Great White Sharks Bullied, Become Food for Killer Whales

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Great White Sharks
Great white sharks have long dominated the seas, however killer whales, which are reportedly bullying the great beasts and sometimes eating them, may challenge their authority underwater. The research on this phenomenon is not very extensive, but is showing some promising progress in the realm of understanding why killer whales have started attacking great whites. Some researchers are taking advantage of the opportunity to explore how this new breakthrough can help deflect sharks from coastal areas and popular beaches where high numbers of surfers and beachgoers congregate.

The Farallon Islands, located off the San Francisco coast, are a critical base of research, where scientists monitor—among other things—13 different species of birds, five pinniped species, and great white sharks. The researchers studying the fierce predators arrive to the Farallon Islands in the summertime, when white sharks are known to frequent the area in order to feed on the abundant numbers of pinnipeds, or seals. This season is known to last through the fall months.

It all started back in the late 1990s when a group of researchers made the annual trek to the Farallon Islands to observe the great white feeding season. They recorded the presence of killer whales in the area, which also feed on the pinnipeds, and thereafter witnessed a killer whale bully a great white. The orca proceeded to kill the great white. Researchers also noted that great white sightings ceased following the event. It was still the height of the feeding season.

A 2014 report of predatory activity at the Farallon Islands mentions a similar happening in 2009. Following a “depredation event” on a great white shark by a killer whale, the remaining white sharks left earlier than normal, as if bullied out of the area. Researchers also observed a pod in the area this past fall, and wonder if that had anything to do with the lower-than-average number of shark predations on pinnipeds for the season.

The connection between great whites and orcas has attracted the attention of many marine researchers. In western Australia, documentary makers are looking to experiment with killer whale audio to see if it will deter sharks in the immediate area. Researchers have over three hours worth of audio to work with, so they hope that in observing shark responses they can isolate the specific killer whale sounds that are the most effective shark repellants.

Eyewitnesses have reported different killer whale bullying methods. In some cases the whale rams the great white shark, effectively “stunning” it by catching it off-guard. In other more elaborate scenarios, the killer whales engage in what has been dubbed by one researcher, Dr. Ingrid Visser, as the “karate chop.” In this case, the killer whale produces a vortex by way of an “up-thrust of its tail” in the open water, forcing the shark up to the water’s surface. At this point, the killer whale “pivots,” raises its caudal fin out of the water, and slams down with the entire force of its tail. The blow is reportedly devastating to the white shark.

Despite the initial difference in methodology, all killer whale attacks on sharks include one vital element: flipping the shark upside down. This apparently induces what is called “tonic immobility,” an unlearned reflex that induces a trance-like stupor. The killer whale continues to hold the shark down in this position causing it to suffocate, according to the reports.

There has been a great deal of speculation as to why the killer whales have engaged in this kind of deadly bullying behavior, and some researchers suggest that it is not necessarily “new” behavior so much as it is newly observed behavior. Others propose that it is a matter of resource competition. Killer whales and great white sharks are known to feast off of the same food sources. Regardless of the reason, some researchers are taking advantage of the opportunity to make beaches safer for beachgoers. Killer whale audio may prove to be a deterrent for great white sharks, although the effects and implications of faux whale calls on actual killer whales in the vicinity should be considered.

By Courtney Anderson

Shark Trust
Point Blue
The West Australian Regional
The Telegraph
Marine Science Today

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