New orca population could be hunting ocean's largest predators: researchers

Scientists at the University of British Columbia say they have identified a potentially new population of killers whales that hunt the planet's largest predators in the open ocean.

A group of 49 orcas has been seen hunting sperm whales, elephant seals, dolphins and even a leatherback turtle as far as 300 kilometres off the coast of California and Oregon, according to a peer-reviewed study published in the journal Aquatic Mammals last week.

And it seems the killer whales haven't been studied before, according to co-author Andrew Trites, a professor at UBC's Institute for the Oceans and Fisheries. 

"It appears that these are a unique group of killer whales," he told CBC's On The Coast on Monday. "We think they're probably related to the transient type, but for now, we're calling them oceanics and just making people aware that there's something else out there that we don't fully understand."

Researchers say the orcas were observed in nine encounters from 1997 to 2021, and lead author Josh McInnes stressed the group of orcas are not a new species but likely a subpopulation.

"They're still killer whales ... that have just spent more time in the open ocean that we just haven't seen before," he said in an interview.

In a 1997 encounter around 130 kilometres from the coast of California, around 35 killer whales hunted a herd of nine sperm whales and made off with one after chasing them over three kilometres.

"Small concentrated groups of four to five killer whales randomly targeted and attacked individual sperm whales in the rosette," the study said.

A rosette is a term describing how the sperm whales gathered in a circle with their heads together and their tails pointing outward. 

"Fresh blood and an oil slick of animal fat could be seen at the surface following each attack," the study continued.

The whales' varied diet was what stood out most to Erin Gless, executive director of the Washington-based Pacific Whale Watch Association, who was not involved in the study.

"I have read about killer whales attacking sea turtles in the tropics, but never in places like California and Oregon that are much colder waters," she said.

"I think that it's just indicative of the fact that they live in these really open water conditions and so they don't have the beaches full of seals, for example, like we have here in B.C., so they need to pretty much eat whatever they come across."

The killer whale populations in B.C. include southern resident killer whales, who mostly eat salmon and other fish, and Bigg's (transient) killer whales, who hunt larger mammals like sea lions, sea otters and sometimes whales.