Puget Sound’s killer whales prefer to dine on chinook from Fraser River
Taking a bite out of Fraser River chinook
By Les Blumenthal, McClatchy NewspapersMarch 19, 2010 6:27 AM
A study by U.S. and Canadian scientists shows that killer whales in Puget Sound, Wa., mostly are feeding on Fraser River chinook.
Photograph by: Ken Balcomb, Centre for Whale ResearchWhen it comes to dinner, Puget Sound’s killer whales show no respect for international boundaries.
It’s long been known that their favourite meal is chinook salmon. However, using new genetic tests on the orcas’ feces, and fish tissue and scales taken from the waters near where the whales are feasting, scientists say that as much as 90 per cent of the chinook they eat are from B.C.’s Fraser River.
Though the dietary habits of killer whales may not seem like a big deal, the orcas and various salmon species are protected on both sides of the border. Efforts to revive endangered species that share the same ecosystem can become intertwined.
“It is fascinating the whales specialize in a particular species, and the species they focus on is one of the rarer ones and in some case protected,” [Note] [/NOTE] said Michael Ford, the director of the conservation biology division at the National Marine Fisheries Science Center in Seattle. “Recovery of the whales could be dependent on the recovery of salmon. It is all related.”
Ford was among a group of U.S. and Canadian scientists who published the results of their study in the recent edition of the journal Endangered Species Research.
The problem of killer whales nibbling on declining salmon runs isn’t just an international one. Federal scientists say that Puget Sound killer whales may also be taking their toll on endangered salmon from California.
Though their numbers fluctuate, about 90 killer whales make up the southern resident population that swims the inland waters of Washington state and B.C. from south Puget Sound to the Strait of Georgia. From late spring to early fall, the whales stay in the inland waters. During the winter they’re known to roam the Pacific Ocean from Northern California to Vancouver Island.
The whales weigh between 2,700 and 5,400 kg and can eat up to 140 kg of fish a day.
From 2004 to 2008, scientists from both countries followed the orcas in small boats near the San Juan Islands in Washington state and the western Strait of Juan de Fuca in British Columbia.
“You could see them eating fish, a predator chasing their prey under our boat,” Ford said. As the orcas were feeding, the scientists used swimming pool nets to collect fish scales, fish tissue and whale feces floating in the water.
“It’s not high-tech,” said Brad Hanson, a wildlife biologist with the National Marine Fisheries Service in Seattle and another of the study’s authors.
Hanson said the scientists mostly relied on DNA from the fish scales and tissue.
Beginning in 2006, scientists have been building a DNA database for West Coast salmon that now includes 20,000 samples. While they can’t identify the particular stream a salmon comes from, they’re able to identify a particular watershed.
“It’s an extremely reliable tool,” Hanson said.
Confirming previous studies, the scientists found that chinook, a relatively scarce species, topped the list of the orca’s favoured prey. Using the DNA samples, however, they discovered that 80 to 90 per cent of the chinook in the samples came from the Fraser River, and only six to 14 per cent came from Puget Sound chinook stocks.
No one is quite sure why the orcas seemed hooked on chinook, particularly those from the Fraser River, Hanson said.
It could be because they’re relatively abundant during the summer compared with other salmon species. Others have suggested the killer whales favour chinook because they’re larger — averaging roughly nine kg — and contain more fat than other salmon species. Fraser River chinook are generally larger than those in Puget Sound, Hanson said.
“The bigger they are, the more bang for the buck,” he said.
Nine populations of chinook found in the range of the killer whales are listed as either endangered or threatened.
On the Fraser River, some returning runs of chinook were at record low levels in 2009, and Canadian fisheries officials are predicting “very low” returns of summer chinook this year as a result of poor ocean survival rates.
“The research findings have implications for how Canadians manage their Fraser River stocks,” said Brian Gorman, a spokesman for the National U.S. Marine Fisheries Service in Seattle.
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