Cape Town - The disappearance of great white sharks along South Africa’s shores has been a controversial topic, with many speculating that they were being hunted by orcas, causing them to abandon former key habitats which has had knock-on effects for the ecosystem and shark-related tourism.
New direct evidence has been captured by a helicopter and drone pilot on video, and published showing killer whales, orcas, pursuing, capturing and incapacitating great white sharks locally for the first time. The researchers fear that if this continues it will have far wider impacts on ocean ecosystems and shark populations, which already face a lot of pressure.
Previous studies indicated that when killer whales were observed in an area, great white sharks often left the scene and would not return for months, illustrating a flight response in the apex predator when faced with a new, stronger apex predator – the orca.
The paper, published in the Ecological Society of America’s journal, Ecology, details direct observations on the predation of hunting strategies used by killer whales to capture and kill great white sharks, and the subsequent behavioural impact on surviving great whites in the area.
Lead author and a shark scientist at Rhodes University, Alison Towner, said at least two, possibly three great white sharks were killed by a group of killer whales on May 16 in Mossel Bay in 71 minutes. This was filmed by author Christiaan Stopforth, a hobbyist drone pilot using a private drone which observed the five killer whales for about 40 minutes.
This was aired in June, although more of the incident was captured by chopper pilot Duddly Archer from Mossel Bay. Towner said the evidence showed that great white sharks fled the area immediately and remained away for at least seven weeks.
Only two killer whales in South Africa, Starboard and Port, have been previously linked to hunting great whites. Only one of them was observed in the new footage, with four other killer whales. The authors believe the involvement of these four new whales suggests the behaviour may be spreading.
SANParks shark expert Alison Kock said. “We first observed the flight responses of seven gills and white sharks to the presence of killer whales Port and Starboard in False Bay in 2015 and 2017.
“The sharks abandoned former key habitats, which has had knock-on effects for the ecosystem and shark-related tourism.”
kristin.engel@inl.co.za
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