Killer whales are emptying one of South Africa’s top shark-diving destinations of great whites. According to a recent study, two orcas nicknamed Port and Starboard have slaughtered at least eight great white sharks in the last five years along the Gansbaai Coast. Researchers who examined the carcasses say the killer whales are ripping out the sharks’ livers and leaving the remains to drift up on nearby beaches.
As a result of the attacks, the great whites, which are typically at the top of the food chain, have largely abandoned the area. “What we seem to be witnessing is a large-scale avoidance strategy, mirroring what we see used by wild dogs in the Serengeti in Tanzania in response to increased lion presence,” says Alison Towner, the lead author of the study in a press release. “The more the orcas frequent these sites, the longer the great white sharks stay away.”
Gansbaai has been a popular destination for ecotourists who dive in shark cages to view great whites. Eight cage-diving outfitters give daily tours year-round, using chum and seal decoys to attract sharks. Researchers used shark and orca sightings from these boats and telemetry of tagged sharks to document how orcas hunted the sharks. They found that shark sightings dropped from nearly 7 per day before the attacks began to one per day after the first shark death. The detection of tagged sharks also dropped to zero, and telemetry data showed that the great whites fled in all directions, sometimes traveling hundreds of miles from Gansbaai within a few days of an attack and staying away for as long as six months.
Necropsies of the eviscerated sharks showed a single large tear across the pectoral girdle, indicating the orcas had ripped open the sharks by grasping them by their pectoral fins. The killer whales selectively removed the sharks’ livers, and sometimes other organs, including the heart and testicles. Shark livers, which are highly fatty and energy-rich, may account for up to one-third of a shark’s body weight. Targeting such nutrient-rich food sources is a common and rewarding strategy in the wild, the researchers note. Bears are known to feast on the lipid-rich roe and brain tissue of salmon, and wolves usually consume the internal organs of elk and deer immediately following a kill.