Jun 24, 2019 | Updated: 11:41 AM EDT

When the Hunter Becomes the Hunted: White Sharks Vacate Preferred Hunting Ground When Killer Whale Confronts

Apr 16, 2019 09:59 AM EDT

When the Hunter Becomes the Hunted: White Sharks Vacate Preferred Hunting Ground When Orcas Confronts
(Photo : Image by skeeze from Pixabay)

There is a challenge to the notion that great white sharks are the most formidable predators in the ocean. The contest appeared in new research from Monterey Bay Aquarium and partner institutions published in Nature Scientific Reports titled; "Killer Whales Redistribute White Sharks Foraging Pressure On Seals."

In the study, it demonstrated how the great white hunter becomes the hunted, and the elephant seal, the common prey of sharks and orcas, emerges as the winner.

Speaking about the study, Dr. Salvador Jorgensen, a senior research scientist at Monterey Bay Aquarium and lead author of the study, when orcas confront the white sharks, they will immediately vacate their favored hunting ground and will not return for up to a year, even though the orcas are only passing through.

The research team included the joint efforts of Jorgensen and Monterey Bay Aquarium Scot Anderson, and research partners from Stanford University, Point Blue Conservation Science and Montana State University.

The study made a document of four encounters between the top predators at Southeast Farallon Island in the Greater Farallones National Marine Sanctuary, off San Francisco, California. The scientists analyzed the interactions using data from 165 white sharks tagged between 2006 and 2013 and compiled 27 years of seal, orca and shark surveys at the Farallones.

All through the cases the researchers examined, while sharks fled the island when orcas arrived and didn't return there until the following season.

The indirect beneficial from the interactions was the elephant seal colonies in the Farallones. Out of four to seven times, the data revealed fewer predation events on elephant seals in the years white sharks left.

Anderson emphasized that on average, they documented around 40 elephant seal predation events by white sharks at Southeast Farallon Island each season. After orcas show up, they didn't see a single shark, and there were no more kills.

Between September and December of each fall, white sharks gather at the Farallones to hunt for young elephant seals, typically spending more than a month circling Southeast Farallon Island. Also, transient orcas feed on elephant seals but only show up occasionally at the island.

Then, the researchers compared data from the electronic shark tags with field observations of orcas sightings to determine when orcas and sharks co-occurred in the area. This analysis made it possible to demonstrate the result of the rare instances when the predators encountered each other.

The results from the electronic tag revealed all white sharks began vacating the area within minutes following brief visits from orcas. Sometimes the orcas were only present for less than an hour. The tags then found white sharks either crowded together at other elephant seal colonies farther along the coast or headed offshore.

Ultimately, there was no conclusion from the researcher whether orcas are targeting white sharks as prey or are bullying the competition for the calories-rich elephant seals.

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