Southern resident killer whales not eating enough: UBC study

The endangered orcas that make their seasonal residence in the Salish Sea aren't getting enough to eat, according to a new study from the University of B.C.

What's more alarming is that the study of the southern resident orcas' eating habits over spring, summer and fall shows a food energy deficit in six of the past 40 years, three of which were in the final years of the study from 2018-20.

An energy deficit means the whales are expending more energy than they get from food, which primarily consists of chinook salmon in the waters off British Columbia, Washington and Oregon. The study did not follow their winter eating habits, as it's unclear where the pods are during that season.

“The average difference in energy is 28,716 calories, or about 17 per cent of the daily required energy for an average adult killer whale,” according to the study's authors.

“With the southern resident population at such a low level, there's a sense of urgency to this kind of research,” said lead author Fanny Couture, a doctoral student at the Institute for the Oceans and Fisheries (IOF) and Ocean Wise.

“Both killer whales and chinook salmon, the southern residents' main prey, are important, iconic species for the west coast of Canada. Studying what is happening to the population may help offer solutions, both for the southern residents and potentially other killer whale populations in the future.”

The southern resident population totalled just 73 orcas during a count in October 2021. That's less than a quarter of the growing northern resident population of roughly 300 animals. Earlier studies suggest a lack of food is among the reasons for the disparity.

That energy deficit — calculated from estimates of the abundance and size of salmon populations each year from 1979 to 2020 — might be directly linked to slow population growth and higher mortality among the southern residents, said co-author Villy Christensen, a professor at the IOF.

The study echoes other research showing a link between salmon abundance and the survival rate and fertility of the southern residents, said Couture, noting declining salmon stocks might be tied to many factors such as climate change, disease and predation by other animals.