A new study funded by UC Davis shows how killer whales (orcas) in the Pacific Northwest accumulate contaminants such as PCBs, which can reduce their ability to fight disease and have healthy offspring.

The contaminants are coming from the chinook salmon that are the majority of the whales' diet, said study lead author Donna Cullon of the Institute of Ocean Sciences, Fisheries and Oceans of Canada. And the salmon are acquiring the contaminants while at sea, not while in rivers -- a finding that could help conservation efforts.

Cullon and colleagues tested young salmon as they headed to sea, and mature salmon as they returned to rivers to spawn. They measured the fishes' levels of persistent organic pollutants, including flame retardants, industrial by-products, and organochlorine pesticides.

A particularly worrisome finding of the study was that the salmon eaten by the southern population of resident whales (off Seattle, Wash., and Vancouver, British Columbia) had much higher concentrations of pollutants than those eaten by the northern resident population (off central and northern British Columbia). While both populations are at risk, the southern population is considered at greater risk and classified as endangered, while the northern is classified as threatened.

The two-year study was conducted by American and Canadian scientists and supported by a competitive grant from the SeaDoc Society, a program of the Wildlife Health Center at the UC Davis School of Veterinary Medicine.

(The SeaDoc Society has funded nearly $2 million in grants to restore and maintain marine ecosystem health in the North American Pacific region. Grant applications for the 2010-2011 funding cycle will be due in fall 2009. More information is online at: http://www.seadocsociety.org/node/47#fundedresearch.)

The study, "Persistent Organic Pollutants in Chinook Salmon (Oncorhynchus tshawytscha): Implications for Resident Killer Whales of British Columbia and Adjacent Waters," is online at http://www.allenpress.com/pdf/ENTC_28.1_148.pdf.