A pod of orcas was recently spotted exhibiting behavior that reads like a Greek tragedy.

Off the coast of Vancouver Island on Canada's west coast, a 28-year-old female killer whale was swimming with her calf. The younger orca was small, its dorsal fin not yet fully erect, meaning it was likely only a day old. The 28-year-old was traveling with two other daughters, five and eight.

Nearby, a 32-year-old male was steadily heading toward the group with his own 46-year-old mother.

Also nearby—a group of scientists were observing the interaction. A nearby research station named OrcaLab had picked up strange calls with an underwater microphone, and a trio of scientists went out to investigate.

The scientists noticed sudden and erratic splashing break out. In the flurry of movement, the whales began circling. The scientists noticed the calf wasn't surfacing.

"We saw some splashing and thought they were eating something," says Jared Towers, a cetacean researcher from Fisheries and Oceans Canada.

It wasn't until the male swam past their research boat that they realized what was happening. The male had grabbed the newborn infant by its fluke and was dragging it away from its mother. Meanwhile, the male's own mother was blocking the calf's mother, preventing it from rescuing the newborn.

When the newborn eventually failed to surface, the researchers knew it had been held under until it drowned.

Realizing they were seeing something rare, the researchers went into autopilot, gathering as much data and recordings as possible.

They say the fight ceased after the infant was drowned. No signs of feeding were observed, leading them to believe the calf was not killed as prey. Because they lost sunlight, they were unable to return for the calf's body to examine it further.

The Motive

Infanticide, or killing infants, has been observed in terrestrial species likes primates and rodents, but the only marine mammal species known to show the behavior are other dolphins.

Towers suspects the male attacked the calf so that it could mate with the 28-year-old female.

When female orcas give birth, they are unable to breed again during the period in which they nurse their offspring. What really surprised scientists was the help the male orca received from its mother.

Oregon State University ecologist Ari Fiedlaender has studied the behavior in East Coast dolphin species, but he says it's the only time he's seen intervention from older females. He thinks the older mother may have intervened to help her son find a mate, thereby passing on her own genes.

"The female, that male's mother, would effectively be helping to pass on her lineage if that male was then successful in breeding with the animal that lost her calf," says Friendlaender.

Tower emphasizes that the older female was instrumental in the attack, and in orca societies, older females often hold a higher status.

"Post-reproductive females are known for leading," he says. "They share ecological knowledge over decades."

That the older mother and male were able to coordinate so well didn't surprise the scientists. Killer whales have been documented carrying out skilled and well-planned attacks on much larger animals like blue whales and bowhead whales.

Researchers had seen physical remnants of aggression, like scars and deformities, but they say this interaction helps piece together questions about orca behavior. The interaction and the scientists' conclusions are published in the journal Scientific Reports.