Something fishy is under way in the waters of False Bay at the southern tip of South Africa, one of the world's best-known locations for viewing and interacting with the fearsome great white sharks.
Until recently a significant colony of the predators was a permanent fixture in the large bay that lies off Cape Town's eastern coast, making it a key attraction in the Western Cape Province's €2.3-billion-a-year tourism industry.
Thousands of international tourists and scientists travel to False Bay annually to observe the massive sharks in their natural habitat: either from aboard boats, or for the more adventurous, from inside cages lowered into the sea.
A multimillion-euro research and documentary-making industry has even been established around the sharks, which are famed for leaping out of the water – an action known as “breaching” – in False Bay in pursuit of seals.
However, since January not one great white has been officially recorded in the bay, according to research programmes that monitor the animals’ movements and the area’s main cage-diving operators.
Between 2010 and 2016 an average of 205 white shark sightings were recorded per year at 14 False Bay beaches that the predators patrol between October and March, according to a statement released by the City of Cape Town at the end of August.
The number of sightings by the Shark Spotters’ applied research programme fell to 50 in 2018. However, “this year there has not been a single confirmed white shark sighting” by the spotters, said the municipality’s statement. The situation has not changed since then.
Feeding ground
The shark’s absence is also mirrored at Seal Island in the middle of False Bay, which is historically an important feeding ground for great whites during the winter period as it is home to a major fur seal colony.
The lack of sightings of the predator is not the only evidence of change: none of the 40 white sharks that have been electronically tagged for observation purposes in recent years have been detected via its tracking receiver since 2017.
No one is sure why a protected species that was estimated by scientists in 2012 to number between 300 and 500 in False Bay has vanished from the area, but different theories are being investigated.
Some scientists believe the arrival four years ago of a pod of orcas into the bay, which is 1,090km2 in size, is potentially a contributing factor to the great whites’ exodus. Until these killer whales arrived the great whites were the top of the local food chain. But shortly after the orcas moved in, the carcasses of large great whites and sevengill sharks began to wash up along the False Bay coast line.
According to Cape Town-based marine biologist Alison Kock, evidence gathered from the sharks during postmortems suggests the orcas had killed them. Bite marks showed the great whites were targeted for their livers, which the orcas ripped from their bodies before discarding the remains intact.
“There are substantial gaps in our understanding of killer whale behavioural ecology in South Africa,” Kock wrote in an article for the academic journal the Conversation in February, “but what’s evident is that the presence of these shark specialists could have profound and cascading impacts on the ecosystem”.
Livers
But not everyone believes that hundreds of great whites would flee to safer waters solely because of a few killer whales that have acquired a taste for their livers.
Some experts say that long-line fishing is contributing to the great white sharks’ disappearance, because even though the predator is protected in South African waters, its food sources are not. The commercial fishing technique is increasingly used in South Africa to catch soupfin and smooth-hound sharks, which make up a significant portion of the great whites’ diet.
There is no upper limited on the number of smaller shark species that licensed long-line fishing boats can remove from South African waters.
Starvation
Marine biologists suspect that overfishing has collapsed the stocks of the smaller shark species. This, in turn, may have led to the starvation of juvenile great whites and driven the adult animals elsewhere in search of a stable food supply.
Though the great white is the stuff of nightmares for many South Africans, the hope is their absence from False Bay is temporary. The sharks are highly migratory and often travel long distances before returning to their hunting grounds.
Indeed, the fear is that their long-term absence could be devastating for the local marine environment in ways scientists have yet to comprehend.
