It seems that one of the most fear-inducing predators in the ocean may be afraid of its own.
A new study conducted by the Monterey Bay Aquarium and published on Tuesday in the journal Nature found that the great white sharks leave their favorite hunting ground when orcas, also known as killer whales, enter it. In fact, the researchers found that sharks will not return to these areas for about a year, even if the killer whales do not stay that long.
To arrive at this conclusion, the researchers "documented four encounters between the main predators on the Farallon Island of the Southeast in the National Sanctuary of the Farallones de Gran Francisco, California," according to the press release of the Monterey Bay Aquarium. the findings. Then, the scientists "badyzed the interactions using data from 165 white sharks tagged between 2006 and 2013, and compiled 27 years of surveys of seals, killer whales and sharks in the Farallones."
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More specifically, researchers determined when both sharks and killer whales were present in the Farallon Islands by comparing data from shark tags with the "field observations of orca sightings."
"This made it possible to demonstrate the result in the rare cases where the predators were found," according to the study.
The "robust data sources" helped scientists "show conclusively how white sharks clear the area when orcas appear," said Jim Tietz, co-author of the study, in an online statement.
The sharks fled the island when the orcas arrived, and did not return until the following season, in all the cases studied. The data from the electronic tags even showed that all the great white sharks left the area a few minutes after the orcas arrived. This was true even when killer whales were present for less than an hour.
"It turns out that 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."
– Salvador Jorgensen
"On average, we documented about 40 elephant seal predation events by white sharks in the southeast of Farallon Island each season," Monterey Bay aquarium scientist Scot Anderson said in a statement. "After the orcas appear, we do not see a single shark and there are no more deaths."
"These are huge white sharks, some are over 18 feet long and usually rule here," Anderson continued.
It is unclear exactly why sharks are leaving. The researchers suspect that it could be because the sharks are prey to the killer whales, or possibly because they are harbaded by food and eventually expelled.
Sharks that move out of the area had an indirect benefit for elephant seals, which are often the preferred food of sharks and killer whales, in the Farallones. The researchers found there were "four to seven times fewer predation events on elephant seals in the years that the white sharks were left," according to the study.
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"Normally we do not think about how fear and risk aversion could play a role in shaping the hunting of large predators and how that influences ocean ecosystems," added Salvador Jorgensen, lead author of the study. "It turns out that 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."
Jorgensen explained that the study is important because it is one of the few that "shows that food chains are not always linear", especially in the ocean. Interactions between predators are more difficult to document and badyze because of their infrequency.