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Great white sharks are all bark and, well, maybe a little less bite than previously believed – at least when it comes to the ocean’s mafia.
According to new research published in Scientific Reports, white sharks off the coast of Northern California high-tail it whenever orcas show up. Even better? They’ve been documented avoiding that area for up to a year later.
"These are huge white sharks. Some are over 18 feet long (5.5 meters), and they usually rule the roost here," said scientist Scot Anderson in a statement, adding that his team has been observing some of these sharks for the last two decades.
Every September and December, white sharks migrate to the Farallon Islands to hunt young elephant seals for over a month at a time. Orcas, who also feed off the seals, only occasionally join the party. But as soon as they show up, white sharks leave the area within just a few minutes.
"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 Dr Salvador Jorgensen, a senior research scientist at Monterey Bay Aquarium and lead author of the study.
The findings challenge the idea that white sharks are the most voracious predators in the ocean, and shows us that even the giant hunters can become the hunted. When such events happen, the entire food web is impacted. In this case, elephant seal populations experience four to seven times fewer predation events when the sharks are gone.
Researchers analyzed four encounters between white sharks and orcas in the Greater Farallones National Marine Sanctuary off the coast of San Francisco, California. They also looked at data from 165 tagged white sharks between 2006 and 2013 and compared their migration patterns against field observations of orca sightings in the area compiled over 27 years. They found that even brief visits from killer whales made white sharks leave the area, disrupting their feeding patterns for an extended period of time. The sharks preferred to crowd together at other elephant seal colonies farther along the coast or head offshore rather than stay in the vicinity of orcas.
Interactions between apex such as these are important, albeit not well-documented.
"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."
Researchers say they aren’t sure if the orcas are targeting white sharks as prey (they’ve been known to do as much) or if they’re simply bullying competition to get after their preferred meal choice. Regardless, it adds insight into how feeding behaviors influence marine ecosystems.
"I think this demonstrates how food chains are not always linear," Jorgensen said. "So-called lateral interactions between top predators are fairly well known on land but are much harder to document in the ocean. And because this one happens so infrequently; it may take us a while longer to fully understand the dynamics."
