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.
"Having the data in hand that they're taking fish from this huge swath of watershed across western North America was pretty amazing," Hanson, the study's lead researcher, said Wednesday. "We have to have hard data on what these whales are actually doing."
There are officially 74 whales in the three groups of endangered orcas, known as the J, K and L pods of the southern resident killer whales. Three calves have been born since September, but those are not yet reflected in the count because only about half of the babies survive their first year.
Facing a dearth of prey, contaminants that accumulate in their blubber, and vessel noise that hinders their hunting, the whales are at their lowest numbers since the 1970s, when hundreds were captured — and more than 50 were kept — for aquarium display. Scientists warn the population is on the brink of extinction.
The paper, published Wednesday in the journal PLOS One, suggests that efforts to make Chinook more abundant off the coast in the non-summer months could especially pay off, and that Columbia River Chinook hatchery stocks are among the most important for the whales. It also suggests that increasing the numbers of non-salmon species could help fill the gaps for the whales when Chinook aren't available in the open ocean.
NOAA has already used some of the data, which has been available internally as scientists awaited the study's publication, in proposing what areas to designate as critical habitat for the whales. Officials could use it in prioritizing certain habitat restoration efforts or in timing hatchery production of salmon to best benefit the whales, said co-author Lynne Barre of the National Marine Fisheries Service's Protected Resource Division.
The information could also be key in setting limits for fisheries; the Pacific Fisheries Management Council has recommended that NOAA curtail fishing if Chinook abundance is forecast to drop below a certain level.
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