Jaws is afraid of Free Willy.
A new study published in Nature this week demonstrated that when pods of orcas entered an area around South Farallon Island off the coast of San Francisco, the great white sharks in the area cleared out - and didn't return for months.
No ocean predator is more fearsome in the public imagination than the great white shark, but even they appear to steer clear of orcas, highly intelligent pack hunters that have been observed on rare occasions to attack great whites - and eat their livers.
"On one occasion, we had 17 sharks that we were tracking simultaneously at the island when a group of orcas showed up," said Salvador Jorgensen of the Monterey Bay Aquarium, who led the study that involved Stanford University and Point Blue Conservation Science.
Advertisement
Advertise with NZME."We were able to see from the data all the sharks leaving the side of the island the orcas had arrived on," he said, "and within a few hours had vacated the island completely."
The findings are the result of 27 years of research, but Jorgensen suspected the two predators had been doing this dance for a while.
Scientists tagged 165 great white sharks between 2006 and 2013, luring them to boats with seal decoys made out of everyday carpet before affixing them with beacons that sent codes to sensors throughout their territory. This way, scientists could track their movements. Point Blue Conservation Science surveyed orca activity around Southeast Farallon Island, helping the team understand how the orcas and sharks interacted.
"There's some irony to the fact that one of the key cards that this predator has is its ability to know when to fold and run," Jorgensen said of the sharks. "We don't always think of a white shark as deciding to flee, but this may be a key aspect of its behaviour that may have led to the success of last several million years."
The real winner in this ecological dance of predators, however, might be the prey. Great white sharks congregate around Southeast Farallon Island when the juvenile elephant seal population is abundant and are most likely to overlap with orcas there in the late fall or early winter. Although orcas pass through only briefly, great white sharks vacate for an extended period, leaving the seal population in peace.
