Southern Resident killer whales have not had adequate food consumption for several years, which could affect their already small numbers, according to a study released in late June by the University of British Columbia.
Researchers looked at requirements and availability of prey for Northeastern Pacific Southern Resident killer whales. The study found a fluctuating level of salmon from spawning areas on rivers had a detrimental effect on killer whale health, threatening a small and fragile group of whales.
“It really appears like they cannot take (many) more rough years,” Fanny Couture, lead researcher for the study, said in a video interview.
About 75 of the Southern Resident killer whales span from the California coast to Haida Gwaii in British Columbia’s Queen Charlotte Islands.
Southern Resident killer whales are unique in appearance and communication.
They have a regular diet of Chinook salmon that are known to spawn and travel all along the west coast of the U.S. and Canada. However, the number of Chinook has decreased even as fishing regulations attempted to bolster their numbers. The result leaves animals high on the food chain, like killer whales, without adequate prey.
The study showed a significant decrease in salmon between the years 1979 and 2020. Four years lacked enough prey that killer whales expended more energy than they took in. Scientists call that an energy deficit. The final three years of the study, from 2018 to 2020, showed an energy deficit, as did 2008.
Studies have shown that a lack of food intake for killer whales has led to lower birth rates and higher death rates. The current study agreed, showing a slightly higher birth rate in years where the killer whales met their dietary needs.
The study measured salmon counts from three areas: Fraser River, Puget Sound and the Straight of Georgia. Spawn from the Puget Sound, including the Nooksack River, decreased significantly over the course of the study, while those from the Fraser River relatively increased.
A continuation of lower Chinook salmon populations may put the killer whales at risk but solving the issue is easier said than done.
“I think it’s really hard to answer what can be done when we do not have a clear idea of what’s happening to the salmon,” Couture said.
She said there were a number of possibilities affecting the populations of salmon including climate change, being eaten by other predators or disease.
Effects on Chinook salmon can even be seen in Whatcom County. Thousands of Chinook salmon died from high water temperatures due to climate change last year on the Nooksack River’s South Fork, according to earlier reporting in The Bellingham Herald.
Couture said that salmon population decline has been blamed on overfishing, but numbers have not bounced back even after fishing was reduced.
“It’s highly likely that it’s a combination of all those factors together, there’s really this question of what is the primary cause of (Chinook salmon) decline.”