Contaminated Orca Food
Scientists find contaminated orca food
The food supply of Puget Sound's endangered orcas is contaminated, a team of Canadian and Washington scientists has found.
By Lynda V. Mapes Seattle Times staff reporter
The food supply of Puget Sound's endangered orcas is contaminated, a team of Canadian and Washington scientists has found.
The scientists measured persistent organic pollution concentrations in chinook salmon in order to understand the orcas' exposure to contamination in their food supply. Orcas, or killer whales, are actually a type of dolphin, are among the most contaminated marine mammals in the world, and are at risk of extinction in Puget Sound.
The so-called southern resident population of orcas that frequents Puget Sound was listed as an endangered species by the federal government in November 2005.
Southern resident orca whales seem to prefer chinook salmon for their diet — fish that the scientists found were contaminated with PCBs, flame retardants and other persistent chemicals that are retained in body fat.
The scientists found the highest concentrations of toxins in fish sampled in more southerly salmon stocks, including fish sampled near the mouth of the Duwamish River and in the Deschutes River near Olympia. Salmon sampled in more northerly areas, including Johnstone Strait and near the mouth of the Fraser River, were cleaner.
Scientists hypothesized Puget Sound's southern residents therefore are eating a bigger load of toxins in their food supply than the northern resident population of killer whales.
The scientists also estimated the southern residents eat more salmon than the orcas in northern waters, because the salmon the southern residents were eating were less fatty. That would mean the orcas have to eat more to get enough nutrition.
Some scientists found the study, published in this month's edition of Environmental Toxicology and Chemistry, troubling.
"Lots of factors are stacked against southern residents," said David Bain, a contract researcher for the fisheries service. "Cleaning up Puget Sound is something we need to do to get the toxins out. This shows we have more work cut out for us than we knew. "
Other scientists were concerned about reading too much into the study, which is based on samples of chinook from only five locations, and only certain times of year.
The southern residents travel broadly, cruising all the way from inner Puget Sound to the outer coast of Washington, and all the way south to California.
The study had no samples from salmon from the Sacramento and Columbia rivers, for instance, or other locations. The fish samples also were taken only during some months of the year, primarily the fall.
Gaps in the data point to the need for more research, said Michael Ford, director of the conservation-biology division at the Federal Fisheries Service in Seattle. "The question the study addresses is an important one: We need to know how contaminants reach the whales and which stocks might be important to clean up."
posted by San Juan Safaris Whale Watching at
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