Spectators on a Southern California whale-watching cruise were excited when they spotted a gray whale, then amazed when the giant mammal gave birth right in front of them.

The birth and the first moments of the calf’s life were recorded on cellphone and drone video Monday off Dana Point, south of Los Angeles.

Passengers and crew on a boat operated by Capt. Dave’s Dolphin & Whale Safari spotted blood in the water and initially worried the 35-foot (10.6-meter) gray whale might be injured.

The boat’s captain, Gary Brighouse, said when everyone realized they were witnessing a birth, the mood turned celebratory.

“It went from horror to pure joy and astonishment,” Brighouse told the Orange County Register. “It moved me to my core.”

The video shows the mother and baby frolicking around and under the 24-foot (7.3-meter) boat and breaching the surface of the water.

Spectator Stacie Fox, who shot images of the birth from another Capt. Dave’s boat, said she was screaming with excitement.

“It’s once-in-a-lifetime type stuff,” she said.

While it’s not uncommon for gray whales to give birth along their winter journey from feeding grounds near Alaska to warm waters off Mexico, it’s rarely photographed.

“As far as I know, no one has filmed a gray whale giving birth or even seen it before,” Dave Anderson, the owner of Capt. Dave’s, told the Register.