It’s a great white shock

Cape Town 20-07-09 - Shark Cage Diving with the shark spotters - A two and a half meter Great White breaches off Seal Island Picture Brenton Geach

Cape Town 20-07-09 - Shark Cage Diving with the shark spotters - A two and a half meter Great White breaches off Seal Island Picture Brenton Geach

Published Jun 14, 2013

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Cape Town - The great white shark population has not made a marked recovery since being formally protected in 1981 and additional international conservation measures are vital if this globally threatened species is to be protected in the long term.

This is the major conclusion of a five-year population study conducted by marine biologists at Gansbaai, an internationally recognised aggregation site of the great white shark.

The study, reported this week in the peer-reviewed, open-access journal Plos One, involved identifying individual sharks from the unique markings on their dorsal fins and then analysing these with the aid of a special computer program.

During 1 647 trips on a shark-cage diving vessel involving more than 4 000 hours’ sampling, the researchers from the Dyer Island Conservation Trust managed to obtain 1 683 images of acceptable quality of dorsal fins.

They applied special dorsal fin identification software, which traces the fin and assigns a fixed spacing of points along its leading and trailing edges, and then compared this to their catalogue. This allowed them to positively identify 532 individual sharks.

Then, using another program designed to estimate population levels with a 95 percent confidence, they concluded that the southern African “super-population” of great white sharks that move between the Cape, KwaZulu-Natal and Mozambican waters and even venture as far as the west coast of Australia, was just 908 individuals.

Although this is a much larger population estimate than those in other known aggregation areas of this species elsewhere in the world such as Guadalupe Island (off the west coast of Mexico) and California, it is only half as big as expected.

“These results came as a surprise to everyone, as previously unpublished but widely accepted estimates based on non-computerised photographic studies predicted the population was twice this number,” lead author Alison Towner commented.

Their study concluded: “Despite this species being protected since 1981, such a low (population) estimate and lack of recovery suggests the southern African white shark is not receiving adequate protection for population growth. These results highlight the need for effective protective measures within the entire home range.”

Conservation trust founder chairman Wilfred Chivell said the study had, for the first time, produced scientific evidence that the threat to great white sharks was greater than previously thought, and that the government needed to act urgently in international conservation forums.

“It’s time for South Africa to take the initiative because time is clearly not on the side of the great white shark.” - Cape Argus

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