The number of great white sharks could be vastly exaggerated and they may be in more danger than anticipated, a recent study has shown.
The global population of great white sharks is estimated to be between 3 000 and 5 000, but the study done by marine biologists from the Dyer Island Conservation Trust, in the Western Cape, found that the number could be less.
Shark conservationists believe researchers now need to work together to establish a global conservation strategy to save the population.
Great white sharks are listed as a species “vulnerable to extinction in the wild” by the International Union for the Conservation of Nature.
A team of marine biologists of the Dyer Island Conservation Trust worked with the shark cage-diving company Marine Dynamics shark tours.
The tour company is based in Gansbaai, the area with the biggest population of great white sharks in the world.
In the study, which was published in an online journal on Thursday, researchers collected more than 20 000 photographs of great white shark dorsal fins between 2007 and 2012.
Because each shark has a unique dorsal fin, researchers were able to adapt a computerised fin recognition program to accurately identify individual sharks.
In the findings, which took three years to complete, only 532 individual sharks were identified.
“The team used open population statistics to extrapolate their findings in order to estimate the number in this densely populated area is most likely less than 1 000 individuals,” it read.
Alison Towner, one of the researchers, said the results came as a surprise to them.
“Previously unpublished but widely accepted estimates based on non-computerised photographic studies predicted the population was twice the number,” she said.
Towner said the trust believed that South Africa had a responsibility to take the lead in urgent, scientific re-evaluation of the threat to great white sharks.
Alison Kock, Shark Spotters’ research manager, said the results of the study were a good baseline to start improving population management strategies.
“The results are exciting and it’s good to see estimated figures on the (shark) population in South Africa. We have more great whites than other areas, so we also have the responsibility to ensure their conservation.
“Now that we know our sharks go outside our borders, there need to be combined efforts with neighbouring countries,” she said.
Kock said researchers from across the globe needed to collaborate to establish the cause of the fall in shark numbers.
“We have seen fewer sharks on the coast and the big question is, ‘why?’.
“The only way we are going to answer that is if the scientists and researchers work together and establish a global conservation strategy,” she said.
Alan Boyd, of the Department of Environmental Affairs’s coastal and biodiversity conservation branch, said while he was aware of the study, he couldn’t comment on the findings until they had thoroughly examined the data.
“We welcome any new study, but we also have to consider the others still in progress. Our team is examining how the researchers arrived at their findings,” he said.