Great white sharks are apex predators that live in the Cape waters. Listed as “vulnerable”on the International Union for Conservation of Nature’s red list, great whites are protected in South Africa, with anyone found to have killed, fished or harmed one facing a R50 000 fine and up to two years imprisonment. However, a new study by Stellenbosch University (SU) claims that their fight against extinction could be worse than previously estimated.
The study was conducted by Dr Sara Andreotti of the Department of Botany and Zoology at SU over a six year period in Gansbaai, which has the world’s highest concentration of sharks. Over 5 000 pictures of sharks’ dorsal fins were taken (each shark has a unique fin, with notches like a fingerprint) and a biopsy from the animals for genetic sampling was also taken. Using this, Andreotti estimated the population to be between 353 and 522 individuals, 52% lower than previous estimates. In a media release issued by SU on 16 July, Andreotti said, “When looking at the number of adults counted with the photo identification work, we have come to the conclusion that South Africa’s white sharks faced a rapid decline in the last generation and that their numbers might already be too low to ensure their survival. The chances for their survival are even worse than what we previously thought.”
“Between 1978 and 2008 approximately 1063 white sharks were killed in shark protection measures,” Andreotti says, claiming shark nets and baited hooks on the eastern seaboard of South Africa are to blame for the decreasing population. Illegal poaching, decreasing habitat, pollution, and depletion of their food source are also contributing factors. Andreotti warns of dire consequences if great whites become extinct, saying, “White sharks are top predators. They are much like lions. If you take top predators out of the environment, the rest of the environment will collapse.” The most obvious consequence will be an increase in the number of Cape fur seals, great white’s natural prey, which will have a direct impact on fish populations and fisheries.
Research partner and owner of Shark Diving Unlimited Michael Rutzen told News24, “Within three years, all the great white sharks off the shore of Gansbaai will be gone, mark my words.” Despite their infamy, there have only been 25 attacks by sharks on the Cape Peninsula since 1960.
Speaking to Perdeby, Dr Alison Kock, research manager at Sharkspotters, said that the greatest threats to great white sharks in South Africa are accidental catches by commercial fisheries, shark nets along the KZN coast, pollution, and loss of prey and habitats. Dr Kock explained that estimating the population of great white sharks is difficult, as sharks cannot be seen a lot of the time as they move around. She further explained that to overcome these challenges, scientists need to use complex methods and make assumptions when collecting, analysing, and interpreting the data. Different methods and assumptions can lead to different results.
When asked about the possibility of great white sharks becoming extinct in the Gansbaai area, Dr Kock referenced the study at SU and said that although the study was a genuine attempt to estimate the population, there is reason to believe that this contribution needs rigorous examination and testing with further work. She added, “This would not be the first time that estimates of population sizes of white sharks and other species have been disputed. It is a consequence of the difficult nature of such investigations.” Dr Kock explained that one of the assumptions made in the recent study was that the Gansbaai aggregation site represents the entire South African white shark population, and said, “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. Furthermore, the study has not provided evidence on the current trend of the population, whether it is decreasing, increasing or stable.”
When asked about what was being done to conserve the population of the sharks, Dr Kock said that white sharks are fully protected in South Africa but are still vulnerable to a number of threats. She explained that white sharks were not protected across their range, and said that regular reports were received of sharks killed for their meat, fins and jaws in Mozambique. Dr Kock explained that there was a need for greater conservation and management collaboration between South Africa and neighbouring countries and islands. She added that critical areas for feeding and reproduction could be better protected through considerations in marine spatial planning.
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