The results of a study claiming there are only between 353 and 522 individual great white sharks left in South African waters, have raised eyebrows among researchers.
Dr Alison Kock, research manager at Shark Spotters, said that members of the White Shark Research Group, represented by several scientists working in all major aggregation sites in South Africa, would be combining their data collected from different sources to produce a population estimate which they believe would better reflect a national estimate.
Last week, Dr Sara Andreotti, the study’s author and a Stellenbosch University researcher, said her findings, which were published in the journal Marine Ecology Progress Series, were based on six years of fieldwork in Gainsaid.
Andreotti said the study was the first of its kind on white sharks, whose numbers might already be too low to ensure their survival.
But Kock said she believed that although the recent study was a genuine attempt to estimate the white shark population, there was reason to believe that this contribution needed rigorous examination and testing with further work.
Kock added that one of the assumptions made in the recent study was that the Gansbaai aggregation site represented the entire South African white shark population.
“However, we are not convinced that this is true. Overwhelming scientific evidence shows that white sharks are separated by size and sex during part of their lives and that not all white sharks visit Gansbaai. It is therefore possible that the recent estimate underestimates the total population size.”
Alison Towner, a marine biologist with the Dyer Island Conservation Trust, who has been tracking the sharks in Gansbaai since 2007, said the estimate seemed a bit low. Towner said that estimating shark numbers through photo ID had its challenges.
“We will know better when we put together our collaborative effort.”
A statement from Stellenbosch University said the analyses and interpretations of the study underwent rigorous testing.