A NEW STUDY HAS FOUND THAT WHEN KILLER WHALES ARRIVE IN A FEEDING GROUND, GREAT WHITES SHARKS CLEAR OUT. In a study of great white sharks and killer whales, It turns out that great whites, renowned as the oceans’ apex predators, have apex predators of their own in orcas, or killer whales.
Researchers at Monterrey Bay Aquarium and several partner organizations looked at patterns in the Greater Farallones National Marine Sanctuary off San Francisco, a consistent feeding ground for great whites preying on elephant seals.
ENTER ORCAS, EXIT GREAT WHITES
“When confronted by orcas, white sharks will immediately vacate their preferred hunting ground and will not return for up to a year, even though the orcas are only passing through,” said Dr. Salvador Jorgensen, senior research scientist at Monterrey Bay Aquarium and lead author of the study.
The great whites consistently gather at the Farallones each fall to feed on young elephant seals, generally spending a month in the region. Orcas passing through may also feed on the Farallones seals, but aren’t regulars there.
TAGS TELL THE TALE
Monterrey Bay Aquarium researchers have been tagging and tracking great whites frequenting the area for some years. Working with surveys by partner institutions, they correlated data on 165 whites tagged between 2006 and 2018 and 27 years’ worth of seal, orca and shark surveys in the region. Partners in the project included Point Blue Conservation Science, Stanford University and Montana State University. The study was published in the science journal Nature.
“The research in this paper combines two really robust data sources,” said Jim Tietz, co-author of the study and Farallon Program Biologist at Point Blue Conservation Science. “By supplementing the Aquarium’s new shark tagging data with Point Blue’s long-term monitoring of wildlife at the Farallon Islands National Wildlife Refuge, we were able to conclusively show how white sharks clear out of the area when the orcas show up.”
WINNERS: THE ELEPHANT SEALS
The researchers documented four encounters between the orcas and the whites. In every case the whites departed the area immediately and didn’t return until the following season.
Which was good news for the elephant seals, notes Monterrey Bay scientist Scot Anderson. “On average we document around 40 elephant seal predation events by white sharks at Southeast Farallon Island each season,” he said. “After orcas show up, we don’t see a single shark and there are no more kills.”
In fact, when killer whales came within a mile or so of the island, the number of seals killed by sharks dropped by 62 percent compared to previous years, Tietz noted.
Electronic tags showed all white sharks began vacating the area within minutes following brief visits from orcas. Sometimes the orcas were only present for less than an hour. The tags then found the white sharks either crowded together at other elephant seal colonies farther along the coast or headed offshore.
“These are huge white sharks. Some are over 18 feet long (5.5 meters), and they usually rule the roost here,” Anderson said. “We’ve been observing some of these sharks for the past 15 to 20 years — and a few of them even longer than that.”
KILLER WHALE TASTE BUDS, GREAT WHITE LIVERS
While killer whales predation on great whites is not commonly observed, it is clear that it occurs – and that it ends badly for the great whites, notes Ed Yong, a terrific science writer for The Atlantic magazine. Orcas particularly are fond of shark livers, which in a great white can account for up a quarter of its body weight and is rich in fats and oils.
While no one has observed them doing so, it appears that the orcas bite their victims near their pectoral fins and squeeze the liver out through their wounds, Yong notes. Great whites may be power predators, but the ability to hunt in groups and communicate with each other give orcas an advantage, he suggests.
PRINCIPAL SOURCES: “Killer whales redistribute white shark foraging pressure on seals,” Nature; “Study Finds White Sharks Flee Feeding Areas When Orcas Present,” Monterrey Bay Aquarium News Office; “Killer whale presence leads to white shark desertion of Farallon Island feeding grounds,” Point Blue Conservation Science; The Predator That Makes Great White Sharks Flee in Fear,” The Atlantic.