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You made it to the very bottom of this article, which we hope means that you found it valuable. Most of our articles are considered long in today’s digital media world.
The reason you were able to read that whole article without hitting a paywall or being hit with a ton of different ads is because our publication is supported by thousands of readers who we call Tyee Builders. These amazing people chip in an amount that works for them on a monthly, annual or one-time basis so that we can pay our talented journalists and keep our articles freely accessible to everyone.
The Tyee is a non-profit organization which means that we invest every dollar back into our operations. We track every dollar carefully and the vast majority of our revenue goes towards paying for in-depth journalism that you won’t read anywhere else.
The only way all of this works is if readers who appreciate our work step up to support it. From now until June 13, we’re looking for 500 more people to sign up for a monthly or annual commitment to help us meet our budget goals and plan ahead for the future.
You choose the amount that works for you and you can cancel at any time.
We believe that our region needs and deserves quality, investigative journalism that gets to the heart of what matters. If you share that belief, and you’d like to help us keep publishing our stories, please consider joining us today.
Marina Wang, a multimedia journalist from Calgary, is the 2021 Hakai Magazine fellow. Her work has appeared in Atlas Obscura, CBC, Science Magazine, Canadian Geographic and many others.
In the Great Bear Rainforest, in coastal British Columbia, two large bears — one black, one white — wade into a stream. The white bear dips its snout and comes up with a wriggling salmon clutched between its jaws. The black bear does the same. But as time goes on, with the two bears snagging fish after fish, the white bear seems to be having an easier time. It turns out, it is — and there’s an intriguing reason why.
Victoria-based Hakai Magazine, part of the Tula Foundation and Hakai Institute family, is an online magazine publishing fascinating articles about coastal science and societies globally. The information and storytelling are top-notch (the accompanying article was first published there). We strongly encourage you to visit Hakai Magazine here.
Spirit bears are black bears with a recessive genetic mutation that turns their regular charcoal-coloured fur a ghostly white. Fewer than 200 of these unusual bears are estimated to live on B.C.’s north and central coasts, where they have long held a special significance in coastal Indigenous cultures. According to one story from the Kitasoo/Xai’xais, the creator Raven made one out of every 10 bears white to remind people that the land had previously been covered by a glacier, and to appreciate the bounty the landscape offers today.
That ratio — about one out of 10 — has fascinated scientists. Studies have shown that, in certain parts of British Columbia, from 10 to 30 per cent of bears have this distinctive colouration — a rate that is far more frequent than what would be expected if the bears’ white fur was the result of random chance alone. It implies that the white bears may have some sort of evolutionary advantage over the black bears. A new study has teased apart what that advantage could be.
Thomas Reimchen, an ecologist at the University of Victoria who has been studying predator-prey interactions for more than 50 years, hypothesized that salmon can see black bears more easily than white bears. While swimming upstream, he thought, the fish seemed better at avoiding the black bears. The white bears would have an easier time hunting, giving them a better chance at surviving and better odds of passing on their unique genes.
To actually prove this idea, though, Reimchen had to get creative — he had to consider what a hungry bear would look like to a fish.
Reimchen also had to consider something called Snell’s window, an optical phenomenon that distorts light passing through water.
But water in a stream is rarely smooth. When it’s choppy, the amount of the landscape that gets distorted through Snell’s window can open to nearly 180 degrees, cramming in the sightline from horizon to horizon. Choppy water also fragments the image the salmon would see.
To test the idea that the distortion would make spirit bears harder to see than black bears, Reimchen constructed a bear look-alike out of a plastic barrel. Covering the “bear” with white or black fur, and sometimes adding fur-covered PVC legs, he put each version in a stream for 12 minutes to see if the salmon avoided it.
Overall, the experiment confirmed Reimchen’s hypothesis: salmon avoided the models with black bodies twice as often as the models with white bodies. “A white bear against a sky will be a bunch of white fragments against a white sky — so that’s still going to be camouflaged,” explains Reimchen. “But a black bear against a white sky is going to look like little black spots.”
Reimchen says that, over millennia, salmon would have evolved an aversion to these black spots. He adds that a similar reasoning could also explain why fish-eating birds, such as gulls and terns, have evolved white underbellies. Interestingly, the salmon also avoided the bear model with a black body and no legs two to three times more often than the model with no body and black feet. This seems to suggest that salmon rely more on the view through Snell’s window to evade predators than what they can see through the water.
Chris Darimont, a conservation biologist from the University of Victoria and the Raincoast Conservation Foundation who was not involved in the study, lauded Reimchen’s creativity in the experimental design. “While most other researchers would rush in to study it from the perspective of the sexy spirit bear, myself included, Tom thinks about that interaction more comprehensively,” he says. “Any piece of evidence that further increases our understanding of how important salmon are to bears is of keen interest.”
For future studies, Reimchen hopes other scientists will take the view from Snell’s window into closer consideration when studying the interactions between animals on land and in the water.
All illustrations by Marina Wang.
Read more: Science + Tech, Environment
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