Could B.C.'s chinook-loving orcas adapt to a new food source? It's not unthinkable

The fate of the southern resident killer whales is so closely entwined with chinook in the Salish Sea that some fear a decline in the salmon species could lead to the end of B.C.'s cherished orca population.

Killer whales around the world have adapted to feeding on just about everything else that swims in the ocean, including halibut from the deep sea, seals and sea lions from the rocky shoreline, baby whales from their mothers' sides and even the livers of great white sharks.

The urgent question now is whether the southern residents could adjust to the disappearing chinook, expand their palates and open up their menu options.

Lance Barrett-Lennard, director of the marine mammal research program at the Vancouver Aquarium, said it would be difficult — but not impossible.

"Until a few years ago I would have said no, they're just absolutely fixated on chinook and I don't see the prospect for them switching diets to be at all promising. But there is some new evidence coming out," he told CBC.

That new evidence suggests the southern residents enjoy snacking on a wider selection of fish than previously known.

Whether those mildly adventurous habits could save the population will depend on the abundance of other fish species and the orcas' ability to change their hunting techniques.

That's because while killer whales are renowned for their intelligence and ability to learn new things in captivity, in the wild they're creatures of habit, slow to experiment with the unfamiliar.

'A very conservative side'

John Ford, a retired cetacean researcher with Fisheries and Oceans Canada, says hunting chinook is part of a strong, traditional culture for the southern residents.

"The animals have a very conservative side to them," Ford said. "Ultimately, other generations may be innovative enough to specialize on different kinds of prey and make a successful living at it, but in the short term they seem to be behind."

Nonetheless, the whales do like to mix it up now and then.

Scientists have long known that they will sample chum salmon during the fall runs. It's not unheard of for them to munch on coho, either.

But we now know their diet sometimes includes non-salmon species, like halibut and sablefish.

These are high-calorie fish, which is promising, but their numbers aren't necessarily high enough to replace the staple chinook.

"At least it means that they can diversify their food supply a little bit. It's still very interesting that they don't switch to sockeye when sockeye are abundant, or pink salmon," Barrett-Lennard said.

Each fish species requires a slightly different hunting technique.

Halibut and sablefish are often found in deeper waters, and killer whales aren't generally known for their diving skills. That might mean the orcas depend more on the heavier adult males for hunting those species, whereas females tend to do more of the work when salmon is on the menu.

Coho tend to be smaller and more agile than chinook, and Barrett-Lennard says the footage researchers have captured from aerial drones suggests the whales are using up a lot more energy hunting these salmon.

"But one thing about killer whales is they really get good at stuff. They may not be particularly good at it when coho aren't abundant and they don't catch that many of them, but if they really become so despondent, I suspect they'll develop at catching those agile fish," he said.

No taste for mammal flesh

A major shift to something like seals or porpoises is less likely.

As Deborah Giles, science and research director for the Wild Orca non-profit, points out, there have been several accounts of southern residents catching and killing porpoises.

"But they don't eat them. None of them have taken even a bite out of them," she said.

"It's frustrating because that's a humongous amount of food out there."

Switching to marine mammals would also require the whales to learn how to hunt silently. The southern residents rely on echolocation to track salmon — a squeaky, noisy process that would immediately scare off any seals or porpoises in the area.

Still, Giles says all it takes is one whale who's willing to experiment, and new feeding habits could spread throughout the population.

"You get the oddball that's just going to go and be punk rock … We see it in the southern residents, and that's what gives me a little glimmer of hope," she said.

For more on the future of the southern resident killer whales, listen to Killers: J pod on the brink, a CBC British Columbia original podcast hosted by Gloria Macarenko. You can get it now for free at CBC Podcasts.