The City of Cape Town, along with the Shark Spotting Programme, have for the past 18 months been monitoring the now complete disappearance of great white sharks from False Bay.
The Shark Spotters' applied research programme has been monitoring white shark activity and behavioural ecology in False Bay since 2004, the City said in a statement.
Between 2010 and 2016, spotters recorded an average of 205 great white shark sightings per year at their operating beaches during the spring and summer period.
However, in 2018 the total number of shark sightings recorded fell to only 50, and this year there has not been a single confirmed sighting by the spotters. Neither has the Shark Spotters applied research programme detected any of the tagged white sharks on their tracking receivers since 2017.
This pattern has been mirrored at Seal Island in the middle of False Bay. Shark activity at Seal Island, historically an important feeding ground for great whites during the winter period, has plummeted.
No sharks seen in 2019
The shark cage diving eco-tourism operators, who would normally witness multiple individual sharks visiting their vessels, and up to 30 seal predations daily, have not had a single white shark sighting at Seal Island in 2019.
Further supporting evidence of the absence of these large apex predators is the lack of any feeding or bite marks on the whale carcasses the City has removed from False Bay this year.
"To our knowledge the absence of great white sharks from False Bay has not been recorded or reported before," the statement read.
"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."
Great white sharks, through the eco-tourism and documentary filmmaking sectors, contribute significantly to Cape Town’s local economy.
Changes in ecosystem
"Despite the lack of great white shark activity our tourism operators have managed to view seven gill sharks. Gill sharks were previously not present at Seal Island, and this confirms that there are changes happening within our ecosystem."
Despite the disappearance of great white sharks from False Bay, the City will still continue with the Shark Spotting Programme at the very popular beaches of Fish Hoek, Clovelly, Kalk Bay, Muizenberg, Monwabisi and Caves at Kogel Bay.
The Fish Hoek shark exclusion barrier will also be deployed for the annual Spring Splash on September 1, over weekends, public holidays, and school holidays during October 2019, and April 2020; and daily from November 1 to March 31 next year, weather permitting.
Beachgoers are advised that certain seasonal spotting beaches will not have spotters during the 2019/20 summer season, namely Glencairn, The Hoek in Noordhoek and Danger Beach in St James.
"The City will review the situation in June 2020 and will adjust operations accordingly, pending the return of the great white sharks to False Bay."
"It is important that the City and Shark Spotters maintain an adaptive management approach to shark risk and that we use our resources responsibly. We have assessed all of the information at our disposal and we believe that a change in the spotters' operating locations is a responsible approach to the new situation," said the City's Mayoral Committee Member for Spatial Planning and Environment, Marian Nieuwoudt.
All of the spotters will remain part of the programme.
"We want to be flexible and adaptable. Thus, to ensure that there are no job losses as a result of this change, the individuals who are employed to do spotting at Glencairn, The Hoek and Danger Beach, will be redeployed within the Shark Spotters programme to enhance their environmental education and applied research programmes. They will also assist with important marine and coastal conservation activities in partnership with the City," said Nieuwoudt.
Not known whether sharks will return
The marine ecosystem is dynamic. It is uncertain at this point in time whether the great white sharks have left False Bay for good, or whether this reduced presence is only short-term. It is also true that the sharks may return at any time, and for the risk to increase accordingly, the City said.
"Residents and visitors should therefore remain vigilant and cautious when visiting beaches. The spotters still regularly observe other large shark species in the inshore area, such as bronze whaler sharks.
"While these do not pose as a significant threat to water users as white sharks, it is often hard to distinguish between the two species. Better to avoid being in close proximity to them, especially when prey is in the area. The great white sharks may also return at any time. We urge water users to behave responsibly and to adhere to Shark Spotters' warnings and to leave the ocean immediately when they hear the siren or are told to do so by a spotter or lifeguard," said Nieuwoudt.
The City and the Shark Spotters applied research programme will continue to monitor shark activity in False Bay and they remain hopeful that the absence of white sharks is a short-term cycle in a larger, long-term ecological pattern.
"The permanent loss of these charismatic and ecologically important apex predators could be potentially devastating for our local marine environment, Cape Town’s sense of place, and for our economy through the eco-tourism and documentary film-making sectors.
"We remain hopeful that the great whites will return to False Bay and will announce our first sighting when this happens," said Nieuwoudt.