The bears, lured by the scent, would sniff around, rub themselves on the snares, and leave stray hairs behind.
The team then genetically analyzed the hairs to identify individual bears. There were 50 to 60 bears congregating along a 5-mile-long (8 kilometers) stretch of river, Filardi said. (For comparison, Yellowstone National Park's grizzly population boasts just a few hundred, he noted.)
Many came all three years of the study, but a significant fraction came one year and not the next, or vice versa, suggesting the underlying grizzly population was fairly large, he added.
Over the course of the study, they team counted fewer new bears, which suggests the population was decreasing along the Koeye River, likely because fewer salmon were spawning there
By coordinating their findings with those of other First Nations tribes, the team found that some of those bears were coming from many miles away, along several bear "highways," with "on" and "off" ramps at certain key sites, Filardi said.
In some spots bears' footprints have worn holes the size of dinner plates in the mossy forest floor, Filardi said.
"The bears have just been stepping in each other's footprints for hundreds of years," Filardi said.
Those footprints make it easy to figure out how some bears reach the Koeye River watershed. But there may be many more as-yet-undiscovered bear migration routes to piece together, Housty said.
The Heiltsuk are now creating a map of these bear trails, though they are not sharing the map with outsiders, to avoid giving trophy hunters clues on where to hunt, Filardi said.
The map could help conservationists and the Heiltsuk regulate hunting in the region, making trophy hunting off-limits wherever the grizzlies like to congregate, Housty said.
"The support for the trophy hunt has decreased significantly in the last couple of years. I think it's only a matter of time, probably within the next regional election, that we'll have the trophy hunt banned from these areas," Housty said.
The research is detailed in the June issue of the journal Ecology and Society.
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