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This photo, supplied by UBC, shows one of the unknown orcas. Cookiecutter shark bite scars on the whales indicated they spent most of their time in the open ocean, not along the coasts with other populations.UBC

Researchers from the University of British Columbia believe they have identified a new population of killer whales, based on the orcas’ hunting habits and their propensity for hanging out in the open ocean off California and Oregon rather than closer to the coasts.

A key clue that the whales could be a unique population, according to the study published Friday in the Aquatic Mammals journal, is that nearly all of them had scars left by the cookiecutter shark. Named for their habit of taking small, round plugs of flesh from the larger creatures they feed on, these sharks are found in open ocean waters.

Cookiecutter shark bite scars on the whales indicated they spent most of their time in the open ocean, not along the coasts with other populations. Of coastal whales studied from Southeast Alaska to Southern California, none identified have had such scars, said Josh McInnes, the study’s lead author.

“They basically grasp and leave a nasty wound, these cookiecutter bite marks, on a whole bunch of different species – but it really gave us a clue of what we were looking at,” said Mr. McInnes, a master’s student in The UBC Institute for the Oceans and Fisheries, in an interview.

The researchers’ conclusions were based on studying orcas that had been spotted before, but had not been linked to other known groups of the three ecotypes of killer whale – residents, transients and offshores – that live along the California and Oregon coasts.

The study analyzed nine encounters with 49 orcas that took place from 1997 to 2021 and came from four different sources, including the United States National Oceanic and Atmospheric Administration, a birding expedition and a whale-watching tour. The UBC researchers began to dig into the nine sightings after being unable to match details of those encounters with photos or descriptions of documented populations.

Killer whales are widely studied, identified by their distinctive markings and the shape of the dorsal fins, with scientists able to use such markers to determine family groups, feeding habits and migratory patterns. Canada has five orca populations, including the endangered southern resident killer whales, of which only 74 remain.

Eventually, the researchers concluded that the 49 orcas could belong to a subpopulation of transient killer whales or a unique oceanic population.

The study also shed light on what those whales are eating. Along coastal habitats and shorelines, whales gorge on fish, including chinook salmon, a mainstay for southern resident killer whales.

In the ocean, they go for bigger prey, including adult sperm whales, a northern elephant seal and a leatherback turtle.

The new whales work together to land their meals; in one encounter described in the report, six orcas closed in on a herd of Risso’s dolphins.

As one dolphin began to fall behind, one of the whales surfaced beneath it and launched it into the air, the report says, repeating the manoeuvre three times before securing the dolphin and pulling it below the surface. All six of the whales from that sighting had scars from cookiecutter sharks, the report says.

Asked what the implications of the study are for killer whales in general, Mr. McInnes said it is too soon to say and that much remains to be learned – a goal he hopes to pursue through an ocean expedition this summer.

In the meantime, he and his colleagues are collecting sightings from ocean birding expeditions, fishing crews and whale-watching tours, adding to a pool of information they hope will expand to include DNA samples to confirm if and how the whales in their study differ from already documented populations.

Finding a new population is “very rare,” Mr. McInnes said.

“Right now, all I can say is that this is a group of killer whales that we have not previously seen before. And these whales have been seen in a habitat that is unusual. And I think the next steps are to continue to look for sightings.”

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