Southern Resident killer whales are salmon specialists: 80% of their diet is Chinook (or King salmon), but they do eat other salmon species, with coho at around 15%.
Chinook salmon is the largest and fattiest of all the Pacific salmon and therefore supplies the most calories for the effort expended in catching it. The Southern Residents are extremely active with high energy needs, and this is most likely why they favor Chinook. In the past, Chinook was plentiful and available year-round. It’s only in the last few decades that they’ve become scarce due to human activities and it’s the loss of these healthy salmon runs that have also endangered these orcas.
Many people ask why they won’t switch prey, like other populations of killer whales in the world eat different prey types, with some eating both fish and mammals. However, the type of prey and hunting techniques and associated communications are all inherited—cultural knowledge shared across generations.
Given sufficient time, it’s possible they might adapt to eat other salmon or fish species, but the current rate of change is simply too rapid for long-lived species like these orcas. Without access to enough Chinook salmon, they’re sadly destined for extinction and their unique culture with them.