Salmon aren't doing very well in most of the world. They've been overfished almost everywhere. Their natural habitats have been destroyed in numerous ways, including by agriculture, logging and oil spills. Their freshwater rivers have been blocked up with dams. And climate change may be affecting their migration from river to sea and back.
This decline in salmon isn't good for grizzly bears.
For thousands of years, bears in salmon-rich areas have been able to rely on the fact that the fish would come each fall. Losing a source of food is generally a stressful event, and to measure stress in the bears, Heather Bryan of the University of Calgary and colleagues looked at cortisol levels in grizzly bear fur.
A grizzly bear. (Credit: Flickr/Scott Calleja)
Cortisol is a steroid hormone released in times of stress. By measuring it in bear hair, the researchers got a picture of an animal's level of stress over that whole period, including during the salmon spawning. They gathered hair from 2009 through 2011 in coastal and inland British Columbia, and also got samples from bears that had been killed between 2004 and 2009.
Bears on the coast and inland had similar levels of cortisol. But when the scientists looked at how cortisol levels varied with the amount of salmon consumed, they saw that as the amount of salmon eaten increased, cortisol levels decreased.
The researchers wrote that this would lead to "unknown, but probably adverse, fitness costs" (Sarah Zielinski, Science News, Dec. 9).
Reprinted from ClimateWire with permission from Environment & Energy Publishing, LLC. 202-628-6500.
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