When faced with a killer whale, it seems even Jaws might take pause for thought — as new research reveals great white sharks beat a hasty retreat if orcas are around.
What happens when top-level predators meet on land is well documented, but little is known about similar interactions in our oceans.
To find out, a US research team led from the Monterey Bay Aquarium searched for encounters between great whites — among the most ferocious of all sharks — and orcas (killer whales), in electronic tagging and observational data.
In every case where the two predators came into contact, the sharks actually turned tail and fled from the killer whales, researchers found.
Sporadic reports of orcas attacking great whites have been recorded, but this is the first evidence of sharks actively avoiding the whales.
Elephant seals may be the real winner of the battle of the predators as the exodus of sharks means more of their young pups survive.
Predator on predator encounters — dubbed 'lateral interactions' — are well known on land, but how they play out in the ocean is poorly understood.
To investigate, a research team led by Monterey Bay Aquarium's Salvador Jorgensen, set about to see what happens in the rare cases when sharks and orcas end up occupying the same waters.
They focused their study on the seas around Southeast Farallon Island, which lies off of the coast of San Francisco.
The team cross-referenced data from electronic shark tags with field observations of orca sightings.
The shark data included 165 of the predators that had been tagged between 2006 and 2013.
The monitoring data from the Farallon Islands went back further — spanning 27 years — and included surveys of local orca, seal and shark numbers.
'The research in this paper combines two really robust data sources,' commented paper co-author Jim Tietz, who is a biologist from Point Blue Conservation Science.
'By supplementing the Aquarium's new shark tagging data with Point Blue's long-term monitoring of wildlife at the Farallon Islands National Wildlife Refuge, we were able to conclusively show how white sharks clear out of the area when the orcas show up.'
In total, the researchers report four different encounters between the two top-tier predators around the Southeast Farallon Island during the study period.
'When confronted by orcas, white sharks will immediately vacate their preferred hunting ground and will not return for up to a year,' said Dr Jorgensen.
This happens, he added, 'even though the orcas are only passing through,'
It is not presently clear whether the killer whales are actively targeting white sharks, or if they simply present unwanted competition for the calorie-rich elephant seals.
Data from the electronic tags revealed that the sharks fled the area within just minutes of the orcas turning up.
'These are huge white sharks. Some are over 18 feet long (5.5 metres), and they usually rule the roost here,' Anderson said.
'We've been observing some of these sharks for the past 15 to 20 years — and a few of them even longer than that.'
Having been displaced by the arrival of killer whales, the sharks could be found either farther down the coastline, targeting different elephant seal colonies, or headed offshore, the researchers said.
Although the sharks may be unexpectedly turning tail from the orcas, other animals are profiting from the predators being scared off.
White sharks typically gather at the Farallon Islands between September and December each year in order to prey on young elephant seals.
The shark usually spend a month circling around the Southeast Farallon Island on the hunt for seals.
'On average we document around 40 elephant seal predation events by white sharks at Southeast Farallon Island each season,' Anderson said.
However, after the orcas show up, he added, 'we don't see a single shark and there are no more kills.'
As a result, the data shows that there were 4–7 times fewer elephant seals murdered by sharks in the years that the orcas turned up.
Although transient orcas have also been known to prey on elephant seals, they only show up at the island on rare occasions.
The results of the study highlight the importance of considering the interactions between such top marine predators as sharks and orcas, say the researchers.
Even the orca–shark interactions in the new study happen relatively infrequently — so it may take a while for the dynamics to be fully understood, Dr Jorgensen notes.
'I think this demonstrates how food chains are not always linear,' he said.
'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.'
'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,' he concluded.
The full findings of the study were published in the journal Scientific Reports.