The waters of Cape Town, once a regular hang out for great white sharks, have fallen suspiciously quiet recently.
The City of Cape Town, working with the local Shark Spotter program, is reporting the “complete disappearance” of great white sharks from False Bay over the past 18 months, according to a statement given to IFLScience.
Between 2010 and 2016, researchers recorded an average of 205 great white shark sightings per year around False Bay, the 28-kilometer-wide (18-mile) basin on the southwest corner of South Africa near the city of Cape Town. By 2018, that figure had slipped to 50. This year, there hasn't been a single confirmed sighting yet.
“Shark Spotters have recorded a significant decline in white shark activity both along the inshore and at Seal Island over the past two years,” Shark Spotters, a Cape Town-based shark safety and research organization, said in a statement on Facebook.
If you’ve ever seen footage or photographs of a white shark emerging out of the water in a spectacular leap while hunting prey, there’s a high chance this was in False Bay. This behavior is unpredictable and difficult to study, but it's thought to be a learned behavior that's mainly performed in this South African bay.
Along with concerns for the great white sharks, there’s also fear about the potential knock-on effect this could have on the area’s ecosystem. As apex predators, they play a central role in managing the ecosystem by both controlling prey density and restricting smaller predators. The species are also a major pull for the local tourist economy.
So far, there is no clear explanation for the apparent disappearance, but there’s been plenty of speculation regarding a new group of orcas in town. After all, orcas are one of the few animals that can immediately move a great white shark out of its hunting grounds.
“While the exact reason for this is unclear, the arrival of a specific ecotype of Orca that predates on sharks appears to have had a significant effect on the distribution of white sharks in our area.”
When this decline in white sharks was first being talked about last year, some locals pointed to another suspect. Speaking to Yale Environment 360, Yale University’s environmental magazine, local shark researchers pinned the blame on overfishing. Long-line fishing in the area has been known to target smaller species of sharks that are a cornerstone of the great whites’ diet. They also suspected that the fisheries might be illegally hooking and killing young great whites. Alternatively, this loss of great whites in the area could be a symptom of climate change and wider environmental shifts.
“There could be some shift in the environment happening,” Meaghen McCord, founding director of the South African Shark Conservancy, told Yale Environment 360 in August 2018. “We’re just not sure, and with us being on the cusp of possible large climate-related shifts, few scientists are prepared to say anything conclusive just yet.”