Cape Town - The first direct evidence of orcas killing white sharks in South Africa has been captured by both a helicopter and drone pilot, and a paper published on Monday in The Ecological Society of America’s journal Ecology presents both sets of video footage, providing new evidence that orcas are capable of pursuing, capturing and incapacitating white sharks.
One predation event was filmed on a drone, but the researchers believe three other sharks may also have been killed.
While a clip of the drone footage was aired in June, this was only part of an hour-long hunt of multiple sharks, as revealed by the exclusive helicopter footage, and the new paper offers more extensive footage, along with data from tags, drone surveys and shark-tour boats showing that white sharks fled from the Mossel Bay region for several weeks.
Orcas have been observed preying on other shark species, but direct observation of predation on white sharks locally has been lacking – until now.
“This behaviour has never been witnessed in detail before, and certainly never from the air,” said lead author Alison Towner, PhD candidate at the Department of Ichthyology and Fisheries Science at Rhodes University, and SA senior shark scientist at Marine Dynamics Academy in Gansbaai.
Only two killer whales in South Africa have been previously linked to hunting white sharks, but have never been seen “in action”. Only one of those animals was observed in the new footage, along with four other killer whales. The authors believe the involvement of these four new whales suggests the behaviour may be spreading.
The study also gives new insights into sharks’ attempts to evade capture by orcas. On two occasions, orcas approached sharks closely and slowly, while the shark, instead of fleeing, stayed close to the orca, keeping it in view –a common strategy that seals and turtles use to evade sharks. However, orcas are social and hunt in groups, and the researchers believe these behaviours may render the circling strategy ineffective for white sharks.
“Killer whales are highly intelligent, social animals. Their group hunting methods make them incredibly effective predators,” said marine mammal specialist and study co-author, Dr Simon Elwen, director of Sea Search and a research associate at Stellenbosch University.
The study confirmed that one infamous killer whale, locally known as “Starboard”, was part of the pod and ate what was suspected to be a large piece of shark liver at the ocean surface.
The novel footage also revealed how another killer whale bit into a white shark at the region of the liver.
“I first saw Starboard in 2015 when he and his close-associated ‘Port’ were linked to killing seven gill sharks in False Bay. We saw them kill a bronze whaler [copper shark] in 2019 – but this is something else,” said David Hurwitz, a boat-based whale-watching operator from Simon’s Town Boat Company.
The new study also analysed drone and cage dive boat survey data before and after these predation events. White sharks were seen every day prior to the predation and multiple sharks were seen on the day of the predations. But only a single white shark was seen in the 45 days after the predations. “We first observed the flight responses of seven gills and white sharks to the presence of killer whales in False Bay in 2015 and 2017.
“The sharks ultimately abandoned former key habitats, which has had significant knock-on effects for the ecosystem and shark-related tourism,” said SA National Parks’ shark expert and marine biologist, Dr Alison Kock.
Previous studies show new behaviours spread among killer whales via cultural transmission. The authors say if more killer whales start hunting white sharks, the behaviour will have far wider impacts on shark populations.
Cape Times