A Surprising Number of Brown Bears Fish Arctic Salmon Streams

Brown bears gathering at salmon streams is a familiar sight on the Alaska coast, but rare inland, especially in the Arctic. Studies of brown bear diets in Gates of the Arctic National Park and Preserve found that bears there do eat salmon — unusual in Interior Alaska — with some relying heavily on it and others eating little or none. GPS-collared bears also revealed salmon-bearing streams where bears were probably fishing. That left biologists wondering: how many bears fish these streams?

Counting bears by their hair

The team used DNA to identify individual bears from hair samples. Along heavily used bear trails beside two salmon streams — 7-km sections of the upper Kobuk and upper Koyukuk watersheds — they set unbaited, breakaway hair snares that catch a small tuft of guard hair as a bear walks by. For six weeks each August and early September, in 2016 and 2017, they flew 225 miles by bush plane every two weeks to collect samples and reset the snares.

National Park Service biologists collect brown bear hair from a snare along a salmon stream.

The study area in the southern part of the park, with hair snare sites along the Kobuk and Koyukuk streams, August–September 2016–2017. NPS.

What they found

DNA identified 31 individual brown bears and 5 American black bears along the two streams. From those data, the biologists estimated that about 24 brown bears (95% confidence interval 22–27) used the Kobuk section and about 15 (9–35) used the Koyukuk section — roughly as many as fish some coastal streams with moderate salmon runs.

• More females than males were detected, and more brown bears than black bears.
• Bears using the same stream were more closely related to one another, suggesting that bears learn to fish from other bears.

Such high numbers stand out against the region's generally low bear densities. Because Interior Alaska is poorer in nutrients than the coast, these salmon streams are likely important to local brown bears.

Why it matters

Knowing where, when and how many bears gather is vital for conserving their habitat and preventing conflicts between bears and people. A 354-km industrial road has been permitted along the southern flanks of the Brooks Range, crossing many streams and rivers — including both of those studied — and the researchers identified possible measures to reduce conflicts with bears congregating along salmon streams.

Sources

• National Park Service, Gates of the Arctic National Park and Preserve: "A surprising number of bears congregate at Arctic salmon streams," summarizing Sorum MS, Cameron MD, Crupi A, Sage GK, Talbot SL, Hilderbrand GV, Joly K (2023), "Pronounced brown bear aggregation along anadromous streams in interior Alaska," Wildlife Biology e01057. The article gives the number of hair samples collected as 118 and the study's abstract as 119, so no count is given here.