Killer whales eat 375 pounds of food per day. Now imagine most of that is salmon, the food source they most often in the summer, and you can imagine how devastating that can be to the salmon population of the Pacific Northwest if such whales were higher population. That's equivalent salmon each day to what 200 Americans for a year (<300,000 metric tons per year total consumption.)
Salmon is currently the third most popular fish in the United States (behind shrimp and tuna) and one third of it comes from Pacific salmon, both farmed and in the wild.
The determination about diets was made using an analysis of fish DNA in killer whale poop.
Estimating killer whale diet composition helps scientists understand interactions between predators and prey, but observing their diet directly is difficult. In this study, the authors used genetic analysis of fecal material collected in their summer range in the Salish Sea in the Pacific Northwest, to estimate the diet composition of an endangered population of wild killer whales. They genetically sequenced 175 fecal samples collected from May to September from 2006-2011, which results in nearly 5 million individual sequences that they compared to potential fish from their diet.
They found that salmon made up >98% of the total sequences, which they inferred is the result of their diet. Of the six salmon species, Chinook salmon made up 80% of the sequences, followed by 15% coho salmon. They found that early in the summer their diet was dominated by Chinook salmon and coho salmon was greater than 40% in the late summer. Non-salmon fish were rarely observed. The researchers state their results highlight the importance of Chinook salmon in this population's summer diet and support earlier results based on surface prey remains.
Published in PLOS ONE by Michael Ford from the National Marine Fisheries Service and colleagues.