Marine Biologist Dr Sara Andreotti has called the disappearance of great white sharks off the False Bay Coast an extinction and says the signs of an imminent population collapse were already there in 2012.
Perspectives in the industry differ, however, and Sarah Waries, CEO of Shark Spotters, says not all the data is in yet and she believes that Orca in the bay which have been feeding on the sharks could be an influence.
Dwight Barnard, who runs an agency which puts people in touch with shark cage diving operators, said sharks are nomadic by nature and often move from one area to another.
Dr Andreotti,who has researched great white shark genetic diversity, says: “I would be so happy if I was proven wrong on this. I hope I am. But the sharks are not different groupings in different areas; they are one group which yes, does move around.
“In 2012 already they showed diminishing numbers and in-breeding; which did not herald a good genetic diversity,” she says.
This is important because if the majority of the group with similar genetic structure was susceptible to a certain disease or external factor, then it would cause the death of the majority of the group.
Dr Andreotti believes the reason for the diminished numbers is multi-faceted. Heavy metals in terms of pollution which are accumulated far more readily in large predators is one factor – but more specifically – over-fishing of the sharks’ food sources, climate change and poaching.
Another factor is antiquated shark nets. “In South Africa, the great white shark is protected, but its food sources are not,” she says.
These sharks do not eat only seals; they eat smaller sharks and fish, she said, and their prey is being over-fished or poached.
A report released by the City of Cape Town citing the complete absence of great white sharks along the False Bay says the cause for their disappearance is not known.
Dr Andreotti does not believe that two Orcas in the bay had wiped out an entire population of great white sharks.
Mr Barnard agrees that over-fishing and climate change do have an effect on the great whites. After a hiatus they usually return, he says. “Gaansbaai had a similar thing happen just over 18 months ago – and now the great whites are back there. They reappeared the beginning of this year.” Ms Waries also believes it may be too soon to call extinction, noting that great whites have just been seen in great numbers in Gaansbaai again in the past few weeks after a nearly two-year break in that area.
The Shark Spotters’ applied research programme has been monitoring white shark activity and behavioural ecology in False Bay since 2004. Between 2010 and 2016, spotters recorded an average of 205 white shark sightings each year at their operating beaches during spring and summer.
However, in 2018 the total number of shark sightings recorded fell to only 50, and this year there has not been a single confirmed white shark sighting by the spotters – nor have they detected any of the tagged white sharks on their tracking receivers since 2017.
Shark activity at Seal Island, historically an important feeding ground for white sharks during the winter period, has plummeted.
The City reported that shark cage diving and eco-tourism operators, who would normally see up to 30 seal predations daily, have not had a single white shark sighting at Seal Island this year. This is the first time that there have been no great white sharks recorded in the False Bay, says Marian Nieuwoudt, the City’s mayoral committee member for spatial planning and environment.
“Great white sharks are top apex predators and we do not know how their absence from False Bay would impact the ecosystem. Neither do we know the causes for their disappearance,” she says.
White sharks, through the eco-tourism and documentary film making sectors, contribute significantly to Cape Town’s local economy. Despite the disappearance of great white sharks from False Bay, the City will still continue with the Shark Spotting Programme at Fish Hoek, Clovelly, Kalk Bay and Muizenberg beaches. The Fish Hoek shark exclusion barrier will also be deployed over weekends, public holidays, and school holidays.
Beachgoers at Glencairn, The Hoek in Noordhoek and Danger Beach in St James will not have spotters during the 2019/20 summer season.
All of the spotters will remain part of the programme and spotters from the beaches that have the service withdrawn will be redeployed in other areas.
Ms Niewoudt says it is uncertain whether the great white sharks have left False Bay for good, or whether this reduced presence is only short-term.