A new study into British Columbia's iconic but endangered southern resident orcas found that the animals have for years faced diet deficiencies — getting 17 per cent less food than what they need.
The killer whales' ongoing malnourishment could help shine light on why they haven't been able to rebuild their population, according to the study's lead author, Fanny Couture, with UBC's Institute for the Oceans and Fisheries.
"There is this big question of trying to understand why this population cannot thrive," she said. "If you think about a human — if you did not eat enough, you would find yourself not being able to do other things, like socializing for example."
Only about 75 southern residents remain, despite several promising pregnancies and births in recent years.
Couture and her University of British Columbia-based team of scientists published their findings in the Public Library of Science journal this week.
The new study is the latest to sound the alarm about southern residents' nutritional health.
Ottawa deems them endangered and launched an "enhanced recovery plan" in 2019. And the U.S. government's National Oceanic and Atmospheric Administration (NOAA) declared in January they "continue to face a high risk of extinction and should remain listed as endangered."
UBC's researchers examined how abundant their main food source — Chinook, chum and coho salmon — were in the areas orcas frequent over a four-decade period.
Killer whales need to eat 170,000 calories every day, Couture said. That's roughly the amount of calories 85 humans eat each day.
But for six of the last 40 years, southern residents have not had enough to eat, the study showed.
"The study highlights the urgency of doing something for the killer whales," Couture said. "And what can be done is really to look at the different factors that could affect those prey populations."
The southern resident orca is one of three types of killer whale found off B.C.'s waters, the others being transient or Bigg's orcas, and northern residents. Southern residents eat fish — primarily Chinook salmon — and their range extends from southeast Alaska down to central California; while transient killer whales have a more varied and flexible diet.
Another study, published last August in Ecosphere journal, found that between 2008-2019, southern resident orcas with "depleted fat reserves" faced double or triple the deaths rates of those with healthy body conditions.
Experts say a decline in the population of southern resident killer whales is most likely due to a combination of factors including shipping noise, pollution in their habitats, and declining Chinook salmon numbers.
Couture said her team's next step is to look at the same 40-year data for the northern resident population, which is much larger.
For more on the threats to the southern resident killer whales and the efforts to save them, check out CBC British Columbia's original podcast Killers: J pod on the brink, hosted by Gloria Macarenko.