Whale watchers on a tour of the Monterey Bay this weekend quickly learned how brutal Mother Nature can be when they witnessed a pod of killer whales attacking and killing a baby gray whale.

The group was touring with the Monterey Bay Whale Watch. The group’s Facebook page posted the video with a discretionary message warning viewers about the scene they were about to witness.

The seven killer whales, also known as orcas, worked in unison on Saturday to separate the calf from its mother, and then took turns pushing it down into the water until it gave up. Two of the pod were seen consuming the carcass.

“The Gray Whale mother defended her calf fiercely as she held it on her back and thrashed with her flukes, but the Killer Whales ultimately were successful,” the group wrote. The entire ordeal, culminating with the calf’s death, lasted for over an hour.

The tour mentions that this specialized hunting style is seen specifically in the Bigg’s (transient) killer whale breed located on the U.S. West Coast.

“As hard as this event can be to watch, it is also a once in a lifetime opportunity to see these incredible predators in action,” the group wrote. The heartbroken gray whale mother reportedly swam around the the area her baby had died and charged at the killer whales for several hours after the incident.

Killer whale sightings have increased this time of year as they seek to prey on vulnerable gray whale calves.

Last week, a group of killer whales freaked out a pod of dolphins in the Monterey Bay. The dolphins created a beautiful sight as they created arcs in the water as they swam away to safety.

Follow Adelle Nazarian on Twitter @AdelleNaz