Two orcas have been bloody wreaking havoc among white sharks on the South African coast. In response, Jaws’ ilk seem to have sought safer waters.

White sharks are undeniably impressive creatures. They can be 6 meters long and weigh up to 2500 kilograms – in other words: more than an average car. But ‘boss above boss’ also applies in the sea. Orcas can grow up to 9 meters long and weigh more than 6600 kilograms. And on the South African coast, two of these killer whales focused on the local white shark population. Then, marine biologist Alison Towner of Rhodes University in Makhanda and colleagues write in a new articlethe sharks chose the shark…hare toad.

Disemboweled bellies

Towner and her team conclude this based on several lines of research. First of all, in recent years, two specific orcas have been spotted near the town of Gansbaai: Port and Starboard (‘Port’ and ‘Starboard’), named after the direction in which their dorsal fin hangs.

In addition, five great white sharks washed ashore between February and June 2017. Four of them had their abdomens ripped open and the livers removed, the most energy-rich part of the animals. In addition, one shark was missing its heart and gonads. There was no trace of hooks or nets, so it seems that the killer whales were the culprits. And probably these five sharks were far from their only victims.

Finally, researchers supplied more than a hundred sharks with acoustic tags† small devices that emit ‘pings’. As a result, they were able to determine that the number of sharks tagged at Gansbaai decreased from three to eight per day to zero after the first attack. For the rest of 2017, the number fluctuated between zero and two. The number of white sharks spotted from boats showed the same trend. “These finding suggests that white sharks respond quickly to risk from a new predator,” the researchers said.

too sudden

Could there be something else going on? In theory yes: maybe the white sharks started migrating because the surface temperature of the water changed. Or they left because of fishing – either their own or their prey. But, Towner and colleagues write, the decline in white shark numbers off Gansbaai in early 2017 was actually too sudden for that.

You might then think: oh well, one large predator takes over from the other. How much difference could that make to the rest of marine life?

Well, quite a bit. After the white sharks left the region, the number of copper sharks – which are on the diet of white sharks – increased. The same may be the case with the local seal population. And that last one is bad news for the endangered black-footed penguin† “The effects of killer whales removing great white sharks are likely to be far-reaching,” Towner said in a statement press release†