Editor's note: This slide show is part of a four-part series that Anne Casselman, a freelance writer and regular contributor to Scientific American, reported in early June during a rare opportunity to conduct field reporting on grizzly bears in Heiltsuk First Nation traditional territory in British Columbia. For a first-person reflection on her experience there, click here.

HEILTSUK TRADITIONAL TERRITORY, British Columbia—Diminishing wild salmon runs along British Columbia's central coast have raised concerns in the past several years about the fate of the region's grizzly bears. The nutrient-rich fish make up anywhere from 65 to 95 percent of the bears' annual diet. 

Anecdotes of grizzlies starving to death or becoming scarce are increasingly common along the B.C. central coast but just how big a threat dwindling salmon stocks are to grizzlies remains unknown. Research has shown that salmon availability determines adult bear size as well as females' reproductive output. Beyond that, the extent to which a grizzly's survival relies on the fish is unclear.

"It would be nice to have a mechanistic and quantitative understanding of how bear populations respond to the variation in salmon population," explains Chris Darimont, chief scientist with the Raincoast Conservation Foundation (RCF) and conservation ecologist at the University of California, Santa Cruz.

To that end, RCF operates a long-term study that examines how intertwined grizzly bears are with their chief food source, salmon, to ultimately inform ecosystem-based management  of salmon such that the nutritional needs of grizzlies as well as other coastal large carnivores such as black bears are safeguarded. The scientists conduct non-invasive DNA, isotoe and hormone analysis on grizzly bear hair samples collected from 72 sites spread across 5,000- square kilometers f remote temperate rainforest in Heiltsuk tradition.

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