Southern resident killer whales missing out on thousands of needed daily calories, study finds

British Columbia’s iconic southern resident killer whales are not only endangered — they’re not getting enough to eat for prolonged periods, new research has revealed.

A University of British Columbia study has found the orcas exhausted more energy than they could acquire from food for six of the past 40 years, including a three-year stretch between 2018 and 2020.

The average difference between the amount of energy spent and the amount they could access is 28,716 calories — about 17 per cent of the daily energy they need.

“There is definitely a sense of urgency,” said lead author Fanny Couture, a PhD candidate at UBC’s Institute for Oceans and Fisheries and Ocean Wise, in an interview.

“There are several studies going on at the moment to try and understand how much time we have left with this population.”

There are an estimated 75 southern resident killer whales left in the world. Their primary food source is Chinook salmon, but the study also considered coho and chum stocks in the Salish Sea and on the West Coast of Vancouver Island where they hunt.

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Researchers analyzed how changes in the abundance, age and size of those populations influenced the whales’ daily consumption between 1970 and 2020 for three seasons each year. The study used estimated declines in Chinook salmon abundance and size to show that lower availability of this prey likely contributed to orcas’ energy deficits.

“The years where southern residents were in an energy deficit are also years where other studies report lower population growth rate and higher mortality rates for the killer whales,“ said co-author Villy Christensen, professor at the Institute for Oceans and Fisheries, in a news release.

The study also hypothesized that southern residents would eat more chum than Chinook during years when Chinook was scarcer.

A previous study from UBC claimed to have “debunked” a common belief that southern resident killer whales lacked summer prey in Canadian waters.

It suggested Chinook salmon populations in the Salish Sea during summertime were four to six times more abundant for southern residents than in northern resident feeding grounds, having compared Chinook availability for southern residents in the Strait of Juan de Fuca with availability for northern residents in the Johnstone Strait between 2018 and 2019.

Couture said that the study examined the density of prey at a very specific time and place, while her team examined a broad area over 40 years. She said it’s possible that the density of fish in one area at one time does not equate to enough food overall for the orcas and she would be interested in additional research to determine whether northern resident killer whales experience an energy deficit too.

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Many wild Pacific salmon returns are generally low and stocks are increasingly at risk.

Among the threats to the southern resident’s preferred food source — Chinook salmon — are climate change, susceptibility to disease, and predation by other animals, such as sea lions.

“The predation from marine mammals definitely needs further investigation,” Couture told Global News. “It’s really hard to point to a specific culprit in this situation. More research is definitely needed.”

Couture’s and Christensen’s study, published in the peer-reviewed scientific journal PLOS ONE, did not include winter as it remains unclear precisely where the southern residents are during that season.