Study shows white sharks are fleeing to feeding areas in the presence of orcas

New research from the Monterey Bay Aquarium and partner institutions published today in Nature Scientific reports calls into question the notion that great white sharks are the most formidable predators in the ocean. The study "Killer whales redistribute the pressure of white shark research on seals" shows how the big white hunter becomes hunted, and the elephant seal, common prey of sharks and orcas, appears to be winning.

"When they are faced with killer whales, white sharks will immediately leave their favorite hunting spot and will not return for another year, even if killer whales are just passing by," said Dr. Salvador Jorgensen, senior researcher at the Monterey Bay Aquarium. author of the study.

The research team, which included Scot Anderson scientist from the Monterey Bay Aquarium and Monterey Bay, and research partners from Stanford University, Point Blue Conservation Science and the Montana State University, have documented four encounters between the main predators of Southeast Farallon Island in the Grand Farallones National Marine Sanctuary, off San Francisco, California. Scientists analyzed the interactions using data from 165 white sharks tagged between 2006 and 2013 and compiled 27 years of records of seals, killer whales and sharks at Farallones.

"The research in this article combines two very robust data sources," said Jim Tietz, study co-author and Farallon Program biologist at Point Blue Conservation Science. "By supplementing the Aquarium's new shark tagging data with long-term wildlife monitoring in the Farallon Islands National Wildlife Area by Point Blue, we were able to conclusively show how white sharks are pulling out of the water." the area when the orcas show up. "

In all the cases examined by the researchers, white sharks fled the island when the orcs arrived and did not return until the following season.

Elephant colonies in the Farallones also indirectly benefited from the interactions. The data revealed four to seven times less predation events on elephant seals over the years than white sharks have left.

"On average, we document about 40 elephant predation events by white sharks in southeastern Farallon Island each season," Anderson said. "After the killer whales have come out, we do not see a single shark anymore and there are no more victims."

Each fall, between September and December, white sharks gather at Farallones to hunt young elephant seals. They usually spend more than a month going around the southeast of Farallon Island. Transient killer whales also feed on elephant seals, but only occur occasionally on the island.

To determine when killer whales and sharks co-occurred in the area, the researchers compared shark tag data with field observations of killer whale sightings. This allowed to demonstrate the result on the rare cases where predators met.

The electronic tags showed that all white sharks began leaving the area a few minutes after brief orc visits. Sometimes killer whales were present for less than an hour. The tags then revealed that white sharks were piling up in other seal elephant colonies further down the coast or heading off.

"They are huge white sharks, some are over 5 meters long and they usually do the law here," Anderson said. "We have been watching some of these sharks for 15 or 20 years, and some even longer than that."

The results of the study highlight the importance of interactions between major predators, which are not well documented in the ocean.

"In general, we do not think that fear and risk aversion can affect the hunting of large predators and its influence on ocean ecosystems," said Jorgensen. "It turns out that these risk effects are very important even for large predators such as the white shark – powerful enough to redirect their hunting activities to less desirable but safer areas."

The researchers did not draw any conclusions on whether killer whales targeted white sharks as prey or whether they intimidated competition for high-calorie elephant seals.

"I think that shows how food chains are not always linear," said Jorgensen. "The so-called lateral interactions between top predators are quite well known on Earth but are much more difficult to document in the ocean, and as this rarely happens, it may take a little longer to fully understand. The dynamic."