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In the 2010 science fiction thriller Repo Men, starring Jude Law and Forest Whitaker, artificial organs are fatally taken from individuals if they fail to make regular payments for their use. It’s a nightmare scenario, but one which thankfully hasn’t manifested in the real world.
In the animal kingdom, however, things are a little different, especially if you’re a great white shark in the coastal regions around South Africa. In 2017, two killer whales showed up in the region and promptly began hunting and killing great white sharks. Since then, eight carcasses have washed up on shore, and although that certainly only represents a fraction of their kills, all but one of them had their livers removed. Several were also missing hearts. Analysis of the wounds left on the sharks’ bodies indicates that they have all been killed by the same two animals.
While it is known that killer whales are capable of these sorts of attacks on other large animals, it is unusual that it’s happening so frequently and in such close proximity to the coast. That got scientists wondering about how this shifting dynamic might be impacting shark populations and the rest of the surrounding ocean ecosystem.
Alison Towner from the Department of Ichthyology and Fisheries Science at Rhodes University in Makhanda, South Africa, and colleagues, set to work studying the phenomenon. Their results were recently published in the African Journal of Marine Science.
“Shark-eating killer whales are quite rare. They are generally found more offshore, so it is quite uncommon to see them hunting large sharks so coastal in South Africa,” Towner told SYFY WIRE.
It’s unclear why the killer whales have made their way nearer to the shore, where they’re more frequently interacting with great whites. It’s possible they are responding to a decrease in prey species further afield, but the precise triggering event or events aren’t yet understood. Towner indicated that an updated review of killer whales is ongoing and should shed more light on what’s happening sometime later this year.
The notion that killer whales are attacking sharks and removing their organs might feel rather macabre, especially because we often think of non-human animals as being indiscriminate eaters. However, it actually makes a certain amount of sense, at least from the orca’s point of view.
“A white shark’s liver makes up to about a third of its body weight and is incredibly lipid rich. It’s very nutritious,” Towner said.
There’s some comfort in knowing that the organ removal and subsequent dumping of the bodies isn’t the result of an underwater vengeance scheme meant to send a message to the other sharks. However, even if that isn’t the killer whales’ intention, the sharks have received the message and they’re hightailing it to bluer aquatic pastures.
Using trackers and visual observations, scientists have kept tabs on 14 sharks since the arrival of the orcas in 2017. Those sharks have been seen fleeing the area when killer whales show up. What’s more, the more often the killer whales show up, the longer the sharks stay away. That might sound like a good thing for South African beachgoers and a pleasant change to anyone who’s ever seen Jaws, but it has the potential to throw a wrench in the entire food chain of the region.
“Killer whales are the wolves of the sea, avoiding them is smart on the white sharks’ part. Time will tell exactly what mechanisms the white sharks use, but I suspect the pure trauma of being attacked by more than one killer whale causes them and others to flee in panic. Extended absences may be driven by additional cues such as rotting carcasses or the lack of other sharks in the area,” Towner said.
Great whites might have a reputation as the terror of the deep, but they are an important part of maintaining balance in their wider environment. Their absence could have wide-ranging consequences on other species, and that’s something scientists are trying to get a handle on. The research is ongoing, and Towner indicated that their findings are being used to inform policy decisions in South Africa.
We never thought we’d be wishing for more great white sharks in the ocean, but for the benefit of the entire ecosystem, it might be best if it were a little less safe to go back into the water.