Even one of the most formidable hunters of the ocean, the great white sharks, run away when killer whales are around.
A new study by the Monterey Bay Aquarium, in collaboration with partner institutions, found that the presence of killer whales forces great white sharks to leave hunting grounds. Moreover, great white sharks do not return to the area until the following year.
Whenever this happens, elephant seals, which are the common preys of both great white sharks and killer whales, benefit.
When The Hunter Becomes The Hunted
The team of researchers used electronic tags to monitor the movement and activity of about 165 great white sharks from 2006 to 2013. They also used 27 years worth of seal, orca, and shark surveys from the Southeast Farallon Island in the Greater Farallones National Marine Sanctuary off the coast of San Francisco, California.
"The research in this paper combines two really robust data sources," stated Jim Tietz, Farallon Program biologist and one of the authors of the study published in Scientific Reports. "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."
The electronic tags revealed that when killer whales showed up, the great white sharks immediately vacated the area. Some of them crowded together at other seal colonies while others swam offshore.
Moreover, even when the killer whales were just passing by, their presence is enough to spook the hunting great white sharks. The researchers reported that sometimes, the orcas are only present for less than an hour.
"These are huge white sharks. Some are over 18 feet long (5.5 meters), and they usually rule the roost here," added Monterey Bay Aquarium scientist Scot Anderson, who is also an author of the study.
Sea Elephants Reap The Benefits
Between September and December, great white sharks show up at the Farallones to hunt the elephant seals that live in the area. The predators spend more than a month at Southeast Farallon Island, waiting for their meals.
Killer whales also hunt elephant seals, but they only show up every once in a while.
The researchers said that on average, 40 elephant seals predation events by great white sharks are recorded at Southeast Farallon Island. However, when the orcas show up, the predation events drop significantly.
