BELLINGHAM — Southern Resident killer whales have not had enough food for several years, which could affect their already small numbers, according to a study 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, the Bellingham Herald reported.

“It really appears like they cannot take (many) more rough years,” said Fanny Couture, lead researcher for the study.

About 75 of the Southern Resident killer whales span from the California coast to Haida Gwaii in British Columbia’s Queen Charlotte Islands.

They feed on Chinook salmon, but the number of Chinook has decreased even as fishing regulations attempted to bolster their numbers. That 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.

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.