Great white sharks flee orcas, study finds

The great white shark may not be the main predator of the ocean, after all.

In a study published Tuesday in Nature, scientists discovered that white sharks not only fled killer whales when they arrived at a marine sanctuary near San Francisco, but were dumped until the following season.

"When they are faced with killer whales, white sharks will immediately leave their favorite hunting spot and will not return for another year, even if killer whales are just passing by," said Salvador Jorgensen, principal investigator at the 39, Monterey Bay Aquarium and lead author of the study.

A few minutes after the killer whales appeared to feed on elephant seals, researchers said white sharks were beginning to swim off or gather in other seal colonies further down the coast.

Some of the white sharks that usually dominate the sanctuary extend over 18 feet long, said scientist Scot Anderson of the Monterey Bay Aquarium.

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Researchers compared data from electronic tracking marks on sharks and field observations of killer whales. Researchers say predators often do not meet at the Grand Farallones National Marine Sanctuary, as killer whales visit the area only occasionally, while white sharks usually gather more than a month each fall.

The study found that elephants had also benefited from the interaction, undergoing four to seven times less attacks during years when the white shark had fled. The researchers studied 27 years of surveys on seals, killer whales and sharks in the region, as well as 165 white sharks tagged between 2006 and 2013.

"After the arrival of the killer whales, we do not see a single shark and there are more casualties," Anderson said.

The study was unable to determine if these orcs hunted white shark or harassed their competition, but Jorgensen explained that the study shows how interactions between major predators affect food chains.

The dynamics between marine predators is more difficult to observe than those on land, he added, noting that the relationship between killer whales and white sharks might take longer, as they meet so infrequently.

"In general, we do not think that fear and risk aversion can affect the hunting of large predators and its influence on ocean ecosystems," said Jorgensen. "It turns out that these risk effects are very important even for large predators such as white sharks – powerful enough to redirect their hunting activities to less desirable but safer areas."

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