Southern resident killer whales are not starving due to lack of BC chinook, study finds

Roy L Hales/ Cortes Currents - The widespread belief at-risk southern resident killer whales are starving due to a lack of chinook salmon has been debunked.

A UBC led study found there are actually more than four times as many salmon in their territory than that of their supposedly better fed kinsmen north of Cortes Island.

This was not what the authors expected to find, when they compared the numbers of Chinook entering the Strait of Juan de Fuca to those just north of Campbell River, in the Johnstone Strait, during the summers of 2018 and 2019.

“Measurements from drone footage has shown the southern resident killer whales are thinner on average than the northern residents — which supports the common belief that the southern residents are experiencing a food shortage,” explained Dr. Andrew Trites, director of the Marine Mammal Research Unit at the Institute for the Oceans and Fisheries at UBC, and one of the study’s three authors.

When the southern residents failed to return for four consecutive summers, people assumed that was because there was no Chinook for them.
This is the first study to employ hydro-acoustic technology in an acoustic survey of salmon populations at sea. Up until now, researchers have had to rely on counts of salmon returning to rivers. Fishermen helped point the team to areas where their state-of-the-art fish finders should be deployed. Researchers caught sample fish to validate the accuracy of their equipment.

“There is a food problem, but we are not seeing the problem as being here during the summer time,” concluded Trites. “The reality is killer whales have to eat everyday of the year.”

While BC’s Chinook salmon population is in decline, he suspects the real threat to the southern resident population may occur during the Fall and Winter, when they are south of the border. Prior to the introduction of logging, dams and irrigation, California’s rivers had some of the biggest Chinook runs in the North Pacific Ocean.

“Those runs were destroyed, they used to support four runs of Chinook,” said Trites. “Here we think of Summer and Fall runs, but they also have a winter run that came in around Christmas time and a Spring run as well. Historically their habitat had food throughout it for different times of the year. They haven’t had a proper meal, say in terms of that Christmas dinner, since the 1800s.”

He concluded that if scientists want to find out why southern residents appear to be malnourished, they need to extend their research throughout their entire range - which includes the West Coast of the United States.

Photo credit: A southern resident killer whale seen from a drone swimming past a school of salmon near the mouth of the Fraser River. (photo. K. Holmes, Hakai Institute and University of British Columbia).