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Since the movie "Jaws" of 1975, great white sharks are considered the most formidable predators of the ocean. But new research released Tuesday shows that this may not be the case.
When large seal whiters near the Farallon Islands, off San Francisco, encountered killer whales, known as orcas, swimming nearby, they immediately fled, swimming long distances to distance themselves and were that year, according to a study by researchers from the Monterey Bay Aquarium, Stanford University and Point Blue Conservation Science in Petaluma.
"Once the killer whales show up, we do not see a single shark anymore," said Scot Anderson, expert on white sharks at the Monterey Aquarium.
The great white sharks are extraordinary hunters. They can reach 20 feet long and weigh more than 4,000 pounds. But killer whales are even bigger, up to 30 feet long and weighing 10,000 pounds or more.
White Sharks swim 35 miles an hour – faster than the fastest man in the world, Jamaican sprinter Usain Bolt, can not run. But killer whales swim just as fast, are stronger and hunt in groups, like packs of wolves. And they have been documented, on occasion, eating white sharks, including during a famous incident of 1997 that was filmed off the Farallon Islands. Two years ago, five dead white sharks failed in South Africa after being killed by killer whales. The killer whales had eaten their liver.
"As incredible as it may sound, you will see a shark over 17 feet swimming near the boat, accompanied by a larger predator, the killer whale," said Sal Jorgensen, white shark expert at Monterey Aquarium, while he was sailing in a video boat. Farallons that the aquarium has published Tuesday on its website. "It's pretty humbling to see."
Jorgensen was the main author of the article, which was published in the journal Nature Scientific Reports.
From 2006 to 2013, along with other scientists from the aquarium and Stanford University, he followed 165 great white sharks with hi-tech acoustic tags between Southeast Farallon Island, Tomales Point in Marin County and Año Nuevo Island in San Mateo County. They fixed the tiny tracking tags with the help of a 10-foot pole and a small titanium dart.
Jorgensen and Anderson compared the behavior of sharks to that recorded over 27 years of data compilation by researchers who sighted elephant seals, sea lions and killer whales in the Farallon Islands. The files were collected by researchers at Point Blue Conservation Science, a non-profit group, and other organizations.
The study revealed that it was rare for killer whales to swim in front of the Farallons between September and December, while white sharks are numerous each year to hunt seals. In fact, the killer whales were there only 18 days in the 27 years of autumn and winter.
But when the two formidable predators overlap, white sharks can not escape quickly enough. Hunters have become hunted.
In the best documented case, killer whales from two distinct groups arrived at the Farallons on November 2, 2009, while 17 previously tagged white sharks were present. The killer whales only spent two hours in the area. But the sharks have taken off. Seven of them swam 50 miles south of Año Nuevo Island, while others swam to Tomales Point, 35 miles to the north.
None of the sharks returned before the following year.
Similar examples of "steep and consistent escape" from white sharks occurred in 2011 and 2013 when killer whales arrived in the Farallons, the researchers said.
Beneficiaries? Elephant seals and sea lions.
In a typical year, scientists observe about 40 elephant seals and sea lions eaten by large whites near the Farallon Islands from September to December. But this number has been reduced four to seven times in years when white sharks were fleeing killer whales.
Although relationships between large terrestrial predators have been studied for years, little is known about the interactions between large ocean predators. Scientists say that white sharks might well run away, fearing to be eaten. They could also be bullied by killer whales, who also eat seals and sea lions.
"We generally do not think how fear and risk aversion could play a role in hunting large predators," said Jorgensen. "It turns out that these risk effects are very important even for large predators such as the white shark – powerful enough to redirect their hunting activities to less preferred but safer areas."
More research is needed, he said.
Until then, the predator at the top of the Pacific coast is not the monster of "Jaws", but the same species that for years has played tricks at Sea World and other marine parks: orca.
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