The great white shark might not be the ocean’s top predator, after all.
In research published in Nature, scientists found white sharks not only fled from killer whales when they arrived at a marine sanctuary near San Francisco, US, but cleared out until the next season.
“When confronted by orcas, white sharks will immediately vacate their preferred hunting ground and will not return for up to a year, even though the orcas are only passing through,” said Salvador Jorgensen, senior research scientist at Monterey Bay Aquarium and lead author of the study.
Minutes after orcas appeared to feed on elephant seals, researchers said white sharks began swimming offshore or crowding together at other seal colonies farther along the coast.
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Some of the white sharks that usually dominate the sanctuary stretch more than 18 feet long, said Monterey Bay Aquarium scientist Scot Anderson.
Researchers compared data from electronic tracking tags on sharks and field observations of orca sightings. The predators don’t often encounter each other at the Greater Farallones National Marine Sanctuary, researchers said, because orcas only visit the area occasionally while white sharks usually gather for more than a month each fall.
Elephant seals also benefited from the interaction, the study found, suffering four to seven times fewer attacks in the years white sharks fled. Researchers looked at 27 years of seal, orca, and shark surveys in the area in addition to 165 white sharks tagged between 2006 and 2013.
“After orcas show up, we don’t see a single shark and there are no more kills,” Anderson said.
The study did not conclude whether those orcas hunted white sharks or bullied their competition, but Jorgensen said the research shows how interactions between top predators affect food chains.
Dynamics between marine predators are harder to observe than those on land, he added, noting it may take longer to understand the relationship between orcas and white sharks because they meet so infrequently.
“We don’t typically think about how fear and risk aversion might play a role in shaping where large predators hunt and how that influences ocean ecosystems,” 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.”