warning‘. But the bloodthirsty reputation  of this magnificent shark can be largely ascribed to films and sensation documentaries. GW attacks are extremely rare, even when people swim in close proximity to them.  Still, GWs are  held responsible for the relatively large number of reported and identified fatal shark attacks on humans. One obvious factor that is likely to trigger an attack is the  blood and vibrations spread in the water by a fish speared in its territory. Another factor is that GWs, like some other predator sharks, exhibit a behavior called test biting. Basically, they are interested in spotting what looks  like a food source. An initial bump may be followed by a test  bite on a human,  after which the shark will probably  never return again. Fatalities from shark bites in fact are quite rare  and caused  by blood loss from an initial test bite. Sometimes an attack might occur in  shallow and  turbulent water of the surf, where the shark mistakes the silhouette of a paddling surfer for its natural prey, the seal. Fatalities almost never result from critical organ loss or from whole consumption.

Cage diving  There are currently three  major locations for divers to visit the GW from inside a cage. Cage diving is most common at sites  were whites are frequent, including the  northern Neptune Islands in South Australia, Guadalupe Island in Baja California and off Seal IslandFalse Bay in South Africa.  At Isla Guadalupe several live aboards can be lined up during the high season, forming an avenue of boats. Each with cages underneath and  a couple of divers inside, shivering in the cold water filled with chum. Here the chances of getting a good shot of a GW are pretty good, but too many boats in the area may spread out the sharks and restrict the chances of a successful close passing for the individual UW photographer. I must admit that my visit to the island a couple of years ago did not result in a high ranking  on my list of favorite shark sites.

Cage-free diving with GWs. Man inside, animal outside cage is a slogan  that would probably receive much approval from members of Animal Lib.  Personally I dislike observing wild animals from behind bars (this holds for two directions).  Ever since the moment that divers felt safe to go out in open water to meet sharks, boundaries have been pushed and now include predators that were formerly seen as highly dangerous, such as Tiger Sharks and Oceanic white tips. The GW however was always considered as a special case, a more ‘raw’ and unpredictable species never to be approached in open water. But is there any biologically plausible reason why the GW should be treated as a rare exception? Free diving with GWs means that  a diver leaves a cage or boat to meet or swim with the sharks in open water, sometimes only with a snorkel, fins and mask.Wisely, these GW events are not open for the public, but performed  by experienced divers in favorable sea conditions, with relaxed sharks that often are accustomed to the visiting divers. Baiting could help in diverting the sharks attention from diver to bait, like it does with other species. For example Mike_Rutzen, a south African living in Gansbaai has spent a lifetime with GWs and taken a long time watching them and getting used to their behavior.   He regards cage-free diving with  GWs as something special to be done on unique occasions: a combination of a perfect day, perfect weather and a perfect shark.

Man swimming among apex predators without direct danger of physical injury could help to expose myths created by movies like like Jaws. Perhaps commercial movies and documentaries built upon the sensation side would then loose a part of their profit.  But  they would also receive something else in return.  Namely the opportunity to highlight for the public  the attempts to observe and preserve miraculous creatures that lived for millions of years, but that are now  on the verge  of extinction.   

Links:

https://en.wikipedia.org/wiki/Guadalupe_Island

https://www.facebook.com/gwcsr/

https://en.wikipedia.org/wiki/Rodney_Fox

https://en.wikipedia.org/wiki/Great_white_shark

http://www.rodneyfox.com.au/