Ever since the 1975 movie "Jaws," great white sharks have been considered the most fearsome predators in the ocean. But new research published this week shows that may not be the case.
When great whites hunting for seals near the Farallon Islands off San Francisco encountered killer whales, known as orcas, swimming by, they immediately fled, swimming long distances to get away, and didn't return until the following year, according to a study by researchers at the Monterey Bay Aquarium, Stanford University and Point Blue Conservation Science in Petaluma.
"After orcas show up, we don't see a single shark," said Scot Anderson, a white shark expert at the Monterey aquarium.
Great white sharks are amazing hunters. They can grow up to 20 feet long and weigh more than 4,000 pounds. But killer whales are even bigger, growing up to 30 feet long and weighing 10,000 pounds or more.
White sharks swim 35 miles an hour – faster than the world's fastest man, Jamaican sprinter Usain Bolt, can run. But killer whales swim just as fast, are stronger and hunt in groups, like wolf packs. And they have been documented, on occasion, eating white sharks, including in a famous 1997 incident that was filmed off the Farallon Islands. Two years ago, five dead white sharks washed up in South Africa, having been killed by orcas. The killer whales had eaten their livers.
"As amazing as it seems when you see a 17-foot shark swim by the boat, along comes a bigger predator, the orca," said Sal Jorgensen, a white shark expert at the Monterey aquarium, while sailing in a boat in a video from the Farallons that the aquarium posted Tuesday on its website. "It's pretty humbling to see."
Jorgensen was lead author of the paper, which was published in the journal Nature Scientific Reports on Tuesday.
From 2006 to 2013, he and other scientists from the aquarium and Stanford University tracked 165 great white sharks with high-tech acoustic tags between Southeast Farallon Island, Tomales Point in Marin County and Ano Nuevo Island in San Mateo County. They attached the tiny tracking tags using a 10-foot pole and a small titanium dart.
Jorgensen and Anderson compared the sharks' behavior to that recorded in 27 years of records compiled by researchers observing elephant seals, sea lions and killer whales at the Farallon Islands. The records were gathered by researchers at Point Blue Conservation Science, a non-profit group, and other organizations.
The study found that it was rare for killer whales to swim past the Farallons between September and December, when white sharks are there in large numbers every year to hunt seals. In fact, orcas were there only 18 days in the 27 years during those fall and winter months.
But when the two fearsome predators did overlap, the white sharks couldn't get away fast enough. The hunters became the hunted.
In the best-documented instance, killer whales from two separate pods arrived at the Farallons on Nov 2, 2009, when 17 previously tagged white sharks were present. The killer whales only spent two hours in the area. But the sharks bolted. Seven of them swam 50 miles south to Ano Nuevo Island, while others swam to Tomales Point, 35 miles north.
None of the sharks came back until the following year.
Similar examples of "abrupt and consistent flight" of white sharks happened in 2011 and 2013 when killer whales came to the Farallons, the researchers said.
The beneficiaries? Elephant seals and sea lions.
In a typical year, scientists observe about 40 elephant seals and sea lions being eaten by great whites near the Farallon Islands from September to December. But that number was reduced four to seven times in years when white sharks were fleeing orcas.
Although relationships between large predators on land have been studied for years, little is known about how large predators in the ocean interact. Scientists say the white sharks may well be fleeing out of fear they will be eaten. They might also be being bullied by the killer whales, who also eat seals and sea lions.
"We don't typically think about how fear and risk aversion might play a role in shaping where large predators hunt," Jorgensen said. "It turns out these risk effects are very strong even for large predators like white sharks – strong enough to redirect their hunting activity to less preferred, but safer areas."
More research is needed, he said.
Until then, the apex predator off the Pacific Coast isn't the monster in "Jaws," but the same species that for years performed tricks at Sea World and other marine parks: the orca.