March 4, 2021 — For more than a decade, Brad Hanson and other researchers have tailed the Pacific Northwest’s endangered killer whales in a hard-sided inflatable boat, leaning over the edge with a standard pool skimmer to collect clues to their diet: bits of orca poop floating on the water, or fish scales sparkling just below the surface.
Their work established years ago that the whales depend heavily on depleted runs of Chinook, the largest and fattiest of Pacific salmon species, when they forage in the summer in the inland waters between Washington state and British Columbia.
But a new paper from Hanson and others at the NOAA Fisheries Northwest Fisheries Science Center provides the first real look at what the whales eat the rest of the year, when they cruise the outer Pacific Coast — data that reaffirms the central importance of Chinook to the whales and the importance of recovering Chinook populations to save the beloved mammals.
By analyzing the DNA of orca feces as well as salmon scales and other remains after the whales have devoured the fish, the researchers demonstrated that the while the whales sometimes eat other species, including halibut, lingcod and steelhead, they depend most on Chinook. And they consumed the big salmon from a wide range of sources — from those that spawn in California’s Sacramento River all the way to the Taku River in northern British Columbia.