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Gates Of The Arctic National Park & PreservePage 45 of 101

GPS-collared Bears Led Researchers to Unknown Salmon Streams in Interior Alaska

A grizzly bear sow and cubs fishing for chum salmon in an arctic river

A grizzly bear sow and cubs fishing for chum salmon in Gates of the Arctic National Park and Preserve. NPS/Matt Cameron.

Grizzly bears that live away from the coast are thought to rely on meat from land animals, not salmon. Then GPS collars in Gates of the Arctic National Park and Preserve showed many bears gathering, from mid-July, at streams in the upper Kobuk and Koyukuk watersheds, many of which were not known to hold salmon. National Park Service researchers went to find out why, and the work ended up documenting nearly 400 miles (644 km) of previously unknown salmon habitat.

A hard living in the Arctic

Grizzlies are omnivores, but a simple digestive system and months of hibernation, up to seven a year above the Arctic Circle, mean they must find large amounts of seasonally abundant, energy-rich food. Coastal brown bears typically rely heavily on salmon. In the Arctic, winters can last eight months and summers are cool, soils are poor and permafrost limits plant growth, so primary productivity is low and so are the numbers of herbivores such as moose, Dall's sheep, muskox and caribou. Grizzlies in Arctic Alaska live at the northern limit of the species and are noticeably smaller than southern, salmon-fed coastal bears.

Why the researchers were collaring bears

Northwest Alaska is one of the least developed regions in the world, and a 220-mile (354 km) industrial road, the Ambler Road, has been proposed along the southern flank of the Brooks Range. The researchers say a road there could affect fish and wildlife in and around Gates of the Arctic, including bears, which are good indicators of ecosystem health because they are apex predators and long-lived, some living more than 20 years. Past studies show human development and activity can change bear behavior and habitat use, so the team wanted to understand the ecosystem before development.

They began tracking bears with GPS collars in 2014 and over the next three years gathered movement and body-size data from 53 bears. Collared bears denned in the mountains and generally stayed there through spring. What surprised the team was that, from mid-July, many bears concentrated their movements near streams at the headwaters of the Kobuk and Koyukuk rivers. That is typical when streams hold a food resource such as salmon, but many of the streams were not known to support salmon.

What the field visits found

Field visits to those streams found chum salmon, and bears eating them: piles of salmon jaw bones lined the banks. The GPS data suggested bears were fishing up to 15 different streams across the upper Kobuk and Koyukuk watersheds, many not previously identified as supporting salmon. A stable isotope analysis of diet agreed that salmon were an important food. For at least half of the collared bears, salmon made up more than 25% of the diet, which the team had not expected.

A stream bank with a well-worn bear trail along it

A well-worn trail along the bank of Beaver Creek, made by bears fishing for chum salmon. NPS/Matt Cameron.

A pile of salmon heads and bones left by bears along a stream

Piles of chum salmon remains, like this one found along Beaver Creek in August 2016, suggest that the salmon are fully eaten, leaving only the jaws. NPS/Matt Cameron.

From bear data to salmon streams

Chum salmon turned up in three streams that were not yet in the Alaska Department of Fish and Game's Anadromous Waters Catalog, the state's regulatory catalog of waters known to support salmon and other sea-going fish. Nominating those streams started a discussion with the department's fish inventory team about the lack of systematic surveys of salmon in the upper Kobuk and Koyukuk drainages that the proposed road might affect. The department and the Park Service joined forces and, in summer 2018, surveyed fish across the upper Kobuk and Koyukuk watersheds. They documented nearly 400 miles (644 km) of previously unknown salmon habitat to nominate to the catalog, including 11 streams the proposed road would cross. Listing those streams will add regulatory protection to help reduce the effects of road building on salmon habitat.

The authors say the bears' movement data helped conservation of salmon as well as bears. They plan to keep studying how salmon influence the movement, habitat selection and survival of grizzly bears across the Arctic Interior.

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