British Columbia·Killers

Shark-eating offshore killer whales are the 'mystery animals' of B.C. waters

Out in the deep, deep waters of the Pacific Ocean, far from the whale-watching boats that set off from B.C. shores, there swims a different sort of orca.

Lesser known orca population is rarely seen, making the whales difficult to study

The offshore population of killer whales is rarely seen in inside waters. (Fisheries and Oceans Canada)

Out in the deep, deep waters of the Pacific Ocean, far from the whale-watching boats that set off from B.C. shores, there swims a different sort of orca.

And this one likes to eat sharks.

That's one of the only things scientists know for sure about the offshore killer whales, a population that's genetically and socially distinct from B.C.'s better-studied resident and transient orcas.

"They're the mystery animals," said Lance Barrett-Lennard, director of the marine mammal research program at the Vancouver Aquarium.

Scientists estimate there are about 300 whales in the offshore population, which roams the Pacific all the way from northern Mexico to the Aleutian Islands in Alaska. They're smaller in size than the residents and transients, and their dorsal fins tend to be more nicked and notched.

Most of what we know about these whales is thanks to chance encounters or from necropsies of carcasses that wash up on shore.

GRAPHIC: Worldwide distribution of 10 different killer whale ecotypes

A map of the globe shows, in light blue, the worldwide distribution of different killer whale ecotypes. (CBC/National Oceanic and Atmospheric Administration)

When scientists happen upon a group of offshores in the midst of a meal, they can use nets to scoop up traces of their prey and analyze the DNA, which is how we know what they eat.

An examination of a dead adult female that washed up in Alaska four years ago shows just how much wear and tear can happen when an animal is constantly biting into the rough and tough skin of a shark. The whale's teeth were worn right down to the pulp, and the researchers suggested related tooth and gum diseases likely contributed to the animal's death.

Teeth extracted from an offshore killer whale that stranded in Alaska in 2015 showed significant damage, likely caused by eating sharks. (Journal of Comparative Pathology)

Offshore orcas are also known to feed on fish like halibut and chinook salmon.

'We don't know what the trend is'

But because of their huge range and preference for offshore waters, scientists just don't encounter these whales very often.

The population is designated as threatened under Canada's Species at Risk Act, but Barrett-Lennard said their actual status is pretty unclear — as are the potential threats.

"We do know the population size is fairly small, but we don't know what the trend is," he said.

Setting up a planned study is nearly impossible when there's no telling where you might find the offshore orcas, but Barrett-Lennard has a long list of questions he'd like answered.

For one thing, why are they smaller than other killer whales on the West Coast?

"We don't know if that's genetic or if that's just the fact that they have a less nutritious diet," Barrett-Lennard said.

He also wonders about their social structure. Offshores are often seen in large groups of up to 50 or 60 animals. These groups are fairly consistent, but not as much so as B.C.'s other orca populations.

It will likely take some time before any of these questions are answered. Barrett-Lennard said that while sightings of the offshores have always been few and far between, they've been especially rare in the last year or so.

For more on the future of the southern resident killer whales ...

Killers: J pod on the brink is a CBC British Columbia original podcast about the Southern Resident Killer Whales, hosted by Gloria Macarenko. You can get it now for free at CBC Podcasts

About the Author

Bethany Lindsay

Journalist

Bethany Lindsay has more than a decade of experience in B.C. journalism, with a focus on the courts, health and social justice issues. She has also reported on human rights and crimes against humanity in Cambodia. Questions or news tips? Get in touch at bethany.lindsay@cbc.ca or on Twitter through @bethanylindsay.