Study: Sound orcas eating more toxic salmon

SEATTLE – Puget Sound killer whales appear to be more contaminated than northern orcas because they’re eating salmon that is more toxic, a new study suggests.

Researchers measuring the presence of toxic chemicals in chinook salmon, a prime food for the whales, found higher levels in salmon from Puget Sound than from British Columbia waters.

Canadian and Washington scientists also found that chinook from Puget Sound had lower fat content and were less nutritious than salmon tested farther north.

The scientists think the lower fat content could cause Puget Sound orcas to eat 50 percent more salmon, resulting in more toxic exposure.

“It was an exploration to look at why southern residents might be more contaminated than northern residents,” said Sandra O’Neill, an author and research scientist with the Washington Department of Fish and Wildlife.

“We have to consider not only how contaminated the fish are, but the quality of the fish in terms of lipids and size as a food supply to whales.”

Unlike other killer whales, both “northern resident” and “southern resident” orcas eat fish rather than mammals.

The southern orcas frequent Puget Sound for most of the year, while the northern residents typically ply the waters of the Johnstone Strait area and northern British Columbia.

The endangered Puget Sound orcas now number 83 after seven vanished last year. Lack of food, pollution and noise from vessels are believed to be their biggest threats.

“The results here are pretty much what we expected, and they hammer home the point that it’s urgent we do something,” said David Bain, a Seattle-area marine biologist who has done research on the orcas but wasn’t involved in this study.

“Salmon are getting a lot dirtier, and making it harder for southern residents,” he said.

Researchers measured the presence of persistent organic pollutants in adult chinook and smolts, including polychlorinated biphenyls, or PCBs, and the pesticide DDT, which persist in the environment despite being banned since the 1970s.

O’Neill cautioned that the study was based on a very small sample from two chinook populations in Puget Sound, and southern residents feed on many populations.

Researchers tested adult chinook taken from the mouth of the Duwamish River in Seattle and the Tumwater Falls Hatchery on the Deschutes River near Olympia. They tested the same number of salmon from Johnstone Strait and the mouth of the Fraser River in British Columbia.

They estimate that adult salmon accumulate most of their contaminants while at sea. The Puget Sound fish had higher concentrations of contaminants and lower fat content, the study found.