Predatory orcas hunting great whites off the coast of South Africa have perplexed scientists for a number of years now.
It is believed these killer whales, who hunt them for their lipid rich livers, are partly to blame for the disappearance of SA's Great White population. Now it seems they’ve turned to Copper sharks (also known as the bronze whalers or bronzies) to satisfy their tastes.
A three-meter long copper shark was retrieved from Grotto Beach in Hermanus on the morning of 5 February by the Dyer Island Conservation Trust/Marine Dynamics research team. The researchers have since detailed how the female shark was torn open at the torso with its liver and heart completely removed.
And it is believed two killer whales known as Port and Starboard are responsible.
This Orca pair have “predated on both Sevengill and White shark species in this manner off the Western Cape” - were spotted just a day before, about 100km West of Hermanus where the bronzie washed up in False Bay. This is the first copper shark carcass to be linked to them.
PICS: Where are SA's great white sharks? Right here, says Marine Dynamics
“The pair are known to specifically tear open their shark prey to extract the large lipid rich liver, and discard the body. Their story has gone round the world and generated much interest the last three years.”
The DICT team conducted the necropsy on the copper shark and confirmed “it was very likely the result of Orca predation, as the injuries were identical to other shark species predated on by them. There were also raker marks (tooth impressions) of killer whales on the carcass”.
So what’s causing these orcas to do this. Food pressure due to long-liners is also being considered.
Marine Dynamics owner Wilfred Chivell has previously shared with Traveller24 how shark cage diving is the only crucial monitoring platform of white sharks in South Africa.
“Whilst this species is protected in our waters it is facing many threats, that includes natural predators such as a pair of orcas specialising in hunting sharks for their livers, and human threats of industrial fisheries, pollution and environmental pressures, as well as illegal fishing,”
The predatory orca behaviour is being observed more frequently in SA, causing ripple effects in certain shark species distributions, as well as potentially influencing the ecology of western cape coastal areas, as a consequence of sharks evading their traditional aggregation sites for extended time periods, according to DICT.
In another incident, two killer whales were spotted in Knysna, circling a great white shark. In an extraordinary video captured by tour guide Donavan Smith, the great white is seen trapped by the two orcas.
Smith describes the behaviour as typical hunting behaviour. Marine Dynamics has however confirmed that the whales in this video are not Port and Starboard.
WATCH | Orcas attack great white off the coast of Knysna
And while scarce over the past couple of months, Great whites are still spotted within the Gansbaai shark alley region.
It’s just not as predictable, with a sighting confirmed just last week by the Marine Dynamics team.
Shark biologist, Alison Towner says “Our team was involved in the research and monitoring of white shark behaviour pre and post orca presence in the Gansbaai area, as well as the necropsies on the white sharks that washed up over two years ago - we have a study being published on these results. When dealing with transient marine predators many facts must be considered.
"White sharks are highly migratory animals spending an average of a few weeks in any one area. We know that they respond to a natural predator and our observations support similar distribution shifts seen in California and Australia. However, many other factors influence their distribution, and we believe it is a combination of pressures leading to the shifts we are seeing in South Africa."
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