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NW Fishletter #257, February 9, 2009

[2] More Questions Than Answers Over Salmon/Whale PCB Study

Some Northwest scientists are speculating Puget Sound killer whales may be getting a double dose of lingering organic poisons because they must eat twice as much salmon as their northern cousins to obtain the same level of nourishment.

Other Northwest scientists say the analysis is a start, but needs much more information before any such conclusions can be reached.

The researchers' speculations were included in a recent article in Environmental Toxicology and Chemistry, a peer-reviewed journal. Lead author was Donna Cullon, from the Institute of Ocean Sciences, Fisheries and Oceans Canada, in Sidney, British Columbia.

The authors said their data suggest the southern resident whale population may be ingesting four times as much PCBs [polychlorinated biphenyls] by body weight as the northern B.C. orca population. The Puget pods are listed for protection under the ESA.

PCBs were used widely in the electricity utility industry for their cooling properties, but have been banned since the 1970s.

In humans, PCBs may be a carcinogen, and there is evidence they can hinder learning development in children. For marine mammals, some evidence exists that high PCB levels can harm immune systems.

Scientists have found that over the years, PCBs ending up in oceans have migrated to more northern latitudes, where they enter the complex food webs as far north as the Arctic, which Cullon's paper noted.

"The present study underscores the global nature of contaminant dispersion with chinook salmon acquiring the majority of their POPs [persistent organic pollutants] during their time at sea," it said.

But with the disappearance of seven southern resident orcas in the past year, including two reproductive females, scientists have been taking a closer look at the whales' diet, hoping to find a clue to their decline. Some whale advocates have been quick to blame reduced chinook runs for the problem, including those on the Columbia River. The possibility of adverse effects on whale populations by federal dams on the Columbia and Snake rivers has been addressed in the latest hydro BiOp.

The Cullon et al. paper included data collected by several Canadian and U.S. scientists on PCB levels found in chinook smolts and 24 adult salmon in 2000 and 2001 that ranged from Puget Sound to northern B.C.

Finding different PCB levels in the chinook isn't news. Washington Department of Fish and Wildlife researcher Sandy O'Neill released analyses on PCB levels in 2005, some of which are included in the new paper.

O'Neill found that Puget Sound chinook contained nearly three times as many PCBs as chinook from northern B.C. or Alaska, with levels in the Sound's resident chinook even higher. At that time, she said it would take decades for PCB levels in local fish to diminish by much. Although levels in urban areas will slowly go down, various biological transport mechanisms would raise levels in more pristine areas of the coast, as when wild salmon return to their spawning grounds.

O'Neill told NW Fishletter that a new paper will be out soon that is a much more up-to-date analyses of PCB levels in local salmon. She noted that a good percentage of fall chinook from Puget Sound hatcheries stay in the area most of their lives, not just the late releases for the blackmouth fishery, and these are the fish that tend to show the highest levels of PCBs, since the local herring stocks on which they feed are still showing high levels relative to herring populations in other areas.

What is new about the latest PCB paper is the sense of urgency accompanying it--including a press release sent to the mainstream media that churned up plenty of interest with the headline, "When Food Can Kill..."

Unfortunately, the press release contained inaccuracies. NOAA Fisheries orca researcher Brad Hanson said it was misleading because "it states as facts things that in the paper were speculative."

Alas, many of the news stories stemming from the article's release, from The Seattle Post-Intelligencer to Scientific American, reported some of these speculations as facts, including the paper's estimate the southern residents consume about 6.6 times as many PCBs as the northern pods.

But a closer look at some data displayed in the article doesn't seem to fit its overall message, since it showed that chinook from B.C.'s lower Fraser River carried higher PCB levels than Duwamish River chinook from mid-Puget Sound, but lower levels than salmon from the Deschutes River at the southern end of the Sound.

The lowest levels were found in chinook from the Johnstone Strait area, about halfway up the British Columbia coastline. These fish also carried about twice as many lipid reserves as the other chinook examined.

NOAA researcher Hanson and others have been trying to pin down just where most of the salmon come from that make up the southern orca diet. He and others have found that when the whales are foraging in the San Juan Islands during summer, it seems most chinook they consume come from the Fraser River, and not Puget Sound, as was widely believed.

But the southern residents have a wide range. Two of the three local pods head offshore in the winter as far south as California.

That's when things get complicated. Though Hanson said it's important to study the contaminant patterns in salmon, especially ones the whales eat, he noted the situation is much more complex than the Cullon et al. paper seems to indicate.

"It is important to realize that the whales eat a variety of stocks and eat different stocks in different times of year," Hanson told NW Fishletter by e-mail.

"The stocks samples in the Cullon et al. paper may not be representative of the overall diet of either the N or S population. For example, the salmon collected for this study were all sampled in October--and therefore are predominately fall run fish. These are not likely to be the same fish that the whales are eating during the summer, especially May-July, or in the winter.

"We therefore think that it is misleading to make statements about how diet affects POP concentrations in the S versus N populations based on salmon samples taken only in one month," Hanson said.

Hanson also noted a larger question researchers are grappling with--why the transient orca populations on the West Coast, which have shown the highest PCB levels of any regional whale population, seem to be maintaining steady to growing overall numbers. A dead transient that washed ashore near Port Angeles a few years ago pegged scientists' instruments they used to measure PCB levels.

The transient whales' diet includes seals and sea lions that contain very high levels of PCBs. The northern and southern residents don't eat marine mammals.

Hanson said researchers have also found lower PCB levels in salmon during the winter off California than a study cited in the Cullon et al. paper. Columbia River and Sacramento River chinook contain about half the PCB levels of the Puget Sound chinook. -B. R.

The following links were mentioned in this story:


NW Fishletter 195, April 20, 2005

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