It’s one of the most disturbing videos you’re ever likely to see of killer whales in action, and Mother Nature at her most violent. A group of whale watchers off the coast of Monterey Bay in California had a front-row seat to the gruesome attack of nine killer whales on a baby grey whale calf as its mother helplessly watch, unable to stop the marauding mammals.

It’s part of a killing frenzy that scientists have never seen before off the coast of California. This is the fourth time orcas were spotted conducting a mauling, and scientists aren’t quite sure why it’s happening. In this case, the killer whale pod took only 20 minutes to kill the baby whale. The whales seemed to be quite thin, so it’s possible the mother was unable to use her powerful tale to fend off the predators.

“This has never happened in my thirty years,” Nancy Black, a marine biologist with Monterey Bay Whale Watch, told The San Francisco Chronicle. “Just to witness that out in nature when you usually see that kind of thing on television is really spectacular.”

“Day-to-day killer whale behaviour generally consists of foraging, travelling, resting and socializing,” according to Wikipedia. “Killer whales engage in frequent behaviour at the surface such as breaching (jumping completely out of the water) and tail-slapping. These activities may have a variety of purposes, such as courtship, communication, dislodging parasites, or play. Spyhopping, a behaviour in which a whale holds its head above water, helps the animal view its surroundings. Resident killer whales swim with porpoises, other dolphins, seals, and sea lions, which are common prey for transient killer whales.

“Killer whales are notable for their complex societies. Only elephants and higher primates, such as humans, live in comparably complex social structures. Due to orcas’ complex social bonds and society, many marine experts have concerns about how humane it is to keep these animals in captive situations.”