When salmon runs dwindle on the B.C. coast, the stress levels in grizzlies climb, say researchers who examined hair samples collected from more than 70 bears.
And the bears, which gather along rivers in the fall to feed on spawning salmon, take those high stress levels with them into hibernation, perhaps affecting their long-term health, according to a science paper published Wednesday.
The study is expected to add weight to a growing argument that commercial salmon harvests on the West Coast should be managed not just for people, but also to reflect the needs of bears and other wildlife.
“Part of the reason bears might be experiencing stress is the fact we compete with them for food. And we really need to think about our fisheries not only in terms of our needs as humans but also of the needs of other species,” said lead author, Heather Bryan, a Hakai postdoctoral researcher at University of Victoria and a biologist with Raincoast Conservation Foundation.
In 2010, federal department of Fisheries and Oceans scientists John Ford and Graeme Ellis linked killer-whale survival to the abundance of Chinook salmon, and called on the government to consider setting aside allocations of salmon for whales.
Chris Darimont, who co-authored the grizzly-bear study, said it’s clear bears also need a share.
“Our findings highlight the importance of managing fisheries in a way that ensures enough salmon are allowed past fish nets to meet the needs of bears and other wildlife,” said Dr. Darimont, a UVic professor and the science director at Raincoast.
Dr. Bryan said the research showed the stress hormone, cortisol, was higher in bears that ate less salmon.
“That’s not surprising if you think about how stressful it would be to be going into a winter without enough food,” she said.
The long-term health implications for grizzlies haven’t been studied yet by Dr. Bryan, but other wildlife studies have shown that animals with high cortisol levels can have shortened life spans.
Dr. Bryan’s research was possible because of a network of 71 “hair snags” researchers have been monitoring for several years on a grid that covers 5,000 square kilometres on B.C.’s mainland coast. The area stretches from near northern Vancouver Island to around Prince Rupert.
“We were interested in looking at the health effects of long-term salmon declines on bears. And how we did it is we took a few milligrams of bear hair [from each grizzly] and we used that to gain insights into the health of these several-hundred-kilogram animals,” said Dr. Bryan.
She said some of the hair came from the B.C. archives, where samples from bears killed by hunters are kept. But much of it came from the hair snags – barbed wire wrapped around trees marked with fermented fish oil.
“It’s a delicious odour for bears … they come and check it out … they usually only stay a few seconds but it’s usually long enough to leave behind a strand of hair,” said Dr. Bryan.
She said none of the field workers has ever had a dangerous encounter with the bears, despite spending weeks gathering hair samples in prime grizzly habitat.
Working with only a few strands of hair from each animal, Dr. Bryan said she was able to to both measure the level of cortisol and to determine how rich a bear’s salmon diet was. The data showed that when salmon runs declined on B.C.’s Central Coast, in 2008 and 2009, stress levels increased. And when salmon runs increased, as they did in 2010, the stress levels declined.
In 2009, conservationists and ecotourism guides along the B.C. coast reported a huge drop in the number of bears they were seeing along rivers and they blamed the decline on two successive poor salmon runs. Bear watchers speculated many animals had died during hibernation and that others had stopped breeding because they were starving.