Great white sharks have long been at the top of the food chain in parts of South Africa’s oceans. In their peak winter hunting months, around 1,000 great white sharks a day could be observed off the coast of the Western Cape province. But in 2017, great white shark carcasses began to wash up on beaches at Gansbaai, one of the main sites where the species usually gathered. Some were missing their livers. And the numbers of great white sharks in Gansbaai started to drop. In fact, they just vanished for up to a year at a time. What was the cause?
The culprits appear to be a pair of male killer whales, which researchers have named Port and Starboard, that arrived in the area. They have a signature way of tearing open their prey and they favour the nutrient-rich liver.
Though killer whales are known to hunt sharks far from shore elsewhere in the world, this was the first time the carcasses had washed up on a beach and become available for scientific study.
In today’s episode of Pasha, shark biologist and PhD candidate Alison Towner tells the unfolding story of the impact the killer whales are having on South Africa’s marine ecosystems. Great white sharks are fleeing to other parts of the coast and their absence affects other species like African penguins and Cape fur seals.
Photo “Great white shark” by Mogens Trolle, found on Shutterstock.
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