SAN FRANCISCO, April 20 (Xinhua) -- A new study has found that even great white sharks, the powerful predators on top of the marine food chain, have something to fear -- namely orcas, often known as killer whales.
The study, conducted by researchers from Monterey Bay Aquarium and partner institutions, challenges the notion that great white sharks are the most formidable predators in the ocean.
"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, senior research scientist at Monterey Bay Aquarium and lead author of the study.
The researchers studied four encounters between the top predators at Southeast Farallon Island in the Greater Farallones National Marine Sanctuary off San Francisco, California. They also analyzed data from 165 white sharks tagged between 2006 and 2013 and 27 years of surveys on orcas, sharks and their prey, elephant seals.
Electronic tags showed all white sharks began vacating the area within minutes following brief visits from orcas, even when the orcas were only present for less than an hour, researchers said in a press release published earlier this week.
The tags also found the white sharks either crowded together at other elephant seal colonies farther along the coast or headed offshore, and they didn't return until the following hunting season.
"On average we document around 40 elephant seal predation events by white sharks at Southeast Farallon Island each season," said Scot Anderson, co-author of the study. "After orcas show up, we don't see a single shark and there are no more kills."
The researchers drew no conclusions about whether orcas are targeting white sharks as prey or are bullying the competition for the calorie-rich elephant seals.
"I think this demonstrates how food chains are not always linear," Jorgensen said.
