Scientists Witness Horrific Killer Whale Infanticide for First Time

A female orca attacks a male who had just killed her calf. Gary Sutton

Researchers in Canada have witnessed a horrifying event that, until now, has never been documented by science: A killer whale drowning and killing an infant of the same species.

The incident took place on December 2, 2016 off the coast of Vancouver Island, British Columbia. Now the sighting has been described in a paper published in the journal Scientific Reports.

The marine scientists were out on a research expedition when they detected strange calls on their vessel's underwater microphones, alerting them to the presence of killer whales in their vicinity.

After finding the whales responsible for the noises, the researchers noticed some splashing that they thought might be a sign that the orcas were hunting. However, they quickly realized that an infant calf in the group wasn't surfacing.

"Then a male, who was unrelated to the mother of the calf, swam past the boat with the calf hanging out of its mouth, and that's when we were really quite horrified and fascinated," Jared Towers, a cetacean researcher from Fisheries and Oceans Canada, told CBC News.

The stricken calf's mother and her relatives then frantically pursued the 32-year-old male in an attempt to rescue the youngster, but the male—with help from his own mother—managed to fend them off.

The researchers describe how the chase eventually ended with the mother of the infant hitting the male so hard with her flipper that blood flew through the air, although by this point, the calf was already dead.

This is the first time that a killer whale has been observed killing a calf of the same species, according to the study, although infanticide has been observed among many animals before.

"Among terrestrial mammals, it is mostly reported in primates, carnivores and rodents," the researchers wrote in the study. "However, compelling evidence for infanticide in cetaceans [a group of animals containing whales, dolphins and porpoises] exists in just three species of dolphin."

Towers said the scene was distressing, however, the research team decided to watch until the end in the knowledge that they were witnessing a rare event.

Because the offending male and his mother did not eat the dead infant, the scientists suggest that the killing may be an example of so-called "sexually selected behavior"—which means that the male killed the calf to mate with its mother.

"In other mammals, we know that in a lot of cases males kill infants, because it forces the infant's mom into a fertile state much quicker," Towers said.

What is interesting in this case is that the mother of the male became involved in the killing.

"Killer whale moms are notorious for helping their adult sons and daughters by sharing food with them and leading them, and maybe even providing mating opportunities for adult male offspring," Towers added.

The researchers say the recent findings cast doubt on some long-held assumptions regarding the sexual behavior of orcas. Scientists have generally thought that female orcas have free reign when it come to choosing their mates because they are often found at the top of the pod hierarchy.

But in light of the recent encounter, Towers suggests that the females may not have as much choice as previously believed.