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Salmon shortage stresses orcas more than boat noise

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A new research study of stress hormones in Puget Sound orcas shows that the whales actually were under less stress at times of higher vessel traffic – at least when their key food source, chinook salmon, was abundant.  Only when salmon were scarce did boat noise seem to increase stress levels.

Ken Balcomb of the Center for Whale Research said he wasn’t surprised by this, noting that there were far more orcas years ago when there were also more fishing boats, with the whales not seeming to mind the boats’ presence.

Sam Wasser, director of University of Washington’s Department of Biology Center for Conservation Biology, said the study points to the importance of putting fish first as managers look for the priority management steps, amid reducing toxins and pollution, vessel noise and improving food supply, for orca recovery.

“If you are a manager, you really want to know what are the relative importance of those, and how do they interact, and our study did that; it found that fish are the most important,” Wasser said.

Ed. note: While these results confirm what most have long known, that declining salmon runs are the major factor in recent orca declines, it’s also worth noting that during times when salmon are less abundant, boat noise did increase stress levels in the orcas.  While perhaps a secondary factor, boat noise remains a chronic feature of orca life, with measurable changes in stress at times when food is not abundant.  This supports the initiatives underway in recent years to try to moderately reduce noise and other impacts by requiring whale watching boats to stay farther from whales.  Earlier research has also suggested that foraging for salmon in boat noise may cost whales more energy than foraging in quieter conditions.

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