The Farallon Islands sit 28 miles off the shores of San Francisco. There in 1997, biologists documented a natural drama for the first time: orcas killing and eating a great white shark. While it was a first for biologists, this was no extraordinary event: Orcas find great whites’ livers especially delicious. It is orcas, not the feared sharks, that are top of the marine food chain. And great whites know it.
Incredibly, the sharks plan accordingly. In April 2019, researchers discovered that when orcas arrive at the Farallon Islands, great white sharks flee, sometimes for as long as a year.
This is #15 on Inverse’s 20 most incredible stories about our planet from 2019.
Great white sharks typically hang out around the islands between September and December — prime hunting season for young elephant seals. To track the marine life’s movements, the researchers used 27 years-worth of surveys of seals, orcas, and sharks around these islands, as well as data from 165 sharks tagged between 2006 and 2013.
The sharks follow a particular pattern: When orcas are within two miles of the islands, the great whites leave their hunting grounds and move elsewhere. It’s unknown how often the orcas target the sharks as prey, but scientists do know that it’s often enough that the great whites decide sticking around just isn’t worth it.
While it’s not a great situation for the sharks, it’s a pretty good one for the elephant seals. In a year when when orcas don’t show up, an average of 40 elephant seals are eaten by sharks. But when orcas are on the scene, the number of seals killed by sharks dropped by 62 percent. Scientists worry that the drop signals a changing ocean ecosystem — but the elephant seals probably don’t mind.
As 2019 draws to a close, Inverse is revisiting the year’s 20 most incredible stories about our planet. Some are gross, some are fascinating, and others are truly incredible. This has been #15. Read the original article here.